Abstract
The effect of temperature changes on the light output of LAB based liquid scintillator is investigated in a range from -5 to 30,^{circ }C with alpha -particles and electrons in a small scale setup. Two PMTs observe the scintillator liquid inside a cylindrically shaped aluminum cuvette that is heated or cooled and the temperature dependent PMT sensitivity is monitored and corrected. The alpha -emitting isotopes in dissolved radon gas and in natural Samarium (bound to a LAB solution) excite the liquid scintillator mixtures and changes in light output with temperature variation are observed by fitting light output spectra. Furthermore, also changes in light output by compton electrons, which are generated from external calibration gamma -ray sources, is analysed with varying temperature. Assuming a linear behaviour, a combined negative temperature coefficient of {(-0.29 pm 0.01)}{,%/^{circ }}hbox {C} is found. Considering hints for a particle type dependency, electrons show {(-0.17 pm 0.02)}{,%/^{circ }}hbox {C}, whereas the temperature dependency seems stronger for alpha -particles, with {(-0.35 pm 0.03)}{,%/^{circ }}hbox {C}. Due to a high sampling rate, a pulse shape analysis can be performed and shows an enhanced slow decay component at lower temperatures, pointing to reduced non-radiative triplet state de-excitations.
Highlights
Which is already in use by the Daya-Bay [1] and RENO [2] experiments, will soon be used by SNO+ [3] and is foreseen for future neutrino detectors like JUNO [4]
The SNO+ experiment will be operated at ≈ 12 ◦ C due to the cooled water shielding surrounding the liquid scintillator vessel [3], and JUNO investigated the eventually positive aspects of a significant cooling of the active detector medium on the energy resolution [5]
At the Brookhaven National Laboratory (BNL), natural samarium was loaded into LAB based liquid scintillators, using the surfactant TMHA6 in a single-stage solventsolvent extraction procedure, which can be used to form organometallic compounds that can be dissolved in an organic liquid
Summary
Which is already in use by the Daya-Bay [1] and RENO [2] experiments, will soon be used by SNO+ [3] and is foreseen for future neutrino detectors like JUNO [4]. The temperature of the whole measurement setup was changed, including the PMTs. that work was critically discussed and commonly disqualified by Laustriat, Coche [7,8] and Birks [9]. This study is difficult to interpret quantitatively since the setup is not described, it is not explained how temperature stability on the PMTs is achieved or how this was controlled, and no uncertainties are reported. This can only be seen as an indication that scintillation light output might be quenched at higher temperatures and is enhanced when the liquid is beeing cooled down
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