Use of Li6I(Eu) as a scintillation detector and spectrometer for fast neutrons

Abstract

The scintillation response of europium activated crystals of Li⁶I to neutrons in the energy range 1–14MeV has been investigated with the crystals maintained at various temperatures. The pulse-height spectrum from mono-energetic neutrons incident on a crystal at room temperature demonstrates a poorly defined and broad fast-neutron peak. Upon cooling the crystal, the fast-neutron peak becomes sharper and assumes a nearly Gaussian shape at temperatures below about — 140° C. This behaviour is attributed to an increased scintillation efficiency of LiI(Eu) to alpha particles at low temperatures. Pulse-height spectra from crystals at the liquid nitrogen point are presented for neutrons from the D(d,n)He³, T(d,n)He⁴, and Be⁹(d,n)B¹⁰ reactions, a Po-Be source, and U²³⁵ fission. The principal features of Li⁶I(Eu) as a fast-neutron spectrometer are a relatively high detection efficiency (≈0.1%) and moderate resolution.