Dark Count of 20-inch PMTs Generated by Natural Radioactivity

TL;DR

This paper investigates the origin of large dark count pulses in 20-inch PMTs used in neutrino detection, attributing them mainly to natural radioactivity and muons, which helps estimate environmental radioactivity levels.

Contribution

It identifies the primary sources of large pulses in PMT dark counts through measurements and simulations, providing insights into environmental radioactivity effects.

Findings

Large pulses mainly caused by natural radioactivity and muons

Dark count spectrum can estimate environmental radioactivity levels

Enhanced understanding of PMT background noise

Abstract

The primary objective of the JUNO experiment is to determine the ordering of neutrino masses using a 20-kton liquid-scintillator detector. The 20-inch photomultiplier tube (PMT) plays a crucial role in achieving excellent energy resolution of at least 3% at 1 MeV. Understanding the characteristics and features of the PMT is vital for comprehending the detector's performance, particularly regarding the occurrence of large pulses in PMT dark counts. This research paper aims to further investigate the origin of these large pulses in the 20-inch PMT dark count rate through measurements and simulations. The findings confirm that the main sources of the large pulses are natural radioactivity and muons striking the PMT glass. By analyzing the PMT dark count rate spectrum, it becomes possible to roughly estimate the radioactivity levels in the surrounding environment.