AI Insight
Researchers observed unusually long-delayed afterpulses in several models of large-area photomultiplier tubes (PMTs) used in the Baksan Large Neutrino Telescope project, with delay times ranging from 73 to 260 microseconds after the main pulse. These afterpulses occur with low probability (less than 0.1% per photoelectron) and consistently produce single-photoelectron signals regardless of the main pulse amplitude. The phenomenon was detected across PMTs from two manufacturers (Hamamatsu and NNVT) in various sizes from 8 to 20 inches.
Why it matters
This finding is important for the design and data analysis of neutrino detectors and other experiments using large-area photomultipliers, as these delayed afterpulses could be mistaken for real physics signals or contribute to background noise. Understanding this characteristic helps improve signal discrimination and detector calibration in precision physics measurements.
Understand the Science
Abstract: We report the observation of anomalously long-delayed afterpulses in photomultipliers of the Baksan Large Neutrino Telescope project$~-$ 10-inch R7081-100, 8-inch R5912-100, 20-inch R12860 photomultipliers produced by Hamamatsu Photonics, and 20-inch N6205 photomultipliers produced by NNVT. The mean delay times relative to the main pulses are approximately $85~mu$s, $73~mu$s, $260~mu$s, and $90~mu$s, respectively. The probability of such afterpulses does not exceed 0.1% per photoelectron, and their amplitudes are strictly confined to the single-photoelectron level, regardless of the amplitude of the main pulse. The delay time of these afterpulses shows no significant dependence on the PMT operating voltage.
Source: Anomalously long-delayed afterpulses in large-area photomultipliers