2024 - NISTI, MARCELO; SAUEIA, CATIA; DAMATTO, SANDRA; MADUAR, MARCELO

Biota and human beings are exposed to naturally occurring radionuclides present in several natural resources [1]. Phosphogypsum (PG) is classified as a Naturally Occurring Radioactive Material (NORM) residue of the phosphate fertilizer industry. PG residue presents in its composition radionuclides of the natural U and Th decay series and stored in stacks by the phosphate industries, which can represent risks to environment and human from the radiological protection point of view, such as: atmospheric contamination, pollution of groundwater, trace elements and radionuclides, radon emanation, inhalation of dust and direct exposure to gamma radiation. Some possible applications of this residue are soil conditioners, resulting in an increase of agriculture productivity, or building materials [2]. The Brazilian regulatory body ruled that PG would only be permitted for use in agriculture if 226Ra and 228Ra activity concentrations do not exceed 1 Bq g-1, for each radionuclide [3]. On the other hand, the safe reuse of PG residue avoids depletion of non-renewable resources, decreases the stacks and consequent reduces the possible environmental impact. Also adds value to PG, considering the principles of sustainable development and the principle of the circular economy. This study's aims were to evaluate the estimated radiation doses in biotas and humans considering two scenarios: PG stack and application of PG in agriculture, using the ERICA Tool 2.0 [4] and NORMALYSA Tool 2.0 [5]. For the PG stack, estimated radiation doses (external and internal) to the worker and biota around the stack were evaluated. In the agriculture (soil amended with PG residue), the estimated radiation doses to the farmer (external and internal), consumers of agricultural products (internal) and biota (external and internal) were evaluated. In this paper, one application per year of PG residue in the soil and the maximum value of the Brazilian regulatory were considered.

2024 - ANTONIO, PATRICIA L.; SILVA, ANDERSON M.B.; GONCALVES, JOSEMARY A.C.; BUENO, CARMEN C.; CALDAS, LINDA V.E.

The photo-transfer effect in a phosphor material occurs when displacement of the electrons occurs from deep traps to the shallow traps after its lightning. To verify this effect, the material must be irradiated, thermally treated and exposed to light; after these three phases, its signal is evaluated. LiF:Mg,Ti, commercialized as TLD-100, is the most studied dosimetric material for different applications at the radiation dosimetry research field. The photo-transfer phenomenon can be observed in a luminescent response of certain materials; the phototransferred thermoluminescence (PTTL) and the phototransferred optically stimulated luminescence (PTOSL) are two techniques which allow the study of this effect [1,2]. The primary objective of this work is to verify the presence of PTTL and PTOSL responses of the LiF:Mg,Ti (TLD- 100) dosimeters with irradiation in a 60Co beam and illumination with light-emitting diode (LEDs), and the possibility of application of them in high-dose dosimetry. The luminescence of LiF:Mg,Ti dosimeters was analyzed according to the three steps: 1) TL and OSL after irradiation; 2) TL and OSL after irradiation and post-irradiation thermal treatment (PITT); and 3) PTTL and PTOSL after irradiation, PITT and lightning with LEDs. The irradiations were performed using a 60Co source (absorbed dose of 1 kGy), and all the measurements were taken using the Risø reader system, model TL/OSL-DA-20. For the first step, the TL response occurred with a most intense emission dosimetric peak at about 260ºC with intensity of about 1.5x105 counts; for the OSL response, the beginning of the decay occurred at about 3.2x104 counts. After PITT (second step), the previous TL dosimetric peak did not remain visible, indicating that the traps corresponding to this peak were emptied; for the OSL case, there was not any type of decay, which shows that PITT caused the emission of electrons from traps related to the OSL signal. In the third step, it was possible to measure the PTTL response, because that initial peak, at about 260ºC, rised after lightning (in about 400 counts); the same occurred with the PTOSL response, since the initial signal of the decay increased compared to that of the second stage, and in this third step the result was about 500 counts. The data revealed the presence of photo-transfer effect in the both PTTL and PTOSL responses, and the possibility of using this material with these techniques in high-dose dosimetry. In order to improve this study, giving more consistency to the results, new experimental analyses will be undertaken, as the response in function of the irradiance, wavelength and illumination time.

