- Email: [email protected]
226Th nuclear decay data evaluation
Applied Radiation and Isotopes 155 (2020) 108941
Contents lists available at ScienceDirect
Applied Radiation and Isotopes journal homepage: http://www.elsevier.com/locate/apradiso
226
Th nuclear decay data evaluation
Aurelian Luca Horia Hulubei National Institute for R&D in Physics and Nuclear Engineering, IFIN-HH Bucharest, 30 Reactorului Street, Magurele, Ilfov County, PO Box MG-6, RO077125, Romania
A R T I C L E I N F O
A B S T R A C T
Keywords: Nuclear decay data Alpha-particle Evaluation 226 Th
Following the recent evaluation of the nuclear decay data of 230U, a similar evaluation for its daughter, 226Th, a radionuclide of interest for targeted alpha therapy, was undertaken within the Decay Data Evaluation Project (DDEP) and an IAEA Coordinated Research Project. The nuclear decay data presented are: the half-life, decay energy, alpha-particle emission energies and probabilities, internal conversion coefficients and gamma-ray en ergies and emission intensities. These new data will be included in the DDEP database NUCLEIDE.
1. Introduction
2. Decay scheme and nuclear decay data of
A new evaluation of the nuclear decay data of 226Th was scheduled in the frame of the IAEA CRP F41029 “Nuclear Data for Charged-particle Monitor Reactions and Medical Isotope Production” (2012–2018) (Nichols and Capote Noy, 2013). Following the evaluation of 230U (Luca and Ioan, 2018), the author performed this work according to the rules and procedures adopted within the international collaboration “Decay Data Evaluation Project” (DDEP) (Kellett and Bersillon, 2017). The radionuclide 226 Th decays 100% by alpha emission and it is part of the decay chain that starts with 230U and continues, in order, with 226Th, 222 Ra, 218Rn, 214Po and 210Pb (it should be noted that the two last components mentioned above are also included in the 238U natural radioactive series). The first four daughters of 230U are alpha-particle emitters with short half-lives (maximum 31 minutes), leading to secular equilibrium. The system 230U/226Th can be considered for tar geted alpha therapy (TAT), due to the high cumulative energy of the emitted alpha-particles (about 33.5 MeV), having a strong effect on the targeted malignant cells (Morgenstern et al., 2008). The evaluation of 226Th nuclear decay data was carried out using DDEP software tools and computer codes available from the websites of BNL/NNDC (USA) and IAEA (Luca, 2014). The usual steps of a DDEP type evaluation were followed: identification of references for experi mental data and previous ENSDF evaluations of 226Th, data collection and compilation, analysis and consistency testing of the decay scheme. The main results of this first DDEP evaluation of 226Th decay data are presented below.
2.1. Decay energy, half-life and alpha transitions
226
Th
The decay energy value for the 226Th decay, Q(α), was adopted from the recent atomic mass evaluation by Wang et al. (2017): 6452.5 (10) keV, standard uncertainty with a coverage factor k ¼ 1. The decay scheme of 226Th is presented in Fig. 1. The level spins, parities and energies values were adopted from the most recent masschain evaluation for A ¼ 222, by Singh et al. (2011). The first publica tions of experimental data related to the 226Th decay scheme, used for this evaluation, were the articles of Asaro and Perlman (1956) and Briand et al. (1969). Four measurements of the 226Th half-life were found to be published in the scientific literature and three of them were used to establish the recommended value. Studier and Hyde (1948) gave a value of 30.9 minutes; because this result has no uncertainty assigned, it was not taken into account to establish the recommended value. The three values used to obtain the recommended value of the 226Th half-life were: 30.57 (10) minutes (Miller et al., 1987), 30.83 (1) minutes (Koua et al., 1995) and 30.70 (3) minutes (Pomm�e et al., 2012), respectively. This data set is consistent and the adopted recommended value is the limited weighted mean (LWM), equal with the weighted mean (WM) of the three values: 30.76 (7) minutes. The emission energies of the two alpha-particles (α) with the highest emission probabilities, following the 226Th decay populating the 222Ra ground state and first excited state, were derived as weighted means of the experimental values (consistent data sets) reported by Asaro and Perlman (1956), Vakhtel et al. (1975) and Marouli et al. (2012),
E-mail address: [email protected]. https://doi.org/10.1016/j.apradiso.2019.108941 Received 26 March 2019; Received in revised form 30 August 2019; Accepted 14 October 2019 Available online 17 October 2019 0969-8043/© 2019 Elsevier Ltd. All rights reserved.
