J. Marcazzó

Isothermal decay method for analysis of thermoluminescence: a new approach

A variant of the isothermal decay method to determine the trap activation energy E in thermoluminescence is put forward. The area under the phosphorescence curve recorded at different temperatures is employed to calculate E by re-arranging the original equations by Randall–Wilkins, Garlick–Gibson and May–Partridge. As an example, the proposed method is applied to calculate E for a real phosphor and compared with other well-established methods.

A Tissue-Equivalent Radioluminescent Fiberoptic Probe for In-Vivo Dosimetry Based on Mn-Doped Lithium Tetraborate

The fiberoptic (FO) dosimetry concept, which relies on the assessment of dose by measuring the intensity of the light emitted by a tiny sample of a radioluminescent (RL) compound coupled to an optical fiber cable, is gaining importance as a promising dosimetry technique for in-vivo dosimetry. In this work the design, construction and test of a tissue-equivalent RL probe is described. The intensity of the RL emission of Mn-doped Lithium Tetraborate samples during irradiation is used as an estimate of the relative dose. The influence of spurious luminescence is discussed and a removing method based on simple optical filtering is implemented. Finally, the response of the probe in the context of a typical depth-dose experiment in a 60Co radiotherapy facility is analyzed and compared to the response of a standard ionizing chamber.

Radioluminescence of red-emitting Eu-doped phosphors for fiberoptic dosimetry

Fiberoptic dosimetry (FOD) technique has become an attractive method for real-time dosimetry. Al(2)O(3):Cis one of the most used radioluminescence materials for FOD due to its high efficiency but it presents the drawback of emitting in the spectral region, where spurious luminescence is also important. Optical filtering is the simplest technique to remove spurious luminescence, but is useful when red-emitting scintillators are employed. In this work, the feasibility of using red-emitting Eu-doped phosphors as FOD scintillators has been investigated.

Analysis of the main dosimetric peak of Al2O3:C compounds with a model of interacting traps.

The glow curve of Al2O3:C compounds has been analyzed by employing a model consisting of two active traps, thermally disconnected traps and one recombination centre. The analysis takes into account interaction among traps and the thermal quenching of the thermoluminescent emission.

CsTb2F7: an efficient radioluminescent material for fiberoptic radiation detection

In this article, the feasibility of using CsTb2F7 crystals as scintillating detectors to build radioluminescent fiberoptic dosimetry (FOD) probes has been investigated for the first time. The radioluminescence (RL) efficiency of this compound has been found to be more than twice as high as that of commercial Al2O3:C detectors under excitation with gamma radiation from a 60Co source. Additionally, the intensity of the RL signal shows no dependence on the accumulated dose. Both RL and photoluminescence spectra are nearly identical, showing emission bands at 490 and 550 nm and a minor band at 600 nm, which are compatible with the characteristic emission of Tb3+. In accordance with these results, stoichiometric terbium fluoride seems to be a promising material for use as an RL sensor for FOD in radiation medicine.

Synthesis and stimulated luminescence property of Zn(BO2)2:Tb3+

Zinc borate, Zn(BO2)2, doped with different concentrations of terbium (0.5-8mol%) was synthesized and polycrystalline samples were characterized by Scanning Electron Microscopy and X-Ray Diffraction. The Zn(BO2)2 was formed in the pure samples sintered at 750 and 800°C which has the body centered cubic structure, and a ZnB4O7 primitive orthorhombic phase was present. The thermoluminescent intensity was dependents on the thermal treatment (250-500°C) and also on the impurity concentration. The linear dose-response was obtained between 0.022-27.7Gy and 0.5-50Gy when the samples were exposed to beta and gamma radiation, respectively. The complex structure of the glow curves was analyzed by the Computerized Glow Curve Deconvolution method. The kinetics parameters were calculated assuming the general order kinetics model describing accurately the TL process. The glow curves of Tb3+-doped zinc borate phosphor were well deconvolved by six glow peaks. Zinc borate with 8mol% of impurity concentration exhibited an intense radioluminescent emission. The radioluminescent spectra show their maximum bands at 370, 490, 545 and 700nm related to the terbium ion in the zinc borate. These obtained results suggest that the terbium doped zinc borate is a promising phosphor for use in radiation dosimetry because of its high TL sensitivity to the ionizing radiation.

