Analyzing physical characteristics and shielding efficiency for non-lead medical radiation shielding sheets improved using PMMA

ABSTRACT

Recently, the research for replacing heavy lead goods, such as medical radiation shielding sheets with environmentally friendly shielding materials has been widely carried out. The use of tungsten injected into the base material of polyethylene resin may be a good alternative for manufacturing lightweight shielding sheets. However, the increase of the mass ratio of tungsten in the shielding sheets is accompanied by the degradation of their physical properties such as tensile strength and flexibility. In this report, we have tried to fix this problem by adding Polymethyl Methacrylate (PMMA) to the mixing process of materials. If the portion of the added PMMA is 20%, it leads to a 25% increase of the particle packing ratio while there is a simultaneous 28% enhancement of tensile strength compared to before adding it. In the final test for shielding efficiency, it also turned out that the increase of the particle packing ratio for tungsten exhibits the same shielding efficiency as that of 0.2?mmPb. This consequence may imply that mass production of sheets that can prevent scattering rays in the medical radiation frequency range is possible through the calender process using a 0.3?mm tungsten sheet.     

Comparison of radiation shielding ratios of nano-sized bismuth trioxide and molybdenum

In this study, radiation shielding fibers using non-hazardous nano-sized bismuth trioxide and molybdenum instead of lead were developed and evaluated. Among the elements with high densities and atomic numbers, non-hazardous elements such as bismuth trioxide and molybdenum were chosen as a shielding element. Then, bismuth trioxide (Bi₂O₃) with average particle size 1–500?µm was ball milled for 10?min to produce a powdered form of nanoparticles with average particle size of 10–100?nm. Bismuth trioxide nanoparticles were dispersed to make a colloidal suspension, followed by spreading and hardening onto one or two sides of fabric, to create the radiation shielding fabric. The thicknesses of the shielding sheets using nano-sized bismuth and molybdenum were 0.4 and 0.7?mm. According to the lead equivalent test of X-ray shielding products suggested by KS, the equivalent dose was measured, followed by calculation of the shielding rate. The shielding rate of bismuth with 0.4?mm thickness and at 50?kVp was 90.5%, which is comparable to lead of 0.082?mm thickness. The shielding rate of molybdenum was 51.89%%, which is comparable to lead of 0.034?mm. At a thickness of 0.7?mm, the shielding rate of bismuth was 98.73%, equivalent to 0.101?mm Pb, whereas the shielding rate of molybdenum was 74.68%, equivalent to 0.045?mm?Pb. In conclusion, the radiation shielding fibers using nano-sized bismuth developed in this study are capable of reducing radiation exposure by X-ray and its low-dose scatter ray.     

Evaluation of dosimetry and image of very low-dose computed tomography attenuation correction for pediatric positron emission tomography/computed tomography: phantom study

In this study, phantom was used to evaluate attenuation correction computed tomography (CT) dose and image in case of pediatric positron emission tomography (PET)/CT scan. Three PET/CT scanners were used along with acryl phantom in the size for infant and ion-chamber dosimeter. The CT image acquisition conditions were changed from 10 to 20, 40, 80, 100 and 160 mA and from 80 to 100, 120 and 140 kVp, which aimed at evaluating penetrate dose and computed tomography dose index_volume (CTDI_vol) value. And NEMA PET Phantom? was used to obtain PET image under the same CT conditions in order to evaluate each attenuation-corrected PET image based on standard uptake value (SUV) value and signal-to-noise ratio (SNR). In general, the penetrate dose was reduced by around 92% under the minimum CT conditions (80 kVp and 10 mA) with the decrease in CTDI_vol value by around 88%, compared with the pediatric abdomen CT conditions (100 kVp and 100 mA). The PET image with its attenuation corrected according to each CT condition showed no change in SUV value and no influence on the SNR. In conclusion, if the minimum dose CT that is properly applied to body of pediatric patient is corrected for attenuation to ensure that the effective dose is reduced by around 90% or more compared with that for adult patient, this will be useful to reduce radiation exposure level.     

