by A. L. Nichols 697.8(7) 1971Jo (32) * 1992Un01

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1 Comments on evaluation of decay data by A. L. Nichols Evaluated: July/August 2001 Reevaluated: January 2004 Evaluation Procedures Limitation of Relative Statistical Weight Method (LWM) was applied to average numbers throughout the evaluation. The uncertainty assigned to the average value was always greater than or equal to the smallest uncertainty of the values used to calculate the average. Decay Scheme (T ½ = days) decays 100% by alphaparticle emission (Q(α) = (22) kev) to various excited levels and the ground state of 224 Ra (T ½ = 3.64 days). A reasonably welldefined decay scheme was derived from the alphaparticle studies of 1970Ba20, 1976BaZZ, 1969Pe17, and 1993Ba72, and the gammaray measurements of 1977Ku15, 1982Sa36 and 1984Ge07. An additional gamma transition was added to the proposed decay scheme from equivalent studies of 224 Fr decay by 1981Ku02: kev gamma ray depopulating the kev nuclear level of 224 Ra. Weighted mean relative emission probabilities were calculated for the , , and kev gamma rays, while equivalent data for the other gamma transitions were adopted from the measurements of 1977Ku15; all of these relative emission probabilities were defined in terms of the kev gamma ray. Estimates were made of the uncertainties of the and kev gamma rays. Cluster decay has also been observed, and reviewed by 1995Ar33 and 1997Tr17. O20 emissions were detected, with an estimated branching fraction of 1.1(2)E13. However, this decay mode has not been included in the decaydata summary section. Nuclear Data decay chain is important in quantifying the environmental impact of the decay of naturallyoccurring 232 Th. Specific radionuclides in this decay chain are noteworthy because of their decay characteristics ( 224 Ra alpha decay to 220 Rn; 212 Bi and 208 Tl gammaray emissions). 208 Tl in particular emits highenergy gamma rays that represent a welldefined spectroscopic signature for this decay chain. Halflife Halflife was adopted from the evaluation of Woods for the IAEACRP: Update of X and Gammaray Decay Data Standards for Detector Calibration. The measurements of 1956Ki16, 1971Jo14 and 1992Un01 were considered. Reference Halflife (d) 1956Ki (7) 1971Jo (32) * 1992Un (36) Recommended Value (23) *Uncertainty adjusted to ± 0.33 to reduce weighting below 0.5. Woods evaluation for IAEACRP (2004WoZZ): recommended halflife of (23) days (using above dataset).

2 Gamma Rays Energies All gammaray transition energies were calculated from the structural details of the proposed decay scheme. The nuclear level energies of 1997Ar05 were adopted, and used to determine the energies and associated uncertainties of the gammaray transitions between the various populateddepopulated levels. Emission Probabilities Gammaray emission probabilities have been partially or fully determined in the measurements of 1977Ku15, 1982Sa36 and 1984Ge07. Weighted mean relative emission probabilities were calculated for the , , and kev gamma rays, while equivalent data for the other gamma transitions were directly adopted from the measurements of 1977Ku15. An additional gamma transition was added to the proposed decay scheme from equivalent studies of 224 Fr decay by 1981Ku02 as kev gamma ray depopulating the kev nuclear level of 224 Ra to maintain consistency. All of these relative emission probabilities were defined in terms of the kev gamma ray. Estimates were made of the uncertainties of the and kev gamma rays. Published Gammaray Emission Probabilities E g (kev) P g 1969Pe Ku Sa Ge (1) (3) (4) 142.7(1) (4) 182.3(1) (4) (4) 228.4(2) 700.4(1) (1) 832.0(1) (1) (6) 1.21(6) 4.0(14) 12100(600) 1240(60) 0.013(4) 960(50) 0.052(18) 184(9) 2390(130) 0.18(3) ~ (4) 0.14(2) ~ (1) 0.17(2) 0.13(1) 0.30(2) 100.0(16) 10.70(15) 8.49(12) 1.61(5) 20.78(25) Emission probabilities expressed in terms of photons per 10 6 disintegrations. Emission probabilities published relative to Pγ( kev) for 212 Pb of 43.0%. Gammaray Emission Probabilities: Relative to Pg( kev) of 100 E g (kev) rel P g 1977Ku Sa Ge07 Recommended Values * 74.4(1) (3) (4) 142.7(1) (4) 182.3(1) (4) (4) 228.4(2) 700.4(1) (1) 832.0(1) (1) (6) 0.033(12) 100(5) 10.25(50) (3) 7.9(4) (15) 1.52(7) 19.8(11) (3) ~ (3) (2) ~ (5) 8.9(10) 6.8(5) 15.8(11) 100.0(16) 10.70(15) 8.49(12) 1.61(5) 20.78(25) 0.033(12) 100.0(16) 10.6(2) (3) 8.0(5) (15) 1.58(5) 19.3(15) (3) (8) (3) (2) (4) (3) * Weighted mean values adopted when judged appropriate; remainder derived from proposed decay scheme.

