A Background-Free Direction-Sensitive Neutron Detector

The detection and measurements of properties of neutrons are of great importance in many fields of research, including neutron scattering and radiography, measurements of solar and cosmic-ray neutron flux, measurements of neutron interaction cross sections, monitoring of neutrons at nuclear facilities, oil exploration, and searches for fissile weapons of mass destruction. Many neutron detectors are plagued by large backgrounds from X-rays and gamma rays, and most current neutron detectors lack single-event energy sensitivity or any information on neutron directionality. Even the best detectors are limited by cosmic ray neutron backgrounds. All applications would benefit from improved neutron detection sensitivity and improved measurements of neutron properties. Here, we show data from a new type of detector that can be used to determine neutron flux, energy distribution, and direction of neutron motion. The detector is free of backgrounds from X-rays, gamma rays, beta particles, and relativistic singly charged particles. It is relatively insensitive to cosmic ray neutrons because of their distinctive angular and energy distributions. It is sensitive to thermal neutrons, fission spectrum neutrons, and high-energy neutrons, with detection features distinctive for each energy range. It is capable of determining the location of a source of fission neutrons based on characteristics of elastic scattering of neutrons by helium nuclei. A portable detector could identify 1 g of reactor grade plutonium 1 m away with less than 1 min of observation time.