Comparison of LaCl3:Ce and NaI(Tl) scintillators in γ-ray spectrometry

The commercial sample of LaCl3:(9±1)%Ce with the size of ∅25×25 mm was compared to NaI(Tl). A good light output of 9400±100 photoelectrons per MeV and an energy resolution of 4.2±0.2% for 662 keV γ-rays were measured with the LaCl3:Ce crystal coupled to an XP3212 photomultiplier with bialkali photocathode. Below 122 keV, the energy resolution of LaCl3:Ce was unexpectedly worse than that of NaI(Tl). The estimated photofraction of 17.9% at 662 keV is comparable to 21.4% for NaI(Tl) of ∅25×31 mm size. The radioactive background of the natural 138La radioactive isotope was observed in LaCl3:Ce, estimated to be about 1.07 c/s/cm3 of the crystal. Moreover, the contamination of the crystal by α-emitting isotopes of the uranium series was discovered. The LaCl3:Ce showed a good proportionality of the light yield versus energy within 3% down to 20 keV. The total and intrinsic energy resolutions are discussed.