3 The normalisation factor was calculated for the gammaray emission probabilities by averaging the values determined by three different routes: (i) from direct population of the 224 Ra ground state [ Σ P γi (1 + α i ) to ground state] NF (2) = 1.00 NF = (5) (ii) population/depopulation of the kev nuclear level of 224 Ra [ P γ ( kev)(1 + α( kev)) ΣP γi (1 + α i ) to kev level] NF = 0.262(2) NF = (6) (iii) all α transitions (see Σ P α NF = 1.00, and adopting αparticle emission probability to 224 Ra ground state of 0.732(2) section on alphaparticle emissions), NF = (7) An average value of (5) has been adopted. Multipolarities and Internal Conversion Coefficients The nuclear level scheme specified by 1997Ar05 has been used to define the multipolarities of the gamma transitions on the basis of known spins and parities. Limited studies of the internal conversion coefficients support the proposed transition types: E2 for both the and kev gamma rays (1953As31, 1966Co40, 1969Du06 and 1969Pe17). The kev gamma ray was identified as the only mixed multipolarity transition, and was arbitrarily assigned 50%M1 + 50%E2. All of the recommended internal conversion coefficients have been interpolated from the theoretical tabulations of 1978Ro22. Uncertainties of ± 2% were adopted for all of the E1 and E2 (+M3) gamma transitions (with minor upward adjustments associated with the significant figures for α L and α M+ ), while an uncertainty of ± 10 % was assigned to the ICCs for the keV (50 %M %E2) gamma transition. Internal Conversion Coefficients Reference E g (kev) a 1953As Co Du Pe a L a LII a LIII a M+ a total (3) (9) 18(4) 19.6(14) 21.4(9) Alphaparticle Emissions Energies All alphaparticle energies were calculated from the structural details of the proposed decay scheme. The nuclear level energies of 1997Ar05 and the Qvalue (1995Au04) were used to determine the energies and uncertainties of the alphaparticle transitions to the various levels, while allowing for the significant recoil components.

4 Emission Probabilities An alphaparticle emission probability of 73.2(2) % was derived for the alpha decay directly to the ground state of 224 Ra, based on the various alphaparticle studies. This value and the gammaray data were used in conjunction with the theoretical internal conversion coefficients to determine a normalisation factor of (5), per 100 disintegrations, for the relative emission probabilities of the gamma rays (see above). Published Alphaparticle Emission Probabilities per 100 Disintegrations of E a (kev) P a 1953As Pe Ba BaZZ 1993Ba (3) (3) (4) (3) (26) (23) (22) (22) (22) (2) [73.3(2)] ~ (5) 72.4(10) 26.0(8) 74.0(6) Alphaparticle emission probability data of 1969Pe17 are effectively normalised to 73.3(2)% and 26.7(2)%. 1976BaZZ measurements require normalisation to ( ) = ( ) N = N = to give P α ( kev) of 72.7%, and uncertainty of ± 0.5; and P α ( kev) of 27.3%, and uncertainty of ± Ba72 studies also require normalisation to give P α ( kev) of 73.5% and uncertainty of ± 0.6; and P α ( kev) of 26.5%, and uncertainty of ± 0.6. A weighted mean value of 73.2(2)% (0.732(2)) was determined for P α ( kev), which has been matched with a value of 26.2(2)% (0.262(2)) for P α ( kev). Adjusted Alphaparticle Emission Probabilities per 100 Disintegrations of E a (kev) P a 1953As Pe Ba BaZZ 1993Ba72 Recommended Values * (3) (3) (4) (3) (26) (23) (22) (22) (22) (2) [73.3(2)] ~ (5) 72.7(5) 26.5(6) 73.5(6) 4.4(12) x (3) x (5) x (3) x (7) 0.20(2) 0.38(3) 26.2(2) 73.2(2) *P α ( kev) of 73.2(2) is effectively the weighted mean of the normalised studies, which is subsequently matched against P α ( kev) of 26.2(2); recommended emission probabilities of the lowintensity α transitions were derived from the evaluated gammaray emission probabilities and theoretical internal conversion coefficients.

