R. Meléndrez

Thermoluminescence properties of ZnO and ZnO:Yb nanophosphors

ZnO and ZnO:Yb thermoluminescence nanophosphors have been developed and tested under beta radiation. Spherical nanoparticles of sizes ranging from 130to1200nm were prepared through a glycol mediated chemical synthesis. The Yb doping had a thermoluminescence quenching effect compared to undoped ZnO. The 5% Yb concentration produced a low fading, a single thermoluminescence glow peak structure, and a dose linearity behavior adequate for thermoluminescence dosimetry applications. The ZnO:Yb nanophosphor has a great potential as a dosimeter for monitoring in ionizing radiation fields.

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

Actinometric thermoluminescence response of KCl1−xBrx:Eu2+ mixed crystals

Europium‐doped KCl1−xBrx mixed crystals have been studied as a selective ultraviolet (UV) detector material in the actinometric region (200–300 nm). Thermoluminescence glow curves of room‐temperature UV‐irradiated samples were analyzed as a function of composition x and irradiation wavelength. A thermoluminescence enhancement, relative to the pure KCl and KBr end components is found; for 210–300 nm irradiation the KCl40Br60:Eu2+ solid solution presents a significant increase in thermoluminescence efficiency.

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.

Thermoluminescence, Optical Stimulated Luminescence and Defect Creation in Europium Doped KCl and KBr Crystals

Europium doped alkali halide single crystals have been the subject of very intensive investigation due to its applications in digital medical radiography, optical memories and environmental dosimetry. The performance of these phosphorous materials exhibited in both thermoluminescence and optical stimulated luminescene, is generally explained through mechanisms where the photoionization of impurity is involved. However, no evidence of the presence of the Eu3+ ion has been reported yet. In this paper we present experimental insight into the defect creation processes generated by ionizing radiation, as well as ultraviolet light with energies below the band gap in both phenomena, which show the same 420 nm emission. The F and Fz centers are clearly related to the thermoluminescence glow curve. The results show a similar thermoluminescence and optical stimulated luminescence origin and may suggest the existence of a non-excitonic mechanism involved in the defect creation with ultraviolet non-ionizing radiation light.

Dosimetric characteristics of ultraviolet and x‐ray‐irradiated KBr:Eu2+ thermoluminescence crystals

Thermoluminescence (TL) characteristics of KBr:Eu2+ (150 ppm) previously exposed to ultraviolet (UV) light (200–300 nm) and x‐ray radiation at room temperature have been determined. The TL glow curve of UV‐irradiated samples is composed of six peaks located at 337, 384, 402, 435, 475, and 510 K. The TL glow curves of x‐irradiated samples show mainly a TL peak around 384 K. The TL intensities of UV‐irradiated (402 and 510 K glow peaks) and x‐irradiated specimens present a linear dependence as a function of radiation dose as well as fading stability 300 s after irradiation. These results further enhance the possibilities of using europium‐doped materials in nonionizing (actinic region) and ionizing radiation detection and dosimetry applications.

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 184 °C, respectively. The TL excitation spectrum shows a maximum for 220 nm light.

Dose rate effects on the thermoluminescence properties of MWCVD diamond films

Synthetic CVD diamond, being non-toxic and tissue equivalent, has been proposed as a ionizing radiation passive dosimeter with relevant applications in radiotherapy and clinical dosimetry. In the present work, the thermoluminescence (TL) properties of microwave-assisted chemical vapor deposition (MWCVD) diamond, 6 μm thick film grown on (100) silicon substrates, were studied after room temperature γ-irradiation for 2.4, 3.1, 5.94, 13.1, 20.67, 43.4 and 81.11 Gy min−1 dose rates in the range of 0.05–10 kGy. At fixed irradiation dose the TL efficiency increases as the dose rate increases. As the dose increases the peak temperature at the maximum intensity of the TL glow curve is shifted about 10 K degrees toward the lower temperature side. The TL glow curve shape resembles first-order kinetics for low-radiation doses and second-order kinetics for higher doses. Linear dose behavior was found for doses below 200 Gy and supralinear for higher doses; respectively, with a significant dependence on the dose rate, reaching saturation for higher doses around 2.0 kGy. Due to the dose rate dependence of the TL properties of the CVD diamond sample, it is necessary to take these effects into consideration for dosimetric applications involving synthetic CVD diamond.

Comparative investigations of TL and OSL in KCI:Eu2+ crystals irradiated with UV and X-rays

Abstract We present thermoluminescence (TL) glow curves and optical stimulated luminescence (OSL) response from both KCl:Eu2+ crystals irradiated with soft X-rays (20 KV, 80 μA) and ultraviolet light (230 nm). Two situations take place. First, we observed that for long time F-light bleaching (560 nm) the typical TL glow curve of X-rays irradiated KCl:Eu2+ resembles the TL glow curve of UV-irradiated samples. Second, along with OSL measurements, we have performed a thermal bleaching and we have addressed F and Fz participation in OSL. These results provide us a supportable correlation between F and Fz as responsible centers for OSL and TL processes.

Potassium Halide Detectors: Novel Results and Applications

We present a review of novel investigation results related with the thermoluminescent and dosimetric properties of detectors based on potassium halides doped with divalent europium, such as KCl:Eu2+, KBr:Eu2+ and the crystalline series KCl1–xBrx:Eu2+. We investigated both the existent defects in the crystals and those that are generated by radiation and their interaction, trapping and room-temperature recombination mechanisms in thermally stimulated light emission. The spectral response during the recombination stage was obtained through simultaneous measurements of temperature, emitted light intensity and emission wavelength by using an automated thermoluminescence system with optical fiber couplings and a diode array as detection device. In this manner, it was possible to identify the involved defects in the thermoluminescent processes. Finally, since all potassium halide crystals contain the isotope 40K (0.0117%) with a half-life of 1.28 × 109 years, a self-irradiation effect is produced with an equivalent irradiation dose of 4.9 μGy/h. Taking advantage of this self-irradiation effect, we develop a new and simple calibration method for thermoluminescent dosimeters, which has a marginal error of ≈2%. The shift in the measurements produced by this error is comparable with the obtained error from other sophisticated and expensive calibration methods. Even more, the self-irradiation phenomenon renders the possibility to make corrections in environmental radiation measurements, for including climatic effects and other external factors.