Measurement of Neutron Densities with Crystals of NaI(Tl)

Abstract

Crystals of NaI(Tl) were irradiated in a nuclear reactor and the induced activity in sodium and iodine registered with a photomultiplier tube. It was found that an absolute measurement of the activities can be made in this way. Since sodium is an almost pure "one over $v$" absorber the neutron density can be determined from its activity.Comparisons have also been made between the sodium and iodine cross sections for capture of thermal neutrons. With the sodium cross section equal to 0.47 barn, the cross section of iodine was found to be 5.00 barns.