Strontium and barium iodide high light yield scintillators

Europium-doped strontium and barium iodide are found to be readily growable by the Bridgman method and to produce high scintillation light yields

High Resolution Sensor for Nuclear Waste Characterization

Gamma ray spectrometers are an important tool in the characterization of radioactive waste. Important requirements for gamma ray spectrometers used in this application include good energy resolution, high detection efficiency, compact size, light weight, portability, and low power requirements. None of the available spectrometers satisfy all of these requirements. The goal of the Phase I research was to investigate lanthanum halide and related scintillators for nuclear waste clean-up. LaBr3:Ce remains a very promising scintillator with high light yield and fast response. CeBr3 is attractive because it is very similar to LaBr3:Ce in terms of scintillation properties and also has the advantage of much lower self-radioactivity, which may be important in some applications. CeBr3 also shows slightly higher light yield at higher temperatures than LaBr3 and may be easier to produce with high uniformity in large volume since it does not require any dopants. Among the mixed lanthanum halides, the light yield of LaBrxI3-x:Ce is lower and the difference in crystal structure of the binaries (LaBr3 and LaI3) makes it difficult to grow high quality crystals of the ternary as the iodine concentration is increased. On the other hand, LaBrxCl3-x:Ce provides excellent performance. Its light output is high and it provides fast response. The crystal structures of the two binaries (LaBr3 and LaCl3) are very similar. Overall, its scintillation properties are very similar to those for LaBr3:Ce. While the gamma-ray stopping efficiency of LaBrxCl3-x:Ce is lower than that for LaBr3:Ce (primarily because the density of LaCl3 is lower than that of LaBr3), it may be easier to grow large crystals of LaBrxCl3-x:Ce than LaBr3:Ce since in some instances (for example, CdxZn1-xTe), the ternary compounds provide increased flexibility in the crystal lattice. Among the new dopants, Eu2+ and Pr3+, tried in LaBr3 host crystals, the Eu2+ doped samples exhibited low light output. This was mostly because a large fraction of light was emitted via very slow decay components (>50 ïÃÂís) and as a result was not included in the light estimation performed using gamma-ray spectroscopy where the typical amplifier integration time used is <12 ïÃÂís. The origin of these slow component(s) is most likely related to the presence of defects caused by charge imbalance in the crystals. The charge imbalance occurs when the Eu2+ ions replace the La3+ ions in crystal lattice. This charge neutrality can be restored by codoping the Eu2+ doped LaBr3 crystals with ions such as Hf4+. The Pr3+ doped LaBr3 crystals provided exciting results. They exhibited very high light yield (85,000 photons/MeV) and good energy resolution. While the decay time of LaBr3:Pr is much slower than that for LaBr3:Ce, it is fast enough for many nuclear waste cleanup applications. Furthermore, it should be possible to increase the speed of LaBr3:Pr by adjusting its Pr3+ concentration. The most exciting feature of LaBr3:Pr is that it emits in red-region and is therefore, well suited for silicon photodiode readout. In fact, LaBr3:Pr is the brightest scintillator in the red-region and its light yield is ~15% higher than the light yield of LaBr3 doped with Ce. Overall, the Phase I research has been very successful and has lead to better understanding of the lanthanum halide and related scintillators. It has also opened up some promising avenues to optimize the performance of these exciting scintillators. Based on the Phase I results, we have clearly demonstrated the feasibility of the proposed approach

Crystal growth and scintillation properties of strontium iodide scintillators

Single crystals of SrI{sub 2}:Eu and SrI{sub 2}:Ce/Na were grown from anhydrous iodides by the vertical Bridgman technique in evacuated silica ampoules. Growth rates were of the order of 5-30 mm/day. Radioluminescence spectra of SrI{sub 2}:Eu and SrI{sub 2}:Ce/Na exhibit a broad band due to Eu{sup 2+} and Ce{sup 3+} emission, respectively. The maximum in the luminescence spectrum of SrI{sub 2}:Eu is found at 435 nm. The spectrum of SrI{sub 2}:Ce/Na exhibits a doublet peaking at 404 and 435 nm attributed to Ce{sup 3+} emission, while additional impurity - or defected - related emission is present at approximately 525 nm. The strontium iodide scintillators show very high light yields of up to 120,000 photons/MeV, have energy resolutions down to 3% at 662 keV (Full Width Half Maximum) and exhibit excellent light yield proportionality with a standard deviation of less than 5% between 6 and 460 keV

New scintillating bolometer crystals for rare particle detection

International audienceThe Majorana nature of neutrinos is one of the most important questions being pursued in physics today. This has given the search for neutrinoless double-beta decay (0 ν β β ) a high priority among proposed nuclear physics experiments. In this work, the objective was to evaluate several crystal compositions for possible use as a scintillating bolometer in 0 ν β β research. A crucial characteristic of the investigated crystals is that their compositions must include one of the few elements known to decay with double-beta emission. Therefore, we grew crystals containing molybdenum or selenium as a major constituent. Results are presented here for single-crystals of sodium molybdate and lithium indium diselenide. Scintillating bolometer data were measured at milli-Kelvin temperature and show good discrimination between alpha and beta/gamma emissions, which is crucial for background reduction. The lithium indium diselenide crystal was also used to measure the energy spectrum for the beta emission of indium decay, the first time a beta decay spectrum has been measured from self-emission in a scintillating bolometer