A. Luca
Applied Radiation and Isotopes 155 (2020) 108941
respectively: 6337.5 (10) keV (α0,0) and 6227.6 (10) keV (α0,1), respectively (see data in Table 1). The corrections mentioned in the ENSDF evaluation (Singh et al., 2011) were taken into account: because of changes in calibration energies, the two energies measured by Asaro and Perlman (1956) were increased 4.6 keV, while the corresponding values measured by Vakhtel et al. (1975) were decreased 0.4 keV and 6.1 keV, respectively. For the next three alpha-particle emissions, the adopted energies are from Marouli et al. (2012). These energies are in good agreement with the values from the evaluation of Rytz (1991). The last three adopted alpha-particle energies (5872.9 (50) keV, 5440.4 (50) keV and 5331.5 (50) keV) are calculated from the proposed decay scheme, considering the transition energies corrected for recoil, while the assigned energy uncertainty corresponds to the lowest measured uncertainty. These alpha emissions were not yet observed in experi ments, because the corresponding probabilities are extremely low. The alpha-particle emission probabilities of the three main groups (α0,0, α0,1 and α0,2) were computed as limited weighted means (LWM) of the experimental values published in the literature, according to Table 2. These adopted emission probabilities are in good agreement with the values published in the evaluations of Akovali (1996), Singh et al. (2011) and Rytz (1991), and with the measurements (without uncer tainty reported) of Ruiz (1961). The emission probabilities of α0,3 and α0,4 were adopted from the only measurements published in the literature, by Marouli et al. (2012). The emission probabilities of α0,5 and α0,6 were computed from the decay scheme levels imbalances, taking into account the gamma-ray emission intensities and the internal conversion coefficients (ICC). Finally, the emission probability of α0,7 was computed from the normalization condition of the alpha-particle emissions (the sum of all the seven probabilities must be 1). It must be noted that the last three alpha transitions populating higher energy levels of 222Ra are extremely weak and were not yet observed experimentally; the corresponding alpha-particle energies are expected to be in the range (5300–5900) keV, while the sum of the emission probabilities was estimated to be 3.1 (1) ⋅10 4. The recommended data from Table 3 (results proposed by this new
Table 1 Experimental energy values of the alpha-particles emitted in the (the values of the evaluation done by Rytz (1991) are given, too). Transition
226
Th decay
Alpha-particle energy (keV)
α0,0 α0,1 α0,2 α0,3 α0,4
Asaro and Perlman (1956)
Vakhtel et al. (1975)
Marouli et al. (2012)
Rytz (1991) evaluation
6330 (3) 6220 (3) – – –
6337.5 (10) 6234.0 (10) – – –
6338.2 6229.1 6100.2 6042.5 6027.1
6336.8 (10) 6234 (5) 6099 (5) 6040 (5) 6028 (5)
(10) (50) (50) (50) (50)
evaluation) are almost identical with the most recent experimental data available, published by Marouli et al. (2012), because these data have much lower uncertainties than the previously published experimental results. The hindrance factors were computed using the ALPHAD_RadD computer code (version 1.1, 24-April-2018) with the parameter r0 ¼ 1.5376 (5), and the obtained values are given in Table 3. The correlation matrix of the alpha-particle emission probabilities measured for the first five groups of alphas – the most important ones, was given by Marouli et al. (2012). In the present work, it was not necessary to add an uncertainty component for the correlation in the combined uncertainty of the alpha-particle emission probabilities. This is due to the fact that, for the main alpha-particle emissions, the results of several independent measurements were compiled, while for smaller peaks in the alpha spectra, the corresponding correlation uncertainty component was neglected because the statistical component of the un certainties was dominant. 2.2. Gamma-ray transitions Only two articles reporting measurements of the gamma-ray energies and relative intensities were found in the literature: Kurcewicz et al. (1976) and Briand et al. (1969). The present evaluation adopted the relative gamma-ray intensities from Kurcewicz et al. (1976); the
Fig. 1. Nuclear decay scheme of 2
226
Th.
A. Luca
Applied Radiation and Isotopes 155 (2020) 108941
Table 2 Experimental emission probabilities of the alpha-particles emitted in the 226Th decay (the values of the evaluations done by Rytz (1991) and Akovali (1996) are given, too). Transition
α0,0 α0,1 α0,2 α0,3 α0,4 a b
Alpha-particle emission probability (per 100 decays) Asaro and Perlman (1956)
Ruiz (1961)
Vakhtel et al. (1975)
Marouli et al. (2012)
Rytz (1991) - evaluation
Akovali (1996) - evaluation
79 19.0 (15) 1.70 (15) Sum:0.58 (6)
78 20 – – –
75 (8) 23.0 (23) 1.3 (2) 0.20 0.22
75.39 22.93 1.266 0.181 0.230
75.3 (3) 22.9 (2) – – –
75.5 (3) 22.8 (2) a 1.26 (5) b 0.187 (11) 0.206 (9)
(10) (9) (7) (4) (5)
value measured by Peghaire (1969). value based also on the measurement result of Lederer (1963): 1.2 (4) per 100 decays.
