Analysis of Kr-83m prompt scintillation signals in the PIXeY detector

Prompt scintillation signals from Kr-83m calibration sources are a useful metric to calibrate the spatial variation of light collection efficiency and electric field magnitude of a two phase liquid-gas xenon time projection chamber. Because 83mKr decays in two steps, there are two prompt scintillation pulses for each calibration event, denoted S1a and S1b. We study the ratio of S1b to S1a signal sizes in the Particle Identification in Xenon at Yale (PIXeY) experiment and its dependence on the time separation between the two signals (Delta t), notably its increase at low Delta t. In PIXeY data, the Delta t dependence of S1b/S1a is observed to exhibit two exponential components: one with a time constant of 0.05 +/- 0.02 mu s, which can be attributed to processing effects and pulse overlap and one with a time constant of 10.2 +/- 2.2 mu s that increases in amplitude with electric drift field, the origin of which is not yet understood.