Decay data evaluation of
Radium – 226 and its daughters
V. Chisté, M. M. Bé, C. Dulieu
Laboratoire National Henri Becquerel
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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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Ra-226 1600 (7) a
a
Ra-226 radioactive chain
100 %
Rn-222
a 100 %
b
b
Po-218 0.022
At-218 0.1
%
%
a 100 %
a 99.9 %
Rn-218 T1/2 = 36.0 (19) ms
Pb-214
Po-214 T1/2 = 162.3 (12) ms
-
b-
100 %
-
Bi-214
a
b-
99.98 %
0.02 %
Tl-210
b-
a
a
100 %
T1/2 = 22.23 (12) a
100 %
Pb-210
b
-
a
Hg-206
Bi-210
b-
a
b-
Tl-206
Po-210
a
b-
Pb-206
Stable
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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).
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Evaluation difficulties: 1st Group - Lack of data set (4 examples).
- I) Half-lives
Isotope
Half-life
(T1/2)
% of
DT1/2
N° of
measurements
Most recent
experimental value
Ra-226
1600 (7) a
0.4
12 [5]
1966, H. Ramthun
Rn-222
3.8232 (8) d
0.02
9
2004, H. Schrader
Po-218
3.094 (6) min
0.20
4 [3]
1986, G. V. Potapov
At-218
1.4 (2) s
14
2
1989, D. G. Burke
Rn-218
35.5 (13) ms
4
5 [4]
1971, A. Erlik
Pb-214
26.8 (9) min
3.4
1
1931, M. Curie
Bi-214
19.9 (4) min
2
1
1956, H. Daniel
Po-214
161.7 (15) ms
0.9
10 [6]
1993, J. W. Zhou
Tl-210
1.30 (3) min
2.3
3 [2]
1964, P. Weinzierl
Pb-210
22.23 (12) a
0.5
14 [11]
2002, G. A. Rech
Bi-210
5.012 (5) d
0.1
6
1959, J. Robert
Po-210
138.3763 (17) d
0.001
9 [7]
1964, J. F. Eichelberger
[]: n° of measurements with uncertainty.
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- II) a and b- Emission probabilities: lack of measured values.
Isotope
Type of decay
Situation
Ra-226
a (100 %)
Two measurements in 1963 and 2001.
Rn-222
a (100 %)
Last measurements in 1958.
Po-218
a (99.978 %)
b- (0.022 %)
Last measurements in 1958.
Last measurements in 1952.
At-218
a (99.9 %)
b- (0.1 %)
Last measurements in 1958.
Last measurements in 1948.
Rn-218
a (100 %)
No direct measurements available.
Pb-214
b- (100 %)
No direct measurements available.
Bi-214
a (0.02 %)
b- (99.98 %)
Last measurements in 1960.
No direct measurements available.
Po-214
a (100 %)
No direct measurements available.
Tl-210
a (100 %)
Last measurements in 1964.
Pb-210
a (1.9 10-6 %)
b- (~ 100 %)
Three measurements in 1961, 1962 and 1964.
Five measurements between 1953 and 1963.
Bi-210
a (1.4 10-4 %)
b- (~ 100 %)
Five measurements between 1947 and 1962.
No direct measurements available.
Po-210
a (100 %)
No direct measurements available.
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- III) X-ray emissions.
Isotope
Type of emission
Situation
Ra-226
X-rays
Three measurements in 1973, 1983 and 2002.
Rn-222
g-rays
X-rays
No direct measurements available.
Po-218
X-rays
No direct measurements available.
At-218
X-rays
No direct measurements available.
Rn-218
X-rays
No direct measurements available.
Pb-214
X-rays
Two measurements in 1969 and 1983.
Bi-214
X-rays
No recent measurements since 1983.
Po-214
X-rays
No direct measurements available.
Tl-210
g-rays
X-rays
No recent measurements since 1964.
Pb-210
X-rays
Four measurements in: 1957, 1971, 1987 and
1990.
Bi-210
g-rays
X-rays
No direct measurements available.
Po-210
X-rays
No direct measurements available.
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- IV) Example of decay
scheme particularly
unknown:
Tl-210 b-decay to Pb-210
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This decay scheme is based
on the measurements of
P. Weinzierl (1964):
Energy (keV)
83(a)
Relative g-ray Emission intensity (%)
2.0
97
4 (2)
296
80 (10)
356
(a)
4 (2)
382
(a)
3 (2)
480
670
Experimental data set
of the relative g-ray
emission intensities.
2 (1)
(a)
799
100
860
7 (2)
910
(a)
3 (2)
1070
12 (5)
1110
7 (2)
1210
17 (4)
1316
21 (5)
1410
5 (2)
1490
(a)
2 (1)
1540
(a)
2 (1)
1590
1650
(a)
2010
2090
Laboratoire
National
Henri
Becquerel
(a)
Not placed
in the
decay
scheme
2 (1)
(a)
2 (1)
2 (1)
7 (2)
5 (2)
2270
3 (2)
2360
8 (3)
2430
9 (3)
9
Experimental values of
transition probabilities.
b-
Level
Energy (keV)
P. Weinzierl
(1964We06)
Adopted
values
11
1380 (12)
25 %
2%
10
1603 (12)
9
1860 (12)
8
2024 (12)
7
2413 (12)
3
4290 (12)
31 %
2
4386 (12)
13 %
Q(Audi) =
5482 (10) keV
7%
56 %
24 %
10 %
19 %
Qeff = 4390
(1600) keV
10 %
 Pb- = 97 %
Qeff = 5470
(1000) keV
Conclusion: New measurements are strongly suggested.
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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).
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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).
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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
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Evaluation difficulties: 3rd Group- Decay scheme balance.
1) Pb-214 b- decay.
Internal conversion coefficients (ICC’s) for g-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  Pb- = 100.6 %
ICC’s given using BRICC computer code (Band’s values)  Pb- = 102 %
Eg (keV)
Multiporality
aT (Rösel)
aT (BRICC)
53.2275 (21)
M1 + E2,
d = 0.030 (10)
1.288 (39) E+01
1.214 (19) E+01
241.997 (3)
M1 (+E2),
d = 0.00 (15)
8.88 (27) E-01
8.38 (18) E-01
295.224 (2)
M1 + E2,
d = 0.30 (13)
4.82 (14) E-01
4.6 (3) E-01
351.932 (2)
M1 (+E2),
d = 0.00 (32)
3.19 (10) E-01
3.00 (25) E-01
Q(Audi) = 1019 (11) keV
Qeff = 1024 (11) keV
Rel. Error = 0.51 %
Qeff = 1029 (15) keV
Rel. Error = 0.99 %
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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.
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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 radionuclides 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.
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More information about evaluations can be obtained at:
http://www.nucleide.org/NucData.htm
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