Portable neutron energy spectrometer utilizing microstructured semiconductor neutron detectors (MSND)

The portable neutron energy spectrometer is designed to identify an unknown neutron source. The spectrometer is cylindrical in shape with a diameter of 12 cm and a length of 33 cm. This allows for a large surface area for incident neutrons to interact with and sufficient moderating material to thermalize neutrons up to 14.1 MeV in energy. The spectrometer utilizes eleven 2 cm × 2 cm high-efficiency microstructured semiconductor neutron detector (MSND) devices. The detectors are arranged linearly along the central axis of the spectrometer. The spectrometer's volume consists of alternating layers of MSNDs, high-density polyethylene (HDPE), and cadmium. The HDPE acts as a moderator for the epithermal and fast neutrons, allowing them to disperse energy linearly within the spectrometer's volume thereby, becoming thermalized and counted by the detectors. The 2 mm thick cadmium layer after each detector prevents thermal neutrons from backscattering to a previous detector. Extensive modeling of the portable spectrometer was conducted using MCNPS. The modeling was used to optimize the number of MSNDs and the thickness of the HDPE layers. Also, reference library templates for a variety neutron sources were simulated, including;
²⁵²
Cf,
²⁵²
Cf + D
₂
O, PuBe, AmBe, and a 14.1 MeV fusion neutron source. A Figure-of-Merit calculation was used to identify the experimental neutron source. The spectrometer is a light-weight, portable, self-contained unit, weighing less than 20 lbs. It is powered by a rechargeable 6V battery contained within the main housing. The measurement data and identified neutron source information is displayed on the built-in LCD screen.