/sup 6/LiI(Eu) in neutron and /spl gamma/-ray spectrometry - a high sensitive thermal neutron detector

Europium activated ⁶LiI crystal (enriched to 96% ⁶Li) has been studied in neutron and gamma-ray spectrometry. Two crystals of Oslash50 mm times 5 mm and Oslash30 mm times 3 mm size coupled to a calibrated Photonis XP5200 photomultiplier were tested. A response of ⁶LiI(Eu) to neutrons emitted from a paraffin moderated Pu-Be source has been investigated and the thermal neutron peak has been found to be located at gamma equivalent energy (GEE) of about 3.5 MeV. High sensitivity of the ⁶LiI(Eu) crystal is demonstrated as the neutron peak is observed at the rate as low as 10^-2 counts per second. Apart from neutron spectra a light output, energy resolution and non-proportionality of the ⁶LiI(Eu) response versus gamma-ray energy have been measured for the two crystals. The light yield of 1.5times10⁴ ph/MeV (about 40% of NaI(Tl)) was obtained and the energy resolution at 662 keV (Cs-137) of 7.5plusmn0.1% was found for the large crystal. The non-proportionality has been measured to have more proportional character as compared to NaI(Tl). Due to the high sensitivity to thermal neutrons and good proportionality against gamma-ray energy, the ⁶LiI(Eu) crystal was brought under testing with few samples of fissile nuclear materials. Shielded fissile samples can be recognized via detection of neutrons followed spontaneous fission.