Collisions between Neutrons and Diplons

Abstract

WHEN a stream of neutrons passes through a sheet of matter, neutrons are lost from the beam both by absorption and scattering. The latter can be avoided by placing the source of neutrons in the centre of a spherical scatterer, since with this arrangement as many neutrons must be scattered into the beam as are lost from it by scattering. In these circumstances any diminution of the number of neutrons in the beam must be attributed to absorption by the material of the sphere. The usual method of estimating the intensity of a neutron beam is to measure the induced radioactivity produced in a thin layer of matter such as aluminium or rhodium by means of a tube counter. The radioactivity so produced is proportional to the length of the neutron path in the detecting substance and will be given by k.n.d. sec _m (k, number of radioactive atoms produced per cm. path; n, number of neutrons in the beam; d, thickness of the sheet; and _m, the mean angle of incidence).