Detection of neutrons in the field typically consists of
measurements of charge deposition in a gaseous detector system.
This method of detection results in relatively high efficiency, but
pulse height analysis for neutron energy distributions and incident
neutron direction is difficult if not impossible. In previous work,
the preliminary analysis of a neutron sensor system which can
measure neutron count rates as well as incident neutron energy and
direction was explored. This resulted in proving the fundamental
feasibility of using all of the following reactions as indicators
of neutron direction: (1) the (n,a)
reaction in B-10, (2) inelastic scattering reactions, and (3) the
(n,p) reaction in He-3 inside a cloud chamber. The first two of
these reactions produce characteristics gamma rays as well as
charged particles (in the form of alpha particles and recoil
nuclei). The gamma rays produced from these reactions can be
measured in a high-resolution gamma spectroscopy system (such as an
HPGe) and will have characteristic gamma lines that are produced
from the de-excitation of recoil nuclei. These nuclei decay in
flight (i.e., while moving either toward or away from the detector)
and produced Doppler broadened gamma lines. The differential
between the observed gamma-ray energy and the nonrelativistic
gamma-ray energy is a function of the velocity vector of the recoil
nuclei with respect to an interaction point in the gamma ray
detector. If the energy of the reaction products, the energy of the
characteristic gamma line, and the coordinates of the interaction
point can be measured, then the direction of the incident neutron
(actually a cone of directions) may be determinable via simple
kinematics. Simulations of these systems demonstrated the
feasibility of the measurement method; however, analysis of the
effects of uncertainties and construction of prototype devices is
needed to generate a preliminary design.
- G.R. Spence,
"A Boron Loaded Approach to Directionally Sensitive Neutron Detectors,"
Proceedings of the INMM 52nd Annual Meeting, Palm Desert, CA, July 17-21, 2011.
- G.R. Spence and W.S. Charlton,
"Directionally Sensitive Neutron Detectors for Portal Monitors,"
Proceedings of the 2009 Annual Meeting of the Institute of Nuclear Materials Management, Tucson, AZ, July 12-15, 2009.