Shielding Calculations Research Articles

Radiation shielding calculations of some selected rare earth oxides

Radiation shielding parameters of oxidized compounds of some selected rare earth elements were determined. These parameters are mass absorption coefficient, effective atomic number, electron density, half-value layer, tenth value layer, and mean free path values. A variable energy x-ray (VEX) source was used as an exciter in the system, where these basic parameters will be determined. An experimental setup was prepared in attenuation geometry. Experimentally measured and theoretically calculated mass attenuation values of the target materials were used to calculate radiation protection parameters. As can be seen from previous works, the WinXCOM program efficiently calculates theoretical atomic cross-sections and mass absorption coefficients. As a result of the search for alternatives to this software, ParShield and Phy-X programs have emerged at different times. In this study, the validity of ParShield and Phy-X programs produced as other options to the WinXCOM program were tested, and the results were found to be entirely satisfactory.

Stabilization of a flavoprotein for solid-state photo-CIDNP MAS NMR at room temperature by embedding in a glassy sugar matrix

Hyperpolarization via the solid-state photochemically induced dynamic nuclear polarization (photo-CIDNP) effect can be detected in frozen solutions of electron transfer proteins generating a radical-pair upon illumination. The effect has been observed in various natural photosynthetic reaction centers and in light-oxygen-voltage (LOV) sensing domains incorporating a flavin mononucleotide (FMN) as chromophore. In LOV domains, where a highly conserved cysteine is mutated to a flavin to interrupt its natural photochemistry, a radical-pair is generated by electron transfer from a nearby tryptophan to the photoexcited triplet state of FMN. During the photocycle, both the LOV domain and the chromophore are photochemically degraded, e.g., by the formation of singlet oxygen. This limits the time for collection of hyperpolarized nuclear magnetic resonance (NMR) data. We show that embedding of the protein into a trehalose sugar glass matrix stabilizes the protein for 13C solid-state photo-CIDNP NMR experiments which can be conducted at room temperature in a powder sample. Additionally, this preparation allows for incorporation of high amounts of protein further boosting the intensity of the detected signals from FMN and tryptophan at natural abundance. Signal assignment is aided by quantum chemical calculations of absolute shieldings. The underlying mechanism for the surprising absorption-only signal pattern is not yet understood. Comparison to calculated isotropic hyperfine couplings imply that the enhancement is not due to the classical radical-pair mechanism (RPM). Analysis of the anisotropic hyperfine couplings associated with solid-state photo-CIDNP mechanisms also show no simple correlation, suggesting a more complex underlying mechanism.

Simulation of neutron shielding performance of Al-Cd alloy for radioactive waste container

Neutron shielding material is necessary for the container of radioactive waste emitting neutrons, such as spent fuel from research reactor. This study aimed to determine the shielding performance of Al-Cd material for neutron radiation emitted by radioactive radiation. The calculations of neutron shielding were carried out using MNCP5 software. The Al-Cd shielding was simulated to withstand a neutron radiation source with 2.538×10−8 MeV energy and 4.5 MeV energy moderated with paraffin. The Al-Cd was simulated as a homogeneously-mixed alloy and Al coated with Cd. The results show that addition of Cd to Al increased the neutron shielding performance for thermal and fast neutron. With the addition of 10% Cd to Al, the neutron shielding performance increased by more than 90% for thermal neutron, and 30% for fast energy neutron moderated with 5 cm thick paraffin. It shows that Al-Cd alloy is potential for radioactive waste container which requires high neutron shielding performance.

Shielding design aspects of SR in 3 GeV ILSF

Iranian Light Source Facility (ILSF) is an under-construction synchrotron radiation accelerator consisting of a 150 MeV linac, a booster synchrotron operating from 150 MeV to 3 GeV, and a 3 GeV storage ring that stores a maximum of 400 mA current of electrons. As the stored beam circulates, a fraction of the beam is lost due to interactions with gas molecules, interactions among beam particles, and orbital bending, which produce radiation. The bulk shielding calculation for the ILSF and the input parameters used for this analysis are discussed in this paper. The potential of skyshine neutrons to cause radiation hazards is investigated as well. Moreover, the design and shielding simulation using the FLUKA Monte Carlo code is presented for the linac beam stop and primary and scattered gas bremsstrahlung for the first optics enclosure of the ILSF spectro microscopy beamline. Our designed radiation shielding system guarantees that the annual dose in all areas around the ILSF machine does not exceed the dose limit of 1 mSv.

