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Decay chains and branching ratios of U-234
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Using both Nucleonica.net and directly JEF 2.2, I’m surprised to find differences in the
daughters given for the 234U: Rn218, At218, Tl210, Tl206, Hg 206 are not considered in
Nucleonica.net, as well as in some other references. Why? Is it linked with their half-life?
K. Beaugelin-Seiller, Institut de Radioprotection et de Sûreté Nucléaire (IRSN), France
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Answer from the Nucleonica.net team |
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Dear Karin,
These isotopes are indeed taken in account in the decay chains of U234 in Nucleonica.net.
You can see this in the Nuclide Explorer by selecting U234 and with the right mouse button
selecting "show decay chain".
If you used the decay module to compute the chains, I would like to draw your attention to
the parameter Min.Prod. (Default 1e-2) which is the minimum branching considered for the
calculation. You need to select a much smaller value to obtain the nuclides you are looking
for (i.e. nuclides with small branching ratios).
To demonstrate this clearly, consider the decay of Pb210 for which (from the Datasheets)
| Decay mode |
Branching ratio |
Daughter |
| ß- |
~1 |
~100% |
Bi 210 |
| Alpha |
1.90E-08 |
1.90E-06% |
Hg 206 |
If your Min.Prod has a value of 1e-2 the alpha decay mode will be ignored and only the Bi210
would be considered as a decay product for computing. To "see" the alpha decay mode you have
to set Min.Prod. to 1e-8. If you are unsure which value to use, just insert 0 and all decay
chains will be shown.
In some cases there are many decay modes, and to save calculation time, one selects a value
of Min.Prod. which typically gives the most important 3-4 chains. With a default value of
Min.Prod. = 1E-2, we see all chains for which the product of the branching ratios is greater
than 1E-2 or 1%.
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Gamma emission branching ratio for Bi-212
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I am involved in the gamma spectrometry measurements above ground areas with increased
U-Ra- and Th-Chain content. These measurements have been performed by a number of
institutions in the context of a comparison at WISMUT sites, which was organized
by the BfS. In particular, I am interested in the detection of Bi-212. When I compared
the branching ratios (for the emitted gamma lines) with Nucleonica.net (see table
below) I found large differences.Could you please explain me why there is such a
difference and where does it come from?
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Nucleonica.net |
Erdtmann (FZK) |
RadDecay (C.Hacker)
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Genie2000 (Canberra ) |
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727 keV |
6.75% |
11.80% |
11.83% |
11.80% |
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1621 keV |
1.49% |
2.75%
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2.75%
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2.75%
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Bernd Horlbeck, Deutsche Gesellschaft zum Bau und Betrieb von Endlagern für Abfallstoffe
mbH(DBE), Germany
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Answer from the Nucleonica.net team
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The values given in Nucleonica.net are from the JEF 2.2 datafile. The values have
recently been re-assessed and in this most recent evaluation (see
http://www.nucleide.org/DDEP_WG/Nuclides/Bi-212_com.pdf), the values are
very close to the JEF.2.2/Nucleonica.net values. The other values you quote (RadDecay,
Erdtmann, etc.) are old and no longer accurate (for more information see
http://www.nucleide.org/DDEP_WG/DDEPdata.htm). Note also that the FZK evaluation
that you mention is the one which is used in the Gammavision isotope standard library
(and probably also for the Genie2000 standard library). This error, however, is
only in the standard libraries - not in the PTB or Berkeley libraries.
PS: In the future edition of Nuclides.net, there will be a special module to create
custom libraries from our databases to be used with both Genie2000 and Gammavision.
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Effective dose coefficient for Po-210 in ICRP 68 and 72
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Po-210 is of broad practical interest: in tabacco, in drinking water, in diet, and
as part of the uranium decay chain. According to the ICRP Publication 72, the effective
dose coefficient for ingestion for members of the public ( eing
(50)=1.2x10-6 Sv/Bq), is much higher than the value given in ICRP 68
for workers ( eing (50)=2.4x10-7 Sv/Bq). This seems
to be a result of the gut transfer factor (f1) for members of the public being raised
from 0.1 to 0.5. How can this be explained?
Helmut Kowalewsky, Germany
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Answer from Alan Phipps. National Radiological Protection Board , UK |
Dear Mr. Kowalewsky,
you are right in saying that the gut uptake fraction (f1 value) is 5 times higher
for members of the public than for workers. This is because the public can be expected
to encounter Po-210 in foodstuffs rather than in the inorganic forms which are likely
to occur in the workplace. ICRP Publication 67 summarises the data from ingestion
of Po in reindeer and crabmeat (by humans) and in milk and liver meat (by rats)
to justify the value of 0.5 chosen for the public. Of course, this leads to a higher
dose coefficient (Sv/Bq) for the public than for workers, by about a factor of 5.
