Gamma-Ray Attenuation Characteristics of Some Essential Amino Acids for 57Co, 192Ir, 18F, and 116mIn Sources

Purpose: In different tissues of the body, proteins are important parts that are made up of building blocks called amino acids. Considering the wide applications of radioactive sources in industry and medicine, the need to study the attenuation characteristics of amino acids is determined. Materials and Methods: To study the attenuation characteristics of five types of amino acids, MCNPX Monte Carlo code and XMuDat program were used. Linear and mass attenuation coefficients, half and tenth value layers, mean free path, effective atomic and electronic cross-sections, effective atomic numbers and effective electron densities were calculated. 57Co, 192Ir, 18F, and 116mIn gamma sources were considered for this study. To validate the theoretical results, the obtained values were compared with the available experimental data. Results: The difference between the theoretical and experimental results was less than 11%. The results showed that with increasing photon energy, the linear and mass attenuation coefficients and effective atomic and electronic cross-sections decreased, while the half and tenth value layers and mean free path quantities increased. Furthermore, the linear attenuation coefficients, the effective atomic and electronic cross-sections, as well as the effective atomic number values increased with increasing amino acid density, while the effective electron density behaves independently of the amino acid density. Conclusion: The presented theoretical methods produced data similar to experimental results with fair accuracy, so by using these methods, attenuation properties of other amino acids can be obtained over a wide range of energies.

Fast Neutron and Gamma-Ray Attenuation Properties of Some HMO Tellurite-Tungstate-Antimonate Glasses: Impact of Sm3+ Ions

Characteristics of tellurite-tungstate-antimonate glasses containing heavy metal oxide were investigated in detail using two methods: the MCNPX Monte Carlo code and the Phy-X/PSD platform. The influence of Sm2O3, translocating with TeO2 at ratios of 0.2, 0.5, 0.8, 1, and 1.5 mol% on radiation shielding properties of glasses, was set forth with five glass structures determined according to the (75-x)TeO2-15Sb2O3-10WO3-xSm2O3 glass composition. Densities of the glasses were prepared by doping a low ratio of Sm2O3 that varied between 5.834 and 5.898 g/cm3. Sample densities, which have an important role in determining radiation shielding character, increased depending on the increase in Sm2O3 concentration. Effective removal cross-section (∑R) values against fast neutrons, as well as linear and mass attenuation coefficients, half-value layer, mean free path, variation of effective atomic number against photon energy, exposure, and energy built-up factors, were simulated with the help of these two methods. As a result of these estimates, it can be concluded that values obtained using both methods are consistent with each other. From the obtained values, it can be concluded that the SM1.5 sample containing 1.5 mol% would have the most efficient role in radiation shielding. An increase of Sm2O3 resulted in a significant increase in linear and mass attenuation coefficients and effective removal cross-section values belonging to fast neutrons and, in addition, resulted in a decrease in the half value layer. Doping HMO glasses with Sm2O3 was observed to contribute directly to the development of radiation shielding properties of the glass.

Control of spectral characteristics of the medical accelerator on the basis of comparison of mass weaking coefficients of different materials

