Design and Performance Evaluation of a Dark Chamber for Optical Noise Eradication in Gamma-ray Spectroscopy using LYSO Scintillator

Abstract

The measurement and analysis of gamma-ray spectra using a scintillation detector system coupled with a photomultiplier tube (PMT) are highly sensitive to fluctuations from visible light noise. This research aims to design, construct, and evaluate the performance of a custom-built Dark Chamber to serve as a controlled environment for low-level radiation measurements, completely free from external photon interference. The dark chamber was constructed using 5-cm-thick wooden boards with dimensions of 70 x 50 x 20 cm. The interior was lined with matte black light-absorbing materials and velvet fabric seal design at the joints to ensure 100% light tightness. The performance evaluation was conducted using a LYSO scintillator crystal coupled to a 9266KB PMT, connected to standard nuclear electronics (Canberra 2022 Amplifier and Tukan 8K MCA). Energy spectra of three radioactive isotopes were measured to cover various energy ranges: Am-241 (59.5 keV), Ba-133 (356 keV), and Cs-137 (662 keV), comparing the conditions outside and inside the dark chamber. The experimental results revealed that the dark chamber successfully eliminated the channel shift. Furthermore, it significantly improved the energy resolution (%R) across all energy ranges. Specifically, for low-energy radiation such as Am-241, the %R improved from 34.33% to 26.39%. This developed equipment demonstrated high stability and low cost, making it highly suitable for future advanced scintillation material or high energy physics research requiring high precision.