Changes in entrance surface dose in relation to the location of shielding material in chest computed tomography

This study examined the effects of entrance surface dose (ESD) on the abdomen and pelvis of the patient when undergoing chest computed tomography (CT) procedure, and evaluated the effects of ESD reduction depending on the location of radiation shield. For CT scanner, the 64-slice multi-detector computed tomography was used. The alderson radiation therapy phantom and optically stimulated luminescence dosimeter (OSLD), which enabled measurement from low to high dose, were also used. For measurement of radiation dose, the slice number from 9 to 21 of the phantom was set as the test range, which included apex up to both costophrenic angles. A total of 10 OSLD nanoDots were attached for measurement of the front and rear ESD. Cyclic tests were performed using the low-dose chest CT and high-resolution CT (HRCT) protocol on the following set-ups: without shielding; shielding only on the front side; shielding only on the rear side; and shielding for both front and rear sides. According to the test results, ESD for both front and rear sides was higher in HRCT than low-dose CT when radiation shielding was not used. It was also determined that, compared to the set-up that did not use the radiation shield, locating the radiation shield on the front side was effective in reducing front ESD, while locating the radiation shield on the rear side reduced rear ESD level. Shielding both the front and rear sides resulted in ESD reduction. In conclusion, it was confirmed that shielding the front and rear sides was the most effective method to reduce the ESD effect caused by scatter ray during radiography.     

Bremsstrahlung shielding parameters in polymer concretes

Concretes are used for shielding in nuclear power plants. Beta radiation is emitted during the nuclear reactions. This beta radiation interacts with the concrete and results in secondary radiation such as bremsstrahlung. Shielding parameters of beta-induced bremsstrahlung in concretes are important in the field of radiation protection. We have evaluated the cross section, yield, intensity and dose rate of beta-induced bremsstrahlung by pure beta nuclides of end point energy ranges from 0.4 to 5?MeV in some polymer-based concretes such as sulfur polymer concrete, barium polymer concrete, calcium polymer concrete, fluorine polymer concrete, chlorine polymer concrete and germanium polymer concrete. We have compared the shielding properties among the studied polymer concretes. The efficiency, intensity and dose rate of bremsstrahlung increases with a maximum energy of beta nuclide and modified atomic number of the concrete. From the detailed study, it is clear that the barium polymer concrete is having large bremsstrahlung dose rate and specific bremsstrahlung constant values than the other studied polymer concretes. This means barium polymer concrete is a good absorber of bremsstrahlung radiation than the other studied polymer concretes.     

Development of a new nanocrystalline alloy for X-ray shielding

The purpose of this study was to develop a new nanocrystalline alloy material, which can replace lead for the purposes of radiation shielding as it is not hazardous to the human body and it is light in weight, to use the developed alloy in a fiber, and to evaluate its performance. This study used tungsten carbide and cobalt as the base metals and developed a new nanocrystalline alloy material. Then, radiation-shielding fibers 0.2 and 0.4?mm thick were created from the prepared tungsten carbide and cobalt powder. Equivalent dose was measured and shielding rate was obtained by the lead-equivalent test method for X-ray protection of goods suggested in the Korean Standard. According to our results, the shielding rate of the 0.2-mm-thick WC–Co alloy was 96.52% at a tube voltage of 50?kVp, 94.86% at a tube voltage of 80?kVp, and 94.10% at a tube voltage of 100?kVp. The shielding rate of the 0.4-mm-thick WC–Co alloy was 97.47% at a tube voltage of 50?kVp, 96.57% at a tube voltage of 80?kVp, and 95.63% at a tube voltage of 100?kVp. It is believed that the nanocrystalline WC–Co alloy developed for radiation shielding in this study will contribute to a decrease in primary X-ray exposure as well as exposure to low-dose secondary X-rays, such as scattered rays. Furthermore, the use of a nanocrystalline WC–Co alloy oxide rather than lead will allow for the development of shielding wear that is lighter and contribute to the development of various radiation-shielding products made of environmentally friendly materials.     