Characterization of the radiation field surrounding the Leksell Gamma Knife® and shielding applications

The aim of this study is to improve the characterization and modeling of the radiation field surrounding the Leksell Gamma Knife®-PerfexionTM. The improved characterization of the radiation field enables more accurate shielding calculations to be performed for the areas adjacent to the treatment room. With the aid of a high-purity germanium detector and a satellite dose rate meter, γ-ray spectra and ambient dose equivalent H*(10) data were acquired at various locations in the field of a Leksell Gamma Knife unit in a treatment room at Karolinska University Hospital, Sweden. These measurements were used to validate the results of the PEGASOS Monte Carlo simulation system with a PENELOPE kernel. The levels of the radiation that passes through the shielding of the machine (leakage radiation) are shown to be much lower than what is suggested by various bodies, e.g. the National Council on Radiation Protection and Measurements, to be used when calculating radiation shielding barriers. The results clearly indicate that Monte Carlo simulations may be used in structural shielding design calculations for γ rays from the Leksell Gamma Knife.

Verification and Analysis of the Problem-Dependent Multigroup Macroscopic Cross-Sections for Shielding Calculations

Multigroup constants are the foundation of neutron and photon transport problems, and the accuracy of multigroup cross-sections has a significant impact on shielding calculation. Challenges have arisen in generating accurate multigroup macroscopic cross-sections for some problems using the widely used cross-section processing code TRANSX 2.15. We developed the multigroup neutron-photon macroscopic cross-section processing module in the shielding transport code ARES. The module is capable of handling the neutron-photon coupled master libraries in MATXS format and providing the problem-dependent multigroup macroscopic cross-sections tailored to each specific shielding physics problem. The self-designed problems with a single nuclide, as well as the iron and OKTAVIAN experiments, are used to verify and analyze the accuracy of neutron and photon macroscopic cross-sections. Results indicate that the macroscopic cross-sections, neutron flux and neutron-photon leakage spectrum obtained by the MGMXS module are consistent with corresponding reference values. As for the JANUS Phase I fixed source shielding benchmark, the relative differences in the reaction rate between the calculation results and experimental data are within 20%. The module provides better problem-dependent multigroup macroscopic cross-sections for neutron and photon shielding calculations that satisfy the accuracy requirements of engineering applications.

First-principles study on the NMR shielding of transition metal semiconductors

The theoretical calculation of chemical shielding can help us understand the information of nuclear magnetic resonance experiment more deeply. In this work, three different functionals had been used to study the isotropic shielding of various transition metal nuclei. The predicted trend of our theoretical results matched the experimental results well. It was found that the large (more than 2000 ppm) variation of measured 93Nb and 51V chemical shifts were mainly determined by the occupied and empty states of d orbitals. Furthermore, the effect of the energy differences between the occupied and empty states of d orbitals had been discussed as well. This work is helpful to understand the sources and differences of chemical shifts of certain nuclei in transition metal semiconductors.

Effective Dose Transmittance of Photons of 85 Radionuclides for Shield Calculation of Radiation Facilities—Additional Data to “Data for Shield Calculation of Radiation Facilities (2015)”—

『放射線施設の遮蔽計算実務（放射線）データ集』（原子力安全技術センター）は遮蔽計算の典拠として広く利用されている。現行の2015年版のデータを補うため，近年重要性が高まっている85核種を対象に，光子の実効線量透過率，放射平衡を示す核種の使用状況を想定しての子孫核種，遮蔽材（鉛・タングステン・鉄・銅・コンクリート及び水）について計算を行った。

Estimation of the yield and angular distribution of neutrons for calculating the biological shielding of reconstructed heavy ion accelerators with energies from 1 to 6 MeV/u

A simple analytical formulas for estimation of the yield and angular distribution of neutrons from thick targets would be useful for calculating the biological protection of heavy ion accelerators with energy (1–6) MeV/nucleon. The results of the calculation with this formulas were compared with those obtained using the LISE++ and FLUKA programs as well as with the available experimental data. As a result, it can be stated that the proposed calculation method can be used for quick assessment. The deviation of the results of such calculations from more accurate ones does not exceed a factor of two, which is comparable with the deviations in the calculation of biological shielding due to a variety in the protection properties of the materials used or in their thickness.

