Christopher R. Varoy

Optically erasable samarium-doped fluorophosphate glasses for high-dose measurements in microbeam radiation therapy

Previous work has demonstrated that fluorophosphate (FP) glasses doped with trivalent samarium (Sm3+) can be used as a dosimetric detector in microbeam radiation therapy (MRT) to measure high radiation doses and large dose variations with a resolution in the micrometer range. The present work addresses the use of intense optical radiation at 405 nm to erase the recorded dose information in Sm3+-doped FP glass plates and examines the underlying physics. We have evaluated both the conversion and optical erasure of Sm3+-doped FP glasses using synchrotron-generated high-dose x-rays at the Canadian Light Source. The Sm-ion valency conversion is accompanied by the appearance of x-ray induced optical absorbance due to the trapping of holes and electrons into phosphorus-oxygen hole (POHC) and electron (POEC) capture centers. Nearly complete Sm2+ to Sm3+ reconversion (erasure) may be achieved by intense optical illumination. Combined analysis of absorbance and electron spin resonance measurements indicates that th...

Structural and Scintillation Properties of Cerium-Doped

A series of cerium-doped compounds with the composition Ba1-xLaxCl2+x and 0 < x < 0.5 have been prepared in ceramic form. We find from the powder X-ray diffraction patterns that the compounds adopt the cubic fluorite structure for 0.05 < x 0.34. Samples with x~ 0.2 are translucent. When doped with trivalent cerium, the materials show photoluminescence emission peaks at 350, 372 nm (for the Ba0.66La0.34Cl2.34 composition); the photoluminescence decay can be fitted with a single exponential with decay time 25 ns. The scintillation pulse height analysis shows a photopeak 137Cs for which can be used to compute a light yield of 4000 photons/MeV. The scintillation decay is non-exponential, with a rapid initial decay which can be represented approximately by a decay constant of ~100 ns, but there is a substantial delayed scintillation which extends over several microseconds.

{\rm Ba}_{{}_{1- \rm x}}{\rm La}_{{}_{\rm x}}{\rm Cl}_{{}_{2+ \rm x }}

We report the photoluminescence and x-ray luminescence of lanthanum-stabilized cubic barium chloride with europium (Eu2+) doping, of general composition Ba1−x−yEuyLaxCl2+x. X-ray diffraction patterns confirm that the material adopts a cubic fluorite structure for x=0.125 and 0<y<0.1. The photoluminescence shows an intense band comprising two components with maxima at 420 and 394 nm. The 394 nm band is assigned to Eu2+ substituting for Ba2+ giving a site of cubic symmetry, based on the excitation spectra which show a T2g band and Eg band similar to those in cubic SrCl2:Eu. The 420 nm band has a very different lifetime and excitation spectrum and is assigned to Eu2+ ions which have an associated chlorine interstitial ion. The two bands are also found in the x-ray luminescence spectra. For both bands, and an additional minor emission at 520 nm found only at low temperatures and for high Eu concentrations, there is a common excitation in the UV from 150 to 200 nm which we attribute to excitons associated with...

Ceramics

Recently, a new class of rare-earth (RE) doped fluorochlorozirconate (FCZ) glass-ceramics has been developed and studied with the goal of using these materials in indirect conversion x-ray imaging applications. We report selected thermal and x-ray induced luminescence (XL) properties of rare-earth (EuF2 and SmF3) doped fluorochlorozirconate glasses and glass-ceramics, and highlight some of their interesting properties. Sm-doped FCZ glasses exhibit XL even in the unannealed state, while annealing at a temperature of 250°C in a reducing atmosphere (5% H2 and 95% Ar) significantly enhances the XL efficiency.

Lanthanum-stabilized europium-doped cubic barium chloride: An efficient x-ray phosphor

There is much interest in various glass-ceramics doped with rare-earth (RE) metals for x-ray storage phosphor and/or x-ray scintillator applications for potential use in high resolution x-ray imaging. The phosphor and scintillator properties of these glass ceramics depend on the formation of RE embedded nanocrystals in their structure. The heat treatment and annealing of the starting RE-doped glasses is critically important to the formation and control of the glass ceramic nanocrystals. We have studied the thermal and photoluminescence properties of Sm-doped fluorochlorozirconate glass ceramics. We selected useful host compositions and appropriate heat treatment and annealing procedures needed to grow the required RE-doped nanocrystals in a glass matrix for sensor applications.