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Decay data evaluation of Radium – 226 and its daughters V. Chisté, M. M. Bé, C. Dulieu

Decay data evaluation of Radium – 226 and its daughters V. Chisté, M. M. Bé, C. Dulieu. 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.

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Decay data evaluation of Radium – 226 and its daughters V. Chisté, M. M. Bé, C. Dulieu

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  1. Decay data evaluation ofRadium – 226 and its daughtersV. Chisté, M. M. Bé, C. Dulieu

  2. 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. Ra-226 1600 (7) a Ra-226 radioactive chain a 100 % Rn-222 a 100 % b- b- T1/2 = 36.0 (19) ms Po-218 At-218 Rn-218 0.022 % 0.1 % a 100 % a a 99.9 % 100 % T1/2 = 162.3 (12) ms Pb-214 b- Bi-214 b- Po-214 100 % 99.98 % a a T1/2 = 22.23 (12) a 0.02 % 100 % b- b- b- Tl-210 Pb-210 Bi-210 Po-210 a a a b- b- Hg-206 Tl-206 Pb-206 Stable

  4. Global Characteristics of the Ra-226 chain. 10 a disintegrations and 9 b- 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 g-rays, mainly in: Pb-214 b- decay to Bi-214 (26 g-rays), Bi-214 b- decay to Po-214 (212 g-rays) and Tl-210 b- decay to Bi-214 (24 g-rays).

  5. Evaluation difficulties: 1st Group -Lack of data set (4 examples). - I) Half-lives []: n° of measurements with uncertainty.

  6. - II)a and b- Emission probabilities: lack of measured values.

  7. - III) X-ray emissions.

  8. IV) Example of decay scheme particularly unknown: • Tl-210 b-decay to Pb-210

  9. This decay scheme is based on the measurements of P. Weinzierl (1964): Experimental data set of the relative g-ray emission intensities. (a) Not placed in the decay scheme

  10.  Pb- = 97 % Qeff = 5470 (1000) keV Experimental values of b- transition probabilities. Conclusion: New measurements are strongly suggested.

  11. Evaluation difficulties: 2nd Group- g-ray emission intensity. Ra-226 radioactive chain: ~ 275 g-rays. 1. Good examples: many and recent articles found about direct measurements. A) Pb-214 b- decay to Bi-214, Bi-214 b- decay to Po-214 and Ra-226 a decay to Rn-222 We have: * 5 measurements of absolute g-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 g-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. B) Pb-210 b- decay to Bi-210 We have 9 measurements of relative g-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 a 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. Evaluation difficulties: 2nd Group - g-ray emission intensity. 2. Difficult examples: no articles found in the literature for direct gamma–ray measurements. A) Measurements of g-ray emission intensity found in the literature come from indirect measurements: * Rn-218 a decay: g-ray emission intensity was deduced from the U-230 decay chain. * Po-214 a decay: g-ray emission intensity was obtained from the Ra-222 decay. OR B) Adopted g-ray emission intensity comes from a and b- intensity measurements: * Rn-222, Po-218 and Bi-210 a decays

  14. Evaluation difficulties: 3rd Group- Decay scheme balance. 1) Pb-214 b- decay. Internal conversion coefficients (ICC’s) for g-raytransitions of Bi-214 have been deduced from Rösel’s tables. These coefficients lead to a better decay scheme. ICC’s given by Rösel  Pb- = 100.6 % ICC’s given using BRICC computer code (Band’s values)  Pb- = 102 %

  15. Evaluation difficulties: 3rd Group - Decay scheme balance. 2) Tl-210 b- 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 (Pb = 97 %) and we wait for new measurements to solve these problems.

  16. Conclusions Taking into account the experimental values of g-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 g-rays). For other nuclear data like half-life, X-rays, b- and a 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 - b- and a 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. More information about evaluations can be obtained at: http://www.nucleide.org/NucData.htm

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