Nanoporous Al sandwich foils using size effect of Al layer thickness during Cu/Al/Cu laminate rolling

The roll bonding technique is one of the most widely used methods to produce metal laminate sheets. Such sheets offer interesting research opportunities for both scientists and engineers. In this paper, we report on an experimental investigation of the ‘thickness effect’ during laminate rolling for the first time. Using a four-high multifunction rolling mill, Cu/Al/Cu laminate sheets were fabricated with a range of thicknesses (16, 40, 70 and 130 μm) of the Al layer. The thickness of the Cu sheets was a constant 300 μm. After rolling, TEM images show good bonding quality between the Cu and Al layers. However, there are many nanoscale pores in the Al layer. The fraction of nanoscale pores in the Al layer increases with a reduction in the Al layer thickness. The finite element method was used to simulate the Cu/Al/Cu rolling process. The simulation results reveal the effect of the Al layer thickness on the deformation characteristics of the Cu/Al/Cu laminate. Finally, we propose that the size effect of the Al layer thickness during Cu/Al/Cu laminate rolling may offer a method to fabricate ‘nanoporous’ Al sandwich laminate foils. Such foils can be used in electromagnetic shielding of electrical devices and noisy shielding of building.     

The effect of Pb2+ dopant in the crystal of CsI and its application as scintillation detector: a study of alpha particles

Scintillation crystals have been used in various fields, such as high energy physics, nuclear instrumentation, radiation measurements, medical imaging, nuclear tomography, astrophysics and other fields of science and engineering. For these applications, the development of scintillation crystals with good performance is required. Scintillation crystals based on cesium iodide (CsI) matrix are matters with relatively low hygroscopicity, easy to handle and of low cost, characteristics that favor their use as radiation detectors. In this study, pure CsI crystal and lead doped CsI crystals were grown using the Bridgman vertical technique. The concentration of the lead doping element (Pb) was studied in the range of 10^?2 to 5×10^?4 M. The distribution of the doping element in the crystalline volume was determined by atomic absorption technique. The CsI:Pb crystal with nominal concentration of 10^?3 M was cut into 14 slices of 6 mm. The results show a higher concentration at the top of the crystal with a decrease in the initial phase of growth. The dopant concentration of Pb showed good uniformity from the slice 2 to the slice 12: the region is, therefore, suitable for use as a radiation detector. The luminescence emission of these crystals was measured. A predominant luminescence band near 450 nm and a single broad band around 320 nm were found with the addition of the Pb²⁺ ions in the CsI matrix. Alpha particles spectrometry measurements were carried out to evaluate the developed scintillators.The resolution of 5.6% was obtained for the CsI:Pb 5×10^?4 M crystal, when excited with alpha particles from a ²⁴¹Am source, with energy of 5.54 MeV.     

Reduction in radiation dose with reconstruction technique in the brain perfusion CT

The principal objective of this study was to verify the utility of the reconstruction imaging technique in the brain perfusion computed tomography (PCT) scan by assessing reductions in the radiation dose and analyzing the generated images. The setting used for image acquisition had a detector coverage of 40 mm, a helical thickness of 0.625 mm, a helical shuttle mode scan type and a rotation time of 0.5 s as the image parameters used for the brain PCT scan. Additionally, a phantom experiment and an animal experiment were carried out. In the phantom and animal experiments, noise was measured in the scanning with the tube voltage fixed at 80 kVp (kilovolt peak) and the level of the adaptive statistical iterative reconstruction (ASIR) was changed from 0% to 100% at 10% intervals. The standard deviation of the CT coefficient was measured three times to calculate the mean value. In the phantom and animal experiments, the absorbed dose was measured 10 times under the same conditions as the ones for noise measurement before the mean value was calculated. In the animal experiment, pencil-type and CT-dedicated ionization chambers were inserted into the central portion of pig heads for measurement. In the phantom study, as the level of the ASIR changed from 0% to 100% under identical scanning conditions, the noise value and dose were proportionally reduced. In our animal experiment, the noise value was lowest when the ASIR level was 50%, unlike in the phantom study. The dose was reduced as in the phantom study.     

