Effect of Humidity on Scintillation Performance in Na and Tl Activated CsI Crystals

Abstract

Time dependent photoluminescence and radioluminescence for sodium (Na) and thallium (Tl) activated cesium iodide (CsI) single crystals exposed to 50% and 75% relative humidity (RH) has been investigated. These results indicate that Tl activated crystals are more robust than the Na activated crystals against humidity induced scintillation degradation. The development of "etching pits" and "inactive" domains are the characteristics of deteriorated Na activated CsI crystals. These "inactive" domains, bearing a resemblance to a polycrystalline appearance beneath the crystal surface, can be readily detected by a 250 nm light emitting diode. These features are commonly observed at the corners and deep scratched areas where moisture condensation is more likely to occur. Mechanisms contributing to the scintillation degradation in Na activated CsI crystals were investigated by Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS). ToF-SIMS depth profiles indicate that Na has been preferentially diffused out of CsI crystal, leaving the Na concentration in these "inactive" domains below its scintillation threshold.

High‐Performance Next‐Generation Perovskite Nanocrystal Scintillator for Nondestructive X‐Ray Imaging

“…Currently thallium‐doped cesium iodide (CsI:Tl) and terbium‐doped gadolinium oxysulfide (Gd 2 O 2 S:Tb, GOS) are widely being used as a scintillator for indirect‐type X‐ray detector. However, the CsI:Tl scintillator requires an expensive and time‐consuming vacuum process to make thick crystalline scintillator film so that it is inherently brittle and fragile, which limits its application to flexible detection such as oral and dental imaging . The gadolinium oxysulfide (GOS) scintillator is relatively cheap and flexible because the GOS microparticles are embedded in flexible matrix.…”

Invisible decay modes in nuclear gamma cascades

“…Since the typical lengths of the dead layers are approximately 1-10 mm, it does not seem likely that these dead regions would cause a background even for 60 Co. In the event of a positive signal, since the problem of the dead layers is confined to potentially big (approximately 100 mm) regions in the inner modules, they could be examined to observe the size of such regions [42].…”

Luminescence of CsI and CsI:Na Films under LED and X-ray Excitation

“…When excited by a higher-energy photon, some of the electrons in the valence band jump over the forbidden gap to the conduction band. In the de-excitation process of the larger width of the forbidden gap, the photons emit UV light in the energy region of 3.7 to 4.3 eV [9,10]. An energy state is generated in the forbidden gap by adding sodium (Na) or thallium (Tl) dopant to the CsI film to convert X-rays and gamma rays into visible light and to increase the luminescent effect [11,12].…”

“…The nature of the inherent luminescence and the mechanism of CsI have been studied since the twentieth century [26][27][28]. The luminescence process is due to the attenuation of two types of self-capturing excitons (STE) [5,9,10,27]. One is the on-center STE, the electrons of which were captured at V k -centers at room temperature.…”