Neutron detection by large NaI crystal

In present days new neutron detection methods are under developed due to the global shortage of He-3 and the toxicity of BF3. Neutrons can be indirectly detected by high-energy photons. The performance of a cylindrical Nal crystal, 4 in. diameter and 8 in. length as an indirect neutron detector has been investigated. Measurements were performed with Cf-252 source with bare and shielded Nal detector. With a proper converter and moderator structure for the Nal detector, the detection efficiencies and the minimum detectable activities are improved, making the method very interesting for security applications. The indirect detection of neutrons by photons has several advantages. First, this method can in principle be suited by any gamma spectrometer with only slight modifications that do not compromise with its gamma spectrometry measurements. Second, fission neutron sources and neutron generators can be discriminated thanks to their different gamma energy spectra, a discrimination easily done by a Nal spectrometer.