Excellent electromagnetic interference shielding effectiveness of chemically reduced graphitic oxide paper at 101 GHz*

Graphitic oxide (GO) was synthesized by oxidation of graphite powder using Hummer’s method and the formed GO is solution processed into paper-like macroscopic form. Subsequently, chemically reduced graphitic oxide paper (CRGOP) is prepared by hydrazine vapours induced reduction of formed GO precursor based paper. The formation of GO and its successful reduction to RGO phase is confirmed by FTIR, Raman Spectroscopy and X-ray diffraction. It has been observed that due to high electrical conductivity ~200 micron thick CRGOP display excellent EMI shielding performance at very high frequency of 101 GHz frequency with total shielding effectiveness (SE) value of ?35.49 dB (i.e. >99.97% blocking of incident EM radiation) which is much higher compared to pristine GO paper (?1.55 dB) or comparable to expanded graphite (EG) sheet (?35.61 dB). Due to their lightweight nature, these freestanding CRGOPs display average specific SE value of ?221.8 dB cm³/g. Besides, their excellent flexibility and makes them potential candidate for lightweight EMI gasketing material compared to other forms of flexible carbons like EG.     

Optimal tube potential and tube current for radiation dose reduction in routine adult head computed tomography scanning

ABSTRACT

We proposed a new, optimised scanning parameter that can reduce the patient’s radiation dose while maintaining image quality in a head computed tomography (CT) scan. We evaluated the clinical CT scan parameters (tube voltage, tube current, slice thickness pitch, scan range, rotation time, and CT dose index) for brain CT examination in a total of 52 multi-detector row spiral CTs (SOMATOM Definition AS+, Siemens Healthcare, Germany). The data were analysed, and the range of valid scan parameters was determined clinically using quartile distribution within the 95% confidence interval. The American Association of Physicists in Medicine performance evaluation phantom was used to acquire images using these scan parameters, and new, optimised CT scan parameters were proposed by analysing CT number accuracy, noise, uniformity, spatial resolution, and contrast resolution. The new CT scan parameters proposed were determined as tube voltage 100?kVp and tube current 300?mAs. Compared with conventional clinical scan parameters, tube voltage was reduced by 16.7% and tube current was decreased by 33.3%. Loss in imaging accuracy and uniformity of CT number was less than 20%, loss in noise was less than 40%, and no change in resolution was observed. Conversely, the CT dose index and effective dose was 20%–50%. A new systematic method for clinically assessing the optimised CT scan parameters were proposed, and the effective dose was decreased, with changing exposure conditions.     

Ion scattering spectroscopy studies of barium and oxygen on tungsten and tungsten-based dispenser cathodes

In order to use Ion Scattering Spectroscopy (ISS) for studies of tungsten dispenser cathodes, the relevant ISS sensitivities must be measured. Calibrations have been made using a polycrystalline tungsten ribbon with controlled coverages of oxygen, barium and combinations thereof. Auger Electron Spectroscopy (AES) was used to monitor these controlled surfaces and the escape depths of the tungsten Auger electrons in barium and oxygen have been measured. The absolute ISS sensitivities of all three elements were found to be strongly dependent on the barium coverage of the tungsten surface. This effect has been attributed to the lowering of the work function of the tungsten surface caused by the barium adsorption. However, the relative ISS sensitivities of the three elements are not affected in this way when both barium and oxygen (or oxygen alone) are present on the tungsten surface. ISS spectra of such surfaces have been analyzed quantitatively and found to be in reasonable agreement with AES measurements. The analysis has also been applied to ISS spectra of uncoated tungsten matrix dispenser cathodes in an active state and following exposure to oxygen. Compared to AES, these spectra indicate less oxygen on the active cathode surfaces as a result of the oxygen (associated with barium) not contributing to the oxygen ISS signal. Comparisons of the spectra from the active and oxygen poisoned cathodes suggest that oxygen adsorbed during the oxygen exposure sits on the topmost barium layer whereas the oxygen on the active cathode surface does not.     

