M. Barboza‐Flores

The role of F centres in the thermoluminescence of low-energy UV- and X-irradiated KCl:Eu2+

The thermoluminescence of ultraviolet- (250 nm) and X-ray-irradiated KCl:Eu2+ is investigated. The peaks are located in the same positions independent of the radiation used to excite the sample, with differences only in the peak intensity ratios. Thermal and optical bleaching methods allow us to relate the thermoluminescence peaks located in the low-temperature region (320-425 K) to Fz centres and those in a higher-temperature region (425-530 K) to F centres.

Dosimetric properties of KCl:Eu2+ under α, β, γ, x ray, and ultraviolet irradiation

The thermoluminescence (TL) characteristics of KCl:Eu2+ subjected to α, β, γ, x ray, and ultraviolet (UV) radiation (200–300 nm), as well as the dose response was investigated. The TL glow curve structure is very similar for any type of irradiation used with differences only in the peak intensities; it has good reproducibility. Also, the dose response is linear for all types of irradiations. These results allowed us to conclude that the KCl:Eu2+ crystals may be used as a dosimeter for ionizing and nonionizing radiation

Nonthermoluminescent dosimetry based on the afterglow response of europium‐doped alkali halides

A new nonthermoluminescent dosimetric technique was developed by using the afterglow response characteristic of alkali halide single crystals doped with europium ions. The afterglow luminescence decayed very slowly and its intensity was proportional to the radiation dose. The radiation dose was measured by the time intergration of the afterglow signal in a selected region. This afterglow dosimetry was compared with the conventional thermoluminescent method, by using single crystals of different alkali halides. The results show that the technique is suitable and versatile for ultraviolet and x‐ray radiation dose determination.

SELF-IRRADIATION IN POTASSIUM HALIDE THERMOLUMINESCENT CRYSTALS

A self‐irradiation process has been observed in potassium halide thermoluminescent crystals. The 0.0117% abundance of the radioactive nuclide 40K in natural potassium, with a halflife of 1.28×109 years, is responsible for about 4.9 μGy/h of self‐irradiation dose. The present finding is of importance in relation to the performance and limitations of recently proposed solid state dosimeters based on doped potassium halide crystals.

Ultraviolet dosimetric properties of α‐Al2O3 crystals

Thermoluminescence (TL) measurements were performed in crystal samples of α‐Al2O3 (TLD 500 K) subjected to UV irradiation in the range of 200–320 nm. The material is very sensitive to UV light and can be considered potentially useful for actinic region dosimetry. The TL glow curve is composed of two glow peaks centered at 58 and 184u2009°C, respectively. The TL excitation spectrum shows a maximum for 220 nm light.

A simple calibration method for potassium halide thermoluminescence dosimeters

We present a simple calibration method for europium‐doped potassium halide dosimeters. The procedure is based on the self‐irradiation absorbed dose of potassium halide thermoluminescence dosimeters due to the natural content of the radionuclide 40K in potassium halide crystals. In the small dose range of the order of 0.5 mGy, the precision of the proposed method is highly competitive with traditional calibration methods, without the need of artificial radiation sources and rather expensive and sophisticated measurement equipment.

Fading and self‐irradiation of potassium halide thermoluminescence dosimeters

The fading characteristics of KCl:Eu2+ (150 ppm) thermoluminescent crystals is determined. It is shown that the fading cannot be correctly measured without taking into account the phenomenon of self‐irradiation of the crystals, due to natural radioactive nuclide 40K which is presented in potassium halide dosimeters. The results obtained can be useful in those applications of KCl: Eu2+ crystals dealing with long‐time exposures, or low‐dose levels of radiation.

Influence of the aggregation-precipitation state on the thermoluminescence of non-irradiated KCl(1-x)Brx:Eu2+ mixed crystals

Abstract Thermoluminescence, absorption and luminescence spectra of as grown and well aged non-irradiated KCI(1-x)Brx crystals, containing an average of 150 ppm of EuCl2 as a dopant are analyzed as a function of the sample composition. The precipitation state of the KCl(1-x)Brx system is characterized by optical absorption and luminescence measurements.

Fabrication and characterization of new LiF:Eu3+ sintered phosphors exposed to beta particles

Pellet-shaped LiF:Eu3+ phosphors were synthesized by sintering. To improve their thermolumine-scence characteristics, different growth conditions were used. Thermal annealing at 750 °C during 5 h under air atmosphere provided the samples with highest sensitivity. Characteristic glow curves exhibit an absolute maximum centered at 203 °C and another less intense peak between 250 and 300 °C. The first peak has a position very suitable for dosimetry applications. Beta-irradiated samples displayed a thermoluminescence response that increases as the radiation dose increased in the 0.16–42.0 Gy range. A fast fading of<20% occurs in the first 10 s after irradiation, followed by a remarkable stability at room temperature. Computerized glow curve deconvolution of experimental data obtained applying the McKeever method to resolve the individual peaks revealed that the glow curves fit to nine individual peaks. Activation energies were computed by using the initial rise method.

Cathodoluminescence in europium doped KCl crystals

Abstract Spectral cathodoluminescence of KCI:Eu2+ (0.2% wt) crystals has beenmeasured at different temperatures. In the 80—300K temperature range the luminescence consists of three main broad emission bands with maxima around 418, 452, and 619 nm. Based on photoluminescence studies the 418 nm could be associated with the 4f65d (t2g)-4f7 (8S7/2) radiative transition of the Eu2+ ions in the KCl matrix. The band with maximum at 452 nm could be associated with the α-centere emission as in pure KCl. The 619 nm band has been considered as a part of the luminescence modified by the absorption of the F centers formed during irradiation. The intensity of all these bands versus temperature shows a minimum around 150K, an indication of a low defect mobility produced with the electron-beam irradiation.