Measurement of gamma rejection of solid state neutron sensors to maximise neutron and minimise gamma sensitivities

"Our company has invested in the development of two main types of novel solid state neutron sensors and which are gaining commercial traction. An obstacle to their commercialisation is lack of hard data on their performance in ""mixed"" radiation fields dominated by high intensity gamma radiation. This is typical of the nuclear cleanup scenario. Our vision for this project is that we attain design rules and hard data for the sensors which quantify the neutron specificity of our silicon carbide neutron sensors in high intensity gamma fields.

The key objectives are to learn which energy ranges of gamma rays interfere with our sensors, and to what extent, whether we can remove those gamma signals by shielding, and whether placement of simple shielding gives rise to secondary radiation which affects the sensors more than the unshielded flux. Once we have learned which energies we most need to shield against, we wish to finally test a realistic ""kit"" which fully represents part of a lightweight remote controlled neutron field survey instrument.

Our concentration will be on the effect of gamma radiation on our electronics alone, on our sensors alone, and the ability of the whole sensor + signal chain to return useful neutron metrology in the presence of a very high gamma photon density. We hope to be able to detect up to 8% of thermal neutrons at 1 n/cm2/sec against a background of 1e10 gammas/cm2/sec at energies above 100keV. We want to know how close to ""gamma blind"" our neutron sensors are.

We believe our silicon AT and silicon carbide HT series heterodiode neutron sensors are the only solid state detectors available where bulk neutron reactive material forms part of the detector structure. This configuration gives our devices approximtely double the detection efficiency of any other solid state thermal neutron detector. The neutron reactive layer we use generates charged particles which can be always be detected in a thin sensitive region. That ""thinness"" reduces the gamma capture probability. This is why we believe our devices will show a very high gamma rejection ratio .

Our sensors are commercially innovative because they allow high efficiency thermal neutron detection in an intrinsically safe, light weight, low power, robust package."