INDC(IND)-35G - IAEA Nuclear Data Services
INDC(IND)-35G - IAEA Nuclear Data Services
INDC(IND)-35G - IAEA Nuclear Data Services
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PKBEQUILIBHIUM PARIICIE EMISSION SPECTRA AND WI/PIPARTICIE<br />
ENACTION CROSS-SUCTIONS OF NIOBIUM*, S.B. Garg and Amar Sinha,<br />
Neutron Physios Division, Bhabha Atomic Besearch Centre,<br />
Trombay, Bombay 400 085<br />
Preequilibriuin model and multistep Hauser-Feshbach<br />
theory are two important tools which are increasingly utilized<br />
in the analysis and prediction of nuclear induced multiparticle<br />
reaction cross-seotions, particle emission spectra and their<br />
angular distributions. We have selected niobium for the application<br />
of these models particularly because its neutron induced<br />
particle emieeion spectra and their angular distributions have<br />
been well measured at 14.6 MeV and it adequately serves as a<br />
test caise for these models. Niobium *is also considered to be<br />
a neutron multiplier in fusion-fission reactor systems and thus<br />
it is a fit case for cross-section evaluation in the MeV energy<br />
range.<br />
V/e have adopted the generalized excitbn model of Mantzouranis<br />
et ai /%/ for the analysis of preequilibrium angular distributions.<br />
According to this model the exciton state of a composite<br />
nucleus is represented by the exciton number n ani a direction -* 1 -<br />
which corresponds to the direction of the incoming particle* H<br />
is assumed that on emission the direction of the emitted particle<br />
coincides with-»1- .<br />
A combination of preequilibrium exciton model and multi-<br />
Btep Hauser-Peshbach theory /2/ has been used to evaluate<br />
(n,n»), (n,2n) , (n,p>, (n,oO. (n»np), (n,pn) and (n,oin) reaction<br />
cross-sections at 10,14.6, 20, and 25.7 MeV. Gamma emission<br />
has been accounted for according to the Brink-Axel giant resonance<br />
theory /3/.<br />
Transmission coefficients for the neutron, proton am!<br />
alpha channels have been computed with the spherical optical<br />
model. The potential parameters for neutrons and protons have<br />
been taken from Perey /4/ and those for alpha particles from<br />
Huizenga and Igo /5/.<br />
The discrete levels of the residual nuclides and their<br />
level density parameters have been taken from ref. /6/ and the<br />
continuum of levels has'been estimated according to Gilbert-<br />
Cameron /7/ formalism of level densities.<br />
The preequilibrium contribution has been obtained by<br />
extracting the value of K- the interaction matrix constant as<br />
given by Kalbach /8/ to fit the angle integrated total neutron<br />
emission spectrum dV
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