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Study of activation cross-sections of deuteron induced reactions on erbium: Production of radioisotopes for practical applications
NIM B Beam Interactions with Materials & Atoms
Nuclear Instruments and Methods in Physics Research B 259 (2007) 829–835 www.elsevier.com/locate/nimb
Study of activation cross-sections of deuteron induced reactions on erbium: Production of radioisotopes for practical applications F. Ta´rka´nyi a, A. Hermanne b, B. Kira´ly a,*, S. Taka´cs a, F. Ditro´i a, M. Baba c, T. Ohtsuki c, S.F. Kovalev d, A.V. Ignatyuk d a
Institute of Nuclear Research of the Hungarian Academy of Sciences (ATOMKI), 4026 Debrecen, Hungary b Cyclotron Laboratory, Vrije Universiteit Brussel (VUB), 1090 Brussels, Belgium c Cyclotron and Radioisotope Center (CYRIC), Tohoku University, Sendai 980-8578, Japan d Institute of Physics and Power Engineering (IPPE), Obninsk 249033, Russia Received 8 January 2007; received in revised form 26 January 2007 Available online 15 February 2007
Abstract Excitation functions of the natEr(d, x)163,165,166,167,168,170Tm and natEr(d, x)171Er reactions have been measured experimentally from their respective thresholds up to 40 MeV for the first time. Cross-sections were determined using the activation method and the stacked foil irradiation technique. The theoretical interpretation was done with the ALICE-IPPE code. From the fitted experimental cross-section data integral production yields were calculated and compared to measured integral yield data reported in the literature. Ó 2007 Elsevier B.V. All rights reserved. PACS: 25.45.z; 27.70.+q Keywords: Natural erbium target; Deuteron induced reaction; Cross-section; Excitation function; Therapeutic radionuclides
1. Introduction The use of compounds and biomolecules labeled with radionuclides of rare earth elements is a fast growing field in therapeutic nuclear medicine. These radionuclides are currently produced by (n, c) caption in a nuclear reactor but to obtain no carrier added end-products with high specific activity, alternative production routes utilizing charged particle induced processes are required. Our systematic study of proton and deuteron induced nuclear reactions shows that it is worth investigating the deuteron induced reactions because in the heavy mass region the (d, 2n) process results in higher yields than the (p, n) channel. Here we report on the production of Tm and Er radioisotopes by (d, x) reactions on erbium targets. Among the possible reaction products the 165Tm ! 165Er, *
Corresponding author. Tel.: +36 52 509200; fax: +36 52 416181. E-mail address: [email protected] (B. Kira´ly).
0168-583X/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2007.01.287
169
Er, 167Tm, 170Tm and 171Er ! 171Tm radionuclei have gained interest in therapy. No experimental results were found in the literature for cross-section of deuteron induced reactions on erbium. 2. Experimental The excitation functions were measured up to 40 MeV using the stacked foil irradiation technique. Commercial (Goodfellow) high purity Er foils (25 and 32 lm) were stacked together with Ti (12 and 31 lm) and Al (100 lm) monitor foils. These foils were inserted evenly in the irradiated target stack allowing measurement of the excitation function of several monitor reaction over the whole investigated energy range. The irradiations were done at the external beam lines of the cyclotrons of the Vrije Universiteit Brussel (VUB, Brussels, Belgium) and of the Cyclotron and Radioisotope Center of the Tohoku University (CYRIC, Sendai, Japan). The radioactivity of each sample
F. Ta´rka´nyi et al. / Nucl. Instr. and Meth. in Phys. Res. B 259 (2007) 829–835
830
and monitor foil was measured nondestructively by an HPGe c-spectrometer. Counting was started about 2–3 h after the end of bombardment (EOB) at VUB and 7–8 h after EOB at CYRIC. Decay data were taken from NUDAT [1], standard cross-section data for the used monitor reactions natTi(d, x)48V and natAl(d, x)22,24Na were
taken from [2,3]. The energy degradation along the stack was determined by calculation [4] and corrected on the basis of the simultaneously measured monitor reactions using the method described in [5]. The excitation functions were hence determined in an accurate way relative to the recommended monitor reactions (Fig. 1). The decay data and the contributing reactions are presented in Table 1. As naturally occurring erbium is composed of six stable isotopes, so called elemental cross-sections were determined supposing that erbium is composed of only one isotope. The experimental techniques and data processing (including calculation of cross-sections and integral yields as well as estimation of the uncertainties) were similar to or identical with what is described in more detail in our earlier reports [6,7].
400 Na-24 this work
Monitor reactions
Na-24 recommended [2]
Cross section (mb)
Na-22 this work
300
Na-22 recommended [2] V-48 this work V-48 recommended [2] V-48 [3]
200
100
3. Theoretical calculations with model codes
0 0
5
10
35
30 15 25 20 Deuteron energy (MeV)
Fig. 1. Excitation functions of the 27Al(d, x)22,24Na and monitor reactions compared to recommended values.
40 nat The measured Er(d, x)163,165,166,167,168,170Tm, 171 Er-(d, x) Er cross-sections were compared to theoretical effective cross-sections calculated by means of the sim-
nat
nat
Ti(d, x)48V
Table 1 Decay characteristics of the investigated reaction products [1] Nuclide
Half-life
171
Ec (keV)
Ic (%)
Contributing process
Q-value (MeV)
Tm Tm 168 Tm
1.92 y 128.6 d 93.1 d
66.731 84.255 198.251 447.515 631.705 720.392 741.355 815.989 821.162
0.143 2.48 53.8 23.7 9.1 12.0 12.6 50.3 11.8
170
Er(d, n) Er(d, 2n) 167 Er(d, n) 168 Er(d, 2n) 170 Er(d, 4n)
4.17 3.32 3.09 4.69 17.95
167
9.25 d
207.801
42
166
Er(d, n) Er(d, 2n) 168 Er(d, 3n) 170 Er(d, 5n)
2.68 3.76 11.53 24.79
170
Tm
170
167
166
Tm
7.70 h
165
Tm
30.06 h
80.585 691.250 705.333 778.814 785.904 1176.704
11.4 7.4 11.0 18.9 9.9 9.5
166
Er(d, 2n) Er(d, 3n) 168 Er(d, 4n) 170 Er(d, 6n)
6.05 12.48 20.25 33.52
242.917
35.5
164
Er(d, n) Er(d, 3n) 167 Er(d, 4n) 168 Er(d, 5n) 170 Er(d, 7n)
2.05 13.07 19.51 27.28 40.54
167
166
163
Tm
1.810 h
171
Er
Abundances (%):
7.516 h 162
Er (0.14),
164
Er (1.61),
166
104.320 241.305
18.6 10.9
162
Er(d, n) Er(d, 3n) 166 Er(d, 5n) 167 Er(d, 6n) 168 Er(d, 7n)
1.46 14.29 29.42 35.85 43.62
111.621 308.291
20.5 64
170
3.46
Er (33.6),
167
Er (22.95),
168
Er (26.8),
164
Er(d, p)
170
Er (14.9).
