1. 1Laboratoire National Henri Becquerel Decay data evaluation of Radium – 226 and its daughters V. Chisté, M. M. Bé, C. Dulieu

2. 2Laboratoire National Henri Becquerel Introduction * Important naturally occurring radioactive chain: 1 – calibration of gamma-ray detectors 2 – environmental controls * Ra-226 chain is included in the Coordinated Research Program – IAEA

3. 3Laboratoire National Henri Becquerel 99.9 % Ra-226 1600 (7) a  100 % Rn-222  100 % Po-218  100 % Pb-214Bi-214 At-218Rn-218 Po-214 Tl-210   100 % 0.02 %      0.022 %0.1 % 100 %99.98 % Pb-210Bi-210Po-210 Hg-206Tl-206Pb-206 Stable      T 1/2 = 22.23 (12) a Ra-226 radioactive chain T 1/2 = 36.0 (19) ms T 1/2 = 162.3 (12)  s

4. 4Laboratoire National Henri Becquerel Global Characteristics of the Ra-226 chain. 10  disintegrations and 9  - disintegrations down to Pb-206 (stable nuclide). Half-lives between some years (Ra-226 and Pb-210) and some fraction of a second (Rn-218 (ms) and Po-214 (µs)). ~ 275  -rays, mainly in: Pb-214  - decay to Bi-214 (26  -rays), Bi-214  - decay to Po-214 (212  -rays) and Tl-210  - decay to Bi-214 (24  -rays).

5. 5Laboratoire National Henri Becquerel Evaluation difficulties: 1 st Group - Lack of data set (4 examples). - I) Half-lives IsotopeHalf-life (T 1/2 ) % of  T 1/2 N° of measurements Most recent experimental value Ra-2261600 (7) a0.412 [5] 1966, H. Ramthun Rn-2223.8232 (8) d0.0292004, H. Schrader Po-2183.094 (6) min0.204 [3]1986, G. V. Potapov At-2181.4 (2) s1421989, D. G. Burke Rn-21835.5 (13) ms45 [4]1971, A. Erlik Pb-21426.8 (9) min3.411931, M. Curie Bi-21419.9 (4) min211956, H. Daniel Po-214161.7 (15)  s0.910 [6]1993, J. W. Zhou Tl-2101.30 (3) min2.33 [2] 1964, P. Weinzierl Pb-21022.23 (12) a0.514 [11]2002, G. A. Rech Bi-2105.012 (5) d0.161959, J. Robert Po-210138.3763 (17) d0.0019 [7]1964, J. F. Eichelberger []: n° of measurements with uncertainty.

6. 6Laboratoire National Henri Becquerel - II)  and  - Emission probabilities: lack of measured values. IsotopeType of decaySituation Ra-226  (100 %) Two measurements in 1963 and 2001. Rn-222  (100 %)Last measurements in 1958. Po-218  (99.978 %)  (0.022 %) Last measurements in 1958. Last measurements in 1952. At-218  (99.9 %)  (0.1 %) Last measurements in 1958. Last measurements in 1948. Rn-218  (100 %)No direct measurements available. Pb-214  (100 %)No direct measurements available. Bi-214  (0.02 %)  (99.98 %) Last measurements in 1960. No direct measurements available. Po-214  (100 %)No direct measurements available. Tl-210  (100 %) Last measurements in 1964. Pb-210  (1.9 10 -6 %)  (~ 100 %) Three measurements in 1961, 1962 and 1964. Five measurements between 1953 and 1963. Bi-210  (1.4 10 -4 %)  (~ 100 %) Five measurements between 1947 and 1962. No direct measurements available. Po-210  (100 %)No direct measurements available.

7. 7Laboratoire National Henri Becquerel - III) X-ray emissions. IsotopeType of emissionSituation Ra-226X-rays Three measurements in 1973, 1983 and 2002. Rn-222  -rays X-rays No direct measurements available. Po-218X-raysNo direct measurements available. At-218X-raysNo direct measurements available. Rn-218X-raysNo direct measurements available. Pb-214X-raysTwo measurements in 1969 and 1983. Bi-214X-raysNo recent measurements since 1983. Po-214X-raysNo direct measurements available. Tl-210  -rays X-rays No recent measurements since 1964. Pb-210X-raysFour measurements in: 1957, 1971, 1987 and 1990. Bi-210  -rays X-rays No direct measurements available. Po-210X-raysNo direct measurements available.

8. 8Laboratoire National Henri Becquerel - IV) Example of decay scheme particularly unknown: Tl-210  -decay to Pb-210

9. 9Laboratoire National Henri Becquerel This decay scheme is based on the measurements of P. Weinzierl (1964): Energy (keV)Relative  -ray Emission intensity (%) 83 (a) 2.0 974 (2) 29680 (10) 356 (a) 4 (2) 382 (a) 3 (2) 4802 (1) 670 (a) 2 (1) 799100 8607 (2) 910 (a) 3 (2) 107012 (5) 11107 (2) 121017 (4) 131621 (5) 14105 (2) 1490 (a) 2 (1) 1540 (a) 2 (1) 15902 (1) 1650 (a) 2 (1) 20107 (2) 2090 (a) 5 (2) 22703 (2) 23608 (3) 24309 (3) Experimental data set of the relative  -ray emission intensities. (a) Not placed in the decay scheme

10. 10Laboratoire National Henri Becquerel Experimental values of  - transition probabilities. LevelEnergy (keV) P. Weinzierl (1964We06) 111380 (12)25 % 101603 (12) 91860 (12)56 % 82024 (12) 72413 (12)19 % 34290 (12) 24386 (12) Q(Audi) = 5482 (10) keV Q eff = 4390 (1600) keV Adopted values 2 % 7 % 24 % 10 % 31 % 13 %  P   Q eff = 5470 (1000) keV Conclusion: New measurements are strongly suggested.

