Neutron multiplicity for neutron induced fission of /sup 235/U, /sup 238/U, and /sup 239/Pu as a function of neutron energy

Abstract

Recent development in the theory and practice of neutron correlation ("coincidence") counting require knowledge of the higher factorial moments of the P v distribution (the probability that (v) neutrons are emitted in a fission) for the case where the fission is induced by bombarding neutrons of more than thermal energies.In contrast to the situation with spontaneous and thermal neutron induced fission, where, with a few exceptions the P v is reasonably well known, in the fast neutron energy region, almost no information is available concerning the multiplicity beyond the average value, <v>, even for the most important nuclides. The reason for this is the difficulty of such » experiments, with consequent statistically poor and physically \ inconsistent results.

Neutron triples counting data for uranium

“…Based on previous work [9] we estimate for our UO 2 F 2 samples the average ߙ value to be to be about 7.2 with a range of ±0.2, and ‫ܯ‬ to be about 1.0027 with a range of <0.0002 and independent of neutron source reaction with roughly 20% of the induced fission taking place in 235 U and the rest in 238 U. For fast (1 MeV) fission we estimate, using the tables of Zucker and Holden [17], the values of ߭ ூଵ , ߭ ூଶ , and ߭ ூଷ to be about 2.449, 4.937, and 8.112 respectively. The exact choice of energy is not crucial since the induced fission factorial moments appear only in ratios.…”

Nuclear explosions: a study

“…Energy-dependent values of ν for 235 U and 239 Pu are obtained by fitting the experimental data of Zucker and Holden [5,6] (see figures 1 and 2). Best linear fits obtained for 235 U and 239 Pu are ν(E) = 2.351 + 0.146E and ν(E) = 2.862 + 0.153E respectively.…”

Incorporating delayed neutrons into the point-model equations routinely used for neutron coincidence counting in nuclear safeguards

“…For the SF of 240 Pu we take ν Sd / ν S1 (0.00675/2.154)= 0.00313, and for IF we adopt 239 Pu with ν Id / (ν I1 -1) (0.00645/(3.009-1)=0.00321. The average prompt neutron choices are based on the prompt neutron multiplicity distribution evaluation work of Holden and Zucker [16] in the case of 240 Pu, and in the case of 239 Pu we have assumed induced fission by incoming 1-MeV neutrons and used the tables of Zucker and Holden [17]. The delayed neutron yield for 240 Pu was estimated using the "systematics" relation of Tuttle [13].…”