Recycled hybrid material for use as shielding in operations with ionizing radiation

One of the most efficient measures to prevent gamma radiation is shielding, which can take the form of protection barriers, storage containers, wall coating, bunkers, or many others aimed at minimizing the exposure of people to radiation. The materials used to this end have not changed much since the invention of X-rays, when materials with high attenuation capacity were employed, such as lead, tungsten, or concrete. These are all high-density materials and, therefore, also very heavy, and some of them are expensive and not environmentally friendly, as they do not have many possibilities with regards to their recycling. Circular economy provides an opportunity to reintroduce subproducts and waste in the same production processes that generated them or as raw matters in others. The use of sustainable materials is one of these options; however, there is little research in the field of radiation protection about the use of recycled material to this end, and there are few alternative sustainable options different from conventional materials that show similar behaviour. In our study, we have designed and built shielded panels called Mixlead® for gammagraphy, made of 100 % recyclable materials with sandwich structures combining polymeric fractions of electric cables and lead-alloy protection sheets used in the packaging of radiographic plates. With a methodology combining shielding calculations and a series of thermomechanical-radiological tests, it was possible to accurately determine the thickness of Mixlead® necessary to perform the tests with security guarantees and meeting sustainability requirements for radioactive sources of Iridium (192Ir) and Selenium (75Se), the use of the former being predominant, with an average activity of 1 GBq. In order to reduce this activity 2 and 10 times, the necessary thickness would be 24 and 79 mm respectively, which represents 3 or 4 layers of Mixlead® material.

Searching for the Best Values of NMR Shielding and Spin-Spin Coupling Parameters: CH4-nFn Series of Molecules as the Example.

Attempts at the theoretical interpretation of NMR spectra have a very long and fascinating history. Present quantum chemical calculations of shielding and indirect spin-spin couplings permit modeling NMR spectra when small, isolated molecules are studied. Similar data are also available from NMR experiments if investigations are performed in the gas phase. An interesting set of molecules is formed when a methane molecule is sequentially substituted by fluorine atoms-CH4-nFn, where n = 0, 1, 2, 3, or 4. The small molecules contain up to three magnetic nuclei, each with a one-half spin number. The spectral parameters of CH4-nFn can be easily observed in the gas phase and calculated with high accuracy using the most advanced ab initio methods of quantum chemistry. However, the presence of fluorine atoms makes the calculations of shielding and spin-spin coupling constants extremely demanding. Appropriate experimental 19F NMR parameters are good but also require some further improvements. Therefore, there is a real need for the comparison of existing NMR measurements with available state-of-the-art theoretical results for a better understanding of actual limits in the determination of the best shielding and spin-spin coupling values, and CH4-nFn molecules are used here as the exceptionally important case.

Benchmark shielding calculations for fusion and accelerator-driven sub-critical systems

We conducted benchmark calculations of neutron-shielding experiments for fusion applications such as (1) Neutron spectra in iron shields with 14 MeV neutrons; and (2) Leakage neutron spectra from various sphere piles by 14 MeV neutrons, and for Accelerator-Driven Sub-Critical system (ADS) such as (3) Neutron energy spectra after transmission through iron and concrete shields using a quasi-monochromatic neutron source, (4) Thick target neutron yield produced by high-energy heavy ion incidence on a thick target, and (5) Induced radio activity in concrete exposed to secondary particles produced by heavy-ion incident reaction on an iron target by using the Particle and Heavy Ion Transport code System (PHITS). For case (1), the calculated neutron energy spectra using the nuclear data libraries, JENDL-4.0, agreed with the experimental data in iron shields. For the cases (2) of Al, Ti, Cr, and As piles, the neutron energy spectra calculated with JENDL-4.0 agreed with the experimental results well. For the case (3), the neutron spectra calculated with JENDL-4.0/HE reproduced the experimental data because the proton data library of7Li can produce source neutrons for proton incident reactions. For the case (4), calculated results for thick target neutron spectra produced by a 400 MeV per nucleon carbon incident reaction on lead reproduced the experimental data well. For the case (5) with a neutron source produced by the 200–400 MeV per nucleon heavy-ion incident reaction, the calculated results of the reaction rate depth profiles of197Au (n, γ)198Au reactions reproduced the experimental results within a factor of 2. Overall, PHITS with nuclear data libraries reproduced the experimental data sufficiently well. Thus, PHITS has a potential application in the design of advanced reactor systems, such as fusion and ADS facilities. This experimental data are also useful in validating nuclear reaction models in other Monte Carlo codes and evaluating nuclear data libraries for advanced reactor systems.

Technical note: Investigating the suitability of existing facilities for a new Lu-177 prostate-specific membrane antigen therapy program.

