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Nonproportional response of the scintillation yield of un-doped SrI2 and SrI2:5o/oEu was studied using highly monochromatic synchrotron irradiation ranging from 10.5 to 100 keV. Measurements were performed at 80 K and 295 K for SrI , and at 80 K, 295 K, 450 K, and 600 K for SrI2:5o/oEu. By making a dense data sampling around the iodine K-edge and using the recently developed K-dip spectroscopy method, the K-shell photoelectron response curves were reconstructed down to 500 eV. Proportionalities of X-ray response and K-shell photoelectron response of both crystals reveal temperature dependence. Energy resolution of the X-ray photopeak was analyzed as a function of temperature and deposited energy. Energy resolution improves with better proportionality.

Lanthanum bromide scintillation detectors produce very high light outputs (∼60,000 ph/MeV) within a very short decay time (typically ∼20 ns) which means that high instantaneous currents can be generated in the photocathode and dynode chain of the photomultiplier tube (PMT) used for the scintillation readout. The net result is that signal saturation can occur long before the recommended PMT biasing conditions can be reached. In search of an optimized light readout system for LaBr3, we have tested and compared two different PMT configurations for detection of gamma-rays up to 15 MeV. This range was chosen as being appropriate for gamma-ray remote sensing and medium energy nuclear physics applications. The experiments were conducted at two facilities: the Laboratori Nazionali del Sud (LNS) in Catania, Italy [1] and the High Intensity Gamma-ray Source (HIγS) at Triangle University Nuclear Laboratory, in Durham, North Carolina, USA [2] . The PMT configurations we have tested are (1) a standard dynode chain operated under-biased; (2) a 4-stage reduced chain operated at nominal inter-dynode bias. The results are that shortening the number of active stages, as in configuration (2), has advantages in preserving energy resolution and avoiding PMT saturation over a large energy range. However, the use of an under-biased PMT, configuration (1), can still be considered a satisfactory solution, at least in the case of PMTs manufactured by Photonis. The results of this study will be used in support of the Mercury Gamma-ray and Neutron Spectrometer (MGNS) on board of BepiColombo, the joint ESA/JAXA mission to Mercury, scheduled for launch in 2014.

Using a conventional fast-shuttered laboratory X-ray source in combination with pulsed laser diode modules, the possibilities for undertaking X-ray/laser interaction spectroscopy in wide band-gap luminescent materials are explored. It is shown that in such materials, a variety of X-ray/laser timing sequences can extract complimentary information regarding the charge-carrier trapping, de-trapping and recombination processes. The effects on the luminescence are illustrated for six example materials (YPO 4 :Ce,Sm, Lu 3 Al 5 O 12 :Pr, Al 2 O 3 :C, natural sodium feldspar NaAlSi 3 O 8 , cubic BN and type IIa natural diamond). By ramping the temperature from 10 to 320 K during repeated X-ray pump/laser-probe activation cycles, a rapid assessment can be made of the important thermally dependent changes to the charge carrier trapping competition processes.

By means of a photomultiplier tube, a Si-photodiode, and a Si-avalanche photodiode, the absolute scintillation yield of recently developed LaBr3:Ce, LaCl3:Ce, and (Lu,Y)2SiO5:Ce scintillators and traditional Lu2SiO5:Ce, Bi4Ge3O12, NaI:Tl, CsI:Tl, and CsI:Na scintillators were determined. These are all well known scintillators that cover emission wavelengths from 250 nm to 750 nm. By comparing the scintillation yield independently measured with the three different photon detectors reliable yield values are obtained.

A combined photoconductivity, absorption, and thermoluminescence study was performed to understand the absence of luminescence from Ce3+ in LaAlO3:Ce3+. It is demonstrated that the absence of luminescence is the result of Ce3+ ionization from the 5d excited states, which are all located in the conduction band. Ce3+ ionization is accompanied by the formation of several broad absorption and photoconductivity bands, which are assigned to electron traps. A time and temperature dependent optical investigation of these traps reveals the conditions under which electrons are transferred from Ce3+ to traps and vice versa, from traps back to Ce4+. The observed difference in energy needed to thermally or optically release electrons from traps is qualitatively explained in terms of the location of the ground and excited states of the electron traps with respect to the conduction band.

The first results of a study on the properties of a gaseous scintillation detector based on a Gas Electron Multiplier (GEM) are reported. The detector is designed for use in position-sensitive dosimetry applications in radiation therapy. A double GEM system, operating in a 90 10% Ar-CO2 gas mixture at a gas amplification factor of similar to 3000, emits a sufficient amount of detectable light to perform measurements of similar to 1 Gy doses in two dimensions. The light yield does not suffer from quenching processes when particles with high stopping power are detected. This operation mode of GEMs offers the dosimetric advantages of a gas-filled detector and the 2D read-out can be performed with a CCD camera. Compared to the existing dosimeters, this system is relatively simple and no complex multi-electrode read-out is necessary. (C) 2002 Elsevier Science B.V. All rights reserved.

A review and new data are presented on the absolute photon yield emitted by "classical" (NaI(Tl/sup +/), CsI(Tl/sup +/), CsI(Na/sup +/), CaF/sub 2/(Eu/sup 2+/), Bi/sub 4/Ge/sub 3/O/sub 12/, and CdWO/sub 4/) and "modern" (BaF/sub 2/, Gd/sub 2/SiO/sub 5/(Ce/sup 3+/), YAlO/sub 3/(Ce/sup 3+/), Lu/sub 2/SiO/sub 5/(Ce/sup 3+/), Lu/sub 3/Al/sub 5/O/sub 12/(Sc/sup 3+/), and K/sub 2/LaCl/sub 5/(Ce/sup 3+/)) scintillation crystals after absorption of X-rays and /spl gamma/-rays of energies ranging from 5 keV to 1 MeV. Factors influencing the energy resolution with which high energy photons can be detected with scintillator-photomultiplier combinations are reviewed. Attention is especially focused on the effects of nonproportionality in the scintillation response on the energy resolution.