be anomalous (Gorozhankin and B�e, 2008); in these cases, important deviation between experimental and theoretical internal conversion coefficients (ICC) can occur. However, as the author did not identify any published experimental ICC values for the 222Ra gamma-ray transitions, the adopted internal conversion coefficients (ICC) are theoretical values calculated with the BrIcc program, using the “Frozen Orbitals” approx imation (Kib�edi et al., 2008). The total ICC values (αT) are presented also in Table 4. The normalization condition written for the ground state of 222Ra (the total intensity of the radiations “coming in” must be 100 %) imposed small adjustments (up to 1 %, within the reported un certainties) for the absolute intensities of the 111.12 keV and 242.11 keV gamma-rays: X Iα0;0 þ ½Pγi0 ⋅ ð1 þ αTi0 Þ� ¼ 100; i ¼ 1; 2; 7 (1)
Table 3 Evaluated nuclear decay data for the alpha-particle (α) transitions in the 226 Th decay. Transition,Alpha-particle emission energy (keV)
Emission probability (%)
Hindrance factor
α0,0: 6337.5 (10) α0,1: 6227.6 (10) α0,2: 6100.2 (50) α0,3: 6042.5 (50) α0,4: 6027.1 (50) α0,5: 5872.9 (50) α0,6: 5440.4 (50) α0,7: 5331.5 (50)
75.39 (10) 22.90 (13) 1.267 (12) 0.181 (4) 0.230 (5) 0.000226 (23) 0.000343 (36) 0.0310 (10)
1.00 1.078 (9) 5.02 (6) 18.7 (5) 12.4 (3) 2.28 (24) ⋅103 8.1 (9) 0.0218 (8)
normalization was made using the absolute emission intensity of 2.77 (8) per 100 decays of 222Ra, for the photons of 324.6 keV, as determined by Peghaire (1969). The values of Briand et al. (1969) were not adopted, because there were no uncertainties assigned and only five gamma-rays were reported. The adopted gamma-ray energies are from Kurcewicz et al. (1976) or were calculated from the 222Ra nuclear level energies. The energies and absolute emission intensities of the gamma-rays are shown below, in Table 4. The multipolarities associated with the gamma-ray transitions were, in all cases, either E1 or E2. The E1 gamma-ray transitions are known to
i
where Iα0,0 is the alpha-particle emission intensity of the transition populating the ground state of 222Ra (per 100 decays of 226Th), Pγi0 and αTi0 are the emission intensities of the gamma-rays (i, 0) and the total ICC values associated to the gamma-ray transitions (i and 0 are the initial and final transition levels), respectively. 2.3. Auger electron, X-rays emissions and other atomic data The Auger electron and X-ray absolute emission probabilities were €nfeld and Janssen, 2000) computed by the EMISSION program (Scho from the related decay data (gamma-ray emission intensities, ICC etc.). Table 5 and Table 6 present the evaluated data (energy range, emission probabilities and uncertainties) for the main Auger electrons and X-ray emissions, respectively. In this decay, conversion electron emission is a low probability process with one exception, because most of the gamma-ray transitions have high energies and probabilities lower than 0.01. The exception mentioned above refers to the gamma-ray transition of 111.12 keV (for this transition, the conversion electron emission probability is 0.202 (13)). The adopted fluorescence yield data, the relative K X-ray emission probabilities, the ratios P(KLX)/P(KLL) and P(KXY)/P(KLL) were adopted from Sch€ onfeld and Janssen (1996): ωK ¼ 0:968ð4Þ; ωL ¼ 0:452ð18Þ; ηKL ¼ 0:801ð5Þ:
Table 4 Adopted gamma-ray emission intensities (absolute values), based on the mea surements of Kurcewicz et al. (1976), and total ICC values associated to the gamma-ray transitions. Transition levels (initial, final)
Gamma-ray energy (keV)
Absolute emission intensity (per 100 decays)
Total ICC
(4, (1, (2, (5,
2) 0) 1) 3)
75.18 (5) 111.12 (2) 130.99 (3) 172.37 (9)
0.0022 (6) 3.32 (20) 0.278 (13) 0.00020 (2)
(3, 1) (4, 1)
190.27 (5) 206.17 (5)
0.109 (6) 0.189 (8)
(2, 0) (6, 2)
242.11 (2) 671.89 (30)
0.861 (40) 0.00028 (3)
(7, 4)
707.61 (21)
0.00006 (2)
(7, 3)
723.51 (20)
0.004 (11)
(7, 2)
782.79 (20)
0.00009 (3)
(6, 1)
802.88 (30)
0.00006 (2)
(7, 1)
913.78 (20)
0.000010 (4)
(7, 0)
1024.90 (20)
0.027 (11)
36.7 (6) 6.13 (9) 0.250 (4) 0.1288 (19) 0.702 (10) 0.0839 (12) 0.0575 (8) 0.00661 (10) 0.00599 (9) 0.01711 (20) 0.00497 (7) 0.01384 (20) 0.01009 (13) 0.00859 (10)
Table 5 Evaluated electron emission probabilities (Auger, A) following the decay of 226 Th.
3
Electrons
Energy (keV)
Electrons (per 100 decays)
eAL (Ra) eAK (Ra): KLL KLX KXY
5.8–19.1
8.4 (5) Total: 0.035 (5)
65.15–72.73 79.72–88.47 94.27–103.91
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Applied Radiation and Isotopes 155 (2020) 108941
org/10.1016/j.apradiso.2019.108941.
Table 6 Evaluated X-ray emission probabilities (K and L components) following the decay of 226Th. X-rays
Energy (keV)
Photons (per 100 decays)
XL (Ra) XKα2 (Ra) XKα1 (Ra) XKβ3 (Ra), XKβ1 (Ra), XKβ”5 (Ra) XKβ2 (Ra), XKβ4 (Ra), XKO2,3 (Ra)
10.6–18.4 85.43 88.47 99.43, 100.13, 100.74 102.89, 103.30, 103.74
7.16 (30) 0.313 (18) 0.512 (29) The sum (K’β1): 0.180 (11)
References Akovali, Y.A., 1996. Nuclear data sheets for A¼222. Nucl. Data Sheets 77, 271–298. Asaro, F., Perlman, I., 1956. Alpha-particle and gamma-ray spectra of the U230 decay series. Phys. Rev. 104, 91–99. � Briand, P., Chevallier, P., Touati, A., 1969. Etude des niveaux nucl�eaires du radium 222 excit� es dans la d�esint�egration α du thorium 226. C. R. Acad. Sc. Paris 268, 1105–1108. S� erie B. Gorozhankin, V.M., B� e, M.