Alpha/beta discrimination in a position-sensitive fiber detector based on a pulse height method

Surface contamination monitoring is crucial during the early stages of decommissioning of radiation facilities and nuclear power plants. Conventional survey meters are limited by their small measurement areas and are not optimized for simultaneous alpha/beta discrimination over wide areas. To address these limitations, we previously developed an outer-layer scintillating (OLS) fiber that incorporated a thin scintillation layer on the surface of wavelength-shifting fibers, enabling the detection of short-range charged particles. In this study, we developed a one-dimensional position-sensitive detector using the OLS fiber capable of discriminating alpha and beta particles using a pulse height discrimination method. Simulations using a particle and heavy ion transport code system confirmed that the OLS fiber stops alpha particles (5.48 MeV) and low-energy beta particles (67 keV) within its 47 μm thick scintillator layer, while higher-energy beta particles (up to 2.3 MeV) deposit only a small portion of their energy, which provides the physical basis for pulse height discrimination. To mitigate the position-dependence in the pulse height, we employed the summation signal obtained from both silicon photomultiplier ends in coincidence measurements. Under mixed radiation conditions with ²⁴¹Am and ⁹⁰Sr sources, the system successfully identified alpha-contaminated regions by applying a fixed threshold to the summation signal. The detector demonstrated reliable one-dimensional position sensitivity using time-difference measurements, achieving a spatial resolution of approximately 150 mm over a fiber length of 2.6 m. These results indicate the feasibility of OLS fiber-based detectors for alpha/beta identification over extended areas while further validation is required for longer fiber configurations.