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

Abstract

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 Forster 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.