-M., 2008. Assessment of internal conversion coefficients for anomalous electric dipole transitions. Appl. Radiat. Isot. 66, 722–728. Kellett, M.A., Bersillon, O., 2017. The Decay Data Evaluation Project (DDEP) and the JEFF-3.3 radioactive decay data library: combining international collaborative efforts on evaluated decay data. EPJ Web Conf. 146, 02009. Kib� edi, T., Burrows, T.W., Trzhaskovskaya, M.B., Davidson, P.M., Nestor Jr., C.W., 2008. Evaluation of theoretical conversion coefficients using BrIcc. Nucl. Instrum. Methods A 589, 202–229. Koua, Aka A., Barci, V., Ardisson, G., Righetti, R., Le Du, J.F., Trubert, D., 1995. Reinvestigation of decay properties of nuclei belonging to the 230U series using continuous radiochemical separations. Radiochim. Acta 68, 155–160. Kurcewicz, W., Kaffrell, N., Trautmann, N., Plochocki, A., Zylicz, J., Stryczniewicz, K., Yutlandov, I., 1976. Collective states fed by weak α-transitions in the 230U chain. Nucl. Phys. A270, 175–188. Lederer, C.M., 1963. The Structure of Heavy Nuclei: a Study of Very Weak Alpha Branching. Thesis. University of California, UCRL-11028. Luca, A., 2014. Nuclear decay data evaluations at IFIN-HH, Romania. Nucl. Data Sheets 120, 109–111. Luca, A., Ioan, M.-R., 2018. 230U nuclear decay data evaluation. Appl. Radiat. Isot. 134, 426–428. Marouli, M., Pomm�e, S., Paepen, J., Van Ammel, R., Jobb� agy, V., Dirican, A., Suliman, G., Stroh, H., Apostolidis, C., Abbas, K., Morgenstern, A., 2012. Highresolution alpha-particle spectrometry of the 230U series. Appl. Radiat. Isot. 70, 2270–2274. Miller, G., McGeorge, J., Anthony, I., Owens, R., 1987. Half-lives of the actinide nuclei 225 Th, 226Th, 223Ac and 226Ac. Phys. Rev. 36, 420–421. Morgenstern, A., Apostolidis, C., Bruchertseifer, F., Capote, R., Gouder, T., Simonelli, F., Sin, M., Abbas, K., 2008. Cross-sections of the reaction 232Th(p,3n)230Pa for production of 230U for targeted alpha therapy. Appl. Radiat. Isot. 66, 1275–1280. Nichols, A.L., Capote Noy, R., 2013. Summary Report – First Research Coordination Meeting on Nuclear Data for Charged-Particle Monitor Reactions and Medical Isotope Production. INDC(NDS)-0630. IAEA, Vienna, Austria. Peghaire, A., 1969. Mesures precises d’intensites absolues de rayonnements γ pour des emetteurs α. Nucl. Instrum. Methods 75, 66–70. Pomm�e, S., Altzitzoglou, T., Van Ammel, R., Suliman, G., Marouli, M., Jobb� agy, V., Paepen, J., Stroh, H., Apostolidis, C., Abbas, K., Morgenstern, A., 2012. Measurement of the 230U half-life. Appl. Radiat. Isot. 70, 1900–1906. Ruiz, C.P., 1961. Alpha-decay Studies in the Families of the Light Uranium Isotopes. Thesis. UCRL-9511, University of California, Berkeley, USA. Rytz, A., 1991. Recommended energy and intensity values of alpha particles from radioactive decay. Atomic Data Nucl. Data Tables 47, 205–239. Sch€ onfeld, E., Janssen, H., 1996. Evaluation of atomic shell data. Nucl. Instrum. Methods Phys. Res. A 369, 527–533. Sch€ onfeld, E., Janssen, H., 2000. Calculation of emission probabilities of X-rays and Auger electrons emitted in radioactive disintegration processes. Appl. Radiat. Isot. 52, 595–600. Singh, S., Jain, A.K., Tuli, J.K., 2011. Nuclear data sheets for A ¼ 222. Nucl. Data Sheets 112, 2851–2886. Studier, H., Hyde, E., 1948. A new radioactive series: the Protactinium series. Phys. Rev. 74, 591–600. Vakhtel, V.M., Galovkov, N.A., Dzhelepov, H.S., Ivanov, R.B., Lyatushinski, A., Mikhailova, M.A., Mozzhukhin, A.V., Chumin, V.G., 1975. Alpha-decay of 226Ac, daughter products, program and theses. In: Proceedings of the 23rd Annual Conference on Nuclear Spectroscopic Structure and Atomic Nuclei, Leningrad, p. 156. Wang, M., Audi, G., Kondev, F.G., Huang, W.J., Naimi, S., Xu, X., 2017. The AME2016 atomic mass evaluation (II). Tables, graphs and references. Chin. Phys. C 41, 030003-217 (2017Wa10 NSR code).
The sum (K’β2): 0.059 (4)
3. Energy conservation and discussion The total average emission energy per decay for all emissions involved in the 226Th decay process (α, gamma-rays, X-rays, etc.) is 6451 (11) keV, according to the Q value testing tool of the program SAISINUC (developed by CEA, Laboratoire National Henri Becquerel, France). This value is in very good agreement with the adopted Q value of 6452.5 (10) keV (evaluation of Wang et al., 2017), as the relative difference is only 0.023 %. As most of the gamma-ray emissions have very low probabilities, these are difficult to observe experimentally (the emissions of 75.1 keV, 723.4 keV, 913.7 keV and 1025 keV were not yet observed). Future high quality gamma-ray emissions measurements could confirm the existence of these photon emissions. Experimental determinations of the alphaparticles with very low emission probabilities and of the X-ray emis sions following the decay of 226Th are recommended, too. 4. Conclusions Following this DDEP evaluation of the nuclear decay data of 226Th, new reliable recommended data are available for the international users. The data obtained for 226Th, a radionuclide with potential to be applied in nuclear medicine for targeted alpha therapy, will be included in the NUCLEIDE database of the Decay Data Evaluation Project, http://www.lnhb.fr/ddep_wg/, maintained by CEA/LNE-LNHB (Saclay, France), and through the IAEA – Nuclear Data Section. Acknowledgements This work was funded by the IAEA Research Contract no. 17442/ 2012 and the Program Nucleu - Romanian research project no. PN 18 09 02 03. Financial support to attend the ICRM 2019 international con ference and present this work was granted to the author by the Program Nucleu - research project no. PN 19 06 02 04. The author is grateful to colleagues from CEA/LNE-LNHB, the Romanian National Physics Li brary (Magurele) and the library of CEA, Saclay, France. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.