11. 11Laboratoire National Henri Becquerel Evaluation difficulties: 2 nd Group-  -ray emission intensity. Ra-226 radioactive chain: ~ 275  -rays. 1. Good examples: many and recent articles found about direct measurements. A) Pb-214  - decay to Bi-214, Bi-214  - decay to Po-214 and Ra-226  decay to Rn-222 We have: * 5 measurements of absolute  -ray emission intensities: E. W. A. Lingeman (1969), D. G. Olson (1983), U. Schötzig (1983), W. -J. Li (1991) and J. Morel (2004) * 14 measurements of relative  -ray emission intensities, where: 8 measurements not used because: a) a lack of information in articles – K. Ya. Gromov (1969), G. Wallace (1969) and M. A. Farouk (1982) b) values comes from the same laboratory: A. Hachem (1975), G. Mouze (1981), H. Akcay (1982), G. Mouze (1990) and G. Diallo (1993). Finally, 6 measurements used: G. T. Ewan (1964), V. Zobel (1977), G. Mouze (1990), D. Sardari (2000), J. U. Delgado (2002) and G. L. Molnar (2002).

12. 12Laboratoire National Henri Becquerel B) Pb-210  - decay to Bi-210 We have 9 measurements of relative  -ray emission intensities (the most recent one in 1990), where 4 measurements were not used because of a lack of information in articles (D. K. Butt (1951), C. S. Wu (1953), P. E. Damon (1954) and I. Y. Krause (1958)). C) Po-210  decay to Pb-206 We have 8 (no recent) measurements: M. A. Grace (1951), M. Riou (1952), W. C. Barber (1952), O. Rojo (1955), R. W. Hayward (1955), A. Ascoli (1956), N. S. Shimanskaia (1957) and V. V. Ovechkin (1957).

13. 13Laboratoire National Henri Becquerel Evaluation difficulties: 2 nd Group -  -ray emission intensity. 2. Difficult examples: no articles found in the literature for direct gamma–ray measurements. A) Measurements of  -ray emission intensity found in the literature come from indirect measurements: * Rn-218  decay:  -ray emission intensity was deduced from the U-230 decay chain. * Po-214  decay:  -ray emission intensity was obtained from the Ra-222 decay. OR B) Adopted  -ray emission intensity comes from  and  - intensity measurements: * Rn-222, Po-218 and Bi-210  decays

14. 14Laboratoire National Henri Becquerel Evaluation difficulties: 3 rd Group- Decay scheme balance. 1) Pb-214  - decay. Internal conversion coefficients (ICC’s) for  - ray transitions of Bi-214 have been deduced from Rösel’s tables. These coefficients lead to a better decay scheme. ICC’s given by Rösel  P   ICC’s given using BRICC computer code (Band’s values)  P  = 102 % E  (keV)Multiporality  T (Rösel)  T (BRICC) 53.2275 (21)M1 + E2,  = 0.030 (10) 1.288 (39) E+011.214 (19) E+01 241.997 (3)M1 (+E2),  = 0.00 (15) 8.88 (27) E-018.38 (18) E-01 295.224 (2)M1 + E2,  = 0.30 (13) 4.82 (14) E-014.6 (3) E-01 351.932 (2)M1 (+E2),  = 0.00 (32) 3.19 (10) E-013.00 (25) E-01 Q(Audi) = 1019 (11) keVQ eff = 1024 (11) keV Rel. Error = 0.51 % Q eff = 1029 (15) keV Rel. Error = 0.99 %

15. 15Laboratoire National Henri Becquerel Evaluation difficulties: 3 rd Group - Decay scheme balance. 2) Tl-210  - decay. All decay scheme is based on the only measurement found in the literature given by P. Weinzierl (1964) and several inconsistencies appeared, as shown previously. Because of these inconsistencies, there is a lack of 3 % in decay scheme balance (P  = 97 %) and we wait for new measurements to solve these problems.

16. 16Laboratoire National Henri Becquerel Conclusions Taking into account the experimental values of  -ray emission intensities, we have done a new evaluation of the Ra-226 decay chain down to Pb-206. A total of twelve radionu- clides have been reviewed ( ~ 275  -rays). For other nuclear data like half-life, X-rays,  - and  emission intensities, the situation is as follows: A - Half-lives. Critical cases: Pb-214 (1 measurement by M. Curie in 1931) Bi-214 (1 measurement by H. Daniel in 1956). For four nuclides (Ra-226, Tl-210, Bi-210 and Po-210): no recent measurements since the 1960’s. B – X-rays. Only few measurements for Ra-226, Pb-214, Bi-214, Tl-210 and Pb-210. For the other radionuclides: no direct measurements available. C -  - and  emission intensities. Except for Ra-226 (last measurement in 2001), no recent measurement were found in the literature since 1960’s. To solve all problems in decay scheme of nuclides that belong to Ra-226 decay chain,we need new measurements of these nuclear data.

17. 17Laboratoire National Henri Becquerel More information about evaluations can be obtained at: http://www.nucleide.org/NucData.htm