2024 - LALIC, SUSANA de S.; ALVARENGA, TALLYSON S.; CALDAS, LINDA V.E.; D'ERRICO, FRANCESCO

In this work, we discuss advancements in neutron albedo dosimetry. While personal dosimetry for X, gamma, and beta radiation is straightforward, challenges arise in mixed-field environments involving neutrons and gamma rays, such as nuclear plants, accelerators, and space flights [1]. Neutrons exhibit a wide energy spectrum, ranging from thermal neutrons (~0.025 eV) to fast neutrons exceeding hundreds of MeV [2]. A key aspect of neutron dosimetry is determining the 'dose equivalent', which accounts for the neutron's 'quality factor', dependent on its energy [3]. Neutrons, high linear energy transfer (LET) particles, ionize more densely than electrons. Biological effectiveness, indicated by the quality factor (wR), is 2.5 to 20 times higher for neutrons than photons, complicating mixed-field dosimetry [3]. Neutrons interact with atomic nuclei through several processes, with cross-sections varying with neutron energy and resonances in specific energy ranges [4]. Materials such as 6Li and 10B have notable (n,a) cross-sections for thermal neutrons [4]. Since the 1970s, various neutron dosimeters have been developed [1]. However, personal neutron dosimetry faces challenges due to strong gamma fields, wide-ranging neutron energies, and the difficulty of detecting fast neutrons, which pose higher harm per unit of energy deposited than thermal neutrons [1]. Effective detection mechanisms must differentiate against low-LET radiations and may incorporate materials susceptible to neutrons, such as 6Li or 10B, with high cross-sections [2]. Thermal neutrons are commonly detected using (n,a) reactions. Albedo dosimetry is widely used for personal neutron dosimetry [5]. An albedo dosimeter measures thermal neutron fluence emitted from the body after exposure to thermal and intermediate neutrons, moderated and scattered by the body [5]. Detection of reflected thermal neutrons (albedo) uses pairs of thermoluminescent dosimeters (TLDs), 6LiF (highly sensitive to thermal neutrons) and 7LiF (insensitive to neutrons but sensitive to photons) [5,6]. Accurate calibration provides reasonable estimates of fast neutron doses. Effective albedo dosimeters require removing incident thermal neutrons from the radiation field, often achieved by neutron-capturing materials over TLDs [5,6]. Dosimeters are typically worn over the chest; however, lung tissue's lower density makes it more permeable to neutrons, yielding fewer albedo neutrons for detection. A critical challenge in albedo dosimetry is detecting very fast neutrons, which penetrate deeply and may not reflect back to the detector, potentially underestimating measured doses.This study aims to enhance neutron albedo dosimetry by evaluating measurement protocols. We investigated pairs of TLDs sensitive and insensitive to thermal neutrons across different energies and fluxes in a standard chest phantom, adjusting for dosimeter placement effects. We combined dosimeters for neutron transmission and reflection, assessing response variations to energy changes and neutron fluxes. Our presentation will highlight the differences in TLD responses and their implications for accurate neutron dose assessment.

2024 - GONCALVES, JOSEMARY A.C.; ANTONIO, PATRICIA de L.; SANTOS, LEONARDO C. dos; POTIENS, MARIA da P.A.; CALDAS, LINDA V.E.; BUENO, CARMEN C.

Silicon diodes have been used as relative dosimeters in radiation protection, medical imaging, and radiation therapy. Usually, the diode operates in the short-circuit current mode and remains unbiased to minimize the dark current contribution to the radiation-induced current signal. The dosimetric parameter is the net output current linearly dependent on the dose rate within certain limits. The corresponding collected charge (obtained as the integral of the current signal) is proportional to the dose. Many articles in the literature report several advantages of diode-based dosimeters despite a key drawback regarding their sensitivity decay with increasing accumulated doses. This issue has been tackled by developing devices with different geometries or tailoring the impurity density in the silicon bulk grown through distinct techniques. A combined approach of these strategies outcomes the epitaxial diode under investigation in this work. It has a thin n-type epitaxial layer (50 μm, 25 mm2) grown on a 300 μm Cz Si substrate. The p+-n junction is provided by a highly doped p-type silicon layer (@ 1 μm) on the front side of the diode. This structure, which keeps the active volume constant with a tiny entrance window and negligible dark current, opens up potential applications for radiation protection dosimetry. The diode is housed in a light-tight polymethylmethacrylate probe with an entrance window covered by a thin (8.3 mg/cm2) black paperboard. The planar pad (p+) signal electrode is directly connected to the input of a Keithley® 6517B electrometer with the backplane n+ grounded and the guard ring structure floating. The current measurements are performed in the shortcircuit mode without externally applied voltage to the diode. The sensitivity, repeatability, reproducibility, dose-response linearity, and directional response are evaluated for N60, N80, N100, and N150 beam qualities [1]. Irradiations are performed with a Pantak-Seifert 160HS Isovolt X-ray generator previously standardized by a Radcal 10X5-180 ionization chamber calibrated at the PTB. The probe is positioned at the center of a circular irradiation field of 42 cm diameter, with 99% homogeneity, at 250 cm from the X-ray tube (focal spot). The current signals produced by photon beams of different qualities (60 -150 kV) are stable and characterized by repeatabilities better than 5%. The dose-responses curves are also linear but slightly dependent on the photon energy. The angular dependence and long-term stability parameters remain to be investigated. To give theoretical support to the data sensitivity calculations, assuming the diode is a thin abrupt junction, are underway.