Scintillation decay time and pulse shape discrimination in oxygenated and deoxygenated solutions of linear alkylbenzene for the SNO+ experiment

Abstract

The SNO+ liquid scintillator experiment is under construction in the SNOLAB facility in Canada. The success of this experiment relies upon accurate characterization of the liquid scintillator, linear alkylbenzene (LAB). In this paper, scintillation decay times for alpha and electron excitations in LAB with 2 g/L PPO are presented for both oxygenated and deoxygenated solutions. While deoxygenation is expected to improve pulse shape discrimination in liquid scintillators, it is not commonly demonstrated in the literature. This paper shows that for linear alkylbenzene, deoxygenation improves discrimination between electron and alpha excitations in the scintillator.

Temperature quenching in LAB based liquid scintillator

“…This work found that the slow component of an exponential decay of the scintillation is stronger pronounced at lower temperatures. As the triplet lifetime of benzene matches this slow decay component well [21][22][23][24], this result can be seen as an indication that either more triplet states are populated or that the radiative de-excitation of those is more efficient at lower temperatures. The increased population would fit into the theory of Birks and Conte [9,25], who proposed that the energy transfer between solvent-solvent and solvent-solute molecules is mainly due to excimer formation.…”

Experiment to demonstrate separation of Cherenkov and scintillation signals

“…Two further decaying exponentials are included for LAB/PPO, based on [42]. The simulated time profile is:…”

“…The targets are simulated using properties from [14,15,42,44,45]. The scintillation light yield is set to 1010 photons/MeV for LAB [44] and 10800 photons/MeV for LAB/PPO [15].…”

“…The time profile is modeled in the simulation as described in Sec. III B, with a rise time of τ r = 1 ns for LAB/PPO and and τ r = 7.7 ns for LAB, and decay times of τ 1 = 4.3 ns, τ 2 = 16 ns, τ 3 = 166 ns [42] for LAB/PPO, and τ 1 = 36.6 ns, τ 2 = τ 3 = 0 [44] due to scintillation light. Between 5 and 10 PE are expected on each PMT within the Cherenkov ring due to Cherenkov light alone.…”

Neutrino Physics with SNO+

“…A large fraction of these decays can be identified (tagged) by making use of the fast decay time of LAB which allows for an α-β pulse shape discrimination [4]. For example, the internal decay of 214 Bi (Q ∼ 3.27 MeV) can be identified by the delayed coincidence with the 214 Po α decay for which the half-life is 164 μs.…”