- Email: [email protected]
Measurement of activation cross-sections of natDy(p,x) reactions up to 45 MeV
Nuclear Inst. and Methods in Physics Research B 464 (2020) 74–83
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Nuclear Inst. and Methods in Physics Research B journal homepage: www.elsevier.com/locate/nimb
Measurement of activation cross-sections of 45 MeV
nat
Dy(p,x) reactions up to
T
Muhammad Shahida, Kwangsoo Kima, Haladhara Naika,b, Guinyun Kima,
⁎
a b
Department of Physics, Kyungpook National University, Daegu 702-701, Republic of Korea Radiochemistry Division, Bhabha Atomic Research Centre, Mumbai 400085, India
ARTICLE INFO
ABSTRACT
Keywords: p+natDy process 45-MeV proton beam Stacked-foil activation Off-line γ-ray spectrometric technique Excitation functions Thick target yields
We activated natDy with a 45-MeV energetic proton beam and studied the production cross-sections of the reaction products 162m,161,159Ho, 159,157,155Dy, and 161,160,156,155Tb. The activation was carried out using an external beam from the MC-50 Cyclotron at the Korea Institute of Radiological and Medical Sciences, Korea. The stacked-foil activation method and off-line γ-ray spectrometry were used to measure the excitation functions of the natDy(p,x) reactions. The thick target yields of the reaction products were also estimated. The excitation functions of the natDy(p,x) reactions were theoretically calculated using TALYS 1.9 code. The measured results were compared with the literature data and the calculated values from the TENDL-2017 library and were found to be in close agreement for most of the reactions.
1. Introduction Like other rare earth metals, dysprosium has many applications. The good metallurgical properties of its alloys (dysprosium-oxide-nickel cermet’s) such as high thermal neutron absorption cross-section and high melting point makes them desirable for manufacturing control rods to cool nuclear reactors. Therefore, the study of proton-activation cross-sections is also important to understand the radiation hardening process and other characteristics of dysprosium. Likewise, calcium sulfate and calcium fluoride crystals doped with dysprosium have good scintillation properties and hence can be used for dosimetry to measure radiation doses [1,2]. The study of proton-induced reactions on dysprosium may be helpful to understand the scintillation and dosimetric behavior of the crystals. Natural dysprosium as a target material activated with proton can be used for the production of many radioisotopes that are important for medical applications. The chemical characteristics of Tb radioisotopes produced from natDy(p,x) reactions allow for the preparation of radiopharmaceuticals for diagnostic and therapeutic applications. The radionuclide 155Tb (T1/2 = 5.32 d) decays due to electron capture (EC) and emits low energy γ-rays with Eγ = 86.55 keV (Iγ = 32%) and Eγ = 105.3 keV (Iγ = 25%). Thus, 155Tb can be used for single-photon emission computed tomography (SPECT). Other γ-lines emitted by 155 Tb are very weak; hence, the patient dose is low. The other isotope of terbium i.e. 161Tb (T1/2 = 6.89 d) emits low-energy β- -particles with an
⁎
average energy Eβ = 154 keV (Iβ = 100%). The emission of beta particles with suitable energy makes 161Tb applicable for therapeutic purposes. The radionuclide 161Tb also emits low energy γ-rays with Eγ = 48.92 keV (Iγ = 17%), Eγ = 57.19 keV (Iγ = 1.8%), and Eγ = 74.57 keV (Iγ = 10%), which are suitable for cancer treatment. Therefore, 161Tb can be a suitable therapeutic agent [3–5]. A literature review revealed that few researchers [6–8] have reported the natDy(p,x) reaction cross-sections and thick target yields in the medium energy range. In EXFOR [9] compilation extensive experimental data for nuclear reactions have been reported. The reported data are not saturated and further investigation is required to determine the standard values. The motivation of the present work is to investigate the excitation function of natDy(p,x) reactions and report the thick target yields for the reaction products from their threshold to the incident proton energy. 2. Experimental details and data analysis In this study, 25 µm thick and 99.9% pure metallic form of natDy with isotopic composition of 156Dy-0.056%, 158Dy-0.095%, 160Dy2.329%, 161Dy-18.889%, 162Dy-25.475%, 165Dy-24.896%, and 166Dy28.260% manufactured by Alfa Aesar was used as the target material. Monitor foils of natural copper (99.9% purity, 107.1-µm thickness) manufactured by Alfa Aesar, natural nickel (> 99% purity, 49.96-µm thickness) and natural titanium (99.5% purity, 19.51-µm thickness)
Corresponding author. E-mail address: [email protected] (G. Kim).
https://doi.org/10.1016/j.nimb.2019.12.009 Received 9 September 2019; Received in revised form 10 December 2019; Accepted 12 December 2019 0168-583X/ © 2019 Published by Elsevier B.V.
Nuclear Inst. and Methods in Physics Research B 464 (2020) 74–83
M. Shahid, et al.
Table 1 Decay data of the radionuclides produced from the Nuclide 159
Ho
161
Ho
Half-life 33.05 m
nat
Decay Mode (%) +
EC (99.78); β
(0.22)
Dy(p,x) reactions. Gamma-lines shown in bold fonts were used in cross-section derivation. Eγ (keV)
Iγ (%)
Reaction
Q-value (MeV)
Threshold value (MeV)
121.01 131.97 252.96 309.59 838.62
36.2 23.6 13.7 17.2 3.84
158
Dy(p,γ) Dy(p,2n) Dy(p,3n) 162 Dy(p,4n) 163 Dy(p,5n) 164 Dy(p,6n) 160 Dy(p,γ) 161 Dy(p,n) 162 Dy(p,2n) 163 Dy(p,3n) 164 Dy(p,4n) 161 Dy(p,γ) 162 Dy(p,n) 163 Dy(p,2n) 164 Dy(p,3n) 156 Dy(p,d) 156 Dy(p,pn) 158 Dy(p,tn) 158 Dy(p,d2n) 158 Dy(p,p3n) 160 Dy(p,t3n) 160 Dy(p,d4n) 160 Dy(p,p5n) 155 Ho→155Dy decay 158 Dy(p,d) 158 Dy(p,pn) 160 Dy(p,tn) 160 Dy(p,d2n) 160 Dy(p,p3n) 161 Dy(p,t2n) 161 Dy(p,d3n) 161 Dy(p,p4n) 162 Dy(p,t3n) 162 Dy(p,d4n) 162 Dy(p,p5n) 163 Dy(p,t4n) 157 Ho→157Dy decay 160 Dy(p,d) 160 Dy(p,pn) 161 Dy(p,t) 161 Dy(p,dn) 161 Dy(p,p2n) 162 Dy(p,tn) 162 Dy(p,d2n) 162 Dy(p,p3n) 163 Dy(p,t2n) 163 Dy(p,d3n) 163 Dy(p,p4n) 164 Dy(p,t3n) 164 Dy(p,d4n)
4.21 −11.20 −17.65 −25.85 –32.12 −39.78 4.81 −1.64 −9.84 −16.11 –23.77 5.27 −2.92 −9.19 −16.85 −7.22 −9.44 −16.98 –23.24 −25.47 –32.39 −38.65 −40.87
0.00 11.27 17.76 26.01 32.32 40.02 0.00 1.65 9.90 16.21 23.91 0.00 2.94 9.25 16.95 7.27 9.50 17.09 23.39 25.63 32.60 38.89 41.13
−6.83 −9.05 −15.98 –22.24 −24.46 –22.43 −28.69 −30.92 −30.63 −36.89 −39.11 −36.90
6.87 9.11 16.08 22.38 24.62 22.58 28.87 31.11 30.82 37.12 39.36 37.13
−6.35 −8.58 −6.55 −12.81 −15.03 −14.75 −21.00 –23.23 −21.02 −27.27 −29.50 −28.68 −34.93
6.39 8.63 6.59 12.89 15.12 14.84 21.13 23.37 21.15 27.44 29.68 28.85
164
−37.16
37.78
−6.57 0.00 −14.11 −14.87 −18.14 −20.36 –22.59 −9.70 −21.03 −27.29 −29.52 −30.28 –33.55 −35.77 −38.00
6.61 5.71 14.20 14.96 18.26 20.49 22.73 9.76 21.16 27.46 29.70 30.47 33.76 36.00 38.24
−7.96 −13.45 −15.68 −2.79 −20.38
8.01 13.54 15.78 2.81 20.51
2.48 h
Ɛ (100)
77.42 103.05 157.26 175.42
1.9 3.9 0.49 0.43
162m
67 m
IT (62); Ɛ (38)
57.74
4.4
155
9.9 h
EC (98.62); β+ (1.38)
184.56 226.92
3.37 68.4
157
8.14 h
EC (98.62); β+ (1.38)
182.42 326.34
1.33 93
159
144.4 d
Ɛ (100)
58.0
2.27
Ho
Dy
Dy
Dy
35.15
160 161
Dy(p,p5n) Ho→159Dy decay 156 Dy(p,2p) 158 Dy(p,α) 158 Dy(p,pt) 158 Dy(p,n3He) 158 Dy(p,2d) 158 Dy(p,npd) 158 Dy(p,2p2n) 160 Dy(p,α2n) 160 Dy(p,2t) 160 Dy(p,ndt) 160 Dy(p,2npt) 160 Dy(p,3n3He) 160 Dy(p,2n2d) 160 Dy(p,3npd) 160 Dy(p,4n2p) 155 Dy→155Tb decay 158 Dy(p,3He) 158 Dy(p,pd) 158 Dy(p,n2p) 160 Dy(p,nα) 160 Dy(p,dt) 159
155
5.32 d
Ɛ (100)
86.55 105.32 148.64 161.29 163.28 180.08 262.27
32.0 25.1 2.65 2.76 4.44 7.5 5.3
156
5.35 d
Ɛ (100)
88.97 199.19 534.29
18.0 41.0 67.0
Tb
Tb
(continued on next page) 75
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Table 1 (continued) Nuclide
Half-life
Decay Mode (%)
Eγ (keV)
Iγ (%)
Reaction
Q-value (MeV)
Threshold value (MeV)
160
–22.60 –23.37 −26.64 −28.86 −31.08 −9.24 −20.58 −26.83 −29.06 −29.82 –33.09 −35.31 −37.54 −17.44 −28.77 −35.03 −37.25 −38.02 −41.29 –23.71 −35.04 −41.30 −31.37 −42.70 −7.51 −7.99 −13.48 −15.70 6.32 −13.49 −14.26 −17.53 −19.75 −21.98 −1.34 −18.93 −21.15 −21.92 −25.18 −27.41 −27.41 −8.01 −6.56 −12.06 −14.28 6.36 −13.46 −14.22 −17.49 −19.71 −21.94
22.74 23.51 26.80 29.04 31.28 9.30 20.70 27.00 29.24 30.01 33.30 35.54 37.77 17.55 28.95 35.25 37.49 38.25 41.54 23.86 35.26 41.56 31.56 42.96 7.56 8.04 13.56 15.80 0.00 13.58 14.35 17.64 19.87 22.11 1.35 19.04 21.28 22.05 25.34 27.58 27.58 8.06 6.60 12.13 14.37 0.00 13.54 14.31 17.60 19.83 22.07
Dy(p,npt) Dy(p,2n3He) 160 Dy(p,n2d) 160 Dy(p,2npd) 160 Dy(p,3n2p) 161 Dy(p,2nα) 161 Dy(p,2t) 161 Dy(p,ndt) 161 Dy(p,2npt) 161 Dy(p,3n3He) 161 Dy(p,2n2d) 161 Dy(p,3npd) 161 Dy(p,4n2p) 162 Dy(p,3nα) 162 Dy(p,n2t) 162 Dy(p,2ndt) 162 Dy(p,3npt) 162 Dy(p,4n3He) 162 Dy(p,3n2d) 163 Dy(p,4nα) 163 Dy(p,2n2t) 163 Dy(p,3ndt) 164 Dy(p,5nα) 164 Dy(p,3n2t) 161 Dy(p,2p) 162 Dy(p,3He) 162 Dy(p,pd) 162 Dy(p,n2p) 163 Dy(p,α) 163 Dy(p,pt) 163 Dy(p,n3He) 163 Dy(p,2d) 163 Dy(p,npd) 163 Dy(p,2n2p) 164 Dy(p,nα) 164 Dy(p,dt) 164 Dy(p,npt) 164 Dy(p,2n3He) 164 Dy(p,n2d) 164 Dy(p,2npd) 164 Dy(p,nα) 162 Dy(p,2p) 163 Dy(p,3He) 163 Dy(p,pd) 163 Dy(p,n2p) 164 Dy(p,α) 164 Dy(p,pt) 164 Dy(p,n3He) 164 Dy(p,2d) 164 Dy(p,npd) 164 Dy(p,2n2p) 160
160
72.3 d
β- (100)
86.79 298.58 879.38 966.17 1177.95
13.2 26.1 30.1 25.1 14.9
161
6.89 d
β- (100)
74.57 87.94 103.06 106.11 292.40
10.2 0.183 0.101 0.078 0.058
Tb
Tb
manufactured by Nilaco Corporation were used for determination of the beam energy and intensity. A metallic foil of natural cadmium (99.7% purity, 9.74-µm thickness) manufactured by Goodfellow Cambridge Ltd., was also used as the target material. The results of the natCd(p,x) reaction will be published separately. The number of target and monitor foils along with their positions were planned using the computer program SRIM-2013 [10]. The foils were cut in a laboratory to avoid dust and external contamination. The required number of foils with equal size (1.1 cm × 1.1 cm) was cut to position them in a stack. The stack was composed of 83 foils, with 22 nat Dy foils, 21 natCd foils, 16 natCu foils, 12 natNi foils, and 12 natTi foils. The foils were stacked such that the first nine sets were Dy-Cu-Cd-Ni followed by three sets of Dy-Cu-Cd-Ti-Dy-Cu-Cd-Ni, and one set of DyCu-Cd-Ti. The remaining sets were of Dy-Ti-Cd-Ti. The stack was designed such that each sample foil was followed by a monitor foil. The nat Cu and natNi foils were positioned in a high energy region, while the nat Ti foils were positioned in a low energy region because their crosssections are well defined in those energy regions [11]. The activation was carried out at the MC-50 Cyclotron installed at
