Lithium Alkaline Halides—Next Generation of Dual Mode Scintillators

Abstract

We report on a new family of scintillators - Lithium alkaline halides , developed based on the alkaline halides by introducing lithium for dual mode gamma-neutron detection. Many different compositions were grown, among which ${\rm LiSr}_{2}{\rm I}_{5}$ (LSI), ${\rm LiCa}_{2}{\rm I}_{5}$ (LCI), ${\rm LiSr}_{2}{\rm Br}_{5}$ (LSB) activated with divalent Europium show good gamma and neutron detection properties. LSI shows the main emission at ${\sim}$ 497 nm under X-ray excitation. It also shows good proportionality, which in combination with the light yield as high as 60000 photons/MeV, results in an energy resolution of 3.5% at 662 keV. The electron or gamma equivalent energy (GEE) of the thermal neutron peak due to the $^6{\rm Li}$ neutron capture is 4.1 MeV, which amounts to a very high neutron light yield of ${\sim}$ 245000 photons. The decay times for neutrons are faster compared to that for gamma-rays, hence we achieved good pulse shape discrimination (PSD) between gamma and neutron events. Our initial studies on the effects of Eu concentration on the properties of LSI show that 3%–4% Eu concentration is optimal for the best performance in terms of gamma and neutron light yields and pulse shape discrimination. LCI shows the main emission at ${\sim}$ 475 nm under X-ray excitation and a very high gamma light yield of ${\sim}$ 90000 photons/MeV. The measured energy resolution is 6% at 662 keV. The electron equivalent energy for neutron detection has been measured to be around 3 MeV, which gives a neutron light yield of ${\sim}$ 270000 photons. The measured decay times for neutrons are faster compared to gamma decays and the PSD between the gamma-rays and neutrons is not as good as LSI. LSB shows two emissions at ${\sim}$ 410 and 475 nm under X-ray excitation. The measured light yield is ${\sim}$ 32000 ph/MeV gamma-ray with an energy resolution of 6% at 662 keV. The electron equivalent energy of the $^6{\rm Li}$ capture peak was measured to be 3.3 MeV.