ICRP is currently reviewing f1 values for workers. I do not know what value they
are likely to choose for workers, but it remains the case that workers are exposed
to different (generally inorganic) forms of Po than are the public.
Alan Phipps. National Radiological Protection Board , UK Note added by
the Nucleonica.net team: this higher value for the effective dose coefficient for
ingestion for Po-210 has a direct consequence on the reference levels for uranium
(where Po-210 is an equilibrium daughter) in radiotoxicity calculations for spent
nuclear fuel. More information can be found in a
recent publication.
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Decay Heat Calculations with Nucleonica.net
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We are trying to calculate the heat generation in a transport package. The package
contains several nuclides. First we calculated the heat generated by each nuclide
using Nucleonica.net. We used the Q-value and specific activity given in Nucleonica.net
for this purpose. But then we compared these calculated values with the isotopic
powers given in Nucleonica.net. The isotopic power is always lower than the heat generation
we calculated – see the table below. Please, can you tell us the difference
between our calculated heat generation and the given 'isotopic power' of a nuclide?
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three examples: H-3, Fe-55 and Pu-240
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A
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B
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C
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D
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E
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F
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G
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our data
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Nucleonica.net
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Nucleonica.net
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from C and D
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from Nucleonica.net
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E/F
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isotope
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mass
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Q-value
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specific activity
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specific heat
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isotopic power
(a + b + g )
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(g)
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(keV)
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(Bg/g)
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W/g
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W/g
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H-3
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9.60E-03
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18.571
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3.56E+14
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1.06E+00
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3.25E-01
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3.26E+00
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Fe-55
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4.80E-05
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231.10
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8.92E+13
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3.30E+00
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8.40E-02
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3.93E+01
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Pu-240
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1.20E+02
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5255.9
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8.40E+09
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7.07E-03
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7.06E-03
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1.00E+00
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Ralf Steiner and Lars Niemann, Hauptabteilung Dekontaminationsbetriebe, Forschungszentrum
Karlsruhe.
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Answer from the Nucleonica.net team
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1. Case of H-3:
From Nucleonica.net Datasheets: H-3 is a pure ß- emitter. The energy of the emitted
ß- particle is 18.571 keV with an emission probability of 1. This agrees roughly
with the Q-value you quote of 18.6 keV. Note, however, that the mean decay energies
(which are used for the isotopic power calculation) are “electron” =
5.71 keV. This is approximately 1/3 of the Q-value. At a first glance, this seems
to be a contradiction. It is easy to explain however when you note that in beta-
emission, the following reaction occurs in the nucleus
i.e. a neutron is converted to a proton, a ß- particle and an antineutrino v. Note
that beta emission differs from alpha emission in that the beta particle has a continuous
spectrum of energies between 0 and some maximum value called the end-point energy.
Also that the beta energy of 18.571 keV quoted above is the end-point energy. The
average energy of the beta particle is approximately 1/3 the value of the endpoint
energy. This explains the factor 1/3 observed above. Note here that approximately
2/3 of the energy i.e. 12 keV is carried away by antineutrinos. 2. Case of Fe-55:
From Nucleonica.net Datasheets: Fe-55 decays by electron capture (ec). The Q-value
is 231 keV. The decay reaction can be written:
In this reaction, an inner shell electrons in Fe-55 is captured by the nucleus and
combines with a proton in the nucleus to form a neutron and a neutrino. In contrast
to ß- and ß+ emission, the neutrino is mono-energetic. The process of electron capture
leaves a vacancy in an electron shell that is then filled immediately by electrons
from higher levels cascading down. This process is characterized by the emission
of x-rays. Hence the only way that the electron capture process can produce energy
emission is through the x-rays or Auger electrons associated with them. The remaining
energy goes into the neutrino!
Hence for Fe-55, we can see from the datasheets that the average x-ray and electrons
energies are 1.67 and 4.22 eV respectively. The energy difference between the Q-vale
of 231 keV and the x-rays + electrons of 5.89 keV is emitted as mono-energetic neutrinos
(approx. 225 keV).
Hence it is incorrect to use the Q-value for the calculation of decay heat. In this
particular case of electron capture in Fe55, most of the energy is emitted as an
antineutrino. If one use the Q value, the decay heat will be overestimated by a
factor Q/5.89 keV = 39.2. This is exactly the number you given in you table below.
3. Case of Pu-240:
In contrast to ß-, ß+, and ec, in alpha emission there are no neutrinos involved.
For this reason, for decay heat calculations, the Q-value can be used.
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Se-79 half-life
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I get some problems with Se-79 halflife. I found that in some web pages it is defined
as 6.5E+04y, 1.13E+06y, and in Nucleonica.net it is indicated equal to 6.5E+05. What
is the reason for such differences and which number is real halflife of Se-79?