the Korea Institute of Radiological and Medical Sciences (KIRAMS), Korea [12]. The stack was irradiated with an external beam line from the cyclotron. The stack was irradiated with a 45-MeV collimated proton beam with a diameter of 10 mm and a beam current of 100nA for 45 min. The geometry and intensity of the proton beam remained unchanged during activation. Care was taken to position the stack such that it was exposed to a maximum beam current. The activation was carried out in air at room temperature in a shielded environment. After one hour of cooling, the stack was dismantled. The active target and monitor foils were removed one by one, enclosed in zip-lock plastic bags, and mounted on acrylic sheets to measure their induced activities using a γ-ray spectrometer. The gamma spectrometer used was an n-type coaxial ORTEC (PopTop, GMX20) HPGe detector coupled with a 4096 multi-channel analyzer (MCA) and associated electronics. The spectrum acquisition system consist of GammaVision 5.0 (EG&G Ortec) software, which was installed on the computer connected to the HPGe detector. The energy and efficiency calibration of the γ-ray spectrometer was carried out at different distances using standard γ-ray sources (e.g.152Eu, 241Am, 133Ba). 76
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77
7.81 7.74 5.45 4.80 5.25 4.66 5.08 3.42 3.83 4.86 5.61 4.92 4.86 3.95 2.90 1.59 0.60 0.77 0.10 2.41 2.18 1.65 1.60 1.53 2.19 2.07 2.04 1.86 1.95 1.64 1.55 0.84 0.64 0.23 0.11 6.51 5.99 4.62 3.93 3.25 3.14 2.48 1.69 0.95 0.54 0.25 0.16 0.06 0.03 1E-3 4.22 3.80 3.11 2.35 1.93 0.94 0.66 0.54 0.73 0.61 0.74 0.80 0.66 0.34 0.22 0.16 547.3 ± 38.9 536.4 ± 38.0 450.1 ± 32.1 421.3 ± 30.0 421.1 ± 30.2 432.8 ± 31.0 403.1 ± 28.9 360.0 ± 25.9 315.4 ± 22.7 269.0 ± 19.5 230.0 ± 16.8 181.6 ± 13.3 106.8 ± 8.1 27.4 ± 2.5 24.5 ± 2.2 89.15 ± 6.68 60.67 ± 4.65 28.80 ± 2.33 23.81 ± 1.71 16.58 ± 1.20 13.20 ± 0.96 6.30 ± 0.47 2.04 ± 0.17 0.40 ± 0.05 0.52 ± 0.06 0.78 ± 0.08 1.21 ± 0.11 0.97 ± 0.09 0.92 ± 0.09 0.59 ± 0.05 0.08 ± 0.01 0.03 ± 0.01 32.5 ± 2.8 32.6 ± 2.8 57.3 ± 4.6 88.0 ± 6.7 86.8 ± 6.6 103.9 ± 7.8 119.3 ± 8.9 69.9 ± 5.3 67.5 ± 5.0 47.4 ± 3.6 34.6 ± 2.7 6.4 ± 0.6 2.9 ± 0.3 1.0 ± 0.2 0.6 ± 0.1
1.49 1.01 0.82 0.64 0.53 0.39 0.40 0.21 0.23 0.57 0.99 0.68 0.62 0.44 147.6 ± 11.4 174.5 ± 13.4 168.7 ± 13.0 209.2 ± 15.9 219.7 ± 16.7 257.4 ± 19.4 254.8 ± 19.2 258.1 ± 19.5 232.4 ± 17.7 218.8 ± 16.8 214.3 ± 16.5 241.0 ± 18.5 229.4 ± 17.7 204.4 ± 15.9 152.9 ± 11.2 120.9 ± 9.0 32.7 ± 2.7 19.3 ± 1.7 11.8 ± 1.2 421.1 ± 30.5 427.9 ± 30.9 383.6 ± 27.7 361.7 ± 26.1 342.2 ± 24.7 369.0 ± 26.5 356.2 ± 25.6 320.0 ± 23.0 256.7 ± 18.4 232.0 ± 16.7 210.7 ± 15.1 194.0 ± 13.9 103.2 ± 7.4 29.6 ± 2.2 18.9 ± 1.4 7.6 ± 0.6 0.5 ± 0.1 1.4 ± 0.1 1.6 ± 0.1 43.89 ± 0.11 42.3 ± 0.11 40.71 ± 0.11 39.06 ± 0.11 37.34 ± 0.12 35.55 ± 0.12 33.70 ± 0.12 31.78 ± 0.13 29.76 ± 0.14 27.65 ± 0.14 25.87 ± 0.15 23.45 ± 0.16 21.43 ± 0.18 18.63 ± 0.19 16.22 ± 0.21 12.64 ± 0.25 9.20 ± 0.31 7.72 ± 0.35 6.02 ± 0.41 3.88 ± 0.54
161
Ho
159
Cross section (mb) Energy (MeV)
Table 2 The production cross-sections of
162m,161,159
Ho,
Ho
159,157,155
Dy, and
162m
Ho
161,160,156,155
155
Dy
± ± ± ± ± ± ± ± ± ± ± ± ± ±
0.13 0.09 0.08 0.07 0.06 0.05 0.05 0.03 0.03 0.06 0.09 0.07 0.06 0.05
157
Tb radionuclides from the
Dy
nat
159
Dy(p,x) reactions.
Dy
155
Tb
± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
0.33 0.30 0.25 0.19 0.16 0.09 0.07 0.06 0.07 0.06 0.07 0.08 0.07 0.04 0.03 0.03
156
Tb
± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
0.47 0.43 0.33 0.29 0.24 0.23 0.18 0.13 0.07 0.04 0.02 0.02 0.01 5E-3 1E-3
160
Tb
± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
0.20 0.17 0.14 0.13 0.13 0.18 0.16 0.17 0.15 0.16 0.14 0.13 0.08 0.07 0.03 0.02
161
Tb
± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
0.65 0.64 0.48 0.43 0.46 0.42 0.45 0.33 0.36 0.43 0.48 0.43 0.43 0.36 0.29 0.18 0.09 0.11 0.03
The active foils were placed at different distances from the end-cap of the detector to avoid coincidence losses and to ensure a low dead time (< 10%). The data for the active foils were acquired multiple times to confirm the decay characteristics of the radionuclides and to account for possible interference in the γ-lines from different reaction products. The spectra were acquired for sufficient time to ensure that the photo-peaks of the reaction products were significant and prominent. Data acquisition for multiple times was continued for 90 days. The degradation of the proton beam energy at each foil in the stack was calculated using the computer program SRIM-2013 [10]. Data for the target foils were collected to determine the reaction products and their excitation functions. The analysis of the acquired data started with the determination of the beam energy and intensity through measurement of the activities induced in the natCu, natNi, and natTi monitor foils. The data for the natNi(p,x)57Ni, natCu(p,x)62,65Zn, and natTi(p,x)48V reactions were analyzed and measurements were obtained using the data for the recommended cross-sections [11]. We used a well-known activation equation described in our earlier publications [13–15] to determine the proton beam energy and intensity parameters. The number of target atoms was determined by taking into account the area, thickness, and density of the foils. There was a slight variation (5.26%) in the measured beam intensity, which was attributed to uncertainty in the beam intensity. The measurements revealed that the incident beam energy was 45 MeV. The use of multiple monitor foils in the full energy range was helpful to accurately determine the systematic errors in the energy and intensity determination. The production cross-sections for the reaction products were determined using the activation formula described in refs. [13–15]. In order to verify the measurements of a reaction product, the γ-ray spectra acquired at different distances, cooling times (tc), and/or measurement times (tm) were analyzed and consistency was ensured. In the calculations, the required decay data such as the half-life, the γ-ray emission probabilities (Iγ), and the γ-ray energies (Eγ) were taken from the Nuclear Structure & Decay Data (NuDat 2.7) [16]. Information about the Q-values and threshold energies were obtained using a Qvalue calculator [17] with the mass values reported by Wang et al. [18] in Atomic Mass Evaluation. The nuclear decay data and reaction threshold energy information corresponding to each reaction product are given in Table 1. The γ-ray energy values given in bold font were used for the calculations. The measured reaction cross-sections had systematic and statistical uncertainties. The measurements showed that there was uncertainty in the proton energy associated with the foil position in the stack. The proton beam energy value at each foil was an average of the incident (Ein) and outgoing (Eout) energy i.e. E = (Ein + Eout)/2. The uncertainty in energy was represented by a ± difference from the mean value. The measured uncertainties in beam energy ranged from ± 0.11 up to ± 0.54 MeV. The uncertainty increased as the proton energy decreased and vice versa. This is because the energy loss in a foil with a specific thickness depends on the energy of the incident particles. The major uncertainties considered in the measurement of the cross-sections were uncertainty in γ-ray counting (1 ~ 10%), uncertainty in beam intensity (5.2%), uncertainty in the detection efficiency (3 ~ 4%), and uncertainty in the atomic density and thickness (1 ~ 3%). Thus, the overall uncertainties in the cross-section measurements were in the range of 6.2 ~ 12.3%. The measured cross-section and proton energy values along with their uncertainties are given in Table 2. The stack foil technique and selection of thin foils made it possible to study the excitation functions with small energy steps and high accuracy. As the off-line γ-ray spectrometry system was applied, the production cross-sections for short-lived radionuclides were not determined. In this experiment, the production of 162m,161,159Ho, 159,157,155 Dy, and 161,160,156,155Tb radionuclides was identified because they are relatively long-lived. It is expected that the radionuclide 155,156157,158,160,163,164 Ho and 157,158,162,163Tb were also produced but their production was not identified due to very short half-lives or
Nuclear Inst. and Methods in Physics Research B 464 (2020) 74–83
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emission of weak intensity γ-lines. The physical yields for the thick target of the produced radionuclides were obtained from their measured production cross-sections using a yield formula [19]. The stopping power of the proton beam on nat Dy over the energy region from the threshold (Eth) to the maximum energy (E0) was taken from SRIM-2013 calculations with the assumption that the total energy incident for the target was fully absorbed. The obtained physical yields for the thick target were in the unit of MBq/ μA·h and represented the activity corresponding to the number of nuclei produced by proton interactions when the total charge was 1μA⋅h. The measured results for the cross-sections and thick target yields were compared with literature data as well as with theoretical values. Theoretical calculations were performed using TALYS-1.9 code [20] with an energy step of 0.5 MeV. The input parameters were adjusted such that the measured results were the same as those given in the TENDL-2017 library [21]. A comparison of the current measurements with the literature data [6–8] and theoretical values showed that the measured results were comparable with the previously reported data within ± 10% uncertainty with each other in some case. However, the theoretical values were either underestimated or overestimated compared with the experimental data. The measured results are numerically given in Table 2 and plotted in Figs. 1–10.
