A. Mandowski

Semi-localized transitions model for thermoluminescence

A new model for thermoluminescence (TL) kinetics is presented, which is a natural generalization of the standard localized transition model. The model of semi-localized transitions (SLTs) allows trapped charge carriers to be excited to the conduction band. Analytic equations for SLTs are constructed using an enumeration technique which transforms concentrations of carriers to concentrations of states of localized trap–recombination centre pairs. Solving numerically the set of equations, we demonstrate some basic features of the SLT model. It is shown that SLT is able to produce so-called TL displacement peaks that were previously found in one-dimensional TL simulations.

Photoluminescence of gamma-, proton- and alpha-irradiated LiF detectors

Lithium fluoride (LiF), one of the most pervasive alkali halides in optical device research, is routinely used in optical data storage and radiation protection. LiF crystals may contain different aggregate defects produced by several types of ionizing radiation, with the number of defects being proportional to the cumulative radiation dose. Stimulation of irradiated LiF detectors by heating or with blue light causes thermoluminescence (TL) or photoluminescence (PL), respectively. We developed a new PL reader equipped with a blue light-emitting diode for stimulation and a Hamamatsu photomultiplier for registering green emissions, dedicated to examining LiF detectors as well as more broadly investigating TL/PL emission from standard LiF detectors irradiated with gamma rays, 60 MeV protons and alpha particles. The results confirmed very high efficiency PL signal from alpha-irradiated LiF detectors corresponding to their low efficiency after gamma irradiation, and vice versa for TL readout. Combining the TL and PL readouts permits us to discriminate between how different kinds of radiation affect efficiency in LiF detectors.

Thermoluminescent Properties of Undoped and Ce-Doped Lutetium Orthosilicate and Yttrium Orthosilicate Single Crystals and Single Crystalline Films Scintillators

In this work the comparative analysis of thermoluminescent properties of undoped and Ce-doped single crystals (SC) and single crystalline films (SCF) of Lu₂SiO₅ (LSO) and Y₂SiO₅ (YSO) orthosilicates were performed. The SC samples were prepared with the Czochralski method, and SCF were grown by the liquid phase epitaxy technique. We show that such different methods of material preparation resulted in different thermoluminescent properties of undoped and Ce³⁺ doped LSO and YSO SC and SCF caused by the presence host defects (first of all, oxygen vacancies) as trapping centers in SC and formation of Pb²⁺-Ce⁴⁺ pair centers in SCF.

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 Kłodawa 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.

Spectrally resolved thermoluminescence of pure potassium chloride crystals

Alkali halides are wide band gap dielectric materials, which are very important for luminescence dosimetry. Nevertheless, only some of them were studied comprehensively. Potassium chloride (KCl) is alkali halide material, which shows pronounced thermoluminescence (TL) and optically stimulated luminescence (OSL). The material occurs also in natural mineral form as sylvite (or sylvine). This paper presents results of spectrally resolved thermoluminescence (SR-TL) measurements of pure KCl crystals in temperature range 300-550K for various doses of beta irradiation. Four emission bands were found relating to different recombination centers in this material. TL curves relating to these centers have different shape. It indicates that recombination centers are not filled concurrently.

Thermoluminescence properties of LSO:Ce and YSO:Ce films grown from PbO and Bi 2 O 3 fluxes

The comparative analysis of thermoluminescent properties of Ce-doped single crystalline films (SCF) of Lu₂SiO₅ (LSO) and Y₂SiO₅ (YSO) orthosilicates, grown by LPE method from two different (PbO and Bi₂O₃) fluxes were performed in this work. We show that the difference in technology of material preparation resulted in different thermoluminescent behaviors of LSO:Ce and YSO:Ce SCFs caused by the formation of the Pb²⁺-Ce⁴⁺ and Bi³⁺-Ce³⁺ centers in them.

TSL properties of A 2 SiO 5 and A 2 SiO 5 :Ce (A=Y, Lu) single crystals and single crystalline films

In this work the comparative analysis of the thermostimulated luminescence (TSL) properties of various silicate crystals (undoped and Ce-doped Y<inf>2</inf>SiO<inf>5</inf> (YSO) and Lu<inf>2</inf>SiO<inf>5</inf> (LSO) single crystals (SC) and single crystalline films (SCF)) under excitation by alpha and beta particles, gamma quanta and daily light has been performed.