Determining photon energy absorption parameters for different soil samples

Insights into the Effect of Aggregate Sizes on the Soil Radiation Interaction Properties Based on X-ray Fluorescence

Soils subjected to disaggregation can break into aggregates of different sizes composed of sand, clay, and silt particles. Each aggregate contains different oxides, which can vary according to the aggregate size and influence its properties, such as the radiation interaction parameters. These parameters are relevant in the evaluation of radiation shielding and soil physical properties. Thirteen tropical/subtropical soils of contrasting textures (clayey and loamy/sandy) with two aggregate sizes (2-1 mm and <45 μm) were studied. The radiation parameters analyzed were the atomic (σ_A), electronic (σ_E), and molecular (σ_M) cross-sections; the effective atomic number (Z_eff); and the electron density (N_el). We verified that the aggregate sizes affected the major oxides (SiO₂, Al₂O₃, Fe₂O₃). In general, the attenuation coefficient and Z_eff were sensitive to the clayey soils' aggregate sizes (low photon energies). However, the loamy/sandy soils did not exhibit differences among the parameters. As the photon energy increased, only Z_eff presented differences for most soils. We also verified that σ_M, Z_eff, and N_el were the most sensitive parameters to the soil composition. Although the soil chemical composition was influenced by the studied aggregate sizes, the radiation parameters exhibited differences for only some of these parameters. This means that the aggregate size is practically irrelevant when radiation parameters are determined based on X-ray fluorescence.

The Impacts of Vertical Off-Centring, Localiser Direction, Phantom Positioning and Tube Voltage on CT Number Accuracy: An Experimental Study

Background: This study investigates the effects of vertical off-centring, localiser direction, tube voltage, and phantom positioning (supine and prone) on computed tomography (CT) numbers and radiation dose. Methods: An anthropomorphic phantom was scanned using a Discovery CT750 HD—128 slice (GE Healthcare) scanner at different tube voltages (80, 120, and 140 kVp). Images employing 0° and 180° localisers were acquired in supine and prone positions for each vertical off-centring (±100, ±60, and ±30 mm from the iso-centre). CT numbers and displayed volume CT dose index (CTDIvol) were recorded. The relationship between dose variation and CT number was investigated. Results: The maximum changes in CT number between the two phantom positions as a function of vertical-off-centring were for the upper thorax 34 HU (0° localiser, 120 kVp), mid thorax 43 HU (180° localiser, 80 kVp), and for the abdominal section 31 HU (0° localiser, 80 kVp) in the prone position. A strong positive correlation was reported between the variation in dose and CT number (r = 0.969, p < 0.001); 95% CI (0.93, 0.99). Conclusions: Patient positioning demands an approach with a high degree of accuracy, especially in cases where clinical decisions depend on CT number accuracy for tissue lesion characterisation.

Improving the efficiency of small animal 3D-printed compensator IMRT with beamlet intensity total variation regularization

PURPOSE

There is growing interest in the use of modern 3D printing technology to implement intensity-modulated radiation therapy (IMRT) on the preclinical scale that is analogous to clinical IMRT. However, current 3D-printed IMRT methods suffer from complex modulation patterns leading to long delivery times, excess filament usage, and less accurate compensator fabrication. In this work, we have developed a total variation regularization (TVR) approach to address these issues.

METHODS

TVR-IMRT was used to optimize the beamlet intensity map, which was then converted to a thickness of the corresponding compensator attenuation region in copper-doped polylactic acid (PLA) filament. IMRT and TVR-IMRT heart and lung plans were generated for two different mice using three, five, or seven gantry angles. The total compensator thickness, total variation of compensator beamlet thicknesses, total variation of beamlet intensities, and exposure time were compared. The individual field doses and composite dose were delivered to film for one plan and gamma analysis was performed.

RESULTS

In total, 12 mice heart and lung plans were generated for both IMRT and TVR-IMRT cases. Across all cases, it was found that TVR-IMRT reduced the total variation of compensator beamlet thicknesses and beamlet intensities by 54 ± 4 % $54\pm 4\%$ and 50 ± 3 % $50\pm 3\%$ on average when compared to standard 3D-printed compensator IMRT. On average, the total mass of compensator material consumed and radiation beam-on time were reduced by 45 ± 6 % $45\pm 6\%$ and 24 ± 4 % $24\pm 4\%$ , respectively, whereas dose metrics remained comparable. Heart plan compensators were printed and delivered to film and subsequent gamma analysis performed for each of the single fields as well as the composite dose. For the composite delivery, a passing rate of 89.1% for IMRT and 95.4% for TVR-IMRT was achieved for a 3 % / 0.3 $3\%/0.3$ mm criterion.

CONCLUSIONS

TVR can be applied to small animal IMRT beamlet intensities to produce fluence maps and subsequent 3D-printed compensator patterns with significantly less complexity while still maintaining similar dose conformity to traditional IMRT. This can simplify/accelerate the 3D printing process, reduce the amount of filament required, and reduce overall beam-on time to deliver a plan.

