# Compact, directional neutron detectors capable of high-resolution nuclear recoil imaging

## TL;DR

This paper introduces compact 3D neutron detectors using Time Projection Chambers that precisely image nuclear recoils, demonstrating their potential for advanced neutron and dark matter detection applications.

## Contribution

The paper presents a novel compact TPC design capable of high-resolution 3D imaging of nuclear recoils in helium-based gas, suitable for small form factor neutron detection.

## Key findings

- Detectors meet or exceed design specifications.
- Capable of detailed 3D surface shape and charge density profiling.
- Suitable for directional dark matter and neutrino experiments.

## Abstract

We report on the design, production, and performance of compact 40-cm$^3$ Time Projection Chambers (TPCs) that detect fast neutrons by measuring the three-dimensional (3D) ionization distribution of nuclear recoils in $^4$He:CO$_2$ gas at atmospheric pressure. We use these detectors to characterize the fast-neutron flux inside the Belle II detector at the SuperKEKB electron-positron collider in Tsukuba, Japan, where the primary design constraint is a small form factor. We find that the TPCs meet or exceed all design specifications, and are capable of measuring the 3D surface shape and charge density profile of ionization clouds from nuclear recoils and charged tracks in exquisite detail. Scaled-up detectors based on the detection principle demonstrated here may be suitable for directional dark matter searches, measurements of coherent neutrino-nucleus scattering, and other experiments requiring precise detection of neutrons or nuclear recoils.