Theoretical analysis of 2n accidentals rates

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Introduction

A given photon pulse may cause multiple neutron-producing reactions, ranging from zero to "infinity" reactions. The number of neutron-producing reactions in a pulse is hereafter denoted by [math]n[/math]. Being the number of neutron-producing reactions actually occurring per pulse, [math]n[/math] is assumed to follow the Poissonian distribution as a limiting case of the binomial distribution. Each neutron-producing interaction produces [math]v_{i}[/math] neutrons, where [math]v_{i}[/math] is the distribution of the number of neutrons produced from an individual neutron-producing reaction. The beam has a Bremsstrahlung end point of 10.5 MeV, energetically allowing only two possible neutron-producing interactions, 1n-knochout and photofission. Thus, [math]v_{i}[/math] is the photofission neutron multiplicity, but with a larger [math]P(v_{i}=1)[/math] from 1n-knockout events. In other words, a 1n-knockout event and a photo-fission event emitting exactly one neutron are considered identically. In viewing it this way, the analysis is simplified, but the end result is not changed since 1n-knockouts can only contribute to accidentals.