Microscopic beta and gamma data for decay-heat needs Page: 4 of 20
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deduced. Such deductions are occasionally, but not as a rule, augmented by
direct beta-ray decay measurements. As an example, the decay of a well-known
fission product, 137Cs, is exhibited in Fig. 3.
Now, "Microscopic Beta and Gamma Data" (or MBG) can be defined. First
observe that insofar as decay-heat calculations are concerned, the "Beta and
Gamma" data that are needed are just the integral quantities < Eg >p, as de-
fined by Eq. (1), and Ey >Q, their equivalents for fission-product gamma
radiation. However, as pointed out above, these quantities are rarely
directly measured in modern experiments; instead spectral measurements are
made, and these are analyzed to deduce level-structure information. Very
often, then, one must start with the deduced or evaluated level-structure
information to determine the desired integral quantities. So, finally,
"Microscopic" may be defined as the N(EX), where jc is 6 and -y, for the MBG
portion of the title.
In summary, then:
Microscopic Beta and Gamma Data for Decay Heat Needs are Absolute Inten-
sity Spectral Distributions of Beta and Gamma Rays Following Radioactive Decay
of Each Radionuclide Created Directly or Indirectly During Fission.
EXAMPLE: DATA FOR DECAY OF 13?Cs AND 137Ba*
It seems necessary to provide a certain precision to the definition of
the title of this report, because almost always the reported evaluated decay
information do not directly contain all of the "data needs." They often do
not include all of the necessary information to deduce what is required for
the calculations. Such a situation, for example, is illustrated by the in-
formation for 137Cs decay shown in Fig. 3.
This figure exhibits the decay of two fission products: (1) the beta
decay of 137Cs, and (2) the internal-transition decay of the 2.55-min isomer
of 137Ba. Let us investigate the latter decay first. The MBG data given
directly are (a) the gamma-ray energy E^ = 661.4 keV, and (b) the fraction of
the decay, 89.9%, that this gamma-ray represents. We can classify these two
data as "direct" because the function N(Ey) is essentially a delta function,
<5(Ey - E^), having an area equal to 0.899/decay. There is no direct repre-
sentation of the other 10.1% of the decay of this isomer. Let us see how much
of the other 10.1% can be deduced from information given in Fig. 3. Three
data exhibited in this figure will provide some assistance: (a) the transi-
tion energy (661.4 keV), (b) the multipolarity (M4), and (c) the Z (56) of
the Ba nucleus. From these data the total conversion-electron production can
be deduced, using published tables, [18] that is, using information not given
in Fig. 3. The characterization of this decay is not complete, however, for
one must now determine the atomic decay of the disturbed electronic configura-
tion. These can be accomplished using tabulated fluorescent yields [19].
Such information is not given in Fig. 3. However, by using additional infor-
mation as needed, one can complete the characterization of the decay of 137Ba*
so as to provide a complete N(Ey) data set including x-ray contributions, and
a complete N(Ee) E N(Eg) data set including conversion-electron contributions.
Turning now to the beta decay of 137Cs, as represented in Fig. 3, there
are only two MBG data: the two values of Ig, one for each of the two
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Dickens, J.K. Microscopic beta and gamma data for decay-heat needs, article, January 1, 1983; Tennessee. (https://digital.library.unt.edu/ark:/67531/metadc1098208/m1/4/: accessed March 29, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.