5 The absolute emission probabilities of all other alpha particles were calculated from populationdepopulation of the nuclear level of 224 Ra and the gammaray normalisation factor. Although a consistent decay scheme was derived, further detailed alphaparticle measurements are required to develop and support the overall correctness of the proposed decay scheme. Atomic Data The xray data have been calculated using the evaluated gammaray data, and the atomic data from 1996Sc06, 1998ScZM and 1999ScZX. References 1953As31 F. Asaro, F. Stephens and I. Perlman, Complex Alpha Spectra of Radiothorium (Th 228 ) and ThoriumX (Ra 224 ), Phys. Rev. 92(1953)1495.[P α, P γ, ICC] 1956Ki16 H. W. Kirby, G. R. Grove and D. L. Timma, NeutronCapture Cross Section of Actinium 227, Phys. Rev. 102(1956)1140. [Halflife] 1966Co40 M. O. Costa and M. R. S. Grade, Spectre d Électrons de Conversion Interne Associés à la Transmutation du Thorium228 en Radium224, Port. Phys. 4(1966)267. [P ce, ICC] 1968Du06 C. L. Duke and W. L. Talbert, Total Internalconversion Coefficients for Lowenergy E2 Transitions in Ra 224, Th 228, U 234, U 236 and Pu 240, Phys. Rev. 173(1968)1125. [ICC] 1969Pe17 A. Peghaire, Mesures Precises d Intensities Absolues de Rayonnements γ pour des Emitteurs α, Nucl. Instrum. Meth. 75(1969)66. [P α, P γ, ICC] 1970Ba20 S. A. Baranov, V. M. Shatinskii, V. M. Kulakov and Yu. F. Rodionov, Investigation of the α Decay of the Two Isotopes Th 228 and Th 229, Sov. J. Nucl. Phys. 11(1970)515. [P α ] 1971Jo14 K. C. Jordan, G. W. Otto and R. P. Ratay, Calorimetric Determination of the HalfLives of and 224 Ra, J. Inorg. Nucl. Chem. 33(1971)1215. [Halflife] 1976BaZZ S. A. Baranov, A. G. Zelenkov and V. M. Kulakov, The Experimental Investigation of the Alpha Decay of Transactinium Isotopes, IAEA186, Vol III (1976)249, IAEA Vienna. [P α ] 1977Ku15 W. Kurcewicz, N. Kaffrell, N. Trautmann, A. Plochocki, J. Zylicz, M. Matul and K. Stryczniewicz, Collective States Fed by Weak αtransitions in the 232 U Chain, Nucl. Phys. A289(1977)1. [P γ ] 1978Ro22 F. Rösel, H. M. Fries, K. Alder and H. C. Pauli, Internal Conversion Coefficients for all Atomic Shells, ICC Values for Z = 68104, At. Data Nucl. Data Tables 21(1978) [ICC] 1981Ku02 W. Kurcewicz, E. Ruchowska, N. Kaffrell, T. Björnstad and G. Nyman, Collective Excitations in the Transitional Nuclei 224,226 Ra, Nucl. Phys. A356(1981)15. [ kev P γ ] 1982Sa36 S. Sadasivan and V. M. Raghunath, Intensities of Gamma Rays in the 232 Th Decay Chain, Nucl. Instrum. Meth. 196(1982)561. [P γ ] 1984Ge07 R. J. Gehrke, V. J. Novick and J. D. Baker, γray Emission Probabilities for the 232 U Decay Chain, Int. J. Appl. Radiat. Isot. 35(1984)581. [P γ ] 1992Un01 M. P. Unterweger, D. D. Hoppes and F. J. Schima, New and Revised HalfLife Measurements Results, Nucl. Instrum. Meth. Phys. Res. A312(1992)349. [Halflife]

6 1993Ba72 T. Babeliowsky and G. Bortels, ALFA: A Program for Accurate Analysis of Complex Alphaparticle Spectra on a PC, Appl. Radiat. Isot. 44(1993)1349. [P α ] 1995Ar33 G. Ardisson and M. Hussonnois, Radiochemical Investigations of Cluster Radioactivities, Radiochim. Acta 70/71(1995)123. [Cluster decay] 1995Au04 G. Audi and A. H. Wapstra, The 1995 Update to the Atomic Mass Evaluation, Nucl. Phys. A595(1995)409. [Q value] 1996Sc06 E. Schönfeld and H. Janβen, Evaluation of Atomic Shell Data, Nucl. Instrum. Meth. Phys. Res. A369(1996)527. [X K, X L, Auger electrons] 1997Ar05 A. ArtnaCohen, Nuclear Data Sheets for A = 224, Nucl. Data Sheets 80(1997)227. [Nuclear structure, Energies] 1997Tr17 S. P. Tretyakova and V. L. Mikheev, Experimental Investigation of the Cluster Radioactivity of Atomic Nuclei, Nuovo Cimento 110(1997)1043. [Cluster decay] 1998ScZM E. Schönfeld and G. Rodloff, Tables of the Energies of KAuger Electrons for Elements with Atomic Numbers in the Range from Z = 11 to Z = 100, PTB Report PTB , October [Auger electrons] 1999ScZX E. Schönfeld and G. Rodloff, Energies and Relative Emission Probabilities of K Xrays for Elements with Atomic Numbers in the Range from Z = 5 to Z = 100, PTB Report PTB , February [X K ] 2004WoZZ M. J. Woods, Halflife Evaluations for IAEACRP on Update of Xray and Gammaray Decay Data Standards for Detector Calibration and Other Applications (2004). [Halflife evaluation]