F. Ta´rka´nyi et al. / Nucl. Instr. and Meth. in Phys. Res. B 259 (2007) 829–835
ple but successful model code ALICE-IPPE [8]. Reaction cross-sections on the individual target isotopes were calculated up to 50 MeV deuteron energy and a weighted summation (according to the abundance of natural occurrence) was made to obtain the production cross-section on natural target. In all cases all possible direct reactions and precursor decay were taken into account. This procedure enables to understand the importance of the different contributing processes, to extrapolate the excitation function below and beyond the investigated energy range and to investigate the predictivity of the used computer code. The ALICE family code was developed by Blann and is based on the hybrid, the geometry-dependent hybrid (GDH) or the HMS pre-equilibrium models and the Weisskopf–Ewing evaporation formalism. The ALICE-IPPE code [8] is a version of the ALICE-91 code [9] modified by the Obninsk group to include the generalized super-fluid level density model and pre-equilibrium cluster emission. A priori calculations were performed without any parameter adjustment to see the general tendencies. For this mass region parameters should probably be chosen more carefully, particularly the optical model parameters and pre-equilibrium emission rates. As the lack of angular momentum and parity treatment in the Weisskopf–Ewing formalism used in the code makes independent treatment
831
of isomeric states impossible, only total production crosssections were calculated. 4. Results and discussion 4.1. Excitation functions The measured cross-sections are shown in Figs. 2 and 3 and the numerical data are collected in Table 2. To illustrate the tendency of the excitation functions at energies slightly beyond the measured data points the results of the theoretical calculations are shown up to 50 MeV deuteron energy. 4.1.1. Radioisotopes of thulium Due to our measuring circumstances and to the very low intensity, low energy (66.7 keV) gamma line it was impossible to deduce reliable cross-sections for 171Tm produced via the 170Er(d, n) reaction. 170 Tm is produced in the 170Er(d, 2n) reaction. The b-decay of 170Tm is followed by emission of a weak 84.3 keV gamma line. To avoid overlapping and contamination from the 84.94 keV Kb1 X-ray line from gammaray excitation of Pb, present in the normal shielding of the spectrometric set-up, while determining the activity of 800
200 170
Tm
VUB
100
165
Tm
163
Tm
171
Er
600
CYRIC ALICE-IPPE
400
0 168
Tm
200
200
0 Cross section (mb)
Cross section (mb)
100
0 167
Tm
400
200
100
0
200
VUB
37.5
0
CYRIC 166
Tm
ALICE-IPPE
400
25
200
12.5
0
0 0
10
20
30
40
50
Deuteron energy (MeV)
Fig. 2. Excitation functions of the natEr(d, x)170Tm, nat Er(d, x)167Tm and natEr(d, x)166Tm reactions.
0
10
20
30
40
50
Deuteron energy (MeV) nat
Er(d, x)168Tm,
Fig. 3. Excitation functions of the nat Er(d, x)171Er reactions.
nat
Er(d, x)165Tm,
nat
Er(d, x)163Tm,
832
Table 2 Measured cross-sections of the
nat
Er(d, x)163,165,166,167,168,170Tm and
E (MeV)
DE (MeV)
r (mb)
6.3 7.7 9.0 10.2 11.3 12.3 12.7 13.3 14.3 15.5 16.5 16.6 17.7 18.7 19.7 19.8 20.7 22.6 25.2 27.7 29.9 32.1 34.2 36.1 38.0 39.9
1.2 1.1 1.0 0.9 0.9 0.8 1.9 0.7 0.7 0.6 1.7 0.5 0.5 0.4 1.5 0.4 0.3 1.3 1.2 1.0 0.9 0.8 0.6 0.5 0.4 0.3
Tm
2.77 7.2 11.2 12.4
nat
Er(d, x)171Er reactions
165
166
Tm
Dr (mb)
r (mb)
Dr (mb)
0.54 1.1
0.040 0.363 1.75 2.72 2.73 2.65 2.04 2.31 3.11 27.7 89 101 181 287 326 353 410 462 480 628 577 569 551 564 503 572
0.005 0.045 0.20 0.31 0.32 0.31 0.34 0.27 0.36 3.1 10 11 20 32 37 40 46 52 54 71 65 64 62 63 56 64
1.4 1.6
167
Tm
r (mb) 0.77 30.1 107 183 282 298 345 407 446 467 513 483 508 466 508 491 457 474 517 514 543 533 463 362 318
168
Tm
170
Tm
171
Tm
Er
Dr (mb)
r (mb)
Dr (mb)
r (mb)
Dr (mb)
r (mb)
Dr (mb)
r (mb)
Dr (mb)
0.28 3.5 12 21 32 46 39 46 50 62 58 54 57 54 57 55 63 77 60 71 62 75 68 43 41
0.406 10.3 49.6 111 170 225 229 275 344 381 406 456 445 501 479 516 532 507 398 333 265 230 259 283 251 293
0.047 1.2 5.6 12 19 25 26 31 39 43 46 51 50 56 54 58 60 57 45 37 30 26 29 32 28 33
0.394 5.40 34.9 95 151 225 229 252 269 205 160 173 127 110 96 92 84 80 123 181 220 220 194 147 118 97
0.054 0.75 4.0 11 17 25 31 29 30 23 25 20 14 13 25 11 10 21 25 40 36 41 30 27 30 30
1.00 7.3 48.3 67.4 111 136
0.48 1.6 7.9 7.7 15 20
136 123 90
17 15 12
0.528 6.07 22.1 36.1 41.5 44.4 37.2 40.8 38.2 31.2 25.8 32.6 26.7 26.4 19.5 26.5 27.4 15.7 11.7 12.1
0.066 0.71 2.5 4.1 4.7 5.0 4.2 4.6 4.3 3.5 2.9 3.7 3.0 3.1 2.3 3.1 3.2 1.8 1.4 1.5
9.2 8.0 7.8 6.20 6.35
1.1 1.1 1.0 0.80 0.83
71 56.1 58.9
12 9.0 9.2
41 40.0
17 5.0
F. Ta´rka´nyi et al. / Nucl. Instr. and Meth. in Phys. Res. B 259 (2007) 829–835
Deuteron energy
163
F. Ta´rka´nyi et al. / Nucl. Instr. and Meth. in Phys. Res. B 259 (2007) 829–835
4.1.2. Radioisotopes of erbium Considering our measuring circumstances and the very low intensity of the low energy (109.8 keV) gamma line it was impossible to deduce reliable cross-sections for 169Er produced via the 168Er(d, p) and 170Er(d, p2n) reactions. The radionuclide 171Er is produced in the 170Er(d, p) reaction. The measured cross-sections are shown in Fig. 3 in comparison with the results of the model calculation. The ALICE-IPPE significantly underestimates the measured values. The reason is the poor modeling of the deuteron breakup which leads to an underestimation of (d, p) contributions. As it can be seen in Fig. 3 the cross-sections of the (d, p) process are high which is attractive from the point of view of the production of the medically important 171Tm (through the decay of the short lived 171Er parent). 4.2. Integral yields Thick target yields calculated from our fitted cross-sections give reliable estimations for production of medically relevant radioisotopes produced on highly enriched
