Self-activity in lanthanum halides

Scintillators fabricated from lanthanum halides, specifically cerium-activated lanthanum bromide (LaBr₃ [Ce]) and lanthanum chloride (LaCl₃ [Ce]), have been shown to exhibit energy resolution far superior to that for thallium-activated sodium iodide. The high resolution, high Z, and high density (LaBr₃ 5.29 g/cm³ and LaCl₃ 3.79 g/cm³) of these materials hold out the prospect of use for building superior room-temperature, hand-held identification instruments. Recently attention has been devoted to investigating the practical issues connected with the use of these new scintillators. These efforts include attempts to increase the size of the crystals, optimize the Ce dopant concentration, and evaluate the properties of detectors fabricated from existing material. A negative outcome in the property evaluation has been the observation of self-activity, e.g., between 1.7 and 2.7 MeV for LaCl₃. This paper reports on efforts to characterize the use of lanthanum halides for identification including measurements of self-activity and presents a discussion of implications for the minimum detectable activity.