JAERI 1287 JNDC Nuclear Data Library of Fission Products Fir
JAERI 1287 JNDC Nuclear Data Library of Fission Products Fir
JAERI 1287 JNDC Nuclear Data Library of Fission Products Fir
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<strong>JAERI</strong><strong>1287</strong> 2. <strong>Nuclear</strong> <strong>Data</strong> <strong>Library</strong> <strong>of</strong> <strong>Fission</strong> <strong>Products</strong> 15<br />
well-known relation as<br />
t/(A,Z) = l. (2.4.2)<br />
Wahl et al. 43 > had proposed the Gaussian distribution <strong>of</strong> the independent yield in their phenomenological<br />
model. After that several investigations 45>46) presented evidence for the fact<br />
that the even-odd effect in proton- and neutron-pairing distorts the Gaussian distribution <strong>of</strong><br />
the yield. So we modify independent yield distribution as follows. Let FX(A, Z) be a correction<br />
factor for the even-odd effect and letY(A)be the mass yield before delayed-neutron<br />
emission. Then the yield Y(A, Z) is given by<br />
Y(A, Z)=N(A>FX{A, Z)-f(A, Z), (2.4.3a)<br />
, Z) = NVD-I, FXU, Z)f{A, Z), (2.4.3b)<br />
z z<br />
where N(A) is a normalization constant such that the sum <strong>of</strong> yields is 200% per fission. The<br />
F(A, Z) 's are expressed in the following form 41 ' 47 *.<br />
Fx(A,Z) = l + {p+n) foreven/1 - even Z<br />
= l + {p-n) for odd A - even Z<br />
= l-O-«) forodd A -odd Z<br />
= 1 —(/?+«) for even A -odd Z<br />
where p is proton-pairing term and n is neutron-pairing term.<br />
Experimental data are not enough, but indicate that the magnitudes <strong>of</strong> p and n depend<br />
on fissile and incident energy <strong>of</strong> neutron. These values were estimated with the simple empirical<br />
equation proposed by Madland and England 47 ). The results are tabulated in Table 2.4.2.<br />
The Gaussian width parameter a is taken to be 0.56 ± 0.06 44 ) irrespective <strong>of</strong> mass number,<br />
fissile nuclide and neutron energy.<br />
The most probable charge ZP(A) has been estimated by several investigators. Rider and<br />
Meek adopted the values by Wahl et al. 44 ^ and Nethaway 48 ) and added another correction term<br />
for ternary fission, which was estimated by Madland and Stewart 49 *. TheZ^C/Uis expressed<br />
as the sum <strong>of</strong> standard value for thermal-neutron fission <strong>of</strong> 235 U and the small correction terms<br />
Table 2.4.2 Parameters <strong>of</strong> pairing effects on the distribution<br />
<strong>of</strong> independent yield in neutron-induced<br />
fission (taken from the report by Rider and<br />
Meek 41 ))<br />
Fissile<br />
23su(T)a<br />
235 U (F) b<br />
235 U (H) c<br />
238 U(F)<br />
238U(H)<br />
239<br />
Pu(T)<br />
239<br />
Pu (F)<br />
241<br />
Pu(T)<br />
233<br />
U (T)<br />
232<br />
Th (F)<br />
Proton effects (p)<br />
0.228<br />
0.151<br />
0.015<br />
0.329<br />
0.018<br />
0.171<br />
0.124<br />
0.206<br />
0.210<br />
0.327<br />
a thermal neutrons.<br />
b fission spectrum neutrons.<br />
c 14-MeV neutrons.<br />
Neutron effects (n)<br />
0.044<br />
0.029<br />
0.003<br />
0.063<br />
0.003<br />
0.033<br />
0.024<br />
0.040<br />
0.041<br />
0.063