Selected Properties of Cs $_{2}$LiYCl $_{6}$, Cs $_{2}$LiLaCl $_{6}$, and Cs $_{2}$LiLaBr $_{6}$ Scintillators

Homeland security applications often require detection of both neutron and gamma radiation. A combination of two detectors registering neutrons and gammas separately is typically used. Recently, a number of scintillators from the elpasolite crystal family were proposed, that provide detection of both types of radiation. The most promising are Cs
₂
LiYCl
₆
, Cs
₂
LiLaCl
₆
, and Cs
₂
LiLaBr
₆
. All are doped with Ce
³⁺
. They are capable of providing very high energy resolution. The best values achieved for each material are 3.9%, 3.4%, and 2.9% at 662 keV (FWHM), respectively. Since
⁶
Li has an acceptable cross-section for thermal neutron capture, these materials also detect thermal neutrons. In the energy spectra, the full energy thermal neutron peak typically appears above 3 MeV gamma equivalent energy. Thus very effective pulse height discrimination can be implemented with these materials. The CLLC and CLYC emissions consist of two main components: Core-to-Valence Luminescence (CVL; 220 nm to 320 nm) and Ce emission (350 to 500 nm). The former is of particular interest since it appears only under gamma excitation. It is also very fast and decays with less than 2 ns time constant. The CVL provides a significant difference to temporal responses under gamma and neutron excitation thus it may be used for effective pulse shape discrimination.