OSL PROPERTIES IN VARIOUS FORMS OF KCl AND NaCl SAMPLES AFTER EXPOSURE TO IONIZING RADIATION.

The aim of this work was to investigate the optically-stimulated luminescence (OSL) properties of potassium chloride (KCl) and its potential use in radiation dosimetry. The optimal condition for OSL readout with blue light stimulation were designated using a commercially available Risø TL/OSL reader. KCl was studied in three sample forms: crystals, powder and pellets. The following OSL characteristics were determined: signal reproducibility, OSL measurement-induced sensitivity changes, temperature dependence of OSL and signal stability over time. The results show a high reproducibility of KCl samples and strong sensitivity changes, which can be corrected for by using a test-dose. The long-term OSL studies confirmed the occurrence of both inverse fading and fading phenomena in KCl. In addition, a comparison with corresponding measurements using sodium chloride (NaCl) were carried out. Although it was confirmed that NaCl is more suitable for dosimetry, there might be benefits of combining NaCl with KCl for more accurate absorbed dose determinations.

Radiation hardness of the storage phosphor europium doped potassium chloride for radiation therapy dosimetry.

PURPOSE: An important property of a reusable dosimeter is its radiation hardness, that is, its ability to retain its dosimetric merits after irradiation. The radiation hardness of europium doped potassium chloride (KC1:Eu2+), a storage phosphor material recently proposed for radiation therapy dosimetry, is examined in this study. METHODS: Pellet-style KCl:Eu2+ dosimeters, 6 mm in diameter, and 1 mm thick, were fabricated in-house for this study. The pellets were exposed by a 6 MV photon beam or in a high dose rate 137Cs irradiator. Macroscopic properties, such as radiation sensitivity, dose response linearity, and signal stability, were studied with a laboratory photostimulated luminescence (PSL) readout system. Since phosphor performance is related to the state of the storage centers and the activator, Eu2+, in the host lattice, spectroscopic and temporal measurements were carried out in order to explore radiation-induced changes at the microscopic level. RESULTS: KCl:Eu2+ dosimeters retained approximately 90% of their initial signal strength after a 5000 Gy dose history. Dose response was initially supralinear over the dose range of 100-700 cGy but became linear after 60 Gy. Linearity did not change significantly in the 0-5000 Gy dose history spanned in this study. Annealing high dose history chips resulted in a return of supralinearity and a recovery of sensitivity. There were no significant changes in the PSL stimulation spectra, PSL emission spectra, photoluminescence spectra, or luminescence lifetime, indicating that the PSL signal process remains intact after irradiation but at a reduced efficiency due to reparable radiation-induced perturbations in the crystal lattice. CONCLUSIONS: Systematic studies of KCl:Eu2+ material are important for understanding how the material can be optimized for radiation therapy dosimetry purposes. The data presented here indicate that KCl:Eu2+ exhibits strong radiation hardness and lends support for further investigations of this novel material.

Theoretical and empirical investigations of KCl : Eu2+ for nearly water-equivalent radiotherapy dosimetry.