Fig. 2. Excitation function of natDy(p,xn)161(m+g)Ho reaction in comparison with the experimental data and the result from TENDL-2017 data library.
3. Results and discussion We measured the independent and/or the cumulative production cross-sections of 162m,161,159Ho, 159,157,155Dy, and 161,160,156,155Tb radioisotopes from proton-induced reactions of natDy in the energy region between the threshold energy and 45 MeV. The measured production cross-sections are given in Table 2 and graphically presented in Figs. 1–10. Two or more γ-rays or cooling times were used (where possible) for the measurement of each reaction cross-section. In most of cases, the average values were presented. We compared the present data with the literature data [6–8] and with calculated values using TALYS 1.9. The physical yields for thick targets derived from the measured excitation functions are shown in Figs. 11–13. 3.1.
nat
Dy(p,xn)159Ho reaction
The radionuclide 159Ho is directly produced from different natDy (p,xn) reactions with x = 0–6 and threshold energies from 0 to 40.02 MeV. Six different reaction channels opened at different energies and contributed to the production of 159Ho. The decay data showed that 159 Ho had two states, i.e. a very short-lived (T1/2 = 8.3 s) metastable
Fig. 3. Excitation function of natDy(p,xn)162mHo reaction in comparison with the experimental data and the result from TENDL-2017 data library.
Fig. 4. Excitation function of natDy(p,pxn)155Dy reaction in comparison with the experimental data and the result from TENDL-2017 data library.
Fig. 1. Excitation function of natDy(p,xn)159(m+g)Ho reaction in comparison with the experimental data and the result from TENDL-2017 data library. 78
Nuclear Inst. and Methods in Physics Research B 464 (2020) 74–83
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Fig. 5. Excitation function of natDy(p,pxn)157(m+g)Dy reaction in comparison with the experimental data and the result from TENDL-2017 data library.
Fig. 8. Excitation function of natDy(p,2pxn)156(m1+m2+g)Tb reaction in comparison with the experimental data and the result from TENDL-2017 data library.
Fig. 6. Excitation function of natDy(p,pxn)159Dy reaction in comparison with the experimental data and the result from TENDL-2017 data library.
Fig. 9. Excitation function of natDy(p,2pxn)160Tb reaction in comparison with the experimental data and the result from TENDL-2017 data library.
Fig. 7. Excitation function of natDy(p,2pxn)155Tb reaction in comparison with the experimental data and the result from TENDL-2017 data library.
Fig. 10. Excitation function of natDy(p,2pxn)161Tb reaction in comparison with the experimental data and the result from TENDL-2017 data library. 79
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M. Shahid, et al.
Fig. 11. Integral thick target yields for the production of 162mHo, 159 Ho radionuclides in the proton-induced reactions of natDy.
state and a relatively long-lived (T1/2 = 33.0 min) ground state. 159mHo decayed (IT = 100%) to 159gHo, which further decayed (ε; 99.76% & β; 0.24%) to 159Dy (T1/2 = 144.4 d). The decay of 159gHo resulted in the emission of several weak γ-lines. The cross-sections of 159mHo could not be measured because of the short half-life. However, production crosssections of 159gHo were determined using four γ-lines: Eγ = 121.0 keV (Iγ = 36.2%), Eγ = 132.0 keV (Iγ = 23.6%), Eγ = 253.0 keV (Iγ = 13.7%), and Eγ = 309.6 keV (Iγ = 17.2%). The 121.0 keV γ-line has interferes with the 120.6 keV γ-line (Iγ = 0.69%) from 155Tb. Likewise the 132.0 keV γ-line has weak interferences with the γ-lines of 131.95 keV (Iγ = 0.021%), 132.0 keV (Iγ = 0.008%) and 131.8 keV (Iγ = 102E-4%) from 155Dy, 155Tb and 161Tb, respectively. Besides, the γ-line of 309.6 keV interferes with 309.21 keV (Iγ = 0.005%) of 155Dy and 309.56 keV (Iγ = 0.86%) of 160Tb. All these interferences were neglected because their interferences were not considerable. The spectra taken after one hour from the end of bombardment (EOB) were analyzed to measure the production cross-sections. The measured results for 159(m+g)Ho are plotted in Fig. 1 along with the literature data [6,7] and theoretical values from the TENDL-2017 library [21]. Comparison showed good agreement between the current measurements and literature data except in the energy region of 27–37 MeV, where the present data were higher than the data reported by May and Yaffe [6] and Tárkányi et al. [7]. Above the proton energy of 38 MeV, the theoretical data were underestimated compared to the experimental data.
161
Ho, and
3.2.
Fig. 12. Integral thick target yields for the production of radionuclides in the proton-induced reactions of natDy.
155
Dy,
157
Dy,
159
156
Tb,
Dy(p,xn)161Ho reaction
The radionuclide 161Ho was directly produced through the natDy (p,xn) reactions, where x = 0 (Eth = 0 MeV) to 4 (Eth = 23.91 MeV). The decay scheme revealed that the radionuclide had a metastable state, which was very short-lived (T1/2 = 8.3 s) and decayed through the IT (100%) process to a relatively long-lived (T1/2 = 2.48 h) ground state with the emission of one strong γ-line of 211.2 keV (Iγ = 45.5%). The ground state decayed (ε; 100%) to 161Dy (stable) with the emission of several weak γ-lines. The production of 161gHo was determined from the 77.4 keV (Iγ = 1.9%) and 103.0 keV (Iγ = 3.9%) γ-lines. These γlines had weak interference with the γ-lines from other reaction products but their contribution was not considerable and was thus neglected. The measured production cross-sections of 161(m+g)Ho are graphically presented in Fig. 2 along with the literature data [6,7] and theoretical values from the TENDL-2017 library [21]. Comparison showed that the current measurements agreed with the data reported by Tárkányi et al. [7]. However, the data reported by May and Yaffe [6] in the energy region between 10 and 35 MeV were one to two-fold higher than the current measurements. The theoretical values were also over estimated in the energy region between 10 and 35 MeV. The shape of the excitation functions revealed the threshold and contribution of different reaction channels at different energies.
Dy
3.3.
Fig. 13. Integral thick target yields for the production of 155Tb, 161 Tb radionuclides in the proton-induced reactions of natDy.
nat
nat
Dy(p,xn)162Ho reaction
The radionuclide 162Ho was directly produced through the natDy (p,xn) reactions, where x = 0–3 with threshold energy from 0 to 16.95 MeV. The decay scheme showed that the radionuclide had two states. The metastable state 162mHo (T1/2 = 67.0 min) was relatively longer lived than the ground state 162gHo (T1/2 = 15.0 min). The decay of 162mHo into 162gHo resulted in the emission of a few γ-lines. For analysis, the intensive γ-line of 57.7 keV (Iγ = 4.4%) was used. This γline interfered with the 57.0 keV (Iγ = 0.055%) γ-line of 161gHo and thus the contribution was subtracted accordingly. All other interferences were neglected. The results are graphically plotted in Fig. 3 for comparison with the literature data [6,7] and theoretical values from the TENDl-2017 library [21]. Fig. 3 shows that the current measurements are in good agreement with the experimental data reported by Tárkányi et al. [7] in the given energy region, whereas the data obtained by May and Yaffe [6] are inconsistent with the present data.
160
Tb,
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M. Shahid, et al.
Comparison of experimental data and theoretical values showed that the latter are overestimated above 15 MeV. The shape of the excitation function revealed the contribution of different reaction channels that open at different thresholds. 3.4.
nat
Dy(p,pxn)
155
2017 library [21] were underestimated compared with the experimental data. The shape of the excitation function indicated the contribution of different reaction channels at different threshold energies. 3.7.
Dy reaction
nat
Dy(p,pxn)157Dy reaction
3.8.
The 157Dy radionuclide was directly produced through the natDy (p,pxn) reactions and indirectly produced through the decay of 157Ho (T1/2 = 12.6 min). The production of 157Ho was not identified due to its short half-life. Thus, the measured production cross-sections were cumulative. The decay scheme showed that 157Dy had a short-lived (T1/ 2 = 21.6 ms) metastable state and a relatively long-lived (T1/ 157g Dy by EC (100%) to 157Tb 2 = 8.14 h) ground state. The decay of resulted in the emission of several low intense γ-lines. The production cross-sections of 157gDy were measured using a relatively intense 326.3 keV (Iγ = 93%) γ-line that interfered with the γ-lines of other reaction products, but none of the interference was considerable. The measured results are graphically presented in Fig. 5 for comparison with the literature data [6–8]. The data from the current study were consistent with the data from ref. [8], whereas the data reported by Tárkányi et al. [7] and May and Yaffe [6] were lower. The theoretical values (157Ho+157Dy) from TENDL-2017 library [21] were overestimated above 30 MeV compared to the experimental data. The shape of the excitation function depicted the opening of reaction channels at different threshold energies. 3.6.
nat
Dy(p,pxn)
159
Dy(p,2pxn)155Tb reaction
The radionuclide 155Tb was directly produced through the natDy (p,2pxn) reactions. Indirectly, the production of 155Tb was due to the decay of 155Dy (T1/2 = 9.9 h). Three isotopes of dysprosium (156,158,160Dy) mainly contributed to the direct production of 155Tb. Approximately 15 different reactions contributed to the direct production of 155Tb. The decay data showed that the radionuclide had only a ground state (T1/2 = 5.32 d), which decayed (ε; 100%) to 155Gd with the emission of several weak γ-lines. The production cross-section of 155 Tb was determined with two intense 105.3 keV (Iγ = 25.1%) and 148.6 keV (Iγ = 2.65%) γ-lines. The interference to the γ-lines from other reaction products was negligible and was not taken into account. Cumulative (direct and indirect) production cross-sections of 155Tb from the present work along with literature data [7,8] are graphically presented in Fig. 7, which reveals a good agreement with the data reported by Tárkányi et al. [7] but higher values than other data reported by the same authors [8]. The comparison showed that between 22 and 32 MeV and above 38 MeV, theoretical values from the TENDL-2017 library [21] were underestimated. The shapes of the production crosssections trend of 155Tb and 155Dy were somewhat similar, confirming the decay of 155Dy into 155Tb.
The 155Dy radionuclide was directly produced from the 156,158,160Dy (p,pxn) reactions, with the threshold values of 7.27 MeV, 17.09 MeV, and 32.60 MeV, respectively. The abundances of 156,158,160Dy-isotopes in natural dysprosium are very small; therefore, the production of 155Dy through these channels is expectedly low. There is a probability of the indirect production of 155Dy through the decay of 155Ho (T1/ 155 Ho was not identified. Thus, we 2 = 48 min) but the production of assumed the cumulative production of 155Dy. The decay scheme showed that 155Dy had only a ground state, which decayed (ε; 100%) to 155 Tb (T1/2 = 5.32 d), and further decayed to 155Gd (stable). The decay resulted in the emission of several weak γ-lines. We used the γ-line of 226.9 keV (Iγ = 68.4%) for analysis as it had weak interference with the 226.95 keV (Iγ = 0.15%) γ-line of 155Tb and the contribution was neglected. A comparison of the present data with the literature data [7,8] is graphically presented in Fig. 4, which reveals consistency between the data. However, the theoretical values (155Ho+155Dy) from the TENDL-2017 library [21] were underestimated. The shape of the excitation function revealed the major contribution from 160Dy, which contributed significantly to the production of 155Dy. 3.5.
nat
nat
Dy(p,2pxn)156Tb reaction
The radionuclide 156Tb was directly produced through the natDy (p,2pxn) reactions and approximately 29 different reactions contributed to its independent production. The decay scheme showed that 156 Tb had two metastable states 156m1Tb (T1/2 = 5.3 h) and 156m2Tb (T1/2 = 24.4 h) and one ground state 156gTb (T1/2 = 5.35 d). The data were analyzed after the complete decay of the metastable states into the ground state. The two metastable states were not identified because both were mono-energetic γ-ray emitters and their γ-lines were not prominent in the spectra. The production of 156gTb was identified with interference-free and relatively strong 199.2 keV (Iγ = 41%) and 534 keV (Iγ = 68%) γ-lines. The measured cumulative (156m1+m2+gTb) production cross-sections are graphically presented in Fig. 8 for comparison with the literature data [7,8]. It is clear from the comparison that the current measurements agreed with the literature data [7,8]. However, the theoretical values from the TENDL-2017 library [21] were underestimated above 25 MeV. The continuous rise in the excitation function indicates the opening of multiple reaction channels with variations in energy. 3.9.