EMI shielding effectiveness of graphene decorated with graphene quantum dots and silver nanoparticles reinforced PVDF nanocomposites

Graphene decorated with graphene quantum dots (G-D-GQDs) have been successfully synthesized using solvothermal cutting of graphene oxide. The incorporation of G-D-GQDs in polyvinyledene fluoride (PVDF) matrix shows the total EMI shielding effectiveness (SE_T) of 31 dB at 8 GHz. The main mechanism of high EMI shielding effectiveness is reflection and absorption of EM radiation. The high absorption of EM radiation is due to tunneling of electrons from GQDs. Further, decoration of G-D-GQDs with conducting Ag nanoparticles (G-D-GQDsAg) enhances the SE_T value to 43 dB at 8 GHz of PVDF/G-D-GQDsAg nanocomposite, due to increase in electrical conductivity of PVDF/G-D-GQDsAg nanocomposite and enhanced dispersion of G-D-GQDsAg in PVDF matrix. The incorporation of G-D-GQDs and G-D-GQDsAg in PVDF matrix also increases the thermal stability and crystallinity of PVDF. The increase in thermal stability and crystallinity are more for PVDF/G-D-GQDsAg nanocomposite as compare to PVDF/G-D-GQDs nanocomposite, due to better dispersion of G-D-GQDsAg in PVDF matrix. Thus, PVDF/G-D-GQDsAg nanocomposite having high SE_T value can shield 99.9% of electromagnetic radiation in X-band range, which make it suitable for EMI shielding application for consumer electronic equipment’s.     

Shielding effects in fusion reactions with a proton-halo nucleus

To explain the experimental observation that the fusion cross-section of a proton-halo nucleus with a heavy target nucleus is not enhanced as expected,the shielding hypothesis was proposed,where the proton-halo nucleus is polarized and the valence proton shielded by the core.In the frame of the improved quantum molecular dynamics model,the fusion reaction 17F on 208Pb around the Coulomb barrier is simulated.The existence of the shielding effect is verified by the microscopic dynamics simulations.Its influence on the effective interaction potential is also investigated.     

Method for Monitoring of Neutron Fields near High-Energy Accelerators

The monitoring of neutron radiation from high-energy accelerators cannot fully rely on the standard dosimeters and radiometers manufactured in Russia, since these are sensitive only to neutrons with energies below some 10 MeV. This is because neutrons of higher energies can significantly contribute to the personnel doses both close to the accelerator shield and in the neutron multiscattered field around the shield. In this paper, we propose to measure the ambient neutron dose in energy range 10^–2 MeV to 1 GeV with a device consisting of two polyethylene balls with diameters of 3 and 10 in. housing slow-neutron detectors. The larger ball also comprises a lead converter (10'' + Pb). This device can be implemented in zonal radiation monitoring in the near-accelerator area.     

DFT studies of Si- and Al-doping effects on the acetone sensing properties of BC3 graphene

In order to find a novel sensor, reactivity and sensitivity of the intrinsic, Al- and Si-doped BC₃ graphene-like sheets to an acetone molecule were investigated by using B3LYP and ωB97X-D density functional calculations. Adsorption of acetone on the intrinsic, Al- and Si-doped BC₃ sheets releases energies of about 7.2, 36.5 and 24.8 kcal/mol, respectively, using ωB97X-D. The Si-doped sheet presents high sensitivity to acetone compared with the intrinsic and Al-doped sheets indicated by the calculated geometrical structures and electronic properties for these systems. The HOMO/LUMO energy gap of Si-doped BC₃ sheet is significantly decreased from 2.20 to 1.65 eV (B3LYP), which would result in electrical conductance increment. Thus, Si-doped sheet are expected to be a potential candidate for detecting the presence of acetone.     