PURPOSE: The low effective atomic number, reusability, and other computed radiography-related advantages make europium doped potassium chloride (KCl : Eu2+) a promising dosimetry material. The purpose of this study is to model KCl : Eu2+ point dosimeters with a Monte Carlo (MC) method and, using this model, to investigate the dose responses of two-dimensional (2D) KCl : Eu2+ storage phosphor films (SPFs). METHODS: KCl : Eu2+ point dosimeters were irradiated using a 6 MV beam at four depths (5-20 cm) for each of five square field sizes (5 x 5-25 x 25 cm2). The dose measured by KCl : Eu2+ was compared to that measured by an ionization chamber to obtain the magnitude of energy dependent dose measurement artifact. The measurements were simulated using DOSXYZnrc with phase space files generated by BEAMnrcMP. Simulations were also performed for KCl : Eu2+ films with thicknesses ranging from 1 microm to 1 mm. The work function of the prototype KCl : Eu2+ material was determined by comparing the sensitivity of a 150 microm thick KCl : Eu2+ film to a commercial BaFBr0.85 I0.15 : Eu(2+)-based SPF with a known work function. The work function was then used to estimate the sensitivity of a 1 microm thick KCl : Eu2+ film. RESULTS: The simulated dose responses of prototype KCl : Eu2+ point dosimeters agree well with measurement data acquired by irradiating the dosimeters in the 6 MV beam with varying field size and depth. Furthermore, simulations with films demonstrate that an ultrathin KCl : Eu2+ film with thickness of the order of 1 microm would have nearly water-equivalent dose response. The simulation results can be understood using classic cavity theories. Finally, preliminary experiments and theoretical calculations show that ultrathin KCl : Eu2+ film could provide excellent signal in a 1 cGy dose-to-water irradiation. CONCLUSIONS: In conclusion, the authors demonstrate that KCl : Eu(2+)-based dosimeters can be accurately modeled by a MC method and that 2D KCl : Eu2+ films of the order of 1 microm thick would have minimal energy dependence. The data support the future research and development of a KCl : Eu2+ storage phosphor-based system for quantitative, high-resolution multidimensional radiation therapy dosimetry.

Comparative study on mechanoluminescence of irradiated and non-irradiated ionic crystals.

Effect of surrounding gas on mechanoluminescence (ML) of non-irradiated KCl:Ca2+ and X-ray irradiated one has been investigated in order to clarify the ML due to dislocation movement. For both samples, the ML appears only in the narrow pressure range from 10 to 10(3) Pa with a peak at 133 Pa. Emission spectrum of ML for both samples in Ne gas has indicated a prominent peak at 580 nm that coincides with a strong line of Ne gas. Above results indicate that the observed ML is caused by electric discharge at the crystal surface. Discussion is also made on the effect of Ca2+ on both the ML intensity and the charges carried with dislocations.

Thermoluminescence response of new KCl(X)Br(1-X):EuCl3 sintered phosphors exposed to beta and gamma radiation.

Alkali halides crystals have been the subject of intense research for an understanding of their radiation-induced defects and luminescence properties. They exhibit noteworthy thermoluminescence (TL) properties when exposed to ionising radiation. Currently, these materials are grown employing expensive and rather complicated techniques. In this work, the results on the TL properties of new alkali halides phosphors fabricated by a simple and inexpensive procedure are presented. The samples were made by mixing KCl, KBr and EuCl3 salts, and compressing them at a pressure of 3.2 x 10(7) Pa during 3 min, followed by sintering at 700 degrees C during 24 h under air atmosphere. The dosimetric response of the samples showed an increase with radiation dose in the 1.5-20.0 Gy dose range for beta and gamma radiation. The TL glow curves in sintered samples presented significant differences in their peak structures compared with monocrystalline samples, indicating that the nature of the trapping states and the recombination mechanisms may be different.

Thermoluminescence behaviour of KCL(1-x)Br(x):Pb2+ exposed to gamma radiation.

The thermoluminescence (TL) behaviour of solid solutions of lead doped KCl(1-x)Br(x) (X = 0.02, 0.35, 0.50, 0.65, 0.85, 1) mixed crystals exposed to gamma radiation at different doses from 60Co is reported. The TL glow curves of KCl(1-x)Br(x):Pb2+ crystal exposed in the range of 0-140 Gy is strongly dependent on composition X. The maximum temperature of the main TL glow peak was found to shift towards lower temperatures as composition X increased and a significant enhancement of the TL efficiency in KCl(1-x)Br(x):Pb2+ was found for X = 0.50 which is attributed to an increase in the vacancy concentration of the mixed halides at middle composition. The participation of the F-centre in the TL phenomenon particularly related to the main TL glow peak observed in mixed samples was also confirmed.

Study of the phototransferred thermoluminescence in KCl:Eu2+ phosphors.

