October 9, 2023
Mary Ward House Conference and Exhibition Centre
Europe/London timezone
Workshop Registration will close at the end of Monday 2nd October

New method of thermal neutrons imaging using a fast optical camera

Oct 9, 2023, 1:15 PM
1h
Mary Ward House Conference and Exhibition Centre

Mary Ward House Conference and Exhibition Centre

London, UK
Poster Presentation Lunch and Poster Session

Speaker

Tian-Qi Gao (University of Manchester)

Description

We present a novel and condensed imaging technique for thermal neutrons utilizing a fast event mode optical camera (Timepix3) combined with a 6Li:LYSO scintillator. Previous studies have demonstrated the high spatial-resolution imaging capabilities of 6LiF:ZnS scintillators compared to traditional neutron imaging [1]. However, the proposed 6Li:LYSO scintillator exhibits a significantly faster decay time (~35 ns) due to its unique composition, in contrast to the microseconds decay time of 6LiF:ZnS scintillators required for gamma discrimination. Building upon successful statistical analysis-based thermal neutron reconstruction [2], our research encompasses three main components.

The research is separated into three parts:
1. Measurement using the setup.
2. Simulating ways to reduce gamma accompanied with neutron sources.
3. Experimental result analysis and comparison to the simulation.

Firstly, the experimental setup focuses on the interaction products (alpha and tritium) of the thermal neutron with 6Li to produce localized flashes of light in the LYSO crystal scintillator. These photons were guided through an optical path to be captured by a micro-channel plate intensifier connected to a fast optical camera, TPX3CAM, as shown below.

Secondly, we explore ways to reduce the gamma rays arriving at the LYSO scintillator using the TOPAS simulation package. LYSO exhibits peak absolute quantum efficiency at ~200 keV, coinciding with the peak of the AmBe gamma spectrum [3]. Simulation results show that the attenuation of gamma rays using 5 cm of lead allows us to mitigate their impact, at the cost of reducing the total efficiency of the neutrons moderation and the 6Li reaction.

Thirdly, we analyse the acquired data. A centre-of-mass reconstruction algorithm is applied to the data recorded from the Timepix3. Each reconstructed neutron event consists of sub-clusters, representing groups of photons generated by the photon multiplier from a single photon input. Background sources, including gamma rays from the source, Lutetium radiation, and DAC noise, are considered during data analysis. Figure 2 shows an example of an event, each blue dot is a photon. It has 4 photon groups that are all within 40 ns time window of each other and is not shaped as a line, then this event could be determined as the result of a neutron hit.

Our findings demonstrate the potential of this optical neutron imaging technique, enabling remote and long-distance detection with a variable field of view. By employing a faster decaying scintillator, the clustering time window is reduced from milliseconds to nanoseconds, significantly decreasing the "exposure" time required for thermal neutron detection applications such as imaging and nuclear security scans.

References:
[1] Losko, A. S., et al. "New perspectives for neutron imaging through advanced event-mode data acquisition." Scientific reports 11.1 (2021): 1-11.
[2] Gao, T, et al. "Novel imaging technique for thermal neutrons using a fast optical camera." Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment (2022): 167604.
[3] Allahverdy, A, et al. "Gamma Spectrometry in the Presence of Fast Neutrons." Frontiers in Biomedical Technologies 6.1 (2019): 22-27.

Primary author

Tian-Qi Gao (University of Manchester)

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