4
Contents lists available at ScienceDirect
Applied Radiation and Isotopes journal homepage: http://www.elsevier.com/locate/apradiso
226
Th nuclear decay data evaluation
Aurelian Luca Horia Hulubei National Institute for R&D in Physics and Nuclear Engineering, IFIN-HH Bucharest, 30 Reactorului Street, Magurele, Ilfov County, PO Box MG-6, RO077125, Romania
A R T I C L E I N F O
A B S T R A C T
Keywords: Nuclear decay data Alpha-particle Evaluation 226 Th
Following the recent evaluation of the nuclear decay data of 230U, a similar evaluation for its daughter, 226Th, a radionuclide of interest for targeted alpha therapy, was undertaken within the Decay Data Evaluation Project (DDEP) and an IAEA Coordinated Research Project. The nuclear decay data presented are: the half-life, decay energy, alpha-particle emission energies and probabilities, internal conversion coefficients and gamma-ray en ergies and emission intensities. These new data will be included in the DDEP database NUCLEIDE.
1. Introduction
2. Decay scheme and nuclear decay data of
A new evaluation of the nuclear decay data of 226Th was scheduled in the frame of the IAEA CRP F41029 “Nuclear Data for Charged-particle Monitor Reactions and Medical Isotope Production” (2012–2018) (Nichols and Capote Noy, 2013). Following the evaluation of 230U (Luca and Ioan, 2018), the author performed this work according to the rules and procedures adopted within the international collaboration “Decay Data Evaluation Project” (DDEP) (Kellett and Bersillon, 2017). The radionuclide 226 Th decays 100% by alpha emission and it is part of the decay chain that starts with 230U and continues, in order, with 226Th, 222 Ra, 218Rn, 214Po and 210Pb (it should be noted that the two last components mentioned above are also included in the 238U natural radioactive series). The first four daughters of 230U are alpha-particle emitters with short half-lives (maximum 31 minutes), leading to secular equilibrium. The system 230U/226Th can be considered for tar geted alpha therapy (TAT), due to the high cumulative energy of the emitted alpha-particles (about 33.5 MeV), having a strong effect on the targeted malignant cells (Morgenstern et al., 2008). The evaluation of 226Th nuclear decay data was carried out using DDEP software tools and computer codes available from the websites of BNL/NNDC (USA) and IAEA (Luca, 2014). The usual steps of a DDEP type evaluation were followed: identification of references for experi mental data and previous ENSDF evaluations of 226Th, data collection and compilation, analysis and consistency testing of the decay scheme. The main results of this first DDEP evaluation of 226Th decay data are presented below.
2.1. Decay energy, half-life and alpha transitions
226
Th
The decay energy value for the 226Th decay, Q(α), was adopted from the recent atomic mass evaluation by Wang et al. (2017): 6452.5 (10) keV, standard uncertainty with a coverage factor k ¼ 1. The decay scheme of 226Th is presented in Fig. 1. The level spins, parities and energies values were adopted from the most recent masschain evaluation for A ¼ 222, by Singh et al. (2011). The first publica tions of experimental data related to the 226Th decay scheme, used for this evaluation, were the articles of Asaro and Perlman (1956) and Briand et al. (1969). Four measurements of the 226Th half-life were found to be published in the scientific literature and three of them were used to establish the recommended value. Studier and Hyde (1948) gave a value of 30.9 minutes; because this result has no uncertainty assigned, it was not taken into account to establish the recommended value. The three values used to obtain the recommended value of the 226Th half-life were: 30.57 (10) minutes (Miller et al., 1987), 30.83 (1) minutes (Koua et al., 1995) and 30.70 (3) minutes (Pomm�e et al., 2012), respectively. This data set is consistent and the adopted recommended value is the limited weighted mean (LWM), equal with the weighted mean (WM) of the three values: 30.76 (7) minutes. The emission energies of the two alpha-particles (α) with the highest emission probabilities, following the 226Th decay populating the 222Ra ground state and first excited state, were derived as weighted means of the experimental values (consistent data sets) reported by Asaro and Perlman (1956), Vakhtel et al. (1975) and Marouli et al. (2012),
E-mail address: [email protected]. https://doi.org/10.1016/j.apradiso.2019.108941 Received 26 March 2019; Received in revised form 30 August 2019; Accepted 14 October 2019 Available online 17 October 2019 0969-8043/© 2019 Elsevier Ltd. All rights reserved.
