S.O. Souza

Thermoluminescent properties studies of spodumene lilac sample to dosimetric applications

This work investigates the thermoluminescent (TL) dosimetric properties in natural spodumene, LiAlSi2O6, called kunzite, from Minas Gerais State, Brazil. The mineralogical and chemical composition of this material was identified by means X-ray fluorescence and X-ray diffraction. Some dosimetric properties were studied, such as thermoluminescent emission curves as function of gamma dose. The glow curves of annealed kunzite presented two very intense TL peaks at 215 ?C (peak II) and 350 ?C (peak III), after gamma irradiation, being both of first kinetic order. These two most prominent peaks analyzed do not presented a linear growth in the range of 50 to 5000 Gy in the range of doses studied. The peak II also presented a very short calculated lifetime, which means it is hardly can be used in dosimetry, while the peak III has a longer lifetime and could be used in some applications for high doses dosimetry.

Synthesis of MgB4O7 and Li2B4O7 crystals by proteic sol-gel and Pechini methods

Magnesium-tetraborates and lithium-tetraborates are excellent detectors for ionizing radiation. However, manufacturing these crystalline structures is challenging as it involves multi-step chemical processes and toxic reagents. Over the past decades, alternative production methods for crystals have been studied aiming at lowering production costs and environmental impact and at increasing production yield and reproducibility. Among these is the Pechini method, based on the formation of polymer chains containing uniformly distributed metal ions. Another method is a modified proteic sol–gel process using edible gelatins or coconut water instead of the alkoxides used in conventional processes. In this work, we searched optimal conditions for the synthesis of dosimetry-grade MgB4O7 and Li2B4O7 crystals with the Pechini and the proteic sol–gel methods. The crystal phases were characterized by X-ray diffraction and by thermal analyses. We determined that MgB4O7 can be synthesized either by calcination of the reagents at 900 °C for 2 h with the sol–gel approach, or at just 800 °C for 2 h with the Pechini method. Single-phase Li2B4O7 can be synthesized either by calcination of the reagents at 650 °C for 2 h with the sol–gel approach, or at just 600 °C for 2 h with the Pechini method. Our synthesis times and temperatures are lower than those reported in the literature, which reduces significantly production costs and environmental impact.Graphical Abstract

Thermoluminescent dose reconstruction using quartz extracted from unfired buildings

The use of thermoluminescence (TL) is very useful for application in retrospective dosimetry, that is, for inference of the dose of radiation undergone for some material. The calculation of the lifetime of TL peaks can help to clarify which TL intensity is due to the dose of environmental radiation and which is proceeding from the accident with radiation. In this work, the kinetic order (b), activation energy (Et) and the frequency factor (s) were obtained for quartz samples that had been extracted from unfired buldings. It was observed the occurrence of peaks in the 150 °C – 250 °C range, that corresponds to a range commonly used in retrospective dosimetry, due to its shorter lifetime when compared with TL geological signal. The analysis of the peaks was done through several well known methods, namely the peak shape (PS), curve fitting (CF) and heating rate (HR) methods. To confirm the structure of the sample, additional X-ray diffraction was made.

Optimization of oncological 18F‐FDG PET/CT imaging based on a multiparameter analysis

PURPOSE This paper describes a method to achieve consistent clinical image quality in (18)F-FDG scans accounting for patient habitus, dose regimen, image acquisition, and processing techniques. METHODS Oncological PET/CT scan data for 58 subjects were evaluated retrospectively to derive analytical curves that predict image quality. Patient noise equivalent count rate and coefficient of variation (CV) were used as metrics in their analysis. Optimized acquisition protocols were identified and prospectively applied to 179 subjects. RESULTS The adoption of different schemes for three body mass ranges (<60 kg, 60-90 kg, >90 kg) allows improved image quality with both point spread function and ordered-subsets expectation maximization-3D reconstruction methods. The application of this methodology showed that CV improved significantly (p < 0.0001) in clinical practice. CONCLUSIONS Consistent oncological PET/CT image quality on a high-performance scanner was achieved from an analysis of the relations existing between dose regimen, patient habitus, acquisition, and processing techniques. The proposed methodology may be used by PET/CT centers to develop protocols to standardize PET/CT imaging procedures and achieve better patient management and cost-effective operations.

Analysis of the response of innovative neutron detectors with monoenergetic neutron beams

Various neutron detectors are currently under development at the University of Pisa. The response of these devices is investigated using monoenergetic neutron beams produced at the CN accelerator of INFN Legnaro National Laboratories with thin lithium target bombarded by protons at different energies, exploiting the 7Li(p,n)7Be reaction.