Performance of ZnSe(Te) as fiberoptic dosimetry detector.

Fiberoptic dosimetry (FOD) is an experimental technique suitable for in-vivo, real time dosimetry in radiotherapy treatments. FOD relies on using a small scintillator coupled to one end of a long optical fiber. The scintillator is placed at the point where the dose rate is to be determined whereas a light detector at the other end of the fiber measures the intensity of the radioluminescence emitted by the scintillator. One of the problems hampering the straightforward application of this technique in clinics is the presence of Cherenkov radiation generated in the fiber by the ionizing radiation, which adds to the scintillating light and introduces a bias in the dose measurement. Since Cherenkov radiation is more important in short wavelength range of the visible spectrum, using red-emitting scintillators as FOD detectors permits to reduce the Cherenkov contribution by using optical filters. In this work, the performance of red-emitting tellurium-doped zinc selenide crystal as FOD detector is evaluated and compared to the response of an ion-chamber.

Luminescence detection and dose assessment of irradiated Yerba Mate (Ilex paraguariensis) tea leaves.

Imported commercial samples of Yerba Mate (Ilex paraguariensis) tea leaves were characterized by thermoluminescence (TL) and photoluminescence (PSL) physical methods. Samples of Yerba Mate were irradiated between 0.5-50Gy and 20Gy-5kGy gamma doses by using two different dose rates from (60)Co irradiators. The Electron Dispersive Analysis (EDS) shows that the inorganic fraction is mainly composed by quartz and Ca-feldspars minerals. These polyminerals show a good sensitivity to gamma radiation and to UV light (530nm). Linear dose-response curves were obtained between 0.5 and 12Gy at low dose-rate, and with 20 to 500Gy at high dose-rate of gamma radiation. At higher doses (600Gy) an apparent slow saturation effect was observed. Low fading of the TL signal was found. The detection limits of TL and PSL are 6Gy and 300Gy, respectively. Results show that luminescence emission (TL and PSL) is a reliable method for detection of irradiation Yerba Mate.

A novel algorithm to solve the differential equation describing the non-interactive multiple-trap system model in thermoluminescence

ABSTRACT The analysis of glow curves in thermoluminescence requires finding a closed expression for the light emitted as a function of the temperature and the parameters characterizing trap and recombination centers. Since it is not possible to derive a closed expression from the set of coupled differential equations describing the thermoluminescence phenomenon, approximations are made even for the simplest models. All of them resort to an approximation known as the quasi-equilibrium approximation (QE), and to further approximations. In this article, an algorithm is reported that permit the derivation of a closed expression for the emitted light for the model known as the non-interactive multi-trap system (NMTS) model by resorting only to the QE approximation. It is shown that the integration of the first order differential equation related to the NMTS model can be replaced by finding the roots of an analytical expression.

Optically stimulated luminescence of natural NaCl mineral from Dead Sea exposed to gamma radiation

In this work, the continuous wave - optically stimulated luminescence (CW-OSL) emissions of natural salt minerals, collected from Dead Sea in summer of 2015, were studied. The CW-OSL dose response of natural salt showed a linear range between 0.5Gy and 10Gy of gamma radiation of 60Co. Samples exposed at 3Gy exhibited good repeatability with a variation coefficient of 4.6%. The CW-OSL response as function of the preheating temperature (50-250°C) was analyzed. An increase of 15% of the CW-OSL response was observed in NaCl samples during storage period of 336h. The results showed that the natural Dead Sea salt minerals could be applied as natural dosimeter of gamma radiation.