Asta Brazauskaite, Lithuanian Energy Institute
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Answer from the Nucleonica.net team
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The measurement of the half-life of Se-79 is problematic because of its long half-life
and its decay without gamma ray emission. Additionally the maximum beta- energy
is only 151 keV. Many attempts have been made to determine an accurate value for
this half-life, using decay counting or even particle counting. The different values
you've found come from different evaluations in specific database and they might
not agree depending how old the database is and how many entries the evaluator had
to give an average value.The present entry in Nucleonica.net comes from the Nubase
evaluation from 1997. The latest Nubase 2003 edition gives value of 295 ky. On the
other hand, in the 8th Table of Isotopes, they give a value of 1.13E6 y (cut off
from 1998) and a recent measurement (from 2000) gives a values of 1.24E5 y).
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Cs-137 decay gamma lines
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I'm frequently using Nucleonica.net for shielding and dosimetry calculation, but I
have one problem for calculation with radionuclide Cs-137. Starting calculation
program dosimetry leads to the error "no specified ray for this nuclide". Any other
radionuclides are OK. Please help me to solve this problem.
Juraj Hamza, JFM, Slovakia
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Answer from the Nucleonica.net team
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It comes from a common mis-interpretation of the decay of the Cs-137. I guess that
you're looking for the 662 keV line.
The Cs-137 parent isotope beta decays (~95%) with a 30.17y half-life to produce
Ba-137m which in turn decays with a 2.55min. half-live, generating a 661.6
keV gamma ray emission.
In most decay library the 662 keV is then associated to the decay of Cs-137 because
Ba-137m is directly produced by the decay of Cs-137 and coz' the half-life of Ba-137m
is rather short in comparison to Cs-137, thus the two nuclides are in equilibrium.
Therefore in your Nucleonica.net calculation, you should use the Ba-137m nuclide as
source instead of Cs-137.
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Decay of Bi-211
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In some databases it is indicated that a fraction of 16.19% of the Bi-211 decays to the Tl-207 metastable state. Is this correct? Furthermore, the Tl-207m is in the Karlsruhe nuclide chart - when do we obtain Tl-207m if it isn't from the Bi-211 decay?
Gro Salberg, Algeta ASA, Oslo, Norway
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Answer from the Nucleonica.net team
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From the Table of Isotopes (8th Edition, Vol. II: A = 151-272, R. B. Firestone and V. S. Shirley (Eds.) J. Wiley, 1999) we have the following diagram for Bi-211 decay:
The 16.19% you refer to is the decay to the 30 ps state see above. This is NOT the (1.33 s half-life) metastable state referred to in the Karlsruhe nuclide chart (see following diagram) but a very short-lived excited state which then further decays to the ground state. Note from the diagram above (right hand side), that the Bi-211 decays only to the 30 ps state and the ground state. This 30 ps state is very short-lived and decays to the ground state. This is the reason why the Bi-211 decay is regarded to decay only to the ground state of Tl-207.
With regard to the origin of Tl-207m, it can be seen from the above diagram that the 1.33s metastable state of Tl-207 is “fed” from the decay of Hg-207. This is also shown in the Karlsruhe Nuclide Chart shown below.
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Excerpt from the Karlsruhe nuclide chart, 7th edition 2006 for the decay of Bi-211. (for further information see www.nucleonica.net)
According to the symbols used in the Karlsruhe nuclide chart, Bi-211 has two decays modes – α and β- indicated by the colours yellow and blue respectively.
In the α decay mode, the parent Bi-211 decays to the ground state of Tl-207 (4.77m half-life). This is indicated in the bottom line of the Bi-211 “box” where the symbols α→g implies decay to the ground state of the daughter Tl-207.
It can also be seen from the Hg-207 “box” that decay of Hg-207 results in both the metastable (m) and ground (g) states of Tl-207. In fact, according to the notation in the bottom line of the Hg-207 box, i.e. m; g, decay to the metastable state has the higher branching ratio.
In the ß- decay mode, the parent Bi-211 decays to the ground state of Po-211 (0.516 s half-life), This is also indicated in the bottom line of the Bi-211 “box” where the symbol ß-→g implies decay to the ground state of Po-211.
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Decay of Bi-211
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Nucleonica.net presents two half-lives of Po-211: 25.2 sec and 0.516 sec. Is only one of these two variants (the 0.516 sec variant?) produced during Bi-211 decay?
Gro Salberg, Algeta ASA, Oslo, Norway
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Answer from the Nucleonica.net team
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From the Table of Isotopes (8th Edition, Vol. II: A = 151-272, R. B. Firestone and V. S. Shirley (Eds.) J. Wiley, 1999) we have the following diagram for Bi-211 decay:
From this diagram you can see that Bi-211 cannot decay to the 25 s metastable state of Po-211m. This is the reason why only the decay to the ground state is shown in the nuclide chart.
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