Dy reaction
nat
Dy(p,2pxn)160Tb reaction
The radionuclide 160Tb was directly produced through the natDy (p,2pxn) reactions with the contribution of 161,162,163,164Dy, which has more than 97% abundance in natural dysprosium. The decay scheme showed that 160Tb had only a ground state that decayed to 160Dy (stable) with the emission of several low intense γ-lines. The production of 160Tb was identified with two intense and interference-free 298.6 keV (Iγ = 26.1%) and 879.4 keV (Iγ = 30.1%) γ-lines in the spectra taken after 90 days of cooling. The average results measured with two γ-lines are graphically presented in Fig. 9. The measured independent production cross-sections were compared with the literature data [7,8] and the theoretical values from TALYS 1.8 code. The results showed a good agreement among the experimental data whereas the theoretical values from TENDL-2017 library [21] were overestimated above ~ 20 MeV. The graphical representation showed that the theoretical values had different shapes for the excitation functions compared to the experimental data.
The radionuclide 159Dy was directly produced through the natDy (p,pxn) reactions and indirectly produced through the decay of 159Ho (T1/2 = 33.05 min). Approximately 14 reactions contributed to the direct production of 159Dy. The metastable state (159mDy) was very short-lived (T1/2 = 122 μs) and thus could not be detected. However, the production cross-sections of 159gDy were measured using the intense γ-line of 58 keV (Iγ = 2.27%). All other γ-lines were very weak (Iγ ≤ 9.5E-4%). Gamma lines of 58 keV (Iγ = 0.205%) and 57.1 keV (Iγ = 1.79%) from 155Tb and 161Tb interfered with each other, but the interference was negligible. Cumulative production cross-sections of 159g Dy are graphically presented in Fig. 6 for comparison with the literature data [7,8]. The comparison showed that above 27 MeV, the current measurements were higher than the previously reported data [7,8], whereas the values reported by Tárkányi et al. [7] were higher. It is also clear that theoretical values (159Ho+159Dy) from the TENDL81
Nuclear Inst. and Methods in Physics Research B 464 (2020) 74–83
M. Shahid, et al.
The radionuclide 161Tb was directly produced through the natDy (p,2pxn) reactions. The radioisotopes 162,163,164Dy contributed to the independent production of 161Tb. The decay scheme showed that 161Tb decayed to 161Dy with the emission of several low intense γ-lines (< 0.2%) except 74.6 keV (Iγ = 10.2%), which was used for identification in the cross-section measurement. The spectra taken after 1.5 days and 9 days of cooling time were used for analysis and crosssection measurements. The average of the measured results are graphically plotted in Fig. 10 for comparison with the literature data [7,8] and theoretical values from the TENDL-2017 library [21]. The comparison showed that the current measurements were higher than the data reported by Tárkányi et al. [7] but were lower than other reported data by the same authors [8]. The theoretical values were also lower but had somewhat similar shapes for the excitation function with some energy shifts.
data were mostly consistent. In the case of 161,162mHo and 157Dy radionuclides, the measured values were inconsistent with the data reported by May and Yaffe [6]. One possible reason might be the use of old decay data and spectrometry system. Likewise, the data reported by Tárkányi et al. [7,8] in the two different experiments does not totally correlate with each other and is somewhere a little inconsistent with the current measurements due to different experimental setups and acquisitions. Theoretical calculations disagreed with the experimental data in the low energy region. The current study is helpful for researchers involved in medical radioisotope production. Two terbium (155,161Tb) radioisotopes already have medical applications. To improve the production of terbium, the decay mechanism should be followed to allow short-lived holmium radioisotopes to decay. Afterward, terbium can be separated from dysprosium through a chemical process. The yield of the required medical radioisotopes can be easily increased through the selection of specific target samples and the adjustment of energy windows.
3.11. Integral yields for thick targets
Authors Contributions
The integral yields for the thick targets for all investigated radionuclides were determined using their measured cross-sections and the stopping power of the natDy target over the energy range from the threshold to 45 MeV using the equation described in Ref. [14]. It was assumed that all incident energy was absorbed in the natDy target. The deduced integral yields for the production of 162m,161,159Ho, 159,157,155 Dy and 161,160,156,155Tb radionuclides are shown in Figs. 11–13 as a function of the proton energy. The physical thick target yield was not available in the EXFOR database to compare with the present data. It is evident from the integral yields shown in the graphs that the production of holmium radioisotopes is more favorable than that of dysprosium and terbium radioisotopes. It is quite possible to obtain a considerable yield of 162m,161,159Ho with a low energy (8–15 MeV) cyclotron because the yields increased exponentially in this region. The dysprosium (159,157,155Dy) and terbium (161,160,156,155Tb) radioisotopes can be produced with medium energy proton beams. From the point of view of medical radioisotope production, radiocontaminants can be avoided with careful selection of the energy window and irradiation of the selected samples. The contamination of holmium radionuclides in dysprosium and terbium products can be managed easily with chemical separation or letting the holmium products decay as they are short-lived compared with other reaction products. The dysprosium (159,157,155Dy) or terbium (161,160,156,155Tb) radioisotopes can be separated further with chemical process.
Muhammad Shahid: Participated experiment, data analysis and wrote a manuscript. Kwangsoo Kim: Preparing sample and experiment, and participated experiment. Haladhara Naik: Participated experiment and correcting the manuscript. Guinyun Kim: Organized experiment and checking and correcting the manuscript.
3.10.
nat
Dy(p,2pxn)161Tb reaction
Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgements The authors are thankful to the staff of the MC-50 Cyclotron Laboratory in the Korea Institute of Radiological and Medical Sciences (KIRAMS), Korea for the excellent operation of the instrument and their support during the experiment. This research work was supported by the National Research Foundation of Korea through a grant provided by the Ministry of Science and ICT, Korea (NRF-2017R1D1A1B03030484, NRF-2018M7A1A1072274, and NRF-2018R1A6A1A06024970). References [1] J. Emsley, Nature’s Building Blocks: An A-Z Guide to the Elements, second ed., Oxford University Press, New York, 2011. [2] F. Szabadváry, Handbook of the Chemistry and Physics of the Rare Earths vol. 11, Elsevier Science Publishers, 1998. [3] M. Neves, A. Kling, A. Oliveira, J. Radioanal. Nucl. Chem. 266 (2005) 377. [4] C. Müller, K. Zhernosekov, U. Köster, K. Johnston, H. Dorrer, A. Hohn, N.T. van der Walt, A. Türler, R. Schibli, J. Nucl. Med. 53 (2012) 1951. [5] B.J. Stephens, M.H. Mendenhall, Appl. Radiat. Isot. 68 (2010) 1928. [6] M. May, L. Yaffe, J. Inorg. Nucl. Chem. 26 (1964) 479. [7] F. Tárkányi, F. Ditrói, S. Takács, A. Hermanne, A.V. Ignatyuk, Ann. Nucl. Energy 62 (2013) 375. [8] F. Tárkányi, F. Ditrói, S. Takács, A. Hermanne, A.V. Ignatyuk, Appl. Radiat. Isot. 98 (2015) 87. [9] N. Otuka, E. Dupont, V. Semkova, B. Pritychenko, A.I. Blokhin, M. Aikawa, S. Babykina, M. Bossant, G. Chen, S. Dunaeva, R.A. Forrest, T. Fukahori, N. Furutachi, S. Ganesan, Z. Ge, O.O. Gritzay, M. Herman, S. Hlavač, K. Katō, B. Lalremruata, Y.O. Lee, A. Makinaga, K. Matsumoto, M. Mikhaylyukova, G. Pikulina, V.G. Pronyaev, A. Saxena, O. Schwerer, S.P. Simakov, N. Soppera, R. Suzuki, S. Takács, X. Tao, S. Taova, F. Tárkányi, V.V. Varlamov, J. Wang, S.C. Yang, V. Zerkin, Y. Zhuang, Nucl. Data Sheets 120 (2014) 272. [10] J.F. Ziegler, Nucl. Instr. Meth. B 219–220 (2004) 1027. [11] A. Hermanne, A.V. Ignatyuk, R. Capote, B.V. Carlson, J.W. Engle, M.A. Kellett, T. Kibédi, G. Kim, F.G. Kondev, M. Hussain, O. Lebeda, A. Luca, Y. Nagai, H. Naik, A.L. Nichols, F.M. Nortier, S.V. Suryanarayana, S. Takács, F.T. Tárkányi, M. Verpelli, Nucl. Data Sheets 148 (2018) 338. [12] C. Lee, J.C. Kim, J.H. Ha, J.H. Park, S.H. Park, Y.D. Kim, J.Y. Huh, J.H. Lee, C.S. Lee, H.Y. Lee, S.A. Shin, J.S. Chai, Y.S. Kim, J. Korean Phys. Soc. 35 (1999) 105. [13] M. Shahid, K. Kim, G.N. Kim, H. Naik, J. Radioanal. Nucl. Chem. 318 (2018) 2049.
4. Conclusions Excitation functions for the production of 162m,161,159Ho, Dy, and 161,160,156,155Tb radionuclides were measured in proton-induced reactions on natDy using stacked-foil activation and the off-line γ-ray spectrometric technique in the energy range from their thresholds to approximately 45 MeV. The obtained results were compared with the literature data and theoretical values. The results were generally in good agreement with each other. However, there were slight differences at some energy points. The natDy(p,x) reaction is not studied by many researchers; therefore, further investigations are required to eliminate discrepancies. It is anticipated that the radionuclides 155,156,157,158,160,163,164Ho and 157,158,162,163Tb were also produced but their productions were not identified due to very short halflives or low γ-line intensities. The current measurements strengthen the investigations by earlier researchers and provide a justification to update the theoretical values. The set of current measurements will also play an important role in the enrichment of the literature data. The measured results were plotted on a logarithmic scale to clearly show the shape of the excitation functions. Comparison of the current measurements with the literature data showed that the experimental
159,157,155
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Nuclear Inst. and Methods in Physics Research B 464 (2020) 74–83
M. Shahid, et al. [14] M. Shahid, K. Kim, H. Naik, G.N. Kim, Nucl. Instr. Meth. B 322 (2014) 13. [15] K. Kim, M.U. Khandaker, H. Naik, G.N. Kim, Nucl. Instr. Meth. B 322 (2014) 63. [16] National Nuclear Data Center, Brookhaven National Laboratory, NuDat 2.7. Available from: < http://www.nndc.bnl.gov > . [17] National Nuclear Data Center, Brookhaven National Laboratory, Q-value Calculator. Available from: < http://www.nndc.bnl.gov/qcalc/ > . [18] M. Wang, G. Audi, F.G. Kondev, W.J. Huang, S. Naimi, X. Xu, Chinese Phys. C 41 (2017) 030003. [19] S.M. Qaim, F. Tárkányi, P. Obloẑinskỳ, K. Gul, A. Hermanne, M.G. Mustafa, F.M.
Nortier, B. Scholten, Yu. Shubin, S. Takács, Y. Zhuang, IAEA-TECDOC-1211 (2001). Available from: < http://www-nds.iaea.org/medical/ > . [20] A.J. Koning, S. Hilaire, M.C. Duijvestijn, TALYS-1.0, in: O. Bersillon, F. Gunsing, E. Bauge, R. Jacqmin, S. Leray (Eds.), Proceedings of the International Conference on Nuclear Data for Science and Technology, EDP Science, Nice, France, 2008, pp. 211–214 (April 22–27, 2007. Available from: < http://www.talys.eu >). [21] A.J. Koning, D. Rochman, Available from, Nucl. Data Sheets 113 (2012) 2841 http://tendel.web.psi.ch/tendl_2017tendl2017.html.