A. Luca
Applied Radiation and Isotopes 155 (2020) 108941
respectively: 6337.5 (10) keV (α0,0) and 6227.6 (10) keV (α0,1), respectively (see data in Table 1). The corrections mentioned in the ENSDF evaluation (Singh et al., 2011) were taken into account: because of changes in calibration energies, the two energies measured by Asaro and Perlman (1956) were increased 4.6 keV, while the corresponding values measured by Vakhtel et al. (1975) were decreased 0.4 keV and 6.1 keV, respectively. For the next three alpha-particle emissions, the adopted energies are from Marouli et al. (2012). These energies are in good agreement with the values from the evaluation of Rytz (1991). The last three adopted alpha-particle energies (5872.9 (50) keV, 5440.4 (50) keV and 5331.5 (50) keV) are calculated from the proposed decay scheme, considering the transition energies corrected for recoil, while the assigned energy uncertainty corresponds to the lowest measured uncertainty. These alpha emissions were not yet observed in experi ments, because the corresponding probabilities are extremely low. The alpha-particle emission probabilities of the three main groups (α0,0, α0,1 and α0,2) were computed as limited weighted means (LWM) of the experimental values published in the literature, according to Table 2. These adopted emission probabilities are in good agreement with the values published in the evaluations of Akovali (1996), Singh et al. (2011) and Rytz (1991), and with the measurements (without uncer tainty reported) of Ruiz (1961). The emission probabilities of α0,3 and α0,4 were adopted from the only measurements published in the literature, by Marouli et al. (2012). The emission probabilities of α0,5 and α0,6 were computed from the decay scheme levels imbalances, taking into account the gamma-ray emission intensities and the internal conversion coefficients (ICC). Finally, the emission probability of α0,7 was computed from the normalization condition of the alpha-particle emissions (the sum of all the seven probabilities must be 1). It must be noted that the last three alpha transitions populating higher energy levels of 222Ra are extremely weak and were not yet observed experimentally; the corresponding alpha-particle energies are expected to be in the range (5300–5900) keV, while the sum of the emission probabilities was estimated to be 3.1 (1) ⋅10 4. The recommended data from Table 3 (results proposed by this new
Table 1 Experimental energy values of the alpha-particles emitted in the (the values of the evaluation done by Rytz (1991) are given, too). Transition
226
Th decay
Alpha-particle energy (keV)
α0,0 α0,1 α0,2 α0,3 α0,4
Asaro and Perlman (1956)
Vakhtel et al. (1975)
Marouli et al. (2012)
Rytz (1991) evaluation
6330 (3) 6220 (3) – – –
6337.5 (10) 6234.0 (10) – – –
6338.2 6229.1 6100.2 6042.5 6027.1
6336.8 (10) 6234 (5) 6099 (5) 6040 (5) 6028 (5)
(10) (50) (50) (50) (50)
evaluation) are almost identical with the most recent experimental data available, published by Marouli et al. (2012), because these data have much lower uncertainties than the previously published experimental results. The hindrance factors were computed using the ALPHAD_RadD computer code (version 1.1, 24-April-2018) with the parameter r0 ¼ 1.5376 (5), and the obtained values are given in Table 3. The correlation matrix of the alpha-particle emission probabilities measured for the first five groups of alphas – the most important ones, was given by Marouli et al. (2012). In the present work, it was not necessary to add an uncertainty component for the correlation in the combined uncertainty of the alpha-particle emission probabilities. This is due to the fact that, for the main alpha-particle emissions, the results of several independent measurements were compiled, while for smaller peaks in the alpha spectra, the corresponding correlation uncertainty component was neglected because the statistical component of the un certainties was dominant. 2.2. Gamma-ray transitions Only two articles reporting measurements of the gamma-ray energies and relative intensities were found in the literature: Kurcewicz et al. (1976) and Briand et al. (1969). The present evaluation adopted the relative gamma-ray intensities from Kurcewicz et al. (1976); the
Fig. 1. Nuclear decay scheme of 2
226
Th.
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Table 2 Experimental emission probabilities of the alpha-particles emitted in the 226Th decay (the values of the evaluations done by Rytz (1991) and Akovali (1996) are given, too). Transition
α0,0 α0,1 α0,2 α0,3 α0,4 a b
Alpha-particle emission probability (per 100 decays) Asaro and Perlman (1956)
Ruiz (1961)
Vakhtel et al. (1975)
Marouli et al. (2012)
Rytz (1991) - evaluation
Akovali (1996) - evaluation
79 19.0 (15) 1.70 (15) Sum:0.58 (6)
78 20 – – –
75 (8) 23.0 (23) 1.3 (2) 0.20 0.22
75.39 22.93 1.266 0.181 0.230
75.3 (3) 22.9 (2) – – –
75.5 (3) 22.8 (2) a 1.26 (5) b 0.187 (11) 0.206 (9)
(10) (9) (7) (4) (5)
value measured by Peghaire (1969). value based also on the measurement result of Lederer (1963): 1.2 (4) per 100 decays.
