A novel method for detecting neutrons using low density high porosity aerogel and saturated foam

Abstract

As a result of the recent shortage of 3He for neutron detection, several new detectors have been proposed as viable alternatives. Thin-film coated diodes and boron-lined proportional counters are suggested options, but both suffer from the “wall-effect”, where only one interaction product can be measured per event. The “wall-effect” greatly reduces the neutron detection efficiency of the device. A new method is presented using low-density high-porosity materials where both reaction products can escape the absorber and contribute to a single event. Measuring both reaction products simultaneously greatly increases the detection efficiency of the device. Experimentally obtained pulse-height spectra from saturated foam and borosilicate aerogel detectors are presented. Aerogel is a low-density solid, typically less than 50mg/cm3, and can be developed with 10B in the structure. The thermal neutron response pulse-height spectrum from borosilicate aerogel is presented. Additionally, polyurethane foam, another low-density high-porosity material, was saturated with LiF and B2O3 to levels greater than 20 percent by weight and tested as a neutron detection medium. The foam saturated with 4.5 percent 6LiF was cut into 10 sheets, each 2mm thick, and a neutron response pulse-height spectrum was collected. The thermal neutron detection efficiency was measured to be 7.3 percent, and the neutron to gamma-ray rejection ratio, acquired using a 137Cs gamma-ray source, was calculated to be 1.71×106. Theoretical calculations also show that neutron detection efficiencies above 60 percent can be easily achieved using enriched 6LiF foam at 20 percent or higher saturation levels.