Background. Radiation protection of patients undergoing radiation therapy using linear electron accelerators is based on ensuring the constancy of the equipment parameters set during commissioning. Therefore, studying the possibility of operational assessment of the spectrum characteristics consistency of the generated bremsstrahlung is a priority along with standard dosimetric parameter control procedures. Primarily, this refers to specifying the average measured energy of bremsstrahlung which provides an impartial assessment of the constancy of the whole wave path of the accelerator. However, there is no special diagnostic equipment to determine this parameter. At the same time, the literature data represent a growing interest in the use of CdTe sensors for the analysis of high-energy radiation, including the ones in medical accelerators. Purpose – developing and testing special diagnostic equipment based on semiconductor CdTe sensors, which would implement the assessment of the average measured energy of bremsstrahlung of the medical accelerator 6 MeV via comparing the mass attenuation coefficients in lead and aluminum. Materials and Methods. The paper deals with experimental evaluation of the Varian Clinac 600C linear accelerator (USA) spectrum characteristics carried out at Radiation Oncology Department of State Organization «Grigoriev Institute for Medical Radiology and Oncology of the National Academy of Medical Sciences of Ukraine» via determining the average measured energy of bremsstrahlung. The assessment of the average measured energy of the bremsstrahlung of the accelerator was performed based on comparing two mass attenuation coefficients of radiation with materials having significantly different atomic numbers, i.e. Al and Pb. The assessment of the mass attenuation coefficients was performed on the basis of measuring the average amplitudes of CdTe signals of the sensor, operating in the pulse mode in conjunction with a 16-bit ADC. Pulses of bremsstrahlung from the linear accelerator were recorded by a peak detector for 10 seconds of measurement by the hardware-software complex at 400 monitor units by CdTe sensor with aluminum and lead absorber. The study was performed at a distance of «source-surface» 100 cm with an area of the irradiation field of 20x20 cm. The spectral energy profile of the generated field of bremsstrahlung was studied. Results. The developed equipment was tested by CdTe sensor, which was created taking into account the energy sensitivity of the sensor itself as well as the spectraltemporal characteristics of the pulsed radiation of the accelerator. The approach dealing with assessing the average measured energy of bremsstrahlung of the linear electron accelerator, based on the dependence of the attenuation of radiation by the absorber layer on the radiation energy, has been experimentally confirmed. The theoretical dependence of the average measured energy of bremsstrahlung of the linear accelerator on the ratio of the mass attenuation coefficients of lead and aluminum has been obtained. The energy range from 0.1 to 6 MeV corresponds to the ratio of mass absorption coefficients of lead to aluminum, varying nonlinearly from 33.8 to 1.639. The average measured energy of the linear accelerator of 0.8 MeV corresponds to a mass coefficient ratio of about 1.23 for these materials. The assessed absolute error (from the set value during commissioning the linear accelerator) of the specified measured average energy of bremsstrahlung is up to 12.5% (0.72 MeV), corresponding to the ratio of mass attenuation coefficients – 1.340. Conclusions. The special diagnostic equipment for recording the spectrum characteristics of the Varian Clinac 600C linear accelerator (USA) based on semiconductor CdTe sensors, which along with 16-bit ADC make it possible to estimate the average measured energy of bremsstrahlung via comparing mass attenuation coefficients in Al and Pb has been substantiated and reduced to practice. The assessment of mass attenuation coefficients is carried out based on measuring the average amplitudes of pulses of СdTe sensors operating in a pulse mode.

Gamma-Ray Attenuation and Exposure Buildup Factor of Novel Polymers in Shielding Using Geant4 Simulation

Polymers are often used in medical applications, therefore, some novel polymers and their interactions with photons have been studied. The gamma-ray shielding parameters for Polymethylpentene (PMP), Polybutylene terephthalate (PBT), Polyoxymethylene (POM), Polyvinylidenefluoride (PVDF), and Polychlorotrifluoroethylene (PCTFE) polymers were determined using the Geant4 simulation and discussed in the current work. The mass attenuation coefficients (μ/ρ) were simulated at low and high energies between 0.059 and 1.408 MeV using different radionuclides. The accuracy of the Geant4 simulated results were checked with the XCOM software. The two different methods had good agreement with each other. Exposure buildup factor (EBF) was calculated and discussed in terms of polymers under study and photon energy. Effective atomic number (Zeff) and electron density (Neff) were calculated and analyzed at different energies. Additionally, the half-value layer (HVL) of the polymers was evaluated, and the results of this parameter showed that PCTFE had the highest probability of interaction with gamma photons compared to those of the other tested polymers.