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Contents lists available at ScienceDirect
Nuclear Inst. and Methods in Physics Research B journal homepage: www.elsevier.com/locate/nimb
Measurement of activation cross-sections of 45 MeV
nat
Dy(p,x) reactions up to
T
Muhammad Shahida, Kwangsoo Kima, Haladhara Naika,b, Guinyun Kima,
⁎
a b
Department of Physics, Kyungpook National University, Daegu 702-701, Republic of Korea Radiochemistry Division, Bhabha Atomic Research Centre, Mumbai 400085, India
ARTICLE INFO
ABSTRACT
Keywords: p+natDy process 45-MeV proton beam Stacked-foil activation Off-line γ-ray spectrometric technique Excitation functions Thick target yields
We activated natDy with a 45-MeV energetic proton beam and studied the production cross-sections of the reaction products 162m,161,159Ho, 159,157,155Dy, and 161,160,156,155Tb. The activation was carried out using an external beam from the MC-50 Cyclotron at the Korea Institute of Radiological and Medical Sciences, Korea. The stacked-foil activation method and off-line γ-ray spectrometry were used to measure the excitation functions of the natDy(p,x) reactions. The thick target yields of the reaction products were also estimated. The excitation functions of the natDy(p,x) reactions were theoretically calculated using TALYS 1.9 code. The measured results were compared with the literature data and the calculated values from the TENDL-2017 library and were found to be in close agreement for most of the reactions.
1. Introduction Like other rare earth metals, dysprosium has many applications. The good metallurgical properties of its alloys (dysprosium-oxide-nickel cermet’s) such as high thermal neutron absorption cross-section and high melting point makes them desirable for manufacturing control rods to cool nuclear reactors. Therefore, the study of proton-activation cross-sections is also important to understand the radiation hardening process and other characteristics of dysprosium. Likewise, calcium sulfate and calcium fluoride crystals doped with dysprosium have good scintillation properties and hence can be used for dosimetry to measure radiation doses [1,2]. The study of proton-induced reactions on dysprosium may be helpful to understand the scintillation and dosimetric behavior of the crystals. Natural dysprosium as a target material activated with proton can be used for the production of many radioisotopes that are important for medical applications. The chemical characteristics of Tb radioisotopes produced from natDy(p,x) reactions allow for the preparation of radiopharmaceuticals for diagnostic and therapeutic applications. The radionuclide 155Tb (T1/2 = 5.32 d) decays due to electron capture (EC) and emits low energy γ-rays with Eγ = 86.55 keV (Iγ = 32%) and Eγ = 105.3 keV (Iγ = 25%). Thus, 155Tb can be used for single-photon emission computed tomography (SPECT). Other γ-lines emitted by 155 Tb are very weak; hence, the patient dose is low. The other isotope of terbium i.e. 161Tb (T1/2 = 6.89 d) emits low-energy β- -particles with an
⁎
average energy Eβ = 154 keV (Iβ = 100%). The emission of beta particles with suitable energy makes 161Tb applicable for therapeutic purposes. The radionuclide 161Tb also emits low energy γ-rays with Eγ = 48.92 keV (Iγ = 17%), Eγ = 57.19 keV (Iγ = 1.8%), and Eγ = 74.57 keV (Iγ = 10%), which are suitable for cancer treatment. Therefore, 161Tb can be a suitable therapeutic agent [3–5]. A literature review revealed that few researchers [6–8] have reported the natDy(p,x) reaction cross-sections and thick target yields in the medium energy range. In EXFOR [9] compilation extensive experimental data for nuclear reactions have been reported. The reported data are not saturated and further investigation is required to determine the standard values. The motivation of the present work is to investigate the excitation function of natDy(p,x) reactions and report the thick target yields for the reaction products from their threshold to the incident proton energy. 2. Experimental details and data analysis In this study, 25 µm thick and 99.9% pure metallic form of natDy with isotopic composition of 156Dy-0.056%, 158Dy-0.095%, 160Dy2.329%, 161Dy-18.889%, 162Dy-25.475%, 165Dy-24.896%, and 166Dy28.260% manufactured by Alfa Aesar was used as the target material. Monitor foils of natural copper (99.9% purity, 107.1-µm thickness) manufactured by Alfa Aesar, natural nickel (> 99% purity, 49.96-µm thickness) and natural titanium (99.5% purity, 19.51-µm thickness)
Corresponding author. E-mail address: [email protected] (G. Kim).
https://doi.org/10.1016/j.nimb.2019.12.009 Received 9 September 2019; Received in revised form 10 December 2019; Accepted 12 December 2019 0168-583X/ © 2019 Published by Elsevier B.V.
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Table 1 Decay data of the radionuclides produced from the Nuclide 159
Ho
161
Ho
Half-life 33.05 m
nat
Decay Mode (%) +
EC (99.78); β
(0.22)
Dy(p,x) reactions. Gamma-lines shown in bold fonts were used in cross-section derivation. Eγ (keV)
Iγ (%)
Reaction
Q-value (MeV)
Threshold value (MeV)
121.01 131.97 252.96 309.59 838.62
36.2 23.6 13.7 17.2 3.84
158
Dy(p,γ) Dy(p,2n) Dy(p,3n) 162 Dy(p,4n) 163 Dy(p,5n) 164 Dy(p,6n) 160 Dy(p,γ) 161 Dy(p,n) 162 Dy(p,2n) 163 Dy(p,3n) 164 Dy(p,4n) 161 Dy(p,γ) 162 Dy(p,n) 163 Dy(p,2n) 164 Dy(p,3n) 156 Dy(p,d) 156 Dy(p,pn) 158 Dy(p,tn) 158 Dy(p,d2n) 158 Dy(p,p3n) 160 Dy(p,t3n) 160 Dy(p,d4n) 160 Dy(p,p5n) 155 Ho→155Dy decay 158 Dy(p,d) 158 Dy(p,pn) 160 Dy(p,tn) 160 Dy(p,d2n) 160 Dy(p,p3n) 161 Dy(p,t2n) 161 Dy(p,d3n) 161 Dy(p,p4n) 162 Dy(p,t3n) 162 Dy(p,d4n) 162 Dy(p,p5n) 163 Dy(p,t4n) 157 Ho→157Dy decay 160 Dy(p,d) 160 Dy(p,pn) 161 Dy(p,t) 161 Dy(p,dn) 161 Dy(p,p2n) 162 Dy(p,tn) 162 Dy(p,d2n) 162 Dy(p,p3n) 163 Dy(p,t2n) 163 Dy(p,d3n) 163 Dy(p,p4n) 164 Dy(p,t3n) 164 Dy(p,d4n)
4.21 −11.20 −17.65 −25.85 –32.12 −39.78 4.81 −1.64 −9.84 −16.11 –23.77 5.27 −2.92 −9.19 −16.85 −7.22 −9.44 −16.98 –23.24 −25.47 –32.39 −38.65 −40.87
0.00 11.27 17.76 26.01 32.32 40.02 0.00 1.65 9.90 16.21 23.91 0.00 2.94 9.25 16.95 7.27 9.50 17.09 23.39 25.63 32.60 38.89 41.13
−6.83 −9.05 −15.98 –22.24 −24.46 –22.43 −28.69 −30.92 −30.63 −36.89 −39.11 −36.90
6.87 9.11 16.08 22.38 24.62 22.58 28.87 31.11 30.82 37.12 39.36 37.13
−6.35 −8.58 −6.55 −12.81 −15.03 −14.75 −21.00 –23.23 −21.02 −27.27 −29.50 −28.68 −34.93
6.39 8.63 6.59 12.89 15.12 14.84 21.13 23.37 21.15 27.44 29.68 28.85
164
−37.16
37.78
−6.57 0.00 −14.11 −14.87 −18.14 −20.36 –22.59 −9.70 −21.03 −27.29 −29.52 −30.28 –33.55 −35.77 −38.00
6.61 5.71 14.20 14.96 18.26 20.49 22.73 9.76 21.16 27.46 29.70 30.47 33.76 36.00 38.24
−7.96 −13.45 −15.68 −2.79 −20.38
8.01 13.54 15.78 2.81 20.51
2.48 h
Ɛ (100)
77.42 103.05 157.26 175.42
1.9 3.9 0.49 0.43
162m
67 m
IT (62); Ɛ (38)
57.74
4.4
155
9.9 h
EC (98.62); β+ (1.38)
184.56 226.92
3.37 68.4
157
8.14 h
EC (98.62); β+ (1.38)
182.42 326.34
1.33 93
159
144.4 d
Ɛ (100)
58.0
2.27
Ho
Dy
Dy
Dy
35.15
160 161
Dy(p,p5n) Ho→159Dy decay 156 Dy(p,2p) 158 Dy(p,α) 158 Dy(p,pt) 158 Dy(p,n3He) 158 Dy(p,2d) 158 Dy(p,npd) 158 Dy(p,2p2n) 160 Dy(p,α2n) 160 Dy(p,2t) 160 Dy(p,ndt) 160 Dy(p,2npt) 160 Dy(p,3n3He) 160 Dy(p,2n2d) 160 Dy(p,3npd) 160 Dy(p,4n2p) 155 Dy→155Tb decay 158 Dy(p,3He) 158 Dy(p,pd) 158 Dy(p,n2p) 160 Dy(p,nα) 160 Dy(p,dt) 159
155
5.32 d
Ɛ (100)
86.55 105.32 148.64 161.29 163.28 180.08 262.27
32.0 25.1 2.65 2.76 4.44 7.5 5.3
156
5.35 d
Ɛ (100)
88.97 199.19 534.29
18.0 41.0 67.0
Tb
Tb
(continued on next page) 75
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Table 1 (continued) Nuclide
Half-life
Decay Mode (%)
Eγ (keV)
Iγ (%)
Reaction
Q-value (MeV)
Threshold value (MeV)
160
–22.60 –23.37 −26.64 −28.86 −31.08 −9.24 −20.58 −26.83 −29.06 −29.82 –33.09 −35.31 −37.54 −17.44 −28.77 −35.03 −37.25 −38.02 −41.29 –23.71 −35.04 −41.30 −31.37 −42.70 −7.51 −7.99 −13.48 −15.70 6.32 −13.49 −14.26 −17.53 −19.75 −21.98 −1.34 −18.93 −21.15 −21.92 −25.18 −27.41 −27.41 −8.01 −6.56 −12.06 −14.28 6.36 −13.46 −14.22 −17.49 −19.71 −21.94
22.74 23.51 26.80 29.04 31.28 9.30 20.70 27.00 29.24 30.01 33.30 35.54 37.77 17.55 28.95 35.25 37.49 38.25 41.54 23.86 35.26 41.56 31.56 42.96 7.56 8.04 13.56 15.80 0.00 13.58 14.35 17.64 19.87 22.11 1.35 19.04 21.28 22.05 25.34 27.58 27.58 8.06 6.60 12.13 14.37 0.00 13.54 14.31 17.60 19.83 22.07
Dy(p,npt) Dy(p,2n3He) 160 Dy(p,n2d) 160 Dy(p,2npd) 160 Dy(p,3n2p) 161 Dy(p,2nα) 161 Dy(p,2t) 161 Dy(p,ndt) 161 Dy(p,2npt) 161 Dy(p,3n3He) 161 Dy(p,2n2d) 161 Dy(p,3npd) 161 Dy(p,4n2p) 162 Dy(p,3nα) 162 Dy(p,n2t) 162 Dy(p,2ndt) 162 Dy(p,3npt) 162 Dy(p,4n3He) 162 Dy(p,3n2d) 163 Dy(p,4nα) 163 Dy(p,2n2t) 163 Dy(p,3ndt) 164 Dy(p,5nα) 164 Dy(p,3n2t) 161 Dy(p,2p) 162 Dy(p,3He) 162 Dy(p,pd) 162 Dy(p,n2p) 163 Dy(p,α) 163 Dy(p,pt) 163 Dy(p,n3He) 163 Dy(p,2d) 163 Dy(p,npd) 163 Dy(p,2n2p) 164 Dy(p,nα) 164 Dy(p,dt) 164 Dy(p,npt) 164 Dy(p,2n3He) 164 Dy(p,n2d) 164 Dy(p,2npd) 164 Dy(p,nα) 162 Dy(p,2p) 163 Dy(p,3He) 163 Dy(p,pd) 163 Dy(p,n2p) 164 Dy(p,α) 164 Dy(p,pt) 164 Dy(p,n3He) 164 Dy(p,2d) 164 Dy(p,npd) 164 Dy(p,2n2p) 160
160
72.3 d
β- (100)
86.79 298.58 879.38 966.17 1177.95
13.2 26.1 30.1 25.1 14.9
161
6.89 d
β- (100)
74.57 87.94 103.06 106.11 292.40
10.2 0.183 0.101 0.078 0.058
Tb
Tb
manufactured by Nilaco Corporation were used for determination of the beam energy and intensity. A metallic foil of natural cadmium (99.7% purity, 9.74-µm thickness) manufactured by Goodfellow Cambridge Ltd., was also used as the target material. The results of the natCd(p,x) reaction will be published separately. The number of target and monitor foils along with their positions were planned using the computer program SRIM-2013 [10]. The foils were cut in a laboratory to avoid dust and external contamination. The required number of foils with equal size (1.1 cm × 1.1 cm) was cut to position them in a stack. The stack was composed of 83 foils, with 22 nat Dy foils, 21 natCd foils, 16 natCu foils, 12 natNi foils, and 12 natTi foils. The foils were stacked such that the first nine sets were Dy-Cu-Cd-Ni followed by three sets of Dy-Cu-Cd-Ti-Dy-Cu-Cd-Ni, and one set of DyCu-Cd-Ti. The remaining sets were of Dy-Ti-Cd-Ti. The stack was designed such that each sample foil was followed by a monitor foil. The nat Cu and natNi foils were positioned in a high energy region, while the nat Ti foils were positioned in a low energy region because their crosssections are well defined in those energy regions [11]. The activation was carried out at the MC-50 Cyclotron installed at
