Improvement of Energy Resolution and Neutron–Gamma Discrimination of NaI:Tl,6Li Single Crystal Scintillators by Ca2+ and Sr2+ Co-Doping

NaI:Tl,6Li single crystals, due to low use cost and an efficient gamma ray (
$\gamma$
) and neutron (
$n$
) detection capability, have been regarded as promising
$n/\gamma $
scintillators. In this work, NaI:Tl,6Li single crystals co-doped with different Ca
$^{2+}$
and Sr
$^{2+}$
concentrations were grown by the multiampoule Bridgman method. Their
$\gamma $
-ray energy resolution and
$n/\gamma $
discrimination were improved. The
$\gamma $
-ray energy resolution at 662 keV was improved from 7.0% to 6.0% by Ca
$^{2+}$
or Sr
$^{2+}$
co-doping, despite at the expense of scintillation yield by around 20%. The pulse shape discrimination (PSD), expressed as figure-of-merits (FoMs) for neutron and
$\gamma $
-ray, was enhanced from 4.65 for NaI:Tl,6Li to 5.85 for Ca
$^{2+}$
co-doping and 5.72 for Sr
$^{2+}$
co-doping. This work not only highlights the effectiveness of the co-doping strategy on the improvement of NaI:Tl,6Li single crystal scintillator but also makes the crystal more competitive toward neutron and
$\gamma $
-ray detection applications.