300 Integral yield
Tm-167 (*10)
Tm-165 Dmitriev 1986 [11]
Yield (MBq/μAh)
the 170Tm, separate measurements were carried out with an X-ray detector in air, far from any lead material. In spite of these precautions the different X-rays of lead still appear in the spectra but with very low intensity. A correction for the contamination at the 84.3 keV energy of interest was performed on the basis of the well separated 74.97 keV Ka1 X-ray line of Pb. The resulting excitation function is shown in Fig. 2. The comparison with the theory shows a good agreement. Two pronounced maxima appear in the excitation function of 168Tm (Fig. 2). The first corresponds to the sum of the 167Er(d, n) and the 168Er(d, 2n) reactions. According to the model results and to the systematics of the reported experimental data in this mass region, the probability of (d, n) processes is significantly lower than that of (d, 2n) reactions. The second maximum is due to the 170Er(d, 4n) reaction. The theory describes well the experimental data. The measured large maximum for 167Tm comes from a combination of the 166Er(d, n), 167Er(d, 2n) and 168Er(d, 3n) reactions and the raising tail at high energy from the 170 Er(d, 5n) reaction. Good agreement with the theoretical calculation was found (Fig. 2). The resulting cross-section for production of the 166Tm radionuclide in the investigated energy region is composed of the 166Er(d, 2n), 167Er(d, 3n) and 168Er(d, 4n) reactions (Fig. 2). In the production of 165Tm the contribution of the (d, n) reaction on the low abundance 164Er is small. In the investigated energy range the main processes are the 166 Er(d, 3n), 167Er(d, 4n) and 168Er(d, 5n) reactions (Fig. 3). As in the experiment at CYRIC the time between EOB and starting the counting of the irradiated samples was rather long production of the shorter lived 163Tm (T1/2 = 1.8 h) was detected only in the low energy irradiation at VUB (Fig. 3).
833
Tm-167 (*10) Dmitriev 1986 [11]
200
Tm-165
Tm-170 (*1000) Dmitriev 1986 [11]
100
Tm-170 (*1000) Er-171
0 0
10
20 Deuteron energy (MeV)
30
40
Fig. 4. Integral yields of 165,167,170Tm and 171Er calculated from the measured excitation functions. For comparison the thick target yields of nat Er(d, x)165,167,170Tm measured by Dmitriev et al. [11].
mono-isotopic target. The integral yields for 165,167,170Tm and 171Er calculated from the measured excitation functions are shown in Fig. 4 in comparison with the directly measured data of Dmitriev et al. [10–12]. An acceptable agreement was found for production of 170Tm. Our calculated integral yield values for the production of 165Tm and 167 Tm are a little higher than the direct yield data of Dmitriev et al. 5. Comparison of charged particle production routes of 167,170,171 Tm and 165,169Er The comparison of the cross-section data of reactor and accelerator routes for 167,170,171Tm and 165,169Er production are given in Table 3. The cross-sections of proton induced reactions were obtained from the literature [13], from our available preliminary experimental data [14] and from the MENDL-2P database which contains results of ALICEIPPE calculations [15]. The cross-sections for deuteron induced reactions were taken from the present measurements except some reactions where either ALICE-IPPE theoretical data or the systematics of reported experimental data was used. According to Table 3 among the charged particle induced reactions the widely used (p, 2n) reaction provides the highest yields at energies below 30 MeV (standard radionuclide production cyclotron). Due to the broad shape of the excitation functions of proton induced reactions leading for instance to 165Er, 169Yb, 167Tm high energy proton irradiations on cheaper targets having natural isotopic composition and with high production yields could be considered (contributions of channels with successively more emitted neutrons on the different natural occurring isotopes of the target). The radionuclides 169Er and 171Tm can be produced practically at cyclotrons only by deuteron induced reactions. The total amount of 165,169Er and 167,170,171Tm produced at a nuclear reactor is significantly larger than the amount expected via charged particle induced reactions
F. Ta´rka´nyi et al. / Nucl. Instr. and Meth. in Phys. Res. B 259 (2007) 829–835
834
Table 3 Comparison of production routes of
165,169
Er and
167,170,171
Tm using reactor and accelerator
Isotope
Nuclear reactor
Cyclotron
165
164
165
Er
169
Er
167
Tm
170
Tm
171
Tm
165
Er(n, c) Er rth = 13,000 mb Carrier added
Ho(p, n)165Er, rmax = 170 mb (11 MeV) [13] Ho(d, 2n)165Er, rmax = 600 mb (13 MeV) to be published 166 Er(p, 2n)165Tm ! 165Er, rmax = 1300 mb (22 MeV) [14,15] nat Er(p, xn)165Tm ! 165Er, rmax = 420 mb (22 MeV) [14] 169 Tm(p, x)165Tm ! 165Er, rmax = 550 mb (54 MeV) [15] nat Yb(p, x)165Tm ! 165Er, rmax = 140 mb (130 MeV) [15] 164 Er(d, n)165Tm ! 165Er, rmax = 60 mb (10 MeV) this work nat Er(d, x)165Tm ! 165Er, rmax = 630 mb (28 MeV) this work 166 Er(d, 3n)165Tm ! 165Er, rmax = 330 mb (25 MeV) this work No carrier added
168
168
165
Er(n, c)169Er rth = 2000 mb Carrier added
Er(d, p)169Er, rmax = 300 mb (12 MeV) from systematics Yb(p, 2n)169Lu ! 169Yb, rmax = 1300 mb (23 MeV) [15] nat Yb(p, x)169Lu ! 169Yb, rmax = 340 mb (42 MeV) [15] No carrier added
