Advancements in Remote Alpha Radiation Detection: Alpha-Induced Radio-Luminescence Imaging with Enhanced Ambient Light Suppression

Abstract

Heavy nuclides like uranium and their decay products are commonly found in nuclear industries and can pose a significant health risk to humans due to their alpha-emitting properties. Traditional alpha detectors require close contact with the contaminated surface, which can be time-consuming, labour-intensive, and put personnel at risk. Remote detection is urgently needed but very challenging. To this end, a candidate detection mechanism is alpha-induced radio-luminescence. This approach uses the emission of photons from radio-ionised excited nitrogen molecules to imply the presence of alpha emitters from a distance. Herein, the use of this phenomenon to remotely image various alpha emitters with unparalleled levels of sensitivity and spatial accuracy is demonstrated. Notably, the system detected a 29 kBq Am-241 source at a distance of 3 m within 10 min. Furthermore, it demonstrated the capability to discern a 29 kBq source positioned 7 cm away from a 3 MBq source at a 2 m distance. Additionally, a 'sandwich' filter structure is described that incorporates an absorptive filter between two interference filters to enhance the ambient light rejection. The testing of the system is described in different lighting environments, including room light and inside a glovebox. This method promises safer and more efficient alpha monitoring, with applications in nuclear forensics, waste management and decommissioning.

Keywords: alpha fluorescence; alpha radiation detection; long-distance monitoring; radio-luminescence imaging.

Figure 1

Spectrum of alpha-induced RL from artificial air (80% N₂, 20% O₂) at 800 hPa [14].

Figure 2

Alpha sources: 29 kBq and controlled reflection surface (left), 3 MBq (right).

Figure 3

Quantum efficiency of the Andor iKon-M CCD and the Newport CCD.

Figure 4

Overview of the large lens detection system.

Figure 5

Overview of the glovebox and experiment setup inside the glovebox.

Figure 6

Transmission profiles of the various filters.

Figure 7

The upper image illustrates multi-reflections occurring between two stacked interference filters, reducing their overall blocking capability. The lower image depicts the ‘sandwich’ filter structure, showing the strategic arrangement of interference and absorptive filters to optimize ambient light blocking.

Figure 8

Alpha RL signal emanating from a 29 kBq alpha source positioned 3 m away. The images show results from exposure times of 10 min (left) and 5 h (right).

Figure 9

Alpha RL signal emanating from a 3 MBq alpha source at 3 m distance, with an exposure time of 1 min.

Figure 10

29 kBq source and the gasket as the controlled surface (left), 3 MBq source (right).

Figure 11

Visible light images from the 450 nm filter of the 29 kBq and 3 MBq alpha sources placed in close proximity at various distances (top). The corresponding RL signals captured using the 337 nm filter at a 2 m distance with a 1 h exposure time (bottom).

Figure 12

Overlay of alpha RL signals on visible images (bottom) compared with reference images taken by a conventional camera (top). Left: 3 MBq alpha source with a 5-min exposure at 3 m. Right: 29 kBq alpha source with a 15-min exposure at 15 cm.

Figure 13

The peak RL signal from a 3 MBq alpha source change with detection distance.