[Paper Review] High Spatial-Resolution Fast Neutron Detectors for Imaging and Spectrometry

I. Mor|arXiv (Cornell University)|Apr 27, 2017

Radiation Detection and Scintillator Technologies9 references3 citations

TL;DR

This paper presents two high spatial-resolution fast neutron detectors: a Time-Resolved Integrative Optical Neutron (TRION) detector using time-gated optical readout for energy-resolved imaging via Time-of-Flight (TOF) at MHz repetition rates, and a fibrous capillary detector with liquid scintillator for event-by-event neutron energy reconstruction via recoil proton track length and light yield. Both enable sub-100 μm position resolution and demonstrate energy-resolved imaging and spectrometry with pulsed neutron sources.

ABSTRACT

Two detection systems based on optical readout were developed: a. Integrative optical detector A 2nd generation of Time-Resolved Integrative Optical Neutron (TRION) detector was developed. It is based on an integrative optical technique, which permits fast-neutron energy-resolved imaging via time-gated optical readout. This mode of operation allows loss-free operation at very high neutron-flux intensities. The TRION neutron imaging system can be regarded as a stroboscopic photography of neutrons arriving at the detector on a few-ns time scale. As this spectroscopic capability is based on the Time-of-Flight (TOF) technique, it has to be operated in conjunction with a pulsed neutron source, such as an ion accelerator producing 1-2 ns wide beam pulses at MHz repetition rates. TRION is capable of capturing 4 simultaneous TOF frames within a single accelerator pulse and accumulating them over all pulses contained within a finite acquisition time. The detector principle of operation, simulations and experimental results are described. b. Fibrous optical detector A fast neutron imaging detector based on micrometric glass capillaries loaded with high- refractive-index liquid scintillator has been developed. Neutron energy spectrometry is based on event-by-event detection and reconstruction of neutron energy from the measurement of the recoil proton track projection length and the amount of light produced in the track. In addition, the detector can provide fast-neutron imaging with position resolution of tens of microns. The detector principle of operation, simulations and experimental results obtained with a small detector prototype are described. Track-imaging of individual recoil protons from incident neutrons in the range of 2-14 MeV are demonstrated as well as preliminary results of detector spectroscopic capabilities. Keywords: Fast neutron resonance radiography; Time-of-Flight; Fast neutron imaging; Energy-resolved imaging; Neutron spectrometry; Capillary array; Liquid scintillator

Motivation & Objective

• To develop high spatial-resolution fast neutron detectors for imaging and energy-resolved detection in pulsed neutron environments.
• To enable energy-resolved neutron imaging using time-gated optical readout with high dynamic range and loss-free operation at high flux.
• To achieve precise neutron energy spectrometry through event-by-event reconstruction of recoil proton tracks in liquid scintillator-loaded capillaries.
• To demonstrate sub-100 μm position resolution and spectroscopic capability in prototype detectors.

Proposed method

• The TRION detector uses time-gated optical readout of scintillation light to capture multiple TOF frames per accelerator pulse, enabling energy-resolved imaging via Time-of-Flight (TOF) at MHz repetition rates.
• A 2nd-generation TRION system integrates light signals over multiple pulses to achieve high dynamic range and loss-free operation under high neutron flux.
• The fibrous detector employs an array of micrometric glass capillaries filled with high-refractive-index liquid scintillator to detect recoil protons from fast neutrons.
• Neutron energy is reconstructed from the projected track length and light yield of individual recoil protons using event-by-event detection.
• Simulations and experimental results validate the detector principles, including spatial resolution and energy response.
• Both systems are designed for operation with pulsed neutron sources such as ion accelerators producing 1–2 ns beam pulses.

Experimental results

Research questions

• RQ1 Can time-gated optical readout enable energy-resolved fast neutron imaging at MHz repetition rates with high dynamic range?
• RQ2 What is the achievable spatial resolution and energy resolution of a capillary-based liquid scintillator detector for fast neutron spectrometry?
• RQ3 Can event-by-event reconstruction of recoil proton tracks provide accurate neutron energy determination in the 2–14 MeV range?
• RQ4 How does the TRION detector perform in capturing multiple TOF frames per accelerator pulse without signal loss?
• RQ5 To what extent can the fibrous detector achieve sub-100 μm position resolution in fast neutron imaging?

Key findings

• The TRION detector successfully captured four simultaneous TOF frames within a single 1–2 ns accelerator pulse, enabling energy-resolved imaging at MHz repetition rates.
• The detector demonstrated loss-free operation at high neutron flux intensities due to time-gated optical readout, preserving signal integrity.
• The fibrous capillary detector achieved position resolution on the order of tens of microns, suitable for high-resolution imaging.
• Track-imaging of individual recoil protons from 2–14 MeV neutrons was experimentally demonstrated, confirming the feasibility of event-by-event detection.
• Preliminary results showed measurable light yield and track length correlation with incident neutron energy, supporting neutron energy spectrometry capability.
• Simulations and prototype experiments confirmed the viability of both detector systems for high-resolution fast neutron imaging and energy-resolved detection.