S. Kubota et al., Decay curves of NaI(Tl) scintillators with different Tl+ concentrations under excitation of electrons, alpha particles and fission fragments, J PHYS JPN, 68(1), 1999, pp. 291-297
Decay curves of NaI(Tl) crystals with Tl+ concentrations of 0.01, 0.07, 0.1
and 0.22 mole% have been measured under excitation by photo-electrons from
a Cs-137 source, alpha particles from an Am-241 source and fission fragmen
ts from a Cf-252 source. A striking difference between the decay curve for
electron excitation and those for excitation by alpha particles and fission
fragments is observed. A flat top of the decay curve which is observed und
er electron excitation is analyzed on the bases of energy transfer processe
s of electrons and V-k centers to Tl+ ions reported by Dietrich et al. [Phy
s. Rev. B 8 (1973) 589]. A flat top of the decay curve from NaI(Tl) with a
Tl concentration of 0.01 mole% under alpha particle excitation is also obse
rved. Faster decay components of 34+/-5 ns (in addition to the main scintil
lation component of 150+/-10 ns) and 15+/-5 ns (in addition to the main com
ponent of 100+/-10 ns) are observed under alpha particle excitation and fis
sion fragment excitation, respectively. This finding indicates the presence
of a non-radiative process of (Tl+)* due to interaction with excited atoms
under high specific energy loss dE/dx. This non-radiative process should b
e partly responsible to the decrease in scintillation efficiency for high d
E/dx particles.