Fig. 4 Energy spectrum of intrinsic scintillation of LaCl3:Ce. 10000 counts correspond to 88 counts per hour. Note strong peaks due to α-particles identified as those coming from a decay of U series.
An additional γ-spectrum taken on a Ge detector showed characteristic lines of 138La and X-rays of 138Ba, according to final states of the 138La decay; the 40K line of 1460 keV was also detected, but with much lower intensity. The relative abundance of U to La is estimated at 1.4 ppm. In the case of GSO, significant contamination by U series isotopes was connected with the production of the small crystal in the welded crucible of
Ir [12]. Note that NaI(Tl) has no naturally radioactive components