168
167
170
Yb(n, 2n)167Yb ! 167Tm r14MeV = 1900 mb No carrier added
Er(p, n)167Tm, rmax = 500 mb (12 MeV) [15] Er(d, n)167Tm, rmax = 23 mb (10 MeV) this work 168 Yb(p, 2n)167Lu ! 167Yb ! 167Tm, rmax = 1300 mb (24 MeV) [15] nat Yb(p, x)167Lu ! 167Yb ! 167Tm, rmax = 170 mb (62 MeV) [15] No carrier added
169
170
166
Tm(n, c)170Tm rth = 105,000 mb Carrier added
Er(p, n)170Tm, rmax = 130 mb (10 MeV) [15] Er(d, 2n)170Tm, rmax = 120 mb (13 MeV) this work No carrier added
170 Er(n, c)171Er ! 171Tm rth = 6000 mb No carrier added
170
at a cyclotron (Table 3). However, the reactor produced products are only of low specific activity except 171Tm. 6. Summary and conclusions In the frame of a systematic investigation of activation cross-sections induced by deuterons, new experimental excitation functions were measured in the energy range from threshold up to 40 MeV for the production of 163,165,166,167,168,170 Tm and 171Er by irradiation of natEr. The reliability and accuracy of the data is guaranteed by relating them to recommended monitor reaction values. According to our knowledge we present these results for the first time for all investigated reactions. The ALICE-IPPE calculation confirms in most cases the general shape, the value and the energy of the maximum of the excitation curves. The theoretical code needs, however, further improvements for description of (d, p) reactions (breakup process). The measured excitation functions yield useful practical information in several fields. The most important field is the medical isotope production. As concluded in our previous investigations [16] we can confirm that the (d, 2n) process is more productive than the (p, n) reaction in the heavy mass region. The high yield (d, p) + b route can be a substitute for the (n, c) + b process making for instance possible production of the impor-
170
Er(d, n)171Tm, rmax = 12 mb (83 MeV) this work Er(d, p)171Er ! 171Tm, rmax = 300 mb (12 MeV) this work No carrier added 170
tant medical radioisotope 171Tm (after b decay of the parent 171Er) at cyclotrons. The measured excitation functions could be useful in the field of charged particle activation analysis by broadening the nuclear data for the possible marker isotopes. References [1] R.R. Kinsey, C.L. Dunford, J.K. Tuli, T.W. Burrows, The NUDAT/ PCNUDAT Program for Nuclear Data, Capture Gamma-Ray Spectroscopy and Related Topics, Vol. 2, Springer Hungarica Ltd., 1997, p. 657, Data extracted from the NUDAT database, version: 17 May 2002, Available from: (Chapter 4). [3] S. Taka´cs, F. Szelecse´nyi, F. Ta´rka´nyi, M. Sonck, A. Hermanne, Yu.N. Shubin, A.I. Dityuk, M.G. Mustafa, Z. Youxiang, New crosssections and intercomparison of deuteron monitor reactions on Al, Ti, Fe, Ni and Cu, Nucl. Instr. and Meth. B 174 (2001) 235. [4] H.H. Andersen, J.F. Ziegler, Hydrogen stopping powers and ranges in all elements, The Stopping and Ranges of Ions in Matter, Vol. 3, Pergamon Press, 1977, ISBN 0-08-021605-6. [5] F. Ta´rka´nyi, F. Szelecse´nyi, S. Taka´cs, Determination of effective bombarding energies and fluxes using improved stacked foil technique, Acta Radiol., Supplementum 376 (1991) 72.
F. Ta´rka´nyi et al. / Nucl. Instr. and Meth. in Phys. Res. B 259 (2007) 829–835 [6] F. Ta´rka´nyi, S. Taka´cs, F. Ditro´i, A. Hermanne, M. Sonck, Yu.N. Shubin, Excitation functions of deuteron induced nuclear reactions on natural zinc up to 50 MeV, Nucl. Instr. and Meth. B 217 (2004) 531. [7] F. Ta´rka´nyi, B. Kira´ly, F. Ditro´i, S. Taka´cs, J. Csikai, A. Hermanne, M.S. Uddin, M. Hagiwara, M. Baba, Yu.N. Shubin, S.F. Kovalev, Cross sections of deuteron induced nuclear reactions on iridium, Nucl. Instr. and Meth. B 247 (2006) 210. [8] A.I. Dityuk, A.Yu. Konobeyev, V.P. Lunev, Yu.N. Shubin, New advanced version of computer code ALICE – IPPE, Report INDC(CCP)-410, International Atomic Energy Agency, Vienna, 1998. [9] M. Blann, ALICE-91, Report PSR-0146. Available from:. [10] P.P. Dmitriev, G.A. Molin, M.V. Panarin, Yields of 165,166,167,168,170 Tm in reactions with proton, deuteron and alpha particles, Atom. Energiya 48 (1980) 402. [11] P.P. Dmitriev, Radionuclide Yield in Reactions with Protons, Deuterons, Alpha Particles and Helium-3, Energoatomizdat, Moscow, 1986.
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[12] P.P. Dmitriev, M.N. Krasnov, G.A. Molin, Radioactive nuclide yields for thick target at 22 MeV deuterons energy, Yadernie Konstanti (4) (1982) 38. [13] G.J. Beyer, S.K. Zeisler, D.W. Becker, The Auger-electron emitter 165Er: excitation function of the 165Ho(p, n)165Er process, Radiochim. Acta 92 (2004) 219. [14] F. Ta´rka´nyi, S. Taka´cs, F. Ditro´i, B. Kira´ly, S.F. Kovalev, A. Ignatyuk, Experimental excitation functions for proton induced reactions on natEr, in: 9th International Symposium on Synthesis and Applications of Isotopes and Isotopically Labeled Compounds, Edinburgh, UK, 16–20 July, 2006, Book of Abstracts, p. 233. [15] Yu.N. Shubin, V.P. Lunev, A. Yu. Konobeyev, A.I. Dityuk, Proton reaction data library for nuclear activation, MENDL-2P (Medium Energy Nuclear Data Library), IAEA-NDS-204, International Atomic Energy Agency, Vienna, Austria, 1998. [16] A. Hermanne, F. Ta´rka´nyi, S. Taka´cs, Isotope production with medium energy deuterons, in: 9th International Symposium on Synthesis and Applications of Isotopes and Isotopically Labeled Compounds, Edinburgh, UK, 16–20 July 2006, Book of Abstracts, p. 63.
