Study of a NaIL-detector as a neutron detector

Within the past decade a significant shortage of 3 He has occurred. Since this material is widely used in neutron detection applications, e.g. by first responders, during on-site inspections, and in safeguard applications where nuclear and radioactive material has to be localized and possibly identified, alternative materials need to be considered, selected, implemented in a corresponding detector, and thoroughly tested. One of these promising replacement materials is 6 Li, which, e.g., is utilized in a sodium iodide detector (NaIL). There are also other detector applications with Li such as 6 LiF/ZnS, CLYC (Cs2LiYCl6:Ce), and CLLB (Cs2LiLaBr6:Ce) which were investigated elsewhere. NaIL offers the possibility of measuring gamma and neutron radiation simultaneously with good discrimination capability. Within the detection material neutrons are captured by 6 Li, triggering the nuclear reaction 6 Li(n,t)α. The secondary particles then create light pulses in the scintillation crystal which ultimately serve as detection signals. Due to the large Q-value of the reaction of 4.78 MeV, the signals are of the same order of magnitude as those of high energetic gamma photons. The discrimination of neutron and gamma radiation is realized by pulse shape analysis. Measurements with a NaIL-detector have been performed and the detectors’ capabilities verified with measurements of several neutron sources. The possibility of detecting such sources, which create a radiation field only slightly above the background radiation level, is of particular interest. In addition to results gained with different neutron sources, the influence of moderator material (HDPE) was also investigated. Other figures of interest were the FWHM (full width at half maximum) resolution of the gamma spectrum and the detectors’ efficiency, also with regard to detectors equipped with 3 He. The results of these verification tests will serve as supportive information regarding suitable neutron detection materials free of 3 He for first responders and other experts who work in the field of nuclear safety and security.