the Korea Institute of Radiological and Medical Sciences (KIRAMS), Korea [12]. The stack was irradiated with an external beam line from the cyclotron. The stack was irradiated with a 45-MeV collimated proton beam with a diameter of 10 mm and a beam current of 100nA for 45 min. The geometry and intensity of the proton beam remained unchanged during activation. Care was taken to position the stack such that it was exposed to a maximum beam current. The activation was carried out in air at room temperature in a shielded environment. After one hour of cooling, the stack was dismantled. The active target and monitor foils were removed one by one, enclosed in zip-lock plastic bags, and mounted on acrylic sheets to measure their induced activities using a γ-ray spectrometer. The gamma spectrometer used was an n-type coaxial ORTEC (PopTop, GMX20) HPGe detector coupled with a 4096 multi-channel analyzer (MCA) and associated electronics. The spectrum acquisition system consist of GammaVision 5.0 (EG&G Ortec) software, which was installed on the computer connected to the HPGe detector. The energy and efficiency calibration of the γ-ray spectrometer was carried out at different distances using standard γ-ray sources (e.g.152Eu, 241Am, 133Ba). 76
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77
7.81 7.74 5.45 4.80 5.25 4.66 5.08 3.42 3.83 4.86 5.61 4.92 4.86 3.95 2.90 1.59 0.60 0.77 0.10 2.41 2.18 1.65 1.60 1.53 2.19 2.07 2.04 1.86 1.95 1.64 1.55 0.84 0.64 0.23 0.11 6.51 5.99 4.62 3.93 3.25 3.14 2.48 1.69 0.95 0.54 0.25 0.16 0.06 0.03 1E-3 4.22 3.80 3.11 2.35 1.93 0.94 0.66 0.54 0.73 0.61 0.74 0.80 0.66 0.34 0.22 0.16 547.3 ± 38.9 536.4 ± 38.0 450.1 ± 32.1 421.3 ± 30.0 421.1 ± 30.2 432.8 ± 31.0 403.1 ± 28.9 360.0 ± 25.9 315.4 ± 22.7 269.0 ± 19.5 230.0 ± 16.8 181.6 ± 13.3 106.8 ± 8.1 27.4 ± 2.5 24.5 ± 2.2 89.15 ± 6.68 60.67 ± 4.65 28.80 ± 2.33 23.81 ± 1.71 16.58 ± 1.20 13.20 ± 0.96 6.30 ± 0.47 2.04 ± 0.17 0.40 ± 0.05 0.52 ± 0.06 0.78 ± 0.08 1.21 ± 0.11 0.97 ± 0.09 0.92 ± 0.09 0.59 ± 0.05 0.08 ± 0.01 0.03 ± 0.01 32.5 ± 2.8 32.6 ± 2.8 57.3 ± 4.6 88.0 ± 6.7 86.8 ± 6.6 103.9 ± 7.8 119.3 ± 8.9 69.9 ± 5.3 67.5 ± 5.0 47.4 ± 3.6 34.6 ± 2.7 6.4 ± 0.6 2.9 ± 0.3 1.0 ± 0.2 0.6 ± 0.1
1.49 1.01 0.82 0.64 0.53 0.39 0.40 0.21 0.23 0.57 0.99 0.68 0.62 0.44 147.6 ± 11.4 174.5 ± 13.4 168.7 ± 13.0 209.2 ± 15.9 219.7 ± 16.7 257.4 ± 19.4 254.8 ± 19.2 258.1 ± 19.5 232.4 ± 17.7 218.8 ± 16.8 214.3 ± 16.5 241.0 ± 18.5 229.4 ± 17.7 204.4 ± 15.9 152.9 ± 11.2 120.9 ± 9.0 32.7 ± 2.7 19.3 ± 1.7 11.8 ± 1.2 421.1 ± 30.5 427.9 ± 30.9 383.6 ± 27.7 361.7 ± 26.1 342.2 ± 24.7 369.0 ± 26.5 356.2 ± 25.6 320.0 ± 23.0 256.7 ± 18.4 232.0 ± 16.7 210.7 ± 15.1 194.0 ± 13.9 103.2 ± 7.4 29.6 ± 2.2 18.9 ± 1.4 7.6 ± 0.6 0.5 ± 0.1 1.4 ± 0.1 1.6 ± 0.1 43.89 ± 0.11 42.3 ± 0.11 40.71 ± 0.11 39.06 ± 0.11 37.34 ± 0.12 35.55 ± 0.12 33.70 ± 0.12 31.78 ± 0.13 29.76 ± 0.14 27.65 ± 0.14 25.87 ± 0.15 23.45 ± 0.16 21.43 ± 0.18 18.63 ± 0.19 16.22 ± 0.21 12.64 ± 0.25 9.20 ± 0.31 7.72 ± 0.35 6.02 ± 0.41 3.88 ± 0.54
161
Ho
159
Cross section (mb) Energy (MeV)
Table 2 The production cross-sections of
162m,161,159
Ho,
Ho
159,157,155
Dy, and
162m
Ho
161,160,156,155
155
Dy
± ± ± ± ± ± ± ± ± ± ± ± ± ±
0.13 0.09 0.08 0.07 0.06 0.05 0.05 0.03 0.03 0.06 0.09 0.07 0.06 0.05
157
Tb radionuclides from the
Dy
nat
159
Dy(p,x) reactions.
Dy
155
Tb
± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
0.33 0.30 0.25 0.19 0.16 0.09 0.07 0.06 0.07 0.06 0.07 0.08 0.07 0.04 0.03 0.03
156
Tb
± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
0.47 0.43 0.33 0.29 0.24 0.23 0.18 0.13 0.07 0.04 0.02 0.02 0.01 5E-3 1E-3
160
Tb
± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
0.20 0.17 0.14 0.13 0.13 0.18 0.16 0.17 0.15 0.16 0.14 0.13 0.08 0.07 0.03 0.02
161
Tb
± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
0.65 0.64 0.48 0.43 0.46 0.42 0.45 0.33 0.36 0.43 0.48 0.43 0.43 0.36 0.29 0.18 0.09 0.11 0.03
The active foils were placed at different distances from the end-cap of the detector to avoid coincidence losses and to ensure a low dead time (< 10%). The data for the active foils were acquired multiple times to confirm the decay characteristics of the radionuclides and to account for possible interference in the γ-lines from different reaction products. The spectra were acquired for sufficient time to ensure that the photo-peaks of the reaction products were significant and prominent. Data acquisition for multiple times was continued for 90 days. The degradation of the proton beam energy at each foil in the stack was calculated using the computer program SRIM-2013 [10]. Data for the target foils were collected to determine the reaction products and their excitation functions. The analysis of the acquired data started with the determination of the beam energy and intensity through measurement of the activities induced in the natCu, natNi, and natTi monitor foils. The data for the natNi(p,x)57Ni, natCu(p,x)62,65Zn, and natTi(p,x)48V reactions were analyzed and measurements were obtained using the data for the recommended cross-sections [11]. We used a well-known activation equation described in our earlier publications [13–15] to determine the proton beam energy and intensity parameters. The number of target atoms was determined by taking into account the area, thickness, and density of the foils. There was a slight variation (5.26%) in the measured beam intensity, which was attributed to uncertainty in the beam intensity. The measurements revealed that the incident beam energy was 45 MeV. The use of multiple monitor foils in the full energy range was helpful to accurately determine the systematic errors in the energy and intensity determination. The production cross-sections for the reaction products were determined using the activation formula described in refs. [13–15]. In order to verify the measurements of a reaction product, the γ-ray spectra acquired at different distances, cooling times (tc), and/or measurement times (tm) were analyzed and consistency was ensured. In the calculations, the required decay data such as the half-life, the γ-ray emission probabilities (Iγ), and the γ-ray energies (Eγ) were taken from the Nuclear Structure & Decay Data (NuDat 2.7) [16]. Information about the Q-values and threshold energies were obtained using a Qvalue calculator [17] with the mass values reported by Wang et al. [18] in Atomic Mass Evaluation. The nuclear decay data and reaction threshold energy information corresponding to each reaction product are given in Table 1. The γ-ray energy values given in bold font were used for the calculations. The measured reaction cross-sections had systematic and statistical uncertainties. The measurements showed that there was uncertainty in the proton energy associated with the foil position in the stack. The proton beam energy value at each foil was an average of the incident (Ein) and outgoing (Eout) energy i.e. E = (Ein + Eout)/2. The uncertainty in energy was represented by a ± difference from the mean value. The measured uncertainties in beam energy ranged from ± 0.11 up to ± 0.54 MeV. The uncertainty increased as the proton energy decreased and vice versa. This is because the energy loss in a foil with a specific thickness depends on the energy of the incident particles. The major uncertainties considered in the measurement of the cross-sections were uncertainty in γ-ray counting (1 ~ 10%), uncertainty in beam intensity (5.2%), uncertainty in the detection efficiency (3 ~ 4%), and uncertainty in the atomic density and thickness (1 ~ 3%). Thus, the overall uncertainties in the cross-section measurements were in the range of 6.2 ~ 12.3%. The measured cross-section and proton energy values along with their uncertainties are given in Table 2. The stack foil technique and selection of thin foils made it possible to study the excitation functions with small energy steps and high accuracy. As the off-line γ-ray spectrometry system was applied, the production cross-sections for short-lived radionuclides were not determined. In this experiment, the production of 162m,161,159Ho, 159,157,155 Dy, and 161,160,156,155Tb radionuclides was identified because they are relatively long-lived. It is expected that the radionuclide 155,156157,158,160,163,164 Ho and 157,158,162,163Tb were also produced but their production was not identified due to very short half-lives or
Nuclear Inst. and Methods in Physics Research B 464 (2020) 74–83
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emission of weak intensity γ-lines. The physical yields for the thick target of the produced radionuclides were obtained from their measured production cross-sections using a yield formula [19]. The stopping power of the proton beam on nat Dy over the energy region from the threshold (Eth) to the maximum energy (E0) was taken from SRIM-2013 calculations with the assumption that the total energy incident for the target was fully absorbed. The obtained physical yields for the thick target were in the unit of MBq/ μA·h and represented the activity corresponding to the number of nuclei produced by proton interactions when the total charge was 1μA⋅h. The measured results for the cross-sections and thick target yields were compared with literature data as well as with theoretical values. Theoretical calculations were performed using TALYS-1.9 code [20] with an energy step of 0.5 MeV. The input parameters were adjusted such that the measured results were the same as those given in the TENDL-2017 library [21]. A comparison of the current measurements with the literature data [6–8] and theoretical values showed that the measured results were comparable with the previously reported data within ± 10% uncertainty with each other in some case. However, the theoretical values were either underestimated or overestimated compared with the experimental data. The measured results are numerically given in Table 2 and plotted in Figs. 1–10.