High-accuracy mass attenuation coefficients and X-ray absorption spectroscopy of zinc – the first X-ray Extended Range Technique-like experiment in Australia

The first X-ray Extended Range Technique (XERT)-like experiment at the Australian Synchrotron, Australia, is presented. In this experiment X-ray mass attenuation coefficients are measured across an energy range including the zinc K-absorption edge and X-ray absorption fine structure (XAFS). These high-accuracy measurements are recorded at 496 energies from 8.51 keV to 11.59 keV. The XERT protocol dictates that systematic errors due to dark current nonlinearities, correction for blank measurements, full-foil mapping to characterize the absolute value of attenuation, scattering, harmonics and roughness are measured over an extended range of experimental parameter space. This results in data for better analysis, culminating in measurement of mass attenuation coefficients across the zinc K-edge to 0.023–0.036% accuracy. Dark current corrections are energy- and structure-dependent and the magnitude of correction reached 57% for thicker samples but was still large and significant for thin samples. Blank measurements scaled thin foil attenuation coefficients by 60–500%; and up to 90% even for thicker foils. Full-foil mapping and characterization corrected discrepancies between foils of up to 20%, rendering the possibility of absolute measurements of attenuation. Fluorescence scattering was also a major correction. Harmonics, roughness and bandwidth were explored. The energy was calibrated using standard reference foils. These results represent the most extensive and accurate measurements of zinc which enable investigations of discrepancies between current theory and experiments. This work was almost fully automated from this first experiment at the Australian Synchrotron, greatly increasing the possibility for large-scale studies using XERT.

High-accuracy measurement of mass attenuation coefficients and the imaginary component of the atomic form factor of zinc from 8.51 keV to 11.59 keV, and X-ray absorption fine structure with investigation of zinc theory and nanostructure

High-accuracy X-ray mass attenuation coefficients were measured from the first X-ray Extended Range Technique (XERT)-like experiment at the Australian Synchrotron. Experimentally measured mass attenuation coefficients deviate by ∼50% from the theoretical values near the zinc absorption edge, suggesting that improvements in theoretical tabulations of mass attenuation coefficients are required to bring them into better agreement with experiment. Using these values the imaginary component of the atomic form factor of zinc was determined for all the measured photon energies. The zinc K-edge jump ratio and jump factor are determined and results raise significant questions regarding the definitions of quantities used and best practice for background subtraction prior to X-ray absorption fine-structure (XAFS) analysis. The XAFS analysis shows excellent agreement between the measured and tabulated values and yields bond lengths and nanostructure of zinc with uncertainties of from 0.1% to 0.3% or 0.003 Å to 0.008 Å. Significant variation from the reported crystal structure was observed, suggesting local dynamic motion of the standard crystal lattice. XAFS is sensitive to dynamic correlated motion and in principle is capable of observing local dynamic motion beyond the reach of conventional crystallography. These results for the zinc absorption coefficient, XAFS and structure are the most accurate structural refinements of zinc at room temperature.

Measuring Mass Attenuation Coefficient and Elemental Composition for Egbeda Soil Series of Southwestern Nigeria

Information from workers on the profitability of cassava on Iwo and Egbeda soil series in Oyo state, Nigeria have shown the Iwo soil series to be more profitable given the same scale of cassava cultivation. Therefore the need arises to improve on the soil properties of Egbeda soil series which will possibly improve the production efficiency for this category of farmers. In this work, an experimental procedure using gamma attenuation technique to determine the mass attenuation coefficient at different gamma ray energies of 59.5, 661.7, 1173.2 and 1332.5 keV, and at depths of 0 – 15, 15 – 30, 30 – 45, 45 – 60, 60 – 75 and 75 – 90 cm into the Egbeda soil series profile have been studied. Likewise X-ray fluorescence, XRF, method was used to obtain the elemental composition and concentrations at these depths while the XCOM software was applied to obtain the photon mass attenuation coefficients at the different gamma ray energies for the depths. Mass attenuation coefficients, obtained experimentally and that computed theoretically using XCOM varied exponentially with photon energy. The correlation coefficient between the experimentally-obtained and XCOM-obtained μs for the energies considered ranged from 0.89 – 0.96. The variation of with soil depth show that the top soil (0 – 15cm depths) is least attenuating with gamma ray penetrability varying down the profile. Information on the mass attenuation coefficients, elemental composition, and concentrations at varying depths into the soil profile will go a long way in contributing to efforts at improving the soil condition of the Egbeda soil series.