Enhancement Effect of Fused Double Benzene-Ring Structure on the Light Output of Carborane-Loaded Toluene- and Pseudocumene-Based Scintillators

Four sample groups were prepared by adding different concentrations of naphthalene (NP) or of 2,6-diisopropylnaphthalene (DIN) as a secondary solvent (
${{\rm S}_2}$
) in carborane-loaded toluene (TL)- and pseudocumene (PC)-based scintillators. The pulse-height spectra of the samples in response to
$^{137}{\rm Cs}\ \gamma $
-rays and to thermal neutrons were collected to study the light output (
$L$
) enhancement effect of
${{\rm S}_2}$
. It is found that for all sample groups,
$L$
increases to a plateau with the concentration of secondary solvent ([
${{\rm S}_2}$
]). As [
${{\rm S}_2}$
] is increased from 0 to saturation concentration,
$L$
increases by 31–45% and 34–53% in response to
$^{137}{\rm Cs}\ \gamma $
-rays and to thermal neurons, respectively. A first-order approximation model is proposed to fit to the experimental data. The enhancement factor (
${k_h}$
) and maximum
$L$
of each sample group are obtained from curve fitting. The Birks factor (
kB
) and electron equivalent energy (
keVee
) of each sample are calculated by a numerical method based on Birks formula. The
$L$
enhancement is discussed according to the percent changes of these parameters. In conclusion, the enhancement effect is attributed mainly to the fused double benzene-ring structure of NP and DIN, which has more delocalized electrons, and provides faster Förster resonance energy transfer paths than the single benzene-ring structure of TL and PC. Adding NP or DIN leads to a significant increase in absolute scintillation efficiency
$(S)$
and a slight decrease in
kB
for both scintillators. It is believed that DIN has slightly larger enhancement effect than NP. A so-called “dynamic quenching” is confirmed to exist in the scintillation process based on the
${k_h}$
values in response to
$^{137}{\rm Cs}\ \gamma $
-rays and to thermal neutrons.