Nuclear Instruments and Methods in Physics Research B 259 (2007) 829–835 www.elsevier.com/locate/nimb
Study of activation cross-sections of deuteron induced reactions on erbium: Production of radioisotopes for practical applications F. Ta´rka´nyi a, A. Hermanne b, B. Kira´ly a,*, S. Taka´cs a, F. Ditro´i a, M. Baba c, T. Ohtsuki c, S.F. Kovalev d, A.V. Ignatyuk d a
Institute of Nuclear Research of the Hungarian Academy of Sciences (ATOMKI), 4026 Debrecen, Hungary b Cyclotron Laboratory, Vrije Universiteit Brussel (VUB), 1090 Brussels, Belgium c Cyclotron and Radioisotope Center (CYRIC), Tohoku University, Sendai 980-8578, Japan d Institute of Physics and Power Engineering (IPPE), Obninsk 249033, Russia Received 8 January 2007; received in revised form 26 January 2007 Available online 15 February 2007
Abstract Excitation functions of the natEr(d, x)163,165,166,167,168,170Tm and natEr(d, x)171Er reactions have been measured experimentally from their respective thresholds up to 40 MeV for the first time. Cross-sections were determined using the activation method and the stacked foil irradiation technique. The theoretical interpretation was done with the ALICE-IPPE code. From the fitted experimental cross-section data integral production yields were calculated and compared to measured integral yield data reported in the literature. Ó 2007 Elsevier B.V. All rights reserved. PACS: 25.45.z; 27.70.+q Keywords: Natural erbium target; Deuteron induced reaction; Cross-section; Excitation function; Therapeutic radionuclides
1. Introduction The use of compounds and biomolecules labeled with radionuclides of rare earth elements is a fast growing field in therapeutic nuclear medicine. These radionuclides are currently produced by (n, c) caption in a nuclear reactor but to obtain no carrier added end-products with high specific activity, alternative production routes utilizing charged particle induced processes are required. Our systematic study of proton and deuteron induced nuclear reactions shows that it is worth investigating the deuteron induced reactions because in the heavy mass region the (d, 2n) process results in higher yields than the (p, n) channel. Here we report on the production of Tm and Er radioisotopes by (d, x) reactions on erbium targets. Among the possible reaction products the 165Tm ! 165Er, *
Corresponding author. Tel.: +36 52 509200; fax: +36 52 416181. E-mail address: [email protected] (B. Kira´ly).
0168-583X/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2007.01.287
169
Er, 167Tm, 170Tm and 171Er ! 171Tm radionuclei have gained interest in therapy. No experimental results were found in the literature for cross-section of deuteron induced reactions on erbium. 2. Experimental The excitation functions were measured up to 40 MeV using the stacked foil irradiation technique. Commercial (Goodfellow) high purity Er foils (25 and 32 lm) were stacked together with Ti (12 and 31 lm) and Al (100 lm) monitor foils. These foils were inserted evenly in the irradiated target stack allowing measurement of the excitation function of several monitor reaction over the whole investigated energy range. The irradiations were done at the external beam lines of the cyclotrons of the Vrije Universiteit Brussel (VUB, Brussels, Belgium) and of the Cyclotron and Radioisotope Center of the Tohoku University (CYRIC, Sendai, Japan). The radioactivity of each sample
F. Ta´rka´nyi et al. / Nucl. Instr. and Meth. in Phys. Res. B 259 (2007) 829–835
830
and monitor foil was measured nondestructively by an HPGe c-spectrometer. Counting was started about 2–3 h after the end of bombardment (EOB) at VUB and 7–8 h after EOB at CYRIC. Decay data were taken from NUDAT [1], standard cross-section data for the used monitor reactions natTi(d, x)48V and natAl(d, x)22,24Na were
taken from [2,3]. The energy degradation along the stack was determined by calculation [4] and corrected on the basis of the simultaneously measured monitor reactions using the method described in [5]. The excitation functions were hence determined in an accurate way relative to the recommended monitor reactions (Fig. 1). The decay data and the contributing reactions are presented in Table 1. As naturally occurring erbium is composed of six stable isotopes, so called elemental cross-sections were determined supposing that erbium is composed of only one isotope. The experimental techniques and data processing (including calculation of cross-sections and integral yields as well as estimation of the uncertainties) were similar to or identical with what is described in more detail in our earlier reports [6,7].
400 Na-24 this work
Monitor reactions
Na-24 recommended [2]
Cross section (mb)
Na-22 this work
300
Na-22 recommended [2] V-48 this work V-48 recommended [2] V-48 [3]
200
100
3. Theoretical calculations with model codes
0 0
5
10
35
30 15 25 20 Deuteron energy (MeV)
Fig. 1. Excitation functions of the 27Al(d, x)22,24Na and monitor reactions compared to recommended values.