be anomalous (Gorozhankin and B�e, 2008); in these cases, important deviation between experimental and theoretical internal conversion coefficients (ICC) can occur. However, as the author did not identify any published experimental ICC values for the 222Ra gamma-ray transitions, the adopted internal conversion coefficients (ICC) are theoretical values calculated with the BrIcc program, using the “Frozen Orbitals” approx imation (Kib�edi et al., 2008). The total ICC values (αT) are presented also in Table 4. The normalization condition written for the ground state of 222Ra (the total intensity of the radiations “coming in” must be 100 %) imposed small adjustments (up to 1 %, within the reported un certainties) for the absolute intensities of the 111.12 keV and 242.11 keV gamma-rays: X Iα0;0 þ ½Pγi0 ⋅ ð1 þ αTi0 Þ� ¼ 100; i ¼ 1; 2; 7 (1)
Table 3 Evaluated nuclear decay data for the alpha-particle (α) transitions in the 226 Th decay. Transition,Alpha-particle emission energy (keV)
Emission probability (%)
Hindrance factor
α0,0: 6337.5 (10) α0,1: 6227.6 (10) α0,2: 6100.2 (50) α0,3: 6042.5 (50) α0,4: 6027.1 (50) α0,5: 5872.9 (50) α0,6: 5440.4 (50) α0,7: 5331.5 (50)
75.39 (10) 22.90 (13) 1.267 (12) 0.181 (4) 0.230 (5) 0.000226 (23) 0.000343 (36) 0.0310 (10)
1.00 1.078 (9) 5.02 (6) 18.7 (5) 12.4 (3) 2.28 (24) ⋅103 8.1 (9) 0.0218 (8)
normalization was made using the absolute emission intensity of 2.77 (8) per 100 decays of 222Ra, for the photons of 324.6 keV, as determined by Peghaire (1969). The values of Briand et al. (1969) were not adopted, because there were no uncertainties assigned and only five gamma-rays were reported. The adopted gamma-ray energies are from Kurcewicz et al. (1976) or were calculated from the 222Ra nuclear level energies. The energies and absolute emission intensities of the gamma-rays are shown below, in Table 4. The multipolarities associated with the gamma-ray transitions were, in all cases, either E1 or E2. The E1 gamma-ray transitions are known to
i
where Iα0,0 is the alpha-particle emission intensity of the transition populating the ground state of 222Ra (per 100 decays of 226Th), Pγi0 and αTi0 are the emission intensities of the gamma-rays (i, 0) and the total ICC values associated to the gamma-ray transitions (i and 0 are the initial and final transition levels), respectively. 2.3. Auger electron, X-rays emissions and other atomic data The Auger electron and X-ray absolute emission probabilities were €nfeld and Janssen, 2000) computed by the EMISSION program (Scho from the related decay data (gamma-ray emission intensities, ICC etc.). Table 5 and Table 6 present the evaluated data (energy range, emission probabilities and uncertainties) for the main Auger electrons and X-ray emissions, respectively. In this decay, conversion electron emission is a low probability process with one exception, because most of the gamma-ray transitions have high energies and probabilities lower than 0.01. The exception mentioned above refers to the gamma-ray transition of 111.12 keV (for this transition, the conversion electron emission probability is 0.202 (13)). The adopted fluorescence yield data, the relative K X-ray emission probabilities, the ratios P(KLX)/P(KLL) and P(KXY)/P(KLL) were adopted from Sch€ onfeld and Janssen (1996): ωK ¼ 0:968ð4Þ; ωL ¼ 0:452ð18Þ; ηKL ¼ 0:801ð5Þ:
Table 4 Adopted gamma-ray emission intensities (absolute values), based on the mea surements of Kurcewicz et al. (1976), and total ICC values associated to the gamma-ray transitions. Transition levels (initial, final)
Gamma-ray energy (keV)
Absolute emission intensity (per 100 decays)
Total ICC
(4, (1, (2, (5,
2) 0) 1) 3)
75.18 (5) 111.12 (2) 130.99 (3) 172.37 (9)
0.0022 (6) 3.32 (20) 0.278 (13) 0.00020 (2)
(3, 1) (4, 1)
190.27 (5) 206.17 (5)
0.109 (6) 0.189 (8)
(2, 0) (6, 2)
242.11 (2) 671.89 (30)
0.861 (40) 0.00028 (3)
(7, 4)
707.61 (21)
0.00006 (2)
(7, 3)
723.51 (20)
0.004 (11)
(7, 2)
782.79 (20)
0.00009 (3)
(6, 1)
802.88 (30)
0.00006 (2)
(7, 1)
913.78 (20)
0.000010 (4)
(7, 0)
1024.90 (20)
0.027 (11)
36.7 (6) 6.13 (9) 0.250 (4) 0.1288 (19) 0.702 (10) 0.0839 (12) 0.0575 (8) 0.00661 (10) 0.00599 (9) 0.01711 (20) 0.00497 (7) 0.01384 (20) 0.01009 (13) 0.00859 (10)
Table 5 Evaluated electron emission probabilities (Auger, A) following the decay of 226 Th.
3
Electrons
Energy (keV)
Electrons (per 100 decays)
eAL (Ra) eAK (Ra): KLL KLX KXY
5.8–19.1
8.4 (5) Total: 0.035 (5)
65.15–72.73 79.72–88.47 94.27–103.91
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org/10.1016/j.apradiso.2019.108941.
Table 6 Evaluated X-ray emission probabilities (K and L components) following the decay of 226Th. X-rays
Energy (keV)
Photons (per 100 decays)
XL (Ra) XKα2 (Ra) XKα1 (Ra) XKβ3 (Ra), XKβ1 (Ra), XKβ”5 (Ra) XKβ2 (Ra), XKβ4 (Ra), XKO2,3 (Ra)
10.6–18.4 85.43 88.47 99.43, 100.13, 100.74 102.89, 103.30, 103.74
7.16 (30) 0.313 (18) 0.512 (29) The sum (K’β1): 0.180 (11)
References Akovali, Y.A., 1996. Nuclear data sheets for A¼222. Nucl. Data Sheets 77, 271–298. Asaro, F., Perlman, I., 1956. Alpha-particle and gamma-ray spectra of the U230 decay series. Phys. Rev. 104, 91–99. � Briand, P., Chevallier, P., Touati, A., 1969. Etude des niveaux nucl�eaires du radium 222 excit� es dans la d�esint�egration α du thorium 226. C. R. Acad. Sc. Paris 268, 1105–1108. S� erie B. Gorozhankin, V.M., B� e, M.