A Novel Low-Background Photomultiplier Tube Developed for Xenon Based Detectors

TL;DR

This paper reports the development of a low-background 2-inch photomultiplier tube with significantly reduced radioactivity and robust cryogenic performance, suitable for next-generation xenon detectors in dark matter and neutrino research.

Contribution

It introduces a novel low-background PMT with substantially lower radioactivity and improved electrical performance at cryogenic temperatures, advancing detector sensitivity.

Findings

Radioactivity levels reduced 15-fold compared to previous models

Achieved an average gain of 4.23×10^6 at -1000 V and -100°C

Dark count rate of 2.5 Hz per channel

Abstract

Photomultiplier tubes (PMTs) are essential in xenon detectors like PandaX, LZ, and XENON experiments for dark matter searches and neutrino properties measurement. To minimize PMT-induced backgrounds, stringent requirements on PMT radioactivity are crucial. A novel 2-inch low-background R12699 PMT has been developed through a collaboration between the PandaX team and Hamamatsu Photonics K.K. corporation. Radioactivity measurements conducted with a high-purity germanium detector show levels of approximately 0.08 mBq/PMT for $\rm^{60}Co$ and 0.06~mBq/PMT for the $\rm^{238}U$ late chain, achieving a 15-fold reduction compared to R11410 PMT used in PandaX-4T. The radon emanation rate is below 3.2 $\rm \mu$Bq/PMT (@90\% confidence level), while the surface $\rm^{210}Po$ activity is less than 18.4 $\mu$Bq/cm$^2$. The electrical performance of these PMTs at cryogenic temperature was evaluated. With an optimized readout base, the gain was enhanced by 30\%, achieving an average gain of $4.23 \times 10^6$ at -1000~V and -100~$^{\circ}$C. The dark count rate averaged 2.5~Hz per channel. Compactness, low radioactivity, and robust electrical performance in the cryogenic temperature make the R12699 PMT ideal for next-generation liquid xenon detectors and other rare event searches.