40 nat The measured Er(d, x)163,165,166,167,168,170Tm, 171 Er-(d, x) Er cross-sections were compared to theoretical effective cross-sections calculated by means of the sim-
nat
nat
Ti(d, x)48V
Table 1 Decay characteristics of the investigated reaction products [1] Nuclide
Half-life
171
Ec (keV)
Ic (%)
Contributing process
Q-value (MeV)
Tm Tm 168 Tm
1.92 y 128.6 d 93.1 d
66.731 84.255 198.251 447.515 631.705 720.392 741.355 815.989 821.162
0.143 2.48 53.8 23.7 9.1 12.0 12.6 50.3 11.8
170
Er(d, n) Er(d, 2n) 167 Er(d, n) 168 Er(d, 2n) 170 Er(d, 4n)
4.17 3.32 3.09 4.69 17.95
167
9.25 d
207.801
42
166
Er(d, n) Er(d, 2n) 168 Er(d, 3n) 170 Er(d, 5n)
2.68 3.76 11.53 24.79
170
Tm
170
167
166
Tm
7.70 h
165
Tm
30.06 h
80.585 691.250 705.333 778.814 785.904 1176.704
11.4 7.4 11.0 18.9 9.9 9.5
166
Er(d, 2n) Er(d, 3n) 168 Er(d, 4n) 170 Er(d, 6n)
6.05 12.48 20.25 33.52
242.917
35.5
164
Er(d, n) Er(d, 3n) 167 Er(d, 4n) 168 Er(d, 5n) 170 Er(d, 7n)
2.05 13.07 19.51 27.28 40.54
167
166
163
Tm
1.810 h
171
Er
Abundances (%):
7.516 h 162
Er (0.14),
164
Er (1.61),
166
104.320 241.305
18.6 10.9
162
Er(d, n) Er(d, 3n) 166 Er(d, 5n) 167 Er(d, 6n) 168 Er(d, 7n)
1.46 14.29 29.42 35.85 43.62
111.621 308.291
20.5 64
170
3.46
Er (33.6),
167
Er (22.95),
168
Er (26.8),
164
Er(d, p)
170
Er (14.9).
F. Ta´rka´nyi et al. / Nucl. Instr. and Meth. in Phys. Res. B 259 (2007) 829–835
ple but successful model code ALICE-IPPE [8]. Reaction cross-sections on the individual target isotopes were calculated up to 50 MeV deuteron energy and a weighted summation (according to the abundance of natural occurrence) was made to obtain the production cross-section on natural target. In all cases all possible direct reactions and precursor decay were taken into account. This procedure enables to understand the importance of the different contributing processes, to extrapolate the excitation function below and beyond the investigated energy range and to investigate the predictivity of the used computer code. The ALICE family code was developed by Blann and is based on the hybrid, the geometry-dependent hybrid (GDH) or the HMS pre-equilibrium models and the Weisskopf–Ewing evaporation formalism. The ALICE-IPPE code [8] is a version of the ALICE-91 code [9] modified by the Obninsk group to include the generalized super-fluid level density model and pre-equilibrium cluster emission. A priori calculations were performed without any parameter adjustment to see the general tendencies. For this mass region parameters should probably be chosen more carefully, particularly the optical model parameters and pre-equilibrium emission rates. As the lack of angular momentum and parity treatment in the Weisskopf–Ewing formalism used in the code makes independent treatment
831
of isomeric states impossible, only total production crosssections were calculated. 4. Results and discussion 4.1. Excitation functions The measured cross-sections are shown in Figs. 2 and 3 and the numerical data are collected in Table 2. To illustrate the tendency of the excitation functions at energies slightly beyond the measured data points the results of the theoretical calculations are shown up to 50 MeV deuteron energy. 4.1.1. Radioisotopes of thulium Due to our measuring circumstances and to the very low intensity, low energy (66.7 keV) gamma line it was impossible to deduce reliable cross-sections for 171Tm produced via the 170Er(d, n) reaction. 170 Tm is produced in the 170Er(d, 2n) reaction. The b-decay of 170Tm is followed by emission of a weak 84.3 keV gamma line. To avoid overlapping and contamination from the 84.94 keV Kb1 X-ray line from gammaray excitation of Pb, present in the normal shielding of the spectrometric set-up, while determining the activity of 800
200 170
Tm
VUB
100
165
Tm
163
Tm
171
Er
600
CYRIC ALICE-IPPE
400
0 168
Tm
200
200
0 Cross section (mb)
Cross section (mb)
100
0 167
Tm
400
200
100
0
200
VUB
37.5
0
CYRIC 166
Tm
ALICE-IPPE
400
25
200
12.5
0
0 0
10
20
30
40
50
Deuteron energy (MeV)
Fig. 2. Excitation functions of the natEr(d, x)170Tm, nat Er(d, x)167Tm and natEr(d, x)166Tm reactions.
0
10
20
30
40
50
Deuteron energy (MeV) nat
Er(d, x)168Tm,
Fig. 3. Excitation functions of the nat Er(d, x)171Er reactions.
nat
Er(d, x)165Tm,
nat
Er(d, x)163Tm,
832
Table 2 Measured cross-sections of the
nat
Er(d, x)163,165,166,167,168,170Tm and
E (MeV)
DE (MeV)
r (mb)
6.3 7.7 9.0 10.2 11.3 12.3 12.7 13.3 14.3 15.5 16.5 16.6 17.7 18.7 19.7 19.8 20.7 22.6 25.2 27.7 29.9 32.1 34.2 36.1 38.0 39.9
1.2 1.1 1.0 0.9 0.9 0.8 1.9 0.7 0.7 0.6 1.7 0.5 0.5 0.4 1.5 0.4 0.3 1.3 1.2 1.0 0.9 0.8 0.6 0.5 0.4 0.3
Tm
2.77 7.2 11.2 12.4
nat
Er(d, x)171Er reactions
165
166
Tm
Dr (mb)
r (mb)
Dr (mb)
0.54 1.1
0.040 0.363 1.75 2.72 2.73 2.65 2.04 2.31 3.11 27.7 89 101 181 287 326 353 410 462 480 628 577 569 551 564 503 572
0.005 0.045 0.20 0.31 0.32 0.31 0.34 0.27 0.36 3.1 10 11 20 32 37 40 46 52 54 71 65 64 62 63 56 64
1.4 1.6
167
Tm
r (mb) 0.77 30.1 107 183 282 298 345 407 446 467 513 483 508 466 508 491 457 474 517 514 543 533 463 362 318
168
Tm
170
Tm
171
Tm
Er
Dr (mb)
r (mb)
Dr (mb)
r (mb)
Dr (mb)
r (mb)
Dr (mb)
r (mb)
Dr (mb)
0.28 3.5 12 21 32 46 39 46 50 62 58 54 57 54 57 55 63 77 60 71 62 75 68 43 41
0.406 10.3 49.6 111 170 225 229 275 344 381 406 456 445 501 479 516 532 507 398 333 265 230 259 283 251 293
0.047 1.2 5.6 12 19 25 26 31 39 43 46 51 50 56 54 58 60 57 45 37 30 26 29 32 28 33
0.394 5.40 34.9 95 151 225 229 252 269 205 160 173 127 110 96 92 84 80 123 181 220 220 194 147 118 97
0.054 0.75 4.0 11 17 25 31 29 30 23 25 20 14 13 25 11 10 21 25 40 36 41 30 27 30 30
1.00 7.3 48.3 67.4 111 136
0.48 1.6 7.9 7.7 15 20
