On the Class "A" Fission-Neutron Irradiation of Small Laboratory Animals

Average absorbed dose values were calculated in various small laboratory animals (mouse, rat, guinea pig), using an albedo code, and the uniformity of the irradiation was studied. A plane source emitting neutrons with a cosine distribution was used. The neutron spectrum used was that measured in the irradiation facility of the Hungarian Research Reactor. Infinite-length cylinders with radii 1.25, 2.5, and 3.3 cm were used for calculation. The average absorbed dose was 85.2, 72.1, and 64.9% of the free-in-air kerma. None of the irradiations was uniform when unilateral irradiation was assumed. A uniform, Class A irradiation ($D_{{\rm max}}/D_{{\rm min}}<1.15$) could not be achieved in rats and guinea pigs if only bilateral irradiation or rotation was used. With various field-shaping filters, a very uniform irradiation may be performed, with$D_{{\rm max}}/D_{{\rm min}}\leq 1.05$, in all three types of animals. Present calculations were compared with other values (measured or calculated) published in the literature.