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

Europium doped /sup 6/LiI crystals (enriched to 96%/sup 6/Li) have been studied in neutron detection and /spl gamma/-ray spectrometry. Two crystals, 50 mm/spl times/5 mm and 30 mm/spl times/3 mm in size were coupled to a calibrated Photonis XP5200 photomultiplier, were tested. The response of /sup 6/LiI(Eu) to neutrons emitted from a paraffin moderated Pu-Be source has been investigated and the thermal neutron peak has been found at a Gamma Equivalent Energy (GEE) of about 3.5 MeV. The high sensitivity of the /sup 6/LiI(Eu) crystal is demonstrated by the observation of a neutron peak at a dose equivalent as low as 0.05 /spl mu/Sv/h. Apart from the neutron response, the light output, energy resolution and nonproportionality of the /sup 6/LiI(Eu) crystals versus /spl gamma/-ray energies have been measured. The light yield of 1.5/spl times/10/sup 4/ ph/MeV (about 40% of NaI(Tl)) was obtained and the energy resolution at 662 keV (/sup 137/Cs) of 7.5/spl plusmn/0.1% was found for the large crystal. The linearity of the light output with energy has been measured and is better compared to NaI(Tl). Due to the high sensitivity to thermal neutrons and good proportionality against /spl gamma/-ray energy, the /sup 6/LiI(Eu) crystal was tested with a few samples of nuclear materials. Shielded samples can be recognized via detection of neutrons following spontaneous fission.