Comparison of dehydration systems in quality and chemical effects on sunflower seeds.

The present work investigates the quality and the chemical effects of dehydration, using a novel dehydration system based on an electromagnetic induction and low pressures technique, comparing it with the thermo-solar drying system. High oleic sunflower seeds, which are an important oil seed crop, were used due to the fact that they have a special place in the food industry. The seed samples were exposed to electromagnetic induction and low pressures by 0.5 and 1 h, then several chemical characterizations were carried out, in the electrophoresis study, it was found that most proteins in the hull were degraded or denatured, some of them were lost during the time in the thermosolar dryer while in kernel keeps 94.9% of the concentration in control proteins. Otherwise, the electromagnetic induction dryer did not lose the most of proteins in the kernel keeping 99.1% in 0.5 h and 98.4% in 1 h, just degrading its concentration. Germination viability results did not show changes after 0.5 h in the electromagnetic fields, but they decreased in 1 h from 66 to 40% until the thermosolar method fell to 24% in 4 h, both analysis results change proportionally with the treatment time and moisture content and the amount of the oxygen.

Development of a 3D printing process of bolus using BolusCM material for radiotherapy with electrons.

This work presents the optimized parameters of 3D printing for print bolus using BolusCM material. Printing parameters were selected of the homogeneity and absence of air gaps. The dosimetric features of printed bolus were measured with a plane-parallel ionization chamber and EBT3 radiochromic film. Measured features were compared with those estimated with Monte Carlo methods. BolusCM shows good characteristics to be used as bolus material in radiotherapy with electrons, where the printing process allows personalizing the bolus in function of patient characteristics. The material low-cost, the 3D printing and the dosimetric features are few of the advantages of using BolusCM material in radiotherapy with electrons in skin cancer treatment.

Bolus 3D printing for radiotherapy with conventional PLA, ABS and TPU filaments: Theoretical-experimental study.

A theoretical-experimental study of the interaction of electron beams with 3 filaments conventionally used for 3D printing is presented in this paper. Pieces of polylactic acid (PLA), acrylonitrile butadiene styrene (ABS) and thermoplastic polyurethane (TPU) are studied using Monte Carlo simulation with Geant4 and experimental measurements with plane-parallel ionization chambers and radiochromic films. Using different printing parameters and computed tomography, the presence of air gaps and the uniformity in the bolus density made with the different materials are evaluated. The main parameters in the Percentage Depth Dose (PDDs) are determined, the manufacturing process is standardized and the printing profiles are generated for each of the materials in order to obtain uniform attenuation characteristics in the pieces and improve adaptation to irregular anatomical areas.

Dosimetric analysis of graphitic carbon nitride quantum dots exposed to a gamma radiation for a low-dose applications.

In this study, graphitic carbon nitride quantum dots (g-C3N4QDs) were synthesized using different solvents, characterized, and then exposed to a gamma-ray source (137Cs) at irradiation doses of 0.1, 1.48, 2.05 and 3.25 Gy. The intensities of the emission bands progressively were attenuated as the received dose of gamma radiation increased. The changes were quantified with the help of a non-linear fit model. The material showed promising use as a dosimeter for low-dose radiation applications.

Characterization of a novel material to be used as bolus in radiotherapy with electrons.

Features of new material to be used as bolus in external radiotherapy were determined and their performance were evaluated. The characterization was carried out using Monte Carlo methods with the Geant4 code where the Percentage Depth Dose (PDD) due to electrons was estimated. In the Monte Carlo model the linear accelerator head was included. Calculated results were experimentally validated with measurements made for 6, 9, 12 and 16 MeV electron beams. The key characteristics of the implemented material were identified, guaranteeing a low cost bolus, easy to be customized and to be used in clinical applications. In comparison with commercial materials the new materials are superior from the cost to the effectiveness of their use in clinical treatments.

Shielding for transporting an 241Am-Be source for industrial applications.

Paraffin, water and water-extended polyester (WEP) were used as main moderator to design a mobile shielding for a 666 GBq 241Am-Be source used in oil industry. The shielding performance was estimated using Monte Carlo methods where the γ-rays induced by the neutron interaction with the shielding materials were also included. The spectra of neutrons and γ-rays around the shielding were estimated, as well as the total neutron and g-ray total fluences per history. The neutron source strength was used to calculate ambient dose equivalent rates, aiming to satisfy the international recommendation (2 mSv/h at the shielding surface). Moderators modify the neutron spectrum of the source reducing the amount of fast neutrons (0.5-11 MeV) and producing epithermal and thermal neutrons. During neutron transport in the moderator neutron capture and inelastic scattering produce gamma-rays. Paraffin has the best shielding performance however it is not suitable because can be affected by extreme temperatures. WEP and water have similar shielding performance, however water do not satisfy the international recommendations because at one site the neutron and γ-ray doses rates are larger than 2 mSv/h. WEP is the best option because fulfill the international recommendations, it is stable and temperatures where paraffin fails. The WEP-based shielding weights 66 kg.