Study on the effects of gadolinium-based MRI contrast medium on X-ray scanning

Gadolinium has a higher atomic mass (64) than iodine (53). The K-edge absorption energy of gadolinium is 50.2 keV, which is in the absorbed wavelength range of the X-rays used by a CT scanner, suggesting that it has a high X-ray absorption ability. This study examined the effects of a gadolinium-based MRI contrast medium on the quality (mAs) and the quality (kVp) of radiation during a X-ray scan. A contrast medium phantom was manufactured after diluting the contrast medium to various concentrations. A CT scanner (Siemens, Somatom Senation 64, Germany) was used to obtain images by changing the quality of radiation from 80 kVp to 100, 120, and 140 kVp. At a constant quality of radiation of 120 kVp, the mAs was changed from 100 mAs to 200 and 300 mAs and images were obtained under each condition. The Hounsfield units (HUs) in a test tube were measured for analysis and comparison. The contrast enhancement by the contrast medium for CT scanning was 100% at a tube voltage of 80 kVp. The contrast enhancements at 100 kVp, 120 kVp, and 140 kVp were 93.8%, 87.7%, and 69.5%, respectively. In addition, although the quantity increased a fixed tube voltage, the HU of the test tube remained relatively constant, indicating that the absorption of the contrast medium had little association with the quantity of X-rays but had some correlation with the quality of radiation. A tube voltage of 80 kVp or lower is recommended when a MRI contrast medium is used CT scanning. When MRI scanning and X-ray scanning are conducted together, X-ray scanning should be performed first or after sufficient gadolinium contrast medium has been excreted.

     

95 MeV射频电子直线加速器辐射防护分析

应相关建设安评、环评、稳评以及职业健康评估的要求,电子加速器设计过程中即应对其辐射情况进行分析。针对电子能量为40～95 MeV可调的光阴极微波电子枪直线加速器,对其辐射源项进行分析,并讨论了可能的辐射防护措施的效果。采用蒙特卡罗软件FLUKA对电子束流和加速器进行建模,通过模拟计算发现,加速器产生的等效剂量分布主要位于废束桶中,废束桶以外辐射剂量迅速下降,在电子加速器实验大厅四周设置混凝土墙体的情况下辐射等效剂量率将随墙体厚度迅速下降。若混凝土墙体厚度设置为1 m,则墙体外工作人员所在区域辐射等效剂量率不高于1 μSv/h量级,能够有效屏蔽加速器产生的电离辐射,给工作人员提供有效防护。研究方法及结果对同能区同类型加速器建设中的辐射分析及辐射防护评估具有一定的参考价值。     

The effects of shielding around the source on neutron energy spectra

The knowledge of neutron energy spectra contributes to unambiguous identification of neutron sources in the fields of nuclear safeguards and nuclear non-proliferation. Since a real scenario situation includes the presence of shielding around the source, we have investigated the influence of the potential shielding surrounding the source on the shape of energy spectra for a few neutron sources. We have applied the maximum-likelihood, expectation–maximisation (MLEM) method with one-step-late (OSL) algorithm for neutron spectra unfolding. The pulse height distributions used in the unfolding procedures were simulated with the high accuracy by using the MCNP-PoliMi code based on the Monte Carlo method. A possibility to identify the shielded neutron sources by using the unfolding method was examined with two continuous-in-energy sources, such as ²⁵²Cf and ²⁴¹Am–Be in source-shielding configurations with lead (Pb) and polyethylene (PE) blocks. The results of calculations have shown that the identification of ²⁵²Cf and ²⁴¹Am–Be sources with 2.5 cm of Pb and PE shield can be achieved successfully by using the MLEM method with the OSL algorithm. However, the unfolded results for ²⁵²Cf and ²⁴¹Am–Be sources with 10 cm of PE shield significantly deviate from the reference spectra and the sources cannot be correctly identified on the basis of their unfolded energy spectra.