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Phone: þ52 66 225 92 156, Fax: þ52 66 221 26 649Dose rate effects on the thermoluminescence (TL) properties of undoped and 750 ppm nitrogen doped microwave chemical vapor deposition (MWCVD) diamond films were analyzed. The diamond samples were exposed to 2.4-20.67 Gy/min dose rates from a 60 Co source. The TL glow curve of undoped sample showed no apparent dose rate effects. The doped diamond film exhibited dose rate effects consisting in a 10-30% integrated TL increase as the dose rate increased. The TL response as a function of dose rates showed a nonlinear behavior for the doped sample contrary to the undoped diamond film. The dose rate effects were evaluated through the determination of the kinetics parameters by fitting of the TL glow curves. The results indicate that chemical vapor deposition (CVD) diamond may present some dose rate effects on the TL properties in a given dose range, implying that some care should be exercised in order to use CVD diamond films in radiation dose assessments.

The behaviour of afterglow (AG) and thermoluminescence (TL) in nine beta-irradiated HPHT Ib type diamond crystals is presented. The transparent yellow synthetic crystals (Sumicrystal, UP-3510) were purchased from ProDiamond, Germany. Immediately after irradiation, the crystals exhibit pronounced AG (phosphorescence) caused by thermal emptying of the traps responsible for the low temperature TL peaks. All AG decay curves are well fitted with the sum of one, two or three exponential decays with the same decay lifetimes of 6.73, 12.8 and 145 s for the fast, medium and slow decay components, respectively. Two different groups of AG decay curves can be distinguished. The first group (three crystals) exhibits intense AG related to fast emptying of some shallow traps. The initial AG intensity of other crystals (second group) is 2-3 order lower than those of the first group crystals. This difference is due to the absence (or very low intensity) of the shallow traps in these crystals. TL glow curves consist of two sets of peaks. The first one with peak maxima at about 50, 70, 180 and 280 8C has high sensitivity but saturates at doses higher 1 Gy. The second set looks like several strongly overlapped TL peaks that exhibit linear-sublinear behaviour. The intensity of the TL peaks of the second set correlates with the intensity of TL below 100 8C.TL glow curves recorded immediately after beta irradiation with indicated doses; the initial part of the curves (below 30 8C) corresponds to AG at room temperature. The inset shows the dose growth of integrated TL between 30 and 330 8C.

Dose rate effects are important in thermoluminescent (TL) dosimeter applications because a certain absorbed dose given at different dose rates may result in a different TL yield. The present work reports about the dose rate effects on TL glow curves and kinetics properties of microwave plasma assisted chemical vapor deposition (MWCVD) diamond films grown on (100) silicon. The diamond films were exposed to γ radiation at 20.67, 43.4 and 81.11 Gy min–1 dose rates in the range of 0.05–10 kGy. The films showed a linear dose behavior up to 2 kGy and reached saturation for higher doses. The TL intensity varied as a function of dose rate and the samples had a maximum TL response for relatively lower dose rates. A single first order kinetics TL peak was typical for low doses while at higher doses two first order kinetics peaks were necessary to fit the glow curves. The results indicate that dose rate effects may be significant in dosimetric applications of MWCVD diamond. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)