Shielding behavior of artisanal bricks against ionizing photons.

In the work reported in this article, were determined the shielding capabilities of three artisanal bricks used massively in the construction industry in Mexico. The linear attenuation coefficients for photons between 1 keV and 100 GeV are reported; and the half-value layers for energies used in the medical field, show that the three typical artisanal bricks have good shielding capabilities for photons below 50 keV. We compared the effective atomic numbers of one of our bricks against two widely used materials in the construction industry, and our results suggest that the greater the effective atomic number, the less material attenuation capacity. A comparison of the half-value layer of one of our bricks against the half-value layers of two clay bricks with different percentages of fly ash particles published in the literature, suggests that in the region between 0.001 and 2.8 MeV, all the three bricks have practically the same attenuation capacity and that from 2.8 MeV to 100 GeV the clay bricks with different percentages of fly ash particles, need less material to show the same attenuation capacity than our artisanal bricks. Energy Dispersed X-Ray Fluorescence suggests that regardless of the number of constituent elements in a sample, a critical mass per atom is required to have a positive impact on density; and as a consequence, in the capacity of attenuation of the materials. Normalized half-value layers suggest on the other hand, that the uncooked bricks have better shielding capabilities than cooked.

Study of X-ray scattered in a phantom as function of its maximum energy during bimodal PET/CT imaging.

In a simultaneous Bimodal System with Positron Emission Tomography and Computed Tomography, the X-rays from a collimated X-ray tube are scattered over an anatomical region on the patient being scanning and cause a contamination effect on the signal received by the detectors distributed in the shape of a ring of the PET system. To study this phenomenon, each of the components of a bimodal system was modeled and simulated by the Monte Carlo method in Geant4 an X-ray beam produced in a RTW tube MCBM 65B with typical fluences used in medical diagnosis of small animals hitting a cylindrical phantom with a diameter greater than Field of View (FOV) in the tomographic center. The number of ionization events that occur in each of the phoswich detectors of the PET were obtained, the spatial distribution of the scattered X-rays was studied according to three maximum energies of the spectrum and calculation was made to find a filter that was located at the input of the phoswich detector that attenuates the X-rays by 98% and that would allow transmitting the gamma rays of annihilation also by 98%. For this, simulations were carried out using various filter materials, finding that copper is an excellent candidate and were found an optimum thicknesses between 0.5 mm and 1.3 mm, according to the average energy of the X-rays used in the different exploration techniques.

A neutron scattering soil moisture measurement system with a linear response.

A prototype moisture measurement system was designed and constructed, based on neutron scattering, for preforming measurements in the laboratory. The system consisted of a rectangular soil container, an 241Am/Be neutron source and two parallel 10BF3 detectors (one near the source and the other far from it). Neutrons from the source are moderated and backscattered within the soil sample before being detected by two parallel counters, whose count ratios are shown to be linearly related to the soil moisture even within short measurement times. The system's performance was demonstrated using the Monte Carlo simulations, and a series of measurements on soil samples made of clay (40 wt%) and sand (60 wt%), mixed with different percentages of water. The results showed that the detectors response ratio is linear, up to about 25% of water content.

OSL dosimeters for dental panoramic radiography.

The aim of the present work is to determine dosimetric characteristics of commercial optically stimulated luminescence dosimeter (OSLD) to estimate equivalent dose in the patient undergoing panoramic radiography procedure. Digital panoramic unit "Instrumentarium OP200D" was used. OSL dosimeters were optically bleached before any exposure procedure. InLight™ OSL nanodosimeters were placed on the thyroid surface between the head and neck. The exposure parameters for all measurements was standard value consisted in 66 kV, 5 mA, and 14.1 s. Standard size field of view (FOV) scanning mode was used. Dosimeters were calibrated for the air kerma. Reported male adult equivalent doses from 21 to 45 µSv for each scanning for standard size field of view (FOV). Meanwhile reported female adult equivalent doses from 28 to 75 µSv for standard size field of view (FOV) considering all heights. The lowest equivalent dose (21 µSv) was observed in the male thyroid gland surface (S) position for medium height. The highest equivalent dose (75 µSv) was for female small height in the right parotid surface (R) position. In conclusion, the results demonstrate that OSL dosimeters are appropriate in vivo dosimetry system for dental panoramic dose measurements.

