Scheme of the pulsed optically stimulated luminescence (POSL) setup, which is a modification of the system described by Akselrod and McKeever (Ref. 17). The system uses the line of a -switched frequency-doubled Nd:YAG laser (Laser Photonics, KYD-300) operating at (except when stated otherwise) for stimulation. The sample emission is detected using a bialkali PMT (Electron Tubes, 9235QB). A Nd:YAG laser mirror (CVI Laser Corporation) and Hoya U-340 filters are used in front of the PMT to block the laser light while allowing the detection of the UV and -center emission bands. The PMT is connected to a dual-channel gated photon-counter (Stanford Research, SR400). The channels are gated to allow time discrimination between short and long lifetime emissions in . A pulse generator (Berkeley Nucleonics Corporation, BCN 500) was used to synchronize the laser and the photon counter. For lifetime measurements, the filter pack was replaced by a monochromator and the photon counter was replaced by a multichannel scaler/averager (Stanford Research, SR430). The data were recorded in a PC.
Photon counter gating scheme used to discriminate between short and long lifetime luminescences: (a) laser pulses; (b) gate states of channels and of the photon counter. The instant corresponds to the trigger from the pulse generator.
Luminescence of unirradiated and irradiated samples as a function of time after the pulse-generator trigger. The data were obtained connecting the PMT to a multichannel analyzer with the bin width set to .
Lifetime measurement of the (a) long lifetime luminescence and (b) short lifetime luminescence of irradiated samples (Luxel™). The data were obtained connecting the PMT to a multichannel analyzer. Experimental details: (a) stimulation by a Nd:YAG laser KYD-300; (b) stimulation by a diode-pumped solid-state Nd:YAG laser from Intellite; multichannel triggered by the signal of a high-speed silicon detector DET200 from Thorlabs ( rise time).
Example of OSL decay curves at (a) and (b) , obtained with the POSL system equipped with a monochromator.
OSL emission spectrum of samples irradiated with of gamma rays. Each data point corresponds to the OSL measurement of one sample at a fixed wavelength. The main graph presents the integrated OSL emission divided by the period in which channels and were enabled (12 and , respectively). The inset shows the emission spectrum corrected by the optical absorption of the polyester film of the dosimeters. The standard deviation of each data point, estimated by repeated measurements at 330 and and , was smaller than 5%. The shoulder observed at may be an artifact produced by the correction for the spectral response of the system. However, it should be mentioned that a emission band was observed as a shoulder of the emission band by Draeger and Summers (Ref. 31). Different samples were used for each individual readout; i.e., the samples were irradiated and read out only once (i.e., not reused).
(a) Dose response of the UV and -center OSL signals of . (b) Ratio between the signal due to the UV emission band and the signal due to the -center emission. Each data point corresponds to the average and standard deviation obtained from three independent readouts. Different samples were used for each individual readout; i.e., the samples were irradiated and read out only once (i.e., not reused).
Intensity of the UV and -center luminescences of samples as a function of time elapsed since irradiation (beta dose of ). A laser mirror and Hoya U-340 filters were used in front of the PMT. Different samples were used for each individual readout; i.e., the samples were irradiated and read out only once (i.e., not reused).
Relative intensity of the UV and -center luminescences of samples as a function of time elapsed since irradiation (beta dose of ). A laser mirror and Hoya U-340 filters were used in front of the PMT.
Comparison between the normalized OSL decay curves of samples irradiated with 5 and (beta irradiation). Channel corresponds mostly to UV luminescence, whereas channel , to -center luminescence. The insets show the same data before normalization.
OSL curves of (a) beta-irradiated samples and (b) alpha-irradiated samples. The beta dose was . The alpha irradiation period was chosen to produce an OSL signal of similar intensity as the beta dose (actual dose not available).
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