The phototransferred thermoluminescence (PITL) processes play an important role in the optical stimulated luminescence (OSL) and thermoluminescence (TL) dosimetric properties in KCl:Eu2+ crystals. In the present work, experimental evidence is presented about the participation of F and Fz centres in the associated recombination luminescence mechanisms involved with all three phenomena. An analysis of the TL glow curve of KCl:Eu2+ exposed to X ray ionising radiation shows three main thermoluminescence peaks around 370, 390 and 470 K. The 470 K highest intensity peak, considered the dosimetric peak due to its low fading and linear dose behaviour, is strongly correlated to the F and Fz centres. Through optical absorption spectra measurements of an optically bleached specimen, it was found that a minimum occurs at 560 nm, coinciding with the F centre band in KCl:Eu2+. Moreover, the diminishing of the integrated TL 470 K peak intensity is also seen to have a minimum at 560 nm (F centres); it also happens simultaneously with an increase of the integrated TL peak associated to the Fz band. This supports the close relation of the F and Fz centres in the PTTL process in KCl:Eu2+.

Ultraviolet thermoluminscent dosimetry using high temperature peaks in KCl:Eu2+ crystals.

The thermoluminescence (TL) characteristics of KCl:Eu2+ irradiated with solar and monochromatic ultraviolet (UV) light have been investigated. The glow curves exhibit at least five TL peaks between room temperature and 673 K. The low temperature peaks (<500 K) are very sensitive to the UV radiation, but their intensities practically do not depend on the duration of solar irradiation and are determined by the ratio between the creation rate by UV and the bleaching rate by visible light. The high temperature 650 K peak is not so sensitive, but it is more stable under optical bleaching and its intensity increases supralinearly as exposure time increases. The creation spectrum of the 650 K peak presents a broad band with a maximum at 230 nm that extends in the long wavelength range at least up to 360 nm. The results obtained are discussed in relation to the development of a UV dosemeter with wavelength sensitivity dependence close to the action spectra of UV-related biological effects.

Thermoluminescence properties of KCl(1-X)KBrX:Pb2+ mixed crystals.

A study is presented of the thermoluminescence (TL) of phosphors based on potassium halides doped with divalent lead, such as KCl:Pb2+, KBr:Pb2+ and the crystalline series KCl(1-X)Br(X):Pb2+. The defects in the crystals generated by irradiation have been investigated as well as the trapping and room temperature recombination mechanisms. The samples were gamma irradiated to a dose of 10 kGy. The TL 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 fibre couplings and a diode array as a detection device. The TL emission is a broad band in the 350-600 nm range with a maximum strongly dependent upon the mixed composition.

Formation of thiosulfate [35S] by neutron irradiation of potassium chloride and preparation of elementary sulfur [35S].

Potassium chloride was subjected to various kinds of pretreatments and irradiated in a nuclear reactor. Irradiated potassium chloride was dissolved in deaerated aqueous solution of several sulfur-salts. A portion of the solution was chromatographed on a thin layer chromatographic plate and the distribution of 35S-chemical species was determined. Irradiation of potassium chloride degassed at 3x10(-4)Torr resulted in the formation of about 60% of 35S in the form of thiosulfate and remainder was distributed among sulfide, sulfate and elementary sulfur. Thiosulfate[35S] was converted to elementary sulfur[35S] first by reducing to hydrogen sulfide [35S] with nascent hydrogen and then by oxidizing the latter to elementary sulfur[35S] with hexacyanoferrate(III). Elementary sulfur[35S] was finally extracted into benzene. Radiochemically pure elementary sulfur[35S] could be produced by simple procedures with a yield of about 60%. Thiosulfate[35S] was decomposed with acid to elementary sulfur[35S] and sulfur[35S] dioxide. The former was separated by centrifuging and dispersed in boiling water to form colloidal suspension of elementary sulfur[35S]. Approximately 40% of 35S was recovered as colloid.