Optimization by Monte Carlo method of photon fluence from the X-ray beam spectrum in a bimodal tomographic system.

A bimodal tomographic system with a RTW MCBM 65B-50Mo X-ray tube and a XPAD3s semiconductor camera that contains 8 bars, each one with 67,200 hybrid pixels are modeled in GEANT4 simulation code. Several conical X-ray spectra were simulated, particularly a spectrum with a peak energy of 17.4 keV used in tomography on small animals. Three phantoms located in the tomographic center were added to the simulation to evaluate the image quality and its magnification based on the simulation of different photon fluences and the rotation effect of the tomographic system with an average angular velocity of 360o per minute. The images were recorded and analyzed in 2D through ROOT software toolkit in virtual XPAD3 detector. The quantitative method 20-80% of the maximum intensity of radiation was used for obtain the contouring of the phantoms, this method is used in radiotherapy and radiodiagnosis imaging. For this purpose, the images were taken to DICOM format in order to estimate the optical density of the contours and to evaluate the optimum and minimum photon fluence to be used in the tomographic system in order to reduce the absorbed doses in the individuals. This study allowed to determine the optimal fluence to validate it with realistic fluences used in the tomographic prototype ClearPET /XPAD-CT and to make an intercomparison with the absorbed doses measured with detectors located in the tomographic center.

Assessment of the effectiveness of attenuation of Pb aprons by using TLD dosimetry and Monte Carlo calculations.

We developed an experimental set-up by using a continuous emission X-ray (Pantak DXT-3000) and three types of Pb aprons, with thicknesses of 0.25, 0.5, and 0.75mm, coated with Mylar fiber on their surface. Aprons were placed at a distance of 2.5m from the focus. Aluminum filtration was performed at the beam output to reproduce the qualities of narrow beams, N40 (Eeffective =33keV), N80 (Eeffective =65keV), and N100 (Eeffective =83keV), according to the ISO standard 4037 (1-3). Each apron was fixed with 10 thermoluminescent dosimeters (TLDs) over its surface, five dosimeters before and five dosimeters after irradiation with X-rays. Dosimeter readings were noted, and the attenuation coefficients for each effective energy were calculated. To confirm the method of effective energy of ISO-4037 and evaluate the effectiveness of aprons according to the energy range required for different medical practices, a Monte Carlo simulation using GEANT4 code was performed. Thus, the fluence and the absorbed dose in each of the dosimeters were determined, and then the coefficients of linear attenuation were calculated and compared with the experimental data and with those reported by the National Institute of Standards and Technology. Results were consistent between theoretical calculations and experimental measures. This work will serve to make assessments for other personalized radiation protectors made of Pb.

Replacement of Bonner spheres with polyethylene cylinders for the unfolding of an 241Am-Be neutron energy spectrum.

In this study, a conventional Bonner sphere spectrometer, together with 6LiI(Eu) inorganic scintillator used as the central detector, was used to obtain the neutron energy spectrum of an 241Am-Be source. To achieve this, we calculated the response matrices corresponding to eight different sizes of polyethylene spheres for the neutron energies ranging from about 10-7 to 15MeV in 54 energy groups by using the MCNPX2.6 code, and the 241Am-Be neutron spectrum was obtained using a modified version of the neutron spectrum unfolding code, AFITBUNKI. In a feasibility study, similar calculations were performed with different sizes of polyethylene cylinders. A comparison between the unfolded spectra of a typical 241Am-Be neutron source with those of Bonner spheres, cylinders of similar sizes, and standard 241Am-Be neutron energy spectra shows that the spectrometer with polyethylene cylinders can be used as a potential alternative for conventional Bonner spheres.

Neutron spectra due (13)N production in a PET cyclotron.

Monte Carlo and experimental methods have been used to characterize the neutron radiation field around PET (Positron Emission Tomography) cyclotrons. In this work, the Monte Carlo code MCNPX was used to estimate the neutron spectra, the neutron fluence rates and the ambient dose equivalent (H*(10)) in seven locations around a PET cyclotron during (13)N production. In order to validate these calculations, H*(10) was measured in three sites and were compared with the calculated doses. All the spectra have two peaks, one above 0.1MeV due to the evaporation neutrons and another in the thermal region due to the room-return effects. Despite the relatively large difference between the measured and calculated H*(10) for one point, the agreement was considered good, compared with that obtained for (18)F production in a previous work.

