LiSr2I5: Eu (LSI)- Neutron Gamma-Ray Scintillator surpasses those of CLYC in gamma-ray and thermal neutron detection, the first true multi-mode scintillator. The new scintillation material LSI is three times brighter than CLYC for gamma rays and 3.5 times brighter for neutrons. It is also capable of gamma-ray spectroscopy, thermal neutron detection and fast neutron detection, all in one multi-mode scintillation detector. The principal use for LSI will be to serve as a multi-mode detector in the next generation of nuclear non-proliferation and homeland security instruments. Compact, high performance handheld instruments with lower power, weight and cost would result from LSI. Other potential multimode applications include oil well logging, non-destructive testing, diffraction studies, biological and materials research, health physics, dosimetry, medical imaging, high energy particle physics, nuclear waste characterization and astronomy.