136 123 90
17 15 12
0.528 6.07 22.1 36.1 41.5 44.4 37.2 40.8 38.2 31.2 25.8 32.6 26.7 26.4 19.5 26.5 27.4 15.7 11.7 12.1
0.066 0.71 2.5 4.1 4.7 5.0 4.2 4.6 4.3 3.5 2.9 3.7 3.0 3.1 2.3 3.1 3.2 1.8 1.4 1.5
9.2 8.0 7.8 6.20 6.35
1.1 1.1 1.0 0.80 0.83
71 56.1 58.9
12 9.0 9.2
41 40.0
17 5.0
F. Ta´rka´nyi et al. / Nucl. Instr. and Meth. in Phys. Res. B 259 (2007) 829–835
Deuteron energy
163
F. Ta´rka´nyi et al. / Nucl. Instr. and Meth. in Phys. Res. B 259 (2007) 829–835
4.1.2. Radioisotopes of erbium Considering our measuring circumstances and the very low intensity of the low energy (109.8 keV) gamma line it was impossible to deduce reliable cross-sections for 169Er produced via the 168Er(d, p) and 170Er(d, p2n) reactions. The radionuclide 171Er is produced in the 170Er(d, p) reaction. The measured cross-sections are shown in Fig. 3 in comparison with the results of the model calculation. The ALICE-IPPE significantly underestimates the measured values. The reason is the poor modeling of the deuteron breakup which leads to an underestimation of (d, p) contributions. As it can be seen in Fig. 3 the cross-sections of the (d, p) process are high which is attractive from the point of view of the production of the medically important 171Tm (through the decay of the short lived 171Er parent). 4.2. Integral yields Thick target yields calculated from our fitted cross-sections give reliable estimations for production of medically relevant radioisotopes produced on highly enriched
300 Integral yield
Tm-167 (*10)
Tm-165 Dmitriev 1986 [11]
Yield (MBq/μAh)
the 170Tm, separate measurements were carried out with an X-ray detector in air, far from any lead material. In spite of these precautions the different X-rays of lead still appear in the spectra but with very low intensity. A correction for the contamination at the 84.3 keV energy of interest was performed on the basis of the well separated 74.97 keV Ka1 X-ray line of Pb. The resulting excitation function is shown in Fig. 2. The comparison with the theory shows a good agreement. Two pronounced maxima appear in the excitation function of 168Tm (Fig. 2). The first corresponds to the sum of the 167Er(d, n) and the 168Er(d, 2n) reactions. According to the model results and to the systematics of the reported experimental data in this mass region, the probability of (d, n) processes is significantly lower than that of (d, 2n) reactions. The second maximum is due to the 170Er(d, 4n) reaction. The theory describes well the experimental data. The measured large maximum for 167Tm comes from a combination of the 166Er(d, n), 167Er(d, 2n) and 168Er(d, 3n) reactions and the raising tail at high energy from the 170 Er(d, 5n) reaction. Good agreement with the theoretical calculation was found (Fig. 2). The resulting cross-section for production of the 166Tm radionuclide in the investigated energy region is composed of the 166Er(d, 2n), 167Er(d, 3n) and 168Er(d, 4n) reactions (Fig. 2). In the production of 165Tm the contribution of the (d, n) reaction on the low abundance 164Er is small. In the investigated energy range the main processes are the 166 Er(d, 3n), 167Er(d, 4n) and 168Er(d, 5n) reactions (Fig. 3). As in the experiment at CYRIC the time between EOB and starting the counting of the irradiated samples was rather long production of the shorter lived 163Tm (T1/2 = 1.8 h) was detected only in the low energy irradiation at VUB (Fig. 3).
833
Tm-167 (*10) Dmitriev 1986 [11]
200
Tm-165
Tm-170 (*1000) Dmitriev 1986 [11]
100
Tm-170 (*1000) Er-171
0 0
10
20 Deuteron energy (MeV)
30
40
Fig. 4. Integral yields of 165,167,170Tm and 171Er calculated from the measured excitation functions. For comparison the thick target yields of nat Er(d, x)165,167,170Tm measured by Dmitriev et al. [11].
mono-isotopic target. The integral yields for 165,167,170Tm and 171Er calculated from the measured excitation functions are shown in Fig. 4 in comparison with the directly measured data of Dmitriev et al. [10–12]. An acceptable agreement was found for production of 170Tm. Our calculated integral yield values for the production of 165Tm and 167 Tm are a little higher than the direct yield data of Dmitriev et al. 5. Comparison of charged particle production routes of 167,170,171 Tm and 165,169Er The comparison of the cross-section data of reactor and accelerator routes for 167,170,171Tm and 165,169Er production are given in Table 3. The cross-sections of proton induced reactions were obtained from the literature [13], from our available preliminary experimental data [14] and from the MENDL-2P database which contains results of ALICEIPPE calculations [15]. The cross-sections for deuteron induced reactions were taken from the present measurements except some reactions where either ALICE-IPPE theoretical data or the systematics of reported experimental data was used. According to Table 3 among the charged particle induced reactions the widely used (p, 2n) reaction provides the highest yields at energies below 30 MeV (standard radionuclide production cyclotron). Due to the broad shape of the excitation functions of proton induced reactions leading for instance to 165Er, 169Yb, 167Tm high energy proton irradiations on cheaper targets having natural isotopic composition and with high production yields could be considered (contributions of channels with successively more emitted neutrons on the different natural occurring isotopes of the target). The radionuclides 169Er and 171Tm can be produced practically at cyclotrons only by deuteron induced reactions. The total amount of 165,169Er and 167,170,171Tm produced at a nuclear reactor is significantly larger than the amount expected via charged particle induced reactions
