Nuclear Data Section
International Atomic Energy Agency
P.O.Box 100, A-1400 Vienna, Austria
Memo CP-D/585
Date:
To:
From:

16 September 2009
Distribution
N. Otsuka, S. Dunaeva

Subject:

Mass distribution and fractional yield in fission data

NDS is working for compilation of fission fragment mass distribution (S. Singh et al.
[1] and H. Naik et al.[2]). Below a new analysis code GAUSS and revision ofLEXFOR entry “Fission Yields” are proposed.
1. Derivation of total chain yield
In LEXFOR total chain yield of fission fragment Y(A) is defined as follows:Total chain yield (…(…,F)MASS,CHN,FY):
Sum of the cumulative yields of all stable fission products having the same mass A
In two articles [1,2],- S. Singh et al. [1] tabulated cumulative or independent yield of a nuclide for eachmass chain, and then derived Y(A) by charge distribution correction assuming
Gaussian distribution for independent yield and also unchanged charge
distribution (UCD) for the most probable charge (Z p ).
- H. Naik et al. [2] tabulated cumulative yield of a nuclide near beta- stability line
for each mass chain, and then assumed it is approximately equal to Y(A).
Derived total chain yield may depend on the assumptions used by authors (especiallywhen Z p is close to the beta stability line.). Therefore compilers are asked to give
explanation of derivation of total chain yield under ANALYSIS. A new analysis codeis proposed for the total chain yield obtained by charge distribution correction:
Dictionary 23 (Analysis codes)
CHGDS
Corrected by charge distribution(for derivation of total chain yield, typically by Gaussian assumption)

2. Revision of definition of fractional yield in LEXFOR
The following revision of definition for fractional yields in the LEXFOR entry“Fission Yields” is proposed. Main points are.
(1) A.C. Wahl et al. [3] gives fractional independent yield (FIY) without integration
over Δ z=1. Probably this is due to simplification of calculation in old time. Now
independent fractional yield is often treated in integral form. For compilation ofold literature, we would keep both expressions in LEXFOR.
(2) A review by A. C. Wahl [4] to the reference of this LEXFOR entry is proposed.
This article gives a good summary of fission quantities.
LEXFOR entry update (equations and underlined parts):
5. Total chain yield The total chain yield per fission of fission-fragment mass A is thesum of the cumulative yields of all stable fission products having the same mass A.
When only one stable fission product per mass A exists, the total chain yield for mass
A is identical with the cumulative yield of the stable end product Z,A.
REACTION Coding: Branch code CHN in SF5.
Example: (…(N,F)MASS,CHN,FY)
If the total chain yield is derived from cumulative yield by charge distribution
correction assuming Gaussian distribution of independent variable, a code CHGDS
must be coded under the keyword ANALYSIS. In the correction, unchanged charge
distribution (UCD) assumption Z p = Z f A/A f is often used to determine Z p , where A fand Z f are mass and atomic number of compound nucleus, and A is the fragment mass.
…
7. Fractional yields Ratios of fission-product yield to total chain yield Y(A). The
distribution of charge Z within a given fragment mass A is called charge dispersion. Itcan empirically be approximated by a Gaussian distribution with a most probablecharge Z p (see following).
The fractional independent yield FIY(Z,A) and fractional cumulative yield FCY(Z,A)
of a fission product at the beta-minus decay side (after prompt neutron emission) isgiven by:

FIY ( Z , A) = Yind ( Z , A) / Y ( A)~1

∫ exp[− (z − Z ) / 2σ ] dz ~ cπ exp[− (z − Z ) / c]

Z +1 / 2σ 2π z −1 / 22122p

FCY ( Z , A) = Ycum ( Z , A) / Y ( A) ~p1

σ 2π∫ exp[− (z − Z ) / 2σ ] dz

Z +1 / 222p0

The parameters c and σ are width of the distributions related by c~2(σ2+1/12).
…

Reference[1] S. Singh et al., J. Radioanal. Nucl. Chem. 279 (2009) 547 (EXFOR D6077)[2] H. Naik et al., Nucl. Instrum. Meth. B267(2009)1891 (EXFOR G0015)[3] A. C. Whal et al., Phys. Rev. 126 (1962)1112[4] A. C. Wahl, At. Data and Nucl. Data Table 39 (1988) 1

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