197
Analysis By assuming a Maxwell-Boltzmann speed distribution for the moderating medium and the Breit-Wigner formula for a single resonance, Dresner2 has arrived at the following equation for the resonance integral, Ierfrfor a single absorption resonance:
where
k = In f3
+ 5 In 10 In 2
Other terms are defined in the nomenclature. sult The function J ( E , k ) is tabula%ed in ref. 1. The tabulated have been plotted as the family of curves in Fig. B.l. The reduced mass of the neutron p is equal to neutron mass (-1.0)
multiplied by M/(M+l), where M is the mass of the absorbing atoms. Since the mass of thorium is 232, p was taken as unity for these calculations. Table B.l lists the resonance parameters for--eachof the 13 resolved thorium resonances (2). These parameters were used in the equation for Ieff for computing the resonance integral for each resonance. (Since these calculations were performed, additional thorium resonances have been resolved, and improved parameter values for previously resolved resonances have been obtained. The effect of these new values has not been evaluatdd.) The total resonance integral for each energy group is then obtained by adding together the separate integrals for each resonance. Table B.l also