A.N.Panova, E.L.Vinograd, V.I.Goriletsky, S.P.Korsunova, N.N.Kosinov,
A.M.Kudin, K.V.Shakhova
Received March 16, 1998
Effect of NaI concentration
(C) on variations of some CsI(Na) crystal characteristics has been studied.
The characteristics considered include: the optical absorption coefficient
in the activator band; emission intensities of excitons localized at Na+
ions (420 nm) and in the regular lattice (340 nm) in the radioluminescence
(RL) at 80K; yields of stationary RL (241Am, 60keV) (L RL), g-scintillation
(137 Cs, 662 keV) (Lg) and a-scintillation
(241 Am, 5.9 meV) (L a) for CsI(Na) crystals grown under the forced
melt mixing. The number of activator emission centers in those crystals
has been shown to increase linearly as C rises up to about 2.2*10-2mol.%.
The La value attains a maximum at C › 2.3 10-2 mol.% NaI while those
of L RL and L g, at C › 9*10-3 mol.%. The NaI solubility in
CsI has been concluded to be at least 2.2*10-2 mol.% and thus to exceed
substantially the literature data (from 8*10-3mol.% to 1*10-2mol.%). Therefore,
the maximum Lg value is due to a sufficient number of emission centers
at the specified excitation density. The fact that the C value corresponding
to the maximum Lg of CsI(Na) is lower than for CsI(Tl) crystals (about
2.5*10-2mol.% of TlI) is assumed to be caused by a larger size of the distorted
lattice volume in the neighborhood of the light Na+ .