Behavior correction of the inverse square law in irradiation room for volumetric source and detector

The inverse-square law is used to calculate the radiation flux at difference distances from the source. This law is applied for point source and point detector in vacuum. This research aims to study the point behavior of volumetric source and detector by undertaking required corrections on inverse-square law through the elimination of scattered neutrons contribution. The measurements have been performed with a 20Ci 241Am-Be neutron source, a long counter and appropriate shadow cone. The results confirm that the exponent in inverse-square law should be changed to 1.907±0.010 when volumetric neutron source and detector are used. Also, the neutron source activity has been measured as 17.95 Ci, which is 5.82% less than its nominal value.