Development of New Tracking Detector with Fine-grained Nuclear Emulsion for sub-MeV Neutron Measurement

TL;DR

This paper presents a novel sub-MeV neutron detector based on super-fine-grained nuclear emulsion, achieving high resolution, efficiency, and directional sensitivity, with successful calibration and automatic track recognition.

Contribution

The study introduces a new neutron detector using Nano Imaging Tracker with sub-micrometric accuracy and an automatic recognition system, enhancing detection capabilities over previous methods.

Findings

Detection efficiency over 83% for recoil proton tracks

Reconstructed primary neutron energy with 42% accuracy

Automatic track recognition achieved 74% efficiency

Abstract

In this study, we have developed a new sub-MeV neutron detector that has a high position resolution, energy resolution, directional sensitivity, and low background. The detector is based on a super-fine-grained nuclear emulsion, called the Nano Imaging Tracker (NIT), and it is capable of detecting neutron induced proton recoils as tracks through topological analysis with sub-micrometric accuracy. We used a type of NIT with AgBr:I crystals of (98 +- 10) nm size dispersed in the gelatin. First, we calibrated the performance of NIT device for detecting monochromatic neutrons with sub-MeV energy generated by nuclear fusion reactions, and the detection efficiency for recoil proton tracks of more than 2 um range was consistently 100\% (the 1 sigma lower limit was 83%) in accordance with expectations by manual based analysis. In addition, recoil energy and angle distribution obtained good agreement with kinematical expectation. The primary neutron energy was reconstructed by using them, and it was evaluated as 42% with FWHM at 540 keV. Furthermore, we demonstrated newly developed an automatic track recognition system dedicated to the track range of more than a few micrometers. It achieved a recognition efficiency of (74 +- 4)%, and recoil energy and angle distribution obtained good agreement with manual analysis. Finally, it indicated the very high rejection power for gamma-rays.