F. Ta´rka´nyi et al. / Nucl. Instr. and Meth. in Phys. Res. B 259 (2007) 829–835
834
Table 3 Comparison of production routes of
165,169
Er and
167,170,171
Tm using reactor and accelerator
Isotope
Nuclear reactor
Cyclotron
165
164
165
Er
169
Er
167
Tm
170
Tm
171
Tm
165
Er(n, c) Er rth = 13,000 mb Carrier added
Ho(p, n)165Er, rmax = 170 mb (11 MeV) [13] Ho(d, 2n)165Er, rmax = 600 mb (13 MeV) to be published 166 Er(p, 2n)165Tm ! 165Er, rmax = 1300 mb (22 MeV) [14,15] nat Er(p, xn)165Tm ! 165Er, rmax = 420 mb (22 MeV) [14] 169 Tm(p, x)165Tm ! 165Er, rmax = 550 mb (54 MeV) [15] nat Yb(p, x)165Tm ! 165Er, rmax = 140 mb (130 MeV) [15] 164 Er(d, n)165Tm ! 165Er, rmax = 60 mb (10 MeV) this work nat Er(d, x)165Tm ! 165Er, rmax = 630 mb (28 MeV) this work 166 Er(d, 3n)165Tm ! 165Er, rmax = 330 mb (25 MeV) this work No carrier added
168
168
165
Er(n, c)169Er rth = 2000 mb Carrier added
Er(d, p)169Er, rmax = 300 mb (12 MeV) from systematics Yb(p, 2n)169Lu ! 169Yb, rmax = 1300 mb (23 MeV) [15] nat Yb(p, x)169Lu ! 169Yb, rmax = 340 mb (42 MeV) [15] No carrier added
168
167
170
Yb(n, 2n)167Yb ! 167Tm r14MeV = 1900 mb No carrier added
Er(p, n)167Tm, rmax = 500 mb (12 MeV) [15] Er(d, n)167Tm, rmax = 23 mb (10 MeV) this work 168 Yb(p, 2n)167Lu ! 167Yb ! 167Tm, rmax = 1300 mb (24 MeV) [15] nat Yb(p, x)167Lu ! 167Yb ! 167Tm, rmax = 170 mb (62 MeV) [15] No carrier added
169
170
166
Tm(n, c)170Tm rth = 105,000 mb Carrier added
Er(p, n)170Tm, rmax = 130 mb (10 MeV) [15] Er(d, 2n)170Tm, rmax = 120 mb (13 MeV) this work No carrier added
170 Er(n, c)171Er ! 171Tm rth = 6000 mb No carrier added
170
at a cyclotron (Table 3). However, the reactor produced products are only of low specific activity except 171Tm. 6. Summary and conclusions In the frame of a systematic investigation of activation cross-sections induced by deuterons, new experimental excitation functions were measured in the energy range from threshold up to 40 MeV for the production of 163,165,166,167,168,170 Tm and 171Er by irradiation of natEr. The reliability and accuracy of the data is guaranteed by relating them to recommended monitor reaction values. According to our knowledge we present these results for the first time for all investigated reactions. The ALICE-IPPE calculation confirms in most cases the general shape, the value and the energy of the maximum of the excitation curves. The theoretical code needs, however, further improvements for description of (d, p) reactions (breakup process). The measured excitation functions yield useful practical information in several fields. The most important field is the medical isotope production. As concluded in our previous investigations [16] we can confirm that the (d, 2n) process is more productive than the (p, n) reaction in the heavy mass region. The high yield (d, p) + b route can be a substitute for the (n, c) + b process making for instance possible production of the impor-
170
Er(d, n)171Tm, rmax = 12 mb (83 MeV) this work Er(d, p)171Er ! 171Tm, rmax = 300 mb (12 MeV) this work No carrier added 170
tant medical radioisotope 171Tm (after b decay of the parent 171Er) at cyclotrons. The measured excitation functions could be useful in the field of charged particle activation analysis by broadening the nuclear data for the possible marker isotopes. References [1] R.R. Kinsey, C.L. Dunford, J.K. Tuli, T.W. Burrows, The NUDAT/ PCNUDAT Program for Nuclear Data, Capture Gamma-Ray Spectroscopy and Related Topics, Vol. 2, Springer Hungarica Ltd., 1997, p. 657, Data extracted from the NUDAT database, version: 17 May 2002, Available from:
F. Ta´rka´nyi et al. / Nucl. Instr. and Meth. in Phys. Res. B 259 (2007) 829–835 [6] F. Ta´rka´nyi, S. Taka´cs, F. Ditro´i, A. Hermanne, M. Sonck, Yu.N. Shubin, Excitation functions of deuteron induced nuclear reactions on natural zinc up to 50 MeV, Nucl. Instr. and Meth. B 217 (2004) 531. [7] F. Ta´rka´nyi, B. Kira´ly, F. Ditro´i, S. Taka´cs, J. Csikai, A. Hermanne, M.S. Uddin, M. Hagiwara, M. Baba, Yu.N. Shubin, S.F. Kovalev, Cross sections of deuteron induced nuclear reactions on iridium, Nucl. Instr. and Meth. B 247 (2006) 210. [8] A.I. Dityuk, A.Yu. Konobeyev, V.P. Lunev, Yu.N. Shubin, New advanced version of computer code ALICE – IPPE, Report INDC(CCP)-410, International Atomic Energy Agency, Vienna, 1998. [9] M. Blann, ALICE-91, Report PSR-0146. Available from:
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[12] P.P. Dmitriev, M.N. Krasnov, G.A. Molin, Radioactive nuclide yields for thick target at 22 MeV deuterons energy, Yadernie Konstanti (4) (1982) 38. [13] G.J. Beyer, S.K. Zeisler, D.W. Becker, The Auger-electron emitter 165Er: excitation function of the 165Ho(p, n)165Er process, Radiochim. Acta 92 (2004) 219. [14] F. Ta´rka´nyi, S. Taka´cs, F. Ditro´i, B. Kira´ly, S.F. Kovalev, A. Ignatyuk, Experimental excitation functions for proton induced reactions on natEr, in: 9th International Symposium on Synthesis and Applications of Isotopes and Isotopically Labeled Compounds, Edinburgh, UK, 16–20 July, 2006, Book of Abstracts, p. 233. [15] Yu.N. Shubin, V.P. Lunev, A. Yu. Konobeyev, A.I. Dityuk, Proton reaction data library for nuclear activation, MENDL-2P (Medium Energy Nuclear Data Library), IAEA-NDS-204, International Atomic Energy Agency, Vienna, Austria, 1998. [16] A. Hermanne, F. Ta´rka´nyi, S. Taka´cs, Isotope production with medium energy deuterons, in: 9th International Symposium on Synthesis and Applications of Isotopes and Isotopically Labeled Compounds, Edinburgh, UK, 16–20 July 2006, Book of Abstracts, p. 63.