Radiation Dosimetry via the Radio-Photoluminescence of Synthetic Diamond
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RADIATION DOSIMETRY VIA THE RADIO-PHOTOLUMINESCENCE OF SYNTHETIC DIAMOND REX J. KEDDY*, TOM L. NAMt AND SHAWN ARAIKUM*t University of the Witwatersrand, Johannesburg, 2050 South Africa *Department of Medical Physics, tlHealth Physics Service ABSTRACT A method of radiation dosimetry based upon the radiophotoluminescence (RPL) of synthetic diamond crystals is presented. When the RPL is generated by a stimulation wavelength of 296 nm a linear response vs radiation dose of up to 20 kGy can be obtained with selected crystals. The response is very dependent on the chemistry of the synthesized specimen.
INTRODUCTION The methods of radiophotoluminescence (RPL) have been the subject of a number of studies1, 2 which have included LiF and silver activated glass but no investigation of the RPL of diamond, natural or synthetic, seems to have been reported. The investigation reported on here has examined the RPL properties of diamond crystals which were synthesized for use as thermoluminescence (TL) dosimeters. It is now well known that the response of specimen diamonds as any kind of radiation dosimeter, TL or conduction, is very sensitive to the type and quantity of the impu3 rity atoms included in the crystal matrix during formation . It is therefore absolutely essential that the full synthesis process i.e. the chemistry, the temperatures and the temperature gradients be extremely well controlled inside the reaction cell. One of the impurity elements that has been found to have a profound effect on the diamond TL response (and so also the RPL response) to radiation is nitrogen and, although no comprehensive investigation has been conducted by us to determine the RPL response as a function of the nitrogen content, we have used for this project specimens that had nitrogen and other impurity concentrations that were optimum for TL response. The optical properties of the specimens were initially probed for the response of the thermally accessible as well as the deeper, thermally less accessible, charge trapping states as a function of the wavelength of the RPL stimulating light. For the thermally accessible carrier traps - those which are evident in the Glow-Curve and which give rise to the TL characteristics of the crystal - an RPL stimulation at 404 nm was found to be adequate and was employed. We refer to this as RPL-404. For the deeper traps a stimulating wavelength of 296 nm was used. We refer to this as RPL-296 and it is a consequence of RPL-296 that the high doses could be determined. Both RPL-404 and RPL-296 were obtained from a low pressure mercury vapour lamp with wave length selections being made by a combination of selected filters and a computer controlled scanning monochromator system.
PRELIMINARY MEASUREMENTS A characteristic feature of all specimens was the sensitive thermoluminescence response after exposure to a radiation dose. Figure 1 is an example of the typical shape 4 of the 'glow-curves' obtained. The heating cycle used has been reported elsewhere .
Mat. Res. Soc. Symp. Proc. Vol. 302. 01993 Materials R
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