Fig. 2. Excitation function of natDy(p,xn)161(m+g)Ho reaction in comparison with the experimental data and the result from TENDL-2017 data library.
3. Results and discussion We measured the independent and/or the cumulative production cross-sections of 162m,161,159Ho, 159,157,155Dy, and 161,160,156,155Tb radioisotopes from proton-induced reactions of natDy in the energy region between the threshold energy and 45 MeV. The measured production cross-sections are given in Table 2 and graphically presented in Figs. 1–10. Two or more γ-rays or cooling times were used (where possible) for the measurement of each reaction cross-section. In most of cases, the average values were presented. We compared the present data with the literature data [6–8] and with calculated values using TALYS 1.9. The physical yields for thick targets derived from the measured excitation functions are shown in Figs. 11–13. 3.1.
nat
Dy(p,xn)159Ho reaction
The radionuclide 159Ho is directly produced from different natDy (p,xn) reactions with x = 0–6 and threshold energies from 0 to 40.02 MeV. Six different reaction channels opened at different energies and contributed to the production of 159Ho. The decay data showed that 159 Ho had two states, i.e. a very short-lived (T1/2 = 8.3 s) metastable
Fig. 3. Excitation function of natDy(p,xn)162mHo reaction in comparison with the experimental data and the result from TENDL-2017 data library.
Fig. 4. Excitation function of natDy(p,pxn)155Dy reaction in comparison with the experimental data and the result from TENDL-2017 data library.
Fig. 1. Excitation function of natDy(p,xn)159(m+g)Ho reaction in comparison with the experimental data and the result from TENDL-2017 data library. 78
Nuclear Inst. and Methods in Physics Research B 464 (2020) 74–83
M. Shahid, et al.
Fig. 5. Excitation function of natDy(p,pxn)157(m+g)Dy reaction in comparison with the experimental data and the result from TENDL-2017 data library.
Fig. 8. Excitation function of natDy(p,2pxn)156(m1+m2+g)Tb reaction in comparison with the experimental data and the result from TENDL-2017 data library.
Fig. 6. Excitation function of natDy(p,pxn)159Dy reaction in comparison with the experimental data and the result from TENDL-2017 data library.
Fig. 9. Excitation function of natDy(p,2pxn)160Tb reaction in comparison with the experimental data and the result from TENDL-2017 data library.
Fig. 7. Excitation function of natDy(p,2pxn)155Tb reaction in comparison with the experimental data and the result from TENDL-2017 data library.
Fig. 10. Excitation function of natDy(p,2pxn)161Tb reaction in comparison with the experimental data and the result from TENDL-2017 data library. 79
Nuclear Inst. and Methods in Physics Research B 464 (2020) 74–83
M. Shahid, et al.
Fig. 11. Integral thick target yields for the production of 162mHo, 159 Ho radionuclides in the proton-induced reactions of natDy.
state and a relatively long-lived (T1/2 = 33.0 min) ground state. 159mHo decayed (IT = 100%) to 159gHo, which further decayed (ε; 99.76% & β; 0.24%) to 159Dy (T1/2 = 144.4 d). The decay of 159gHo resulted in the emission of several weak γ-lines. The cross-sections of 159mHo could not be measured because of the short half-life. However, production crosssections of 159gHo were determined using four γ-lines: Eγ = 121.0 keV (Iγ = 36.2%), Eγ = 132.0 keV (Iγ = 23.6%), Eγ = 253.0 keV (Iγ = 13.7%), and Eγ = 309.6 keV (Iγ = 17.2%). The 121.0 keV γ-line has interferes with the 120.6 keV γ-line (Iγ = 0.69%) from 155Tb. Likewise the 132.0 keV γ-line has weak interferences with the γ-lines of 131.95 keV (Iγ = 0.021%), 132.0 keV (Iγ = 0.008%) and 131.8 keV (Iγ = 102E-4%) from 155Dy, 155Tb and 161Tb, respectively. Besides, the γ-line of 309.6 keV interferes with 309.21 keV (Iγ = 0.005%) of 155Dy and 309.56 keV (Iγ = 0.86%) of 160Tb. All these interferences were neglected because their interferences were not considerable. The spectra taken after one hour from the end of bombardment (EOB) were analyzed to measure the production cross-sections. The measured results for 159(m+g)Ho are plotted in Fig. 1 along with the literature data [6,7] and theoretical values from the TENDL-2017 library [21]. Comparison showed good agreement between the current measurements and literature data except in the energy region of 27–37 MeV, where the present data were higher than the data reported by May and Yaffe [6] and Tárkányi et al. [7]. Above the proton energy of 38 MeV, the theoretical data were underestimated compared to the experimental data.
161
Ho, and
3.2.
Fig. 12. Integral thick target yields for the production of radionuclides in the proton-induced reactions of natDy.
155
Dy,
157
Dy,
159
156
Tb,
Dy(p,xn)161Ho reaction
The radionuclide 161Ho was directly produced through the natDy (p,xn) reactions, where x = 0 (Eth = 0 MeV) to 4 (Eth = 23.91 MeV). The decay scheme revealed that the radionuclide had a metastable state, which was very short-lived (T1/2 = 8.3 s) and decayed through the IT (100%) process to a relatively long-lived (T1/2 = 2.48 h) ground state with the emission of one strong γ-line of 211.2 keV (Iγ = 45.5%). The ground state decayed (ε; 100%) to 161Dy (stable) with the emission of several weak γ-lines. The production of 161gHo was determined from the 77.4 keV (Iγ = 1.9%) and 103.0 keV (Iγ = 3.9%) γ-lines. These γlines had weak interference with the γ-lines from other reaction products but their contribution was not considerable and was thus neglected. The measured production cross-sections of 161(m+g)Ho are graphically presented in Fig. 2 along with the literature data [6,7] and theoretical values from the TENDL-2017 library [21]. Comparison showed that the current measurements agreed with the data reported by Tárkányi et al. [7]. However, the data reported by May and Yaffe [6] in the energy region between 10 and 35 MeV were one to two-fold higher than the current measurements. The theoretical values were also over estimated in the energy region between 10 and 35 MeV. The shape of the excitation functions revealed the threshold and contribution of different reaction channels at different energies.
Dy
3.3.
Fig. 13. Integral thick target yields for the production of 155Tb, 161 Tb radionuclides in the proton-induced reactions of natDy.
nat
nat
Dy(p,xn)162Ho reaction
The radionuclide 162Ho was directly produced through the natDy (p,xn) reactions, where x = 0–3 with threshold energy from 0 to 16.95 MeV. The decay scheme showed that the radionuclide had two states. The metastable state 162mHo (T1/2 = 67.0 min) was relatively longer lived than the ground state 162gHo (T1/2 = 15.0 min). The decay of 162mHo into 162gHo resulted in the emission of a few γ-lines. For analysis, the intensive γ-line of 57.7 keV (Iγ = 4.4%) was used. This γline interfered with the 57.0 keV (Iγ = 0.055%) γ-line of 161gHo and thus the contribution was subtracted accordingly. All other interferences were neglected. The results are graphically plotted in Fig. 3 for comparison with the literature data [6,7] and theoretical values from the TENDl-2017 library [21]. Fig. 3 shows that the current measurements are in good agreement with the experimental data reported by Tárkányi et al. [7] in the given energy region, whereas the data obtained by May and Yaffe [6] are inconsistent with the present data.
160
Tb,
80
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Comparison of experimental data and theoretical values showed that the latter are overestimated above 15 MeV. The shape of the excitation function revealed the contribution of different reaction channels that open at different thresholds. 3.4.
nat
Dy(p,pxn)
155
2017 library [21] were underestimated compared with the experimental data. The shape of the excitation function indicated the contribution of different reaction channels at different threshold energies. 3.7.
Dy reaction
nat
Dy(p,pxn)157Dy reaction
3.8.
The 157Dy radionuclide was directly produced through the natDy (p,pxn) reactions and indirectly produced through the decay of 157Ho (T1/2 = 12.6 min). The production of 157Ho was not identified due to its short half-life. Thus, the measured production cross-sections were cumulative. The decay scheme showed that 157Dy had a short-lived (T1/ 2 = 21.6 ms) metastable state and a relatively long-lived (T1/ 157g Dy by EC (100%) to 157Tb 2 = 8.14 h) ground state. The decay of resulted in the emission of several low intense γ-lines. The production cross-sections of 157gDy were measured using a relatively intense 326.3 keV (Iγ = 93%) γ-line that interfered with the γ-lines of other reaction products, but none of the interference was considerable. The measured results are graphically presented in Fig. 5 for comparison with the literature data [6–8]. The data from the current study were consistent with the data from ref. [8], whereas the data reported by Tárkányi et al. [7] and May and Yaffe [6] were lower. The theoretical values (157Ho+157Dy) from TENDL-2017 library [21] were overestimated above 30 MeV compared to the experimental data. The shape of the excitation function depicted the opening of reaction channels at different threshold energies. 3.6.
nat
Dy(p,pxn)
159
Dy(p,2pxn)155Tb reaction
The radionuclide 155Tb was directly produced through the natDy (p,2pxn) reactions. Indirectly, the production of 155Tb was due to the decay of 155Dy (T1/2 = 9.9 h). Three isotopes of dysprosium (156,158,160Dy) mainly contributed to the direct production of 155Tb. Approximately 15 different reactions contributed to the direct production of 155Tb. The decay data showed that the radionuclide had only a ground state (T1/2 = 5.32 d), which decayed (ε; 100%) to 155Gd with the emission of several weak γ-lines. The production cross-section of 155 Tb was determined with two intense 105.3 keV (Iγ = 25.1%) and 148.6 keV (Iγ = 2.65%) γ-lines. The interference to the γ-lines from other reaction products was negligible and was not taken into account. Cumulative (direct and indirect) production cross-sections of 155Tb from the present work along with literature data [7,8] are graphically presented in Fig. 7, which reveals a good agreement with the data reported by Tárkányi et al. [7] but higher values than other data reported by the same authors [8]. The comparison showed that between 22 and 32 MeV and above 38 MeV, theoretical values from the TENDL-2017 library [21] were underestimated. The shapes of the production crosssections trend of 155Tb and 155Dy were somewhat similar, confirming the decay of 155Dy into 155Tb.
The 155Dy radionuclide was directly produced from the 156,158,160Dy (p,pxn) reactions, with the threshold values of 7.27 MeV, 17.09 MeV, and 32.60 MeV, respectively. The abundances of 156,158,160Dy-isotopes in natural dysprosium are very small; therefore, the production of 155Dy through these channels is expectedly low. There is a probability of the indirect production of 155Dy through the decay of 155Ho (T1/ 155 Ho was not identified. Thus, we 2 = 48 min) but the production of assumed the cumulative production of 155Dy. The decay scheme showed that 155Dy had only a ground state, which decayed (ε; 100%) to 155 Tb (T1/2 = 5.32 d), and further decayed to 155Gd (stable). The decay resulted in the emission of several weak γ-lines. We used the γ-line of 226.9 keV (Iγ = 68.4%) for analysis as it had weak interference with the 226.95 keV (Iγ = 0.15%) γ-line of 155Tb and the contribution was neglected. A comparison of the present data with the literature data [7,8] is graphically presented in Fig. 4, which reveals consistency between the data. However, the theoretical values (155Ho+155Dy) from the TENDL-2017 library [21] were underestimated. The shape of the excitation function revealed the major contribution from 160Dy, which contributed significantly to the production of 155Dy. 3.5.
nat
nat
Dy(p,2pxn)156Tb reaction
The radionuclide 156Tb was directly produced through the natDy (p,2pxn) reactions and approximately 29 different reactions contributed to its independent production. The decay scheme showed that 156 Tb had two metastable states 156m1Tb (T1/2 = 5.3 h) and 156m2Tb (T1/2 = 24.4 h) and one ground state 156gTb (T1/2 = 5.35 d). The data were analyzed after the complete decay of the metastable states into the ground state. The two metastable states were not identified because both were mono-energetic γ-ray emitters and their γ-lines were not prominent in the spectra. The production of 156gTb was identified with interference-free and relatively strong 199.2 keV (Iγ = 41%) and 534 keV (Iγ = 68%) γ-lines. The measured cumulative (156m1+m2+gTb) production cross-sections are graphically presented in Fig. 8 for comparison with the literature data [7,8]. It is clear from the comparison that the current measurements agreed with the literature data [7,8]. However, the theoretical values from the TENDL-2017 library [21] were underestimated above 25 MeV. The continuous rise in the excitation function indicates the opening of multiple reaction channels with variations in energy. 3.9.
