RBS and XPS analyses of phosphor packages for laser-heat thermoluminescence dosimetry
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Phosphor packages for a laser-heat thermoluminescence radiation-dosimetry system have been analyzed with Rutherford Backscattering Spectrometry and X-ray Photoelectron Spectroscopy. Samples consist of 20-50 fim diameter powder grains of CaSO4 : Tm and LiF: (Mg, Ti) phosphor embedded in a transparent silicone matrix about 60 /j,m thick. Our principal finding with regard to layer morphology indicates an inhomogeneous outer layer of areal density at least ~300 jug/cm 2 depleted of phosphor and contaminated with boron.
I. INTRODUCTION
II. PACKAGE FABRICATION
In an advanced development program for the Navy, International Sensor Technology (1ST), Inc., of Pullman, Washington, is making several components of a personnel dosimetry system for ionizing-radiation exposure. The system1 is based on a method2 for the fast heating of radiation-sensitive phosphors by using laser irradiation. The thermoluminescence (TL) response of the phosphors increases with the greater rate of temperature rise.3 Dosimeter components consist of grains of phosphors embedded in an optically transparent matrix of organic or glass binder material which is relatively thin with respect to ranges of primary and secondary radiations and also for efficient optothermal coupling in the laserheating readout cycle. The system is designed to discriminate gamma, beta, fast neutron, and thermal neutron radiations. Practical fast-neutron dosimetry in a highbackground gamma field would be particularly novel if achievable. By focusing the laser spot to match the ~50-/xm-diameter grain size and by scanning a phosphor package, one could effectively sample discrete crystallite TL emissions associated with tracks of proton recoils initiated by fast-neutron collisions. Distinction of inhomogeneous regions of TL emission above a uniform contribution of gamma dose to a package as a whole would be tantamount to counting neutron fluence. In this paper, we report results of Rutherford backscattering (RBS) and x-ray photoelectron (XPS) spectrometric analyses of several parts of a prototype system of phosphors and binder. The analyses characterize package stoichiometry, layer morphology, and purity, which bear on issues of dosimeter robustness, neutronresponse integrity, and background luminescence.
Two types of phosphor material were prepared and analyzed. Anhydrous crystals of calcium sulfate sensitized with thulium for TL emission4 were prepared at 1ST in a standard way,5 pulverized, and sifted to grain sizes ranging between 20 and 50 /xm in diameter. Calcium sulfate is one of the most sensitive materials used in dosimetry, and the thulium-doped compound has a particularly stable TL response.4'5 In addition, 6 Li- and 7Li-enriched LiF: (Mg, Ti) phosphors (TLD600 and TLD-700 from the Harshaw/Filtrol Partnership, Solon, Ohio) were similarly granulated at 1ST. Some composite packages were prepared containing mixtures of CaSO 4 : Tm and LiF: (Mg, Ti) mixed in a ratio of 3:2 by weight, respectively. One gram of phosphor powder was then mixed with 0.57 g of Dow Corning 96-083
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