-M., 2008. Assessment of internal conversion coefficients for anomalous electric dipole transitions. Appl. Radiat. Isot. 66, 722–728. Kellett, M.A., Bersillon, O., 2017. The Decay Data Evaluation Project (DDEP) and the JEFF-3.3 radioactive decay data library: combining international collaborative efforts on evaluated decay data. EPJ Web Conf. 146, 02009. Kib� edi, T., Burrows, T.W., Trzhaskovskaya, M.B., Davidson, P.M., Nestor Jr., C.W., 2008. Evaluation of theoretical conversion coefficients using BrIcc. Nucl. Instrum. Methods A 589, 202–229. Koua, Aka A., Barci, V., Ardisson, G., Righetti, R., Le Du, J.F., Trubert, D., 1995. Reinvestigation of decay properties of nuclei belonging to the 230U series using continuous radiochemical separations. Radiochim. Acta 68, 155–160. Kurcewicz, W., Kaffrell, N., Trautmann, N., Plochocki, A., Zylicz, J., Stryczniewicz, K., Yutlandov, I., 1976. Collective states fed by weak α-transitions in the 230U chain. Nucl. Phys. A270, 175–188. Lederer, C.M., 1963. The Structure of Heavy Nuclei: a Study of Very Weak Alpha Branching. Thesis. University of California, UCRL-11028. Luca, A., 2014. Nuclear decay data evaluations at IFIN-HH, Romania. Nucl. Data Sheets 120, 109–111. Luca, A., Ioan, M.-R., 2018. 230U nuclear decay data evaluation. Appl. Radiat. Isot. 134, 426–428. Marouli, M., Pomm�e, S., Paepen, J., Van Ammel, R., Jobb� agy, V., Dirican, A., Suliman, G., Stroh, H., Apostolidis, C., Abbas, K., Morgenstern, A., 2012. Highresolution alpha-particle spectrometry of the 230U series. Appl. Radiat. Isot. 70, 2270–2274. Miller, G., McGeorge, J., Anthony, I., Owens, R., 1987. Half-lives of the actinide nuclei 225 Th, 226Th, 223Ac and 226Ac. Phys. Rev. 36, 420–421. Morgenstern, A., Apostolidis, C., Bruchertseifer, F., Capote, R., Gouder, T., Simonelli, F., Sin, M., Abbas, K., 2008. Cross-sections of the reaction 232Th(p,3n)230Pa for production of 230U for targeted alpha therapy. Appl. Radiat. Isot. 66, 1275–1280. Nichols, A.L., Capote Noy, R., 2013. Summary Report – First Research Coordination Meeting on Nuclear Data for Charged-Particle Monitor Reactions and Medical Isotope Production. INDC(NDS)-0630. IAEA, Vienna, Austria. Peghaire, A., 1969. Mesures precises d’intensites absolues de rayonnements γ pour des emetteurs α. Nucl. Instrum. Methods 75, 66–70. Pomm�e, S., Altzitzoglou, T., Van Ammel, R., Suliman, G., Marouli, M., Jobb� agy, V., Paepen, J., Stroh, H., Apostolidis, C., Abbas, K., Morgenstern, A., 2012. Measurement of the 230U half-life. Appl. Radiat. Isot. 70, 1900–1906. Ruiz, C.P., 1961. Alpha-decay Studies in the Families of the Light Uranium Isotopes. Thesis. UCRL-9511, University of California, Berkeley, USA. Rytz, A., 1991. Recommended energy and intensity values of alpha particles from radioactive decay. Atomic Data Nucl. Data Tables 47, 205–239. Sch€ onfeld, E., Janssen, H., 1996. Evaluation of atomic shell data. Nucl. Instrum. Methods Phys. Res. A 369, 527–533. Sch€ onfeld, E., Janssen, H., 2000. Calculation of emission probabilities of X-rays and Auger electrons emitted in radioactive disintegration processes. Appl. Radiat. Isot. 52, 595–600. Singh, S., Jain, A.K., Tuli, J.K., 2011. Nuclear data sheets for A ¼ 222. Nucl. Data Sheets 112, 2851–2886. Studier, H., Hyde, E., 1948. A new radioactive series: the Protactinium series. Phys. Rev. 74, 591–600. Vakhtel, V.M., Galovkov, N.A., Dzhelepov, H.S., Ivanov, R.B., Lyatushinski, A., Mikhailova, M.A., Mozzhukhin, A.V., Chumin, V.G., 1975. Alpha-decay of 226Ac, daughter products, program and theses. In: Proceedings of the 23rd Annual Conference on Nuclear Spectroscopic Structure and Atomic Nuclei, Leningrad, p. 156. Wang, M., Audi, G., Kondev, F.G., Huang, W.J., Naimi, S., Xu, X., 2017. The AME2016 atomic mass evaluation (II). Tables, graphs and references. Chin. Phys. C 41, 030003-217 (2017Wa10 NSR code).
The sum (K’β2): 0.059 (4)
3. Energy conservation and discussion The total average emission energy per decay for all emissions involved in the 226Th decay process (α, gamma-rays, X-rays, etc.) is 6451 (11) keV, according to the Q value testing tool of the program SAISINUC (developed by CEA, Laboratoire National Henri Becquerel, France). This value is in very good agreement with the adopted Q value of 6452.5 (10) keV (evaluation of Wang et al., 2017), as the relative difference is only 0.023 %. As most of the gamma-ray emissions have very low probabilities, these are difficult to observe experimentally (the emissions of 75.1 keV, 723.4 keV, 913.7 keV and 1025 keV were not yet observed). Future high quality gamma-ray emissions measurements could confirm the existence of these photon emissions. Experimental determinations of the alphaparticles with very low emission probabilities and of the X-ray emis sions following the decay of 226Th are recommended, too. 4. Conclusions Following this DDEP evaluation of the nuclear decay data of 226Th, new reliable recommended data are available for the international users. The data obtained for 226Th, a radionuclide with potential to be applied in nuclear medicine for targeted alpha therapy, will be included in the NUCLEIDE database of the Decay Data Evaluation Project, http://www.lnhb.fr/ddep_wg/, maintained by CEA/LNE-LNHB (Saclay, France), and through the IAEA – Nuclear Data Section. Acknowledgements This work was funded by the IAEA Research Contract no. 17442/ 2012 and the Program Nucleu - Romanian research project no. PN 18 09 02 03. Financial support to attend the ICRM 2019 international con ference and present this work was granted to the author by the Program Nucleu - research project no. PN 19 06 02 04. The author is grateful to colleagues from CEA/LNE-LNHB, the Romanian National Physics Li brary (Magurele) and the library of CEA, Saclay, France. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.
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