Dy reaction
nat
Dy(p,2pxn)160Tb reaction
The radionuclide 160Tb was directly produced through the natDy (p,2pxn) reactions with the contribution of 161,162,163,164Dy, which has more than 97% abundance in natural dysprosium. The decay scheme showed that 160Tb had only a ground state that decayed to 160Dy (stable) with the emission of several low intense γ-lines. The production of 160Tb was identified with two intense and interference-free 298.6 keV (Iγ = 26.1%) and 879.4 keV (Iγ = 30.1%) γ-lines in the spectra taken after 90 days of cooling. The average results measured with two γ-lines are graphically presented in Fig. 9. The measured independent production cross-sections were compared with the literature data [7,8] and the theoretical values from TALYS 1.8 code. The results showed a good agreement among the experimental data whereas the theoretical values from TENDL-2017 library [21] were overestimated above ~ 20 MeV. The graphical representation showed that the theoretical values had different shapes for the excitation functions compared to the experimental data.
The radionuclide 159Dy was directly produced through the natDy (p,pxn) reactions and indirectly produced through the decay of 159Ho (T1/2 = 33.05 min). Approximately 14 reactions contributed to the direct production of 159Dy. The metastable state (159mDy) was very short-lived (T1/2 = 122 μs) and thus could not be detected. However, the production cross-sections of 159gDy were measured using the intense γ-line of 58 keV (Iγ = 2.27%). All other γ-lines were very weak (Iγ ≤ 9.5E-4%). Gamma lines of 58 keV (Iγ = 0.205%) and 57.1 keV (Iγ = 1.79%) from 155Tb and 161Tb interfered with each other, but the interference was negligible. Cumulative production cross-sections of 159g Dy are graphically presented in Fig. 6 for comparison with the literature data [7,8]. The comparison showed that above 27 MeV, the current measurements were higher than the previously reported data [7,8], whereas the values reported by Tárkányi et al. [7] were higher. It is also clear that theoretical values (159Ho+159Dy) from the TENDL81
Nuclear Inst. and Methods in Physics Research B 464 (2020) 74–83
M. Shahid, et al.
The radionuclide 161Tb was directly produced through the natDy (p,2pxn) reactions. The radioisotopes 162,163,164Dy contributed to the independent production of 161Tb. The decay scheme showed that 161Tb decayed to 161Dy with the emission of several low intense γ-lines (< 0.2%) except 74.6 keV (Iγ = 10.2%), which was used for identification in the cross-section measurement. The spectra taken after 1.5 days and 9 days of cooling time were used for analysis and crosssection measurements. The average of the measured results are graphically plotted in Fig. 10 for comparison with the literature data [7,8] and theoretical values from the TENDL-2017 library [21]. The comparison showed that the current measurements were higher than the data reported by Tárkányi et al. [7] but were lower than other reported data by the same authors [8]. The theoretical values were also lower but had somewhat similar shapes for the excitation function with some energy shifts.
data were mostly consistent. In the case of 161,162mHo and 157Dy radionuclides, the measured values were inconsistent with the data reported by May and Yaffe [6]. One possible reason might be the use of old decay data and spectrometry system. Likewise, the data reported by Tárkányi et al. [7,8] in the two different experiments does not totally correlate with each other and is somewhere a little inconsistent with the current measurements due to different experimental setups and acquisitions. Theoretical calculations disagreed with the experimental data in the low energy region. The current study is helpful for researchers involved in medical radioisotope production. Two terbium (155,161Tb) radioisotopes already have medical applications. To improve the production of terbium, the decay mechanism should be followed to allow short-lived holmium radioisotopes to decay. Afterward, terbium can be separated from dysprosium through a chemical process. The yield of the required medical radioisotopes can be easily increased through the selection of specific target samples and the adjustment of energy windows.
3.11. Integral yields for thick targets
Authors Contributions
The integral yields for the thick targets for all investigated radionuclides were determined using their measured cross-sections and the stopping power of the natDy target over the energy range from the threshold to 45 MeV using the equation described in Ref. [14]. It was assumed that all incident energy was absorbed in the natDy target. The deduced integral yields for the production of 162m,161,159Ho, 159,157,155 Dy and 161,160,156,155Tb radionuclides are shown in Figs. 11–13 as a function of the proton energy. The physical thick target yield was not available in the EXFOR database to compare with the present data. It is evident from the integral yields shown in the graphs that the production of holmium radioisotopes is more favorable than that of dysprosium and terbium radioisotopes. It is quite possible to obtain a considerable yield of 162m,161,159Ho with a low energy (8–15 MeV) cyclotron because the yields increased exponentially in this region. The dysprosium (159,157,155Dy) and terbium (161,160,156,155Tb) radioisotopes can be produced with medium energy proton beams. From the point of view of medical radioisotope production, radiocontaminants can be avoided with careful selection of the energy window and irradiation of the selected samples. The contamination of holmium radionuclides in dysprosium and terbium products can be managed easily with chemical separation or letting the holmium products decay as they are short-lived compared with other reaction products. The dysprosium (159,157,155Dy) or terbium (161,160,156,155Tb) radioisotopes can be separated further with chemical process.
Muhammad Shahid: Participated experiment, data analysis and wrote a manuscript. Kwangsoo Kim: Preparing sample and experiment, and participated experiment. Haladhara Naik: Participated experiment and correcting the manuscript. Guinyun Kim: Organized experiment and checking and correcting the manuscript.
3.10.
nat
Dy(p,2pxn)161Tb reaction
Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgements The authors are thankful to the staff of the MC-50 Cyclotron Laboratory in the Korea Institute of Radiological and Medical Sciences (KIRAMS), Korea for the excellent operation of the instrument and their support during the experiment. This research work was supported by the National Research Foundation of Korea through a grant provided by the Ministry of Science and ICT, Korea (NRF-2017R1D1A1B03030484, NRF-2018M7A1A1072274, and NRF-2018R1A6A1A06024970). References [1] J. Emsley, Nature’s Building Blocks: An A-Z Guide to the Elements, second ed., Oxford University Press, New York, 2011. [2] F. Szabadváry, Handbook of the Chemistry and Physics of the Rare Earths vol. 11, Elsevier Science Publishers, 1998. [3] M. Neves, A. Kling, A. Oliveira, J. Radioanal. Nucl. Chem. 266 (2005) 377. [4] C. Müller, K. Zhernosekov, U. Köster, K. Johnston, H. Dorrer, A. Hohn, N.T. van der Walt, A. Türler, R. Schibli, J. Nucl. Med. 53 (2012) 1951. [5] B.J. Stephens, M.H. Mendenhall, Appl. Radiat. Isot. 68 (2010) 1928. [6] M. May, L. Yaffe, J. Inorg. Nucl. Chem. 26 (1964) 479. [7] F. Tárkányi, F. Ditrói, S. Takács, A. Hermanne, A.V. Ignatyuk, Ann. Nucl. Energy 62 (2013) 375. [8] F. Tárkányi, F. Ditrói, S. Takács, A. Hermanne, A.V. Ignatyuk, Appl. Radiat. Isot. 98 (2015) 87. [9] N. Otuka, E. Dupont, V. Semkova, B. Pritychenko, A.I. Blokhin, M. Aikawa, S. Babykina, M. Bossant, G. Chen, S. Dunaeva, R.A. Forrest, T. Fukahori, N. Furutachi, S. Ganesan, Z. Ge, O.O. Gritzay, M. Herman, S. Hlavač, K. Katō, B. Lalremruata, Y.O. Lee, A. Makinaga, K. Matsumoto, M. Mikhaylyukova, G. Pikulina, V.G. Pronyaev, A. Saxena, O. Schwerer, S.P. Simakov, N. Soppera, R. Suzuki, S. Takács, X. Tao, S. Taova, F. Tárkányi, V.V. Varlamov, J. Wang, S.C. Yang, V. Zerkin, Y. Zhuang, Nucl. Data Sheets 120 (2014) 272. [10] J.F. Ziegler, Nucl. Instr. Meth. B 219–220 (2004) 1027. [11] A. Hermanne, A.V. Ignatyuk, R. Capote, B.V. Carlson, J.W. Engle, M.A. Kellett, T. Kibédi, G. Kim, F.G. Kondev, M. Hussain, O. Lebeda, A. Luca, Y. Nagai, H. Naik, A.L. Nichols, F.M. Nortier, S.V. Suryanarayana, S. Takács, F.T. Tárkányi, M. Verpelli, Nucl. Data Sheets 148 (2018) 338. [12] C. Lee, J.C. Kim, J.H. Ha, J.H. Park, S.H. Park, Y.D. Kim, J.Y. Huh, J.H. Lee, C.S. Lee, H.Y. Lee, S.A. Shin, J.S. Chai, Y.S. Kim, J. Korean Phys. Soc. 35 (1999) 105. [13] M. Shahid, K. Kim, G.N. Kim, H. Naik, J. Radioanal. Nucl. Chem. 318 (2018) 2049.
4. Conclusions Excitation functions for the production of 162m,161,159Ho, Dy, and 161,160,156,155Tb radionuclides were measured in proton-induced reactions on natDy using stacked-foil activation and the off-line γ-ray spectrometric technique in the energy range from their thresholds to approximately 45 MeV. The obtained results were compared with the literature data and theoretical values. The results were generally in good agreement with each other. However, there were slight differences at some energy points. The natDy(p,x) reaction is not studied by many researchers; therefore, further investigations are required to eliminate discrepancies. It is anticipated that the radionuclides 155,156,157,158,160,163,164Ho and 157,158,162,163Tb were also produced but their productions were not identified due to very short halflives or low γ-line intensities. The current measurements strengthen the investigations by earlier researchers and provide a justification to update the theoretical values. The set of current measurements will also play an important role in the enrichment of the literature data. The measured results were plotted on a logarithmic scale to clearly show the shape of the excitation functions. Comparison of the current measurements with the literature data showed that the experimental
159,157,155
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M. Shahid, et al. [14] M. Shahid, K. Kim, H. Naik, G.N. Kim, Nucl. Instr. Meth. B 322 (2014) 13. [15] K. Kim, M.U. Khandaker, H. Naik, G.N. Kim, Nucl. Instr. Meth. B 322 (2014) 63. [16] National Nuclear Data Center, Brookhaven National Laboratory, NuDat 2.7. Available from: < http://www.nndc.bnl.gov > . [17] National Nuclear Data Center, Brookhaven National Laboratory, Q-value Calculator. Available from: < http://www.nndc.bnl.gov/qcalc/ > . [18] M. Wang, G. Audi, F.G. Kondev, W.J. Huang, S. Naimi, X. Xu, Chinese Phys. C 41 (2017) 030003. [19] S.M. Qaim, F. Tárkányi, P. Obloẑinskỳ, K. Gul, A. Hermanne, M.G. Mustafa, F.M.
Nortier, B. Scholten, Yu. Shubin, S. Takács, Y. Zhuang, IAEA-TECDOC-1211 (2001). Available from: < http://www-nds.iaea.org/medical/ > . [20] A.J. Koning, S. Hilaire, M.C. Duijvestijn, TALYS-1.0, in: O. Bersillon, F. Gunsing, E. Bauge, R. Jacqmin, S. Leray (Eds.), Proceedings of the International Conference on Nuclear Data for Science and Technology, EDP Science, Nice, France, 2008, pp. 211–214 (April 22–27, 2007. Available from: < http://www.talys.eu >). [21] A.J. Koning, D. Rochman, Available from, Nucl. Data Sheets 113 (2012) 2841 http://tendel.web.psi.ch/tendl_2017tendl2017.html.
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