Calculation of fluence and absorbed dose in head tissues due to different photon energies.

Calculations of fluence and absorbed dose in head tissues due to different photon energies were carried out using the MCNPX code, to simulate two models of a patient's head: one spherical and another more realistic ellipsoidal. Both head models had concentric shells to describe the scalp skin, the cranium and the brain. The tumor was located at the center of the head and it was a 1 cm-radius sphere. The MCNPX code was run for different energies. Results showed that the fluence decreases as the photons pass through the different head tissues. It can be observed that, although the fluence into the tumor is different for both head models, absorbed dose is the same.

Neutron spectra at two beam ports of a TRIGA Mark III reactor loaded with HEU fuel.

The neutron spectra have been measured in two beam ports, one radial and another tangential, of the TRIGA Mark III nuclear reactor from the National Institute of Nuclear Research in Mexico. Measurements were carried out with the reactor core loaded with high enriched uranium fuel. Two reactor powers, 5 and 10 W, were used during neutron spectra measurements using a Bonner sphere spectrometer with a (6)LiI(Eu) scintillator and 2, 3, 5, 8, 10 and 12 in.-diameter high-density polyethylene spheres. The neutron spectra were unfolded using the NSDUAZ unfolding code. For each spectrum total flux, mean energy and ambient dose equivalent were determined. Measured spectra show fission, epithermal and thermal neutrons, being harder in the radial beam port.

Doses in sensitive organs during prostate treatment with a 60Co unit.

Using thermoluminiscent dosimeters the absorbed dose in the bladder, rectum and thyroid have been evaluated when 200 cGy was applied to the prostate. The treatment was applied with a (60)Co unit. A water phantom was built and thermoluminiscent dosimeters were located in the position where the prostate, bladder, rectum and thyroid are located. The therapeutic beam was applied in 4 irradiations at 0, 90, 180 and 270° with the prostate at the isocenter. The TLDs readouts were used to evaluate the absorbed dose in each organ. The absorbed doses were used to estimate the effective doses and the probability of developing secondary malignacies in thyroid, rectum and bladder.

Concrete enclosure for shielding a neutron source.

In the aim to design a shielding for a 0.185 TBq (239)PuBe isotopic neutron source several Monte Carlo calculations were carried out using MCNP5 code. First, a point-like source was modeled in vacuum and the neutron spectrum and ambient dose equivalent were calculated at several distances ranging from 5 cm up to 150 cm, these calculations were repeated modeling a real source, including air, and a 1×1×1 m(3) enclosure with 5, 15, 20, 25, 30, 50 and 80 cm-thick Portland type concrete walls. At all the points located inside the enclosure neutron spectra from 10(-8) up to 0.5 MeV were the same regardless the distance from the source showing the room-return effect in the enclosure, for energies larger than 0.5 MeV neutron spectra are diminished as the distance increases. Outside the enclosure it was noticed that neutron spectra becomes "softer" as the concrete thickness increases due to reduction of mean neutron energy. With the ambient dose values the attenuation curve in terms of concrete thickness was calculated.

NSDUAZ unfolding package for neutron spectrometry and dosimetry with Bonner spheres.

NSDUAZ (Neutron Spectrometry and Dosimetry from the Universidad Autónoma de Zacatecas) is a user friendly neutron unfolding package for Bonner sphere spectrometer with (6)LiI(Eu) developed under LabView(®) environment. Unfolding is carried out using a recursive iterative procedure with the SPUNIT algorithm, where the starting spectrum is obtained from a library initial guess spectra to start the iterations. The NSDUAZ performance was evaluated using (252)Cf, (252)Cf/D(2)O, (241)AmBe neutron sources and the neutrons outside the radial beam port of a TRIGA Mark III nuclear reactor running to 10 W.

Neutron and photon spectra in LINACs.

A Monte Carlo calculation, using the MCNPX code, was carried out in order to estimate the photon and neutron spectra in two locations of two linacs operating at 15 and 18 MV. Detailed models of both linac heads were used in the calculations. Spectra were estimated below the flattening filter and at the isocenter. Neutron spectra show two components due to evaporation and knock-on neutrons. Lethargy spectra under the filter were compared to the spectra calculated from the function quoted by Tosi et al. that describes reasonably well neutron spectra beyond 1 MeV, though tends to underestimate the energy region between 10(-6) and 1 MeV. Neutron and the Bremsstrahlung spectra show the same features regardless of the linac voltage.