Abstract
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 through measurements and
simulations. Our results confirm that natural radioactivity and
muons striking the PMT glass are the main sources of the large
pulses. We evaluate their contribution quantitatively by performing
spectrum fitting. By analyzing the PMT dark count spectrum, it
becomes possible to roughly estimate the radioactivity levels in the
surrounding environment.