Optically stimulated luminescence decay and dosimetric properties of cerium-doped potassium sulfate phosphor.

Optically stimulated luminescence (OSL) is used for dating in archaeology and geology, and in dosimetry of ionizing radiation. Some crystalline wide band-gap insulators may be used as OSL radiation detectors. Recently it was found that cerium-doped potassium sulfate crystals have promising luminescence properties. This paper presents some OSL properties of K2 SO4 :Ce crystals that were prepared in the form of pellets. The crystals exhibited a strong luminescence signal, good measurement repeatability, and high sensitivity for ionizing radiation. Best results were obtained after annealing at 1000°C. Dose-dependence characteristics were determined in the range 10 mGy to 11.2 Gy. OSL decay curves consisted of several components. Fast and slow OSL components of the phosphor had different properties. The slow component was quite stable and obeyed power law dependence. It decayed in the 55 days after irradiation. Its luminescence properties depended on sample preparation and the storage time after irradiation.

On the Applicability of Camera Lens Protectors in Emergency Luminescence Dosimetry.

In this work, the optically stimulated luminescence (OSL) properties of camera lens protectors and their potential use in emergency dosimetry were investigated. Camera lens protectors can be attached to mobile phones, which are commonly carried by individuals and may be useful in estimating an emergency dose. The presented results confirm the great potential of this type of glass material for dose determination. The glass protectors exhibit advantageous properties, such as linear dose dependence in the range of at least 0.6-10 Gy, minimum detectable dose at the level of tens of mGy, and good measurement repeatability for samples of the same type. Significant fading during the first day after exposure is an undesirable feature of tested glass. Nevertheless, the application of the correction for fading shows promising results in the dose recovery process.

Investigation on thermally assisted optically stimulated luminescence (TA - OSL) signal in various sodium chloride samples.

Sodium chloride (NaCl) is a phosphor with potential significance in retrospective dosimetry and geological dating. NaCl has been extensively studied for practical use in OSL dosimetry, however, the exact mechanism of the OSL emission is not well explained. This work attempts to extend the information on NaCl luminescent properties by establishing the occurrence of very deep traps in NaCl using the thermally assisted OSL (TA - OSL) method. The studied material was sodium chloride in different forms: halite minerals from Klodawa salt mine in Poland and NaCl in chemically pure form. The isothermal TA - OSL signal was measured at various temperatures between 25 °C and 280 °C after a prior irradiation and TL erasing of shallow and main traps. The appearance of a strong TA - OSL signal indicates the occurrence of very deep traps in all forms of investigated salt. The temperature dependence of TA - OSL was determined and the activation energy for thermal assistance corresponding to deep traps in NaCl was estimated. For selected temperatures of TA - OSL readout (200 °C and 280 °C) the dose response was examined in wide dose range (1-1000 Gy). Sublinearity was found in different dose range depending on the type of samples.

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.

Topology-dependent thermoluminescence kinetics.

Standard kinetic models for thermoluminescence (TL) relate to the simple trap model (STM) and the model of localised transitions (LT). This paper presents a review of TL properties in various spatially correlated systems (SCS), which span the two limiting cases. A classification of kinetic models for SCS is proposed. Numerical results are presented for the isolated clusters model (IC) and the interacting one-dimensional (1-D) and three-dimensional (3-D) systems. For these systems an influence of external electric field on TL is demonstrated. Analytical formulation for the IC model is possible using trap structural functions (TSFs). To calculate the TSFs (analytically or numerically) it is convenient to use their structural and symmetry properties. Analytical equations are presented also for the semi-localised transitions (SLT) model, which is a generalised version of LT. It is shown that in some cases the SLT model leads to the cascade detrapping (CD) phenomenon. The CD mechanism produces very narrow TL peaks that are apparently well described by the first order kinetics with very high frequency factors and very high activation energies.

Calculation and properties of trap structural functions for various spatially correlated systems.

Thermoluminescence (TL) kinetics in spatially inhomogeneous systems can be studied by various Monte Carlo algorithms. Recently, a new analytical approach was suggested for the isolated cluster model. The theory is based on the concept of trap structural functions (TSFs). TSFs depend solely on topological properties of solids. Therefore, knowing TSFs for traps and recombination centres it is possible to calculate TL for various parameters, e.g. different heating schemes and different energy configurations. This paper presents some properties and methods of calculation of TSFs. Structural character of TSFs is verified numerically.

Analysis of spectrally resolved thermoluminescence of LiF:Mg,Cu,P detectors by the surface fitting method using algorithm for unrestricted peak positions.

Recently developed surface fitting technique is a natural replacement for the widely used glow curve deconvolution (GCD) technique. Surface fitting can be applied for advanced spectrally resolved thermoluminescence (TL) measurements. It combines both kinetic and emission-band analysis. Owing to greater number of parameters and data points the algorithm is more time-consuming than usual GCD. However, it offers greater reliability in determination of trap parameters. This is especially important for spectrally resolved measurements that are usually performed at low-light level conditions. This paper demonstrates an application of the surface fitting method to the analysis of TL-3D data from LiF:Mg,Cu,P detectors. The spectra were analysed using two different variants of surface fitting--for restricted and unrestricted peak positions.