First Results of Using a UVTron Flame Sensor to Detect Alpha-Induced Air Fluorescence in the UVC Wavelength Range.

Anita Crompton,Steven Bell,Kelum Gamage,Divyesh Trivedi,Alex Jenkins,Andrew Wilson

doi:10.3390/s17122756

Abstract

In this work, a robust stand-off alpha detection method using the secondary effects of alpha radiation has been sought. Alpha particles ionise the surrounding atmosphere as they travel. Fluorescence photons produced as a consequence of this can be used to detect the source of the alpha emissions. This paper details experiments carried out to detect this fluorescence, with the focus on photons in the ultraviolet C (UVC) wavelength range (180–280 nm). A detector, UVTron R9533 (Hamamatsu, 325-6, Sunayama-cho, Naka-ku, Hamamatsu City, Shizuoka Pref., 430-8587, Japan), designed to detect the UVC emissions from flames for fire alarm purposes, was tested in various gas atmospheres with a 210Po alpha source to determine if this could provide an avenue for stand-off alpha detection. The results of the experiments show that this detector is capable of detecting alpha-induced air fluorescence in normal indoor lighting conditions, as the interference from daylight and artificial lighting is less influential on this detection system which operates below the UVA and UVB wavelength ranges (280–315 nm and 315–380 nm respectively). Assuming a standard drop off in signal, the limit of detection in this configuration can be calculated to be approximately 240 mm, well beyond the range of alpha-particles in air, which indicates that this approach could have potential for stand-off alpha detection. The gas atmospheres tested produced an increase in the detector count, with xenon having the greatest effect with a measured 52% increase in the detector response in comparison to the detector response in an air atmosphere. This type of alpha detection system could be operated at a distance, where it would potentially provide a more cost effective, safer, and faster solution in comparison with traditional alpha detection methods to detect and characterise alpha contamination in nuclear decommissioning and security applications.

Highlights

The ability to detect alpha emissions from nuclear materials is important in nuclear operations, nuclear decommissioning, and nuclear security applications
As objects to be monitored may be in a mixed radiation environment, personnel carrying out detection activities may require personal protective equipment (PPE) and have limited time in which they can safely operate
R9533 is much greater than the distance of alpha particle travel and indicates that this method has potential

Summary

Introduction

The ability to detect alpha emissions from nuclear materials is important in nuclear operations, nuclear decommissioning, and nuclear security applications Due to their positive charge, alpha particles travel only a short distance after emission from nuclear materials, typically around 50 mm through air depending on their energy. Detectors which require direct contact with alpha particles need to be in close proximity to any surface or object to determine if alpha contamination is present, at a distance of less than the mean free path of the alpha particles. This causes a number of issues, as documented by other researchers [1,2,3]. Large structures or complex geometries take significant time to monitor in such close proximity

Methods

Results

Conclusion