Characterization of soy-lignin bonded Rhizophora spp. particleboard as substitute phantom material for radiation dosimetric studies - Investigation of CT number, mass attenuation coefficient and effective atomic number

Experimental particleboards are made from Rhizophora spp. wood trunk with three different percentages of lignin and soy flour (0%, 6% and 12%) as adhesives. The objective was to investigate the equivalence of Rhizophora spp. particleboard as phantom material with human soft tissue using Computed Tomography (CT) number. The linear and mass attenuation coefficient of Rhizophora spp. particleboard at low energy range was also explored using X-ray Fluorescence (XRF) configuration technique. Further characterization of the particleboard was performed to determine the effective atomic number, Zeff using Energy Dispersive X-Ray (EDX) method. Adhesive-bonded Rhizophora spp. particleboard showed close similarities with water, based on the average CT numbers, electron density calibration curve and the analysis of CT density profile, compared to the binderless particleboard. The effective atomic number obtained from the study indicated that the attenuation properties of all the particleboards at different percentages of adhesives were almost similar to water. The mass attenuation coefficient calculated from XRF configuration technique showed good agreement with water from XCOM database, suggesting its potential as phantom material for radiation study.

Monte Carlo simulations and analysis of transmitted gamma ray spectra through various tissue phantoms

Studies of radiation interactions with tissue equivalent material find importance in efforts that seek to avoid unjustifiable dose to patients, also in ensuring quality control of for instance nuclear medicine imaging equipment. Use of the Monte Carlo (MC) simulation tool in such characterization processes allows for the avoidance of costly experiments involving transmitted X- and γ-ray spectrometry. Present work investigates MC simulations of γ-ray transmission through tissue equivalent solid phantoms. Use has been made of a range of radionuclide gamma ray sources, ^99mTc, ¹³¹I, ¹³⁷Cs, ⁶⁰Co (offering photons in the energy range from a few keV up to low MeV), popularly applied in medicine and in some cases for gauging in industry, obtaining the transmission spectra following their interaction with various phantom materials and thicknesses. In validation of the model, the simulated values of mass attenuation coefficients (μ/ρ) for different phantom materials and thicknesses were found to be in good agreement with reference values (NIST, 2004) to within 1.1% for all material compositions. For all of the primary photon energies and medium thicknesses of interest herein, results show that multiple scattering peaks are generally located at energies lower than 100 keV, although for the larger phantom thicknesses it is more difficult to distinguish single, double and multiple scattering in the gamma spectra. Transmitted photon spectra investigated for water, soft tissue, breast, brain and lung tissue slab phantoms are demonstrated to be practically independent of the phantom material, while a significant difference is observed for the spectra transmitted through bone that was proved to be due to the density effect and not material composition.

Training Future Engineers to Be Ghostbusters: Hunting for the Spectral Environmental Radioactivity

Although environmental radioactivity is all around us, the collective public imagination often associates a negative feeling to this natural phenomenon. To increase the familiarity with this phenomenon we have designed, implemented, and tested an interdisciplinary educational activity for pre-collegiate students in which nuclear engineering and computer science are ancillary to the comprehension of basic physics concepts. Teaching and training experiences are performed by using a 4” × 4” NaI(Tl) detector for in-situ and laboratory γ-ray spectroscopy measurements. Students are asked to directly assemble the experimental setup and to manage the data-taking with a dedicated Android app, which exploits a client-server system that is based on the Bluetooth communication protocol. The acquired γ-ray spectra and the experimental results are analyzed using a multiple-platform software environment and they are finally shared on an open access Web-GIS service. These all-round activities combining theoretical background, hands-on setup operations, data analysis, and critical synthesis of the results were demonstrated to be effective in increasing students’ awareness in quantitatively investigating environmental radioactivity. Supporting information to the basic physics concepts provided in this article can be found at http://www.fe.infn.it/radioactivity/educational.

Evaluation of radiation absorption capacity of some soil samples

The aim of the present work is to investigate the radiation absorption capacity of different soil samples in Turkey. For this purpose, we used a γ ray transmission geometry to measure the mass attenuation coefficients of eight soil samples collected between Bingöl city and Solhan district, Turkey at different γ-ray energies in the range of 13.94–88.04 keV. The radioactive sources utilized in the experiment were 241Am, 109Cd and 133Ba. FFAST and WinXCOM programs were used to evaluate the theoretical mass attenuation coefficients values of the selected soil samples. There is a good agreement between experimental and theoretical results. Additionally, the mass attenuation coefficients values used to evaluate different radiation shielding parameters such as effective atomic number, half value layer and mean free path. The variation of shielding parameters was examined for soil composition and photon energy. The obtained results revealed that S6 soil sample is the best soil in terms of shielding effectiveness among all the collected soils due to lower values for half value layer and mean free path. The effective removal cross-section (Σ R ) of fast neutrons for the collected soils was also computed to examine neutrons shielding properties of the soil samples. It is found that the Σ R values for the soil samples are almost constant and lie within the range (0.04286–0.04949 cm−1).

Gamma-ray attenuation to evaluate soil porosity: an analysis of methods

Soil porosity (ϕ) is of a great deal for environmental studies due to the fact that water infiltrates and suffers redistribution in the soil pore space. Many physical and biochemical processes related to environmental quality occur in the soil porous system. Representative determinations of ϕ are necessary due to the importance of this physical property in several fields of natural sciences. In the current work, two methods to evaluate ϕ were analyzed by means of gamma-ray attenuation technique. The first method uses the soil attenuation approach through dry soil and saturated samples, whereas the second one utilizes the same approach but taking into account dry soil samples to assess soil bulk density and soil particle density to determine ϕ. The results obtained point out a good correlation between both methods. However, when ϕ is obtained through soil water content at saturation and a 4 mm collimator is used to collimate the gamma-ray beam the first method also shows good correlations with the traditional one.