177 Lu prostate-specific membrane antigen (PSMA) therapy prolongs survival for some prostate cancer patients. To adopt this technique, institutions may need to evaluate the suitability of existinginfrastructure. Develop a methodology to determine whether existing facilities can accommodate a 177 Lu-PSMA therapy program. Room suitability is defined by both the ability to accommodate 177 Lu-PSMA therapy workflow and to provide appropriate radiation shielding. Two methods of shielding calculation were performed: (1) National Council on Radiation Protection and Measurements report 151 (NCRP-151), with workload defined in terms of the activity of 177 Lu administered, and (2) using the RadPro shielding calculator. This methodology was applied to 131 I therapy, PET-CT uptake, PET-SPECT injection, and orthovoltage therapyrooms. 131 I therapy rooms were found to meet both shielding and workflow requirements. The shielding was found to be adequate for orthovoltage and PET-SPECT facilities, neglecting patient transit between external washrooms. The workflow was the limiting factor for these rooms due to the requirement of dedicated washrooms that shield the patient and contain possible contamination. The PET-CT facility did not meet either criteria. The NCRP-151 method generally predicted a higher dose rate on the other side of shielding than did the RadPro calculator. The dose rate on the other side of concrete shielding as predicted by the NCRP-151 method increased relative to the dose rate predicted by the RadPro calculator as shielding thickness increased. For lead shielding, the dose rate predicted by the NCRP-151 method decreased relative to the result predicted by the RadPro calculator with increasing materialthickness. 131 I therapy, PET-CT uptake, PET-SPECT injection, and orthovoltage therapy rooms were considered. The 131 I treatment rooms were the best candidate for 177 Lu-PSMA therapy, due to their shielding and capability to accommodate the necessary workflow.

NMR chemical shielding in cyclosarcosyl

NMR chemical shifts have a role to play when determining the structure of proteins by NMR methods through their dependence on the local conformation. NMR chemical shielding calculations are presented demonstrating that with an appropriate electronic model and basis set the CαH inequivalence in cyclosarcosyls can be rationalised. In the case of cyclotrisarcosyl the inequivalence is best understood in terms of a steric effect. While for cyclotetrasarcosyl, although significant distant, non-bonded, effects of a peptide group are seen, the vast majority of the large, greater than 2 ppm, inequivalence is attributable to the local conformation between adjacent sarcosine.

Assessment of emission data and transmission factors supporting radiation protection in the use of 225Ac

Purpose225Ac is the most promising alpha emitter for radiopharmaceutical therapy. Labeling PSMA, it showed to be effective in the treatment of prostate cancer and research is undergoing in order to improve its production capacity.Currently, there are still few data published concerning operational radiation protection in its use, both in clinics and in radiopharmacy, and even some basic data are not readily available. This papers aims to estimate the emission gamma-ray constant of 225Ac when at equilibrium with its descendants, and the transmission factors for a broad beam of the gamma-rays emitted by 225Ac and its descendants. Materials & methodsMonte Carlo simulations were performed using FLUKA 4.2, considering firstly the source in air, in absence of any shielding, and secondly by adding an increasing thicknesses of Lead, Concrete or Tungsten. In order to obtain statistically meaningful results, high-statistics simulations were performed by sampling up to 1010 primary decay events. As the shielding thickness increased, an appropriate variance reduction technique (importance biasing) was applied. ResultsThe specific gamma ray emission constant for 225Ac at equilibrium with descendants resulted (3.26 ± 0.03) × 10-5 mSv/h per 1 MBq at a distance of 100 cm. The transmission factors are presented in detail and data have been appropriately interpolated and fitting parameters are reported. ConclusionsThe attenuation curves show a clear bi-exponential trend: performing shielding calculations by adopting a simple approach based on a single value of Half Value Layer (HVL) or Tenth Value Layer (TVL) cannot provide adequate results.In conclusion, our results may be useful in the design of shielded hot cells or accessories necessary for operational radiation protection.

Radiation shielding design for the target area in the pre-separator of HFRS at HIAF

High energy FRagment Separator (HFRS), an essential part of High Intensity heavy-ion Accelerator Facility (HIAF), is used to produce, separate and identify the Radioactive Ions Beams (RIBs). The target area in the pre-separator of HFRS can produce very strong secondary radiation, which seriously threatens the radiation safety of the environment, public and personnel. In this work, the FLUKA code is used to complete the radiation shielding calculation and design of the target area. Firstly, the secondary radiation produced by 25 different typical beam–target combinations are compared. The parameter of 78Kr in fast extraction mode is determined as the basis for the radiation shielding design based on its strongest secondary radiation. Then, the secondary neutron spectrum and the induced radioactivity of the production target and the beam dump are analyzed. The results show that the maximum neutron energy is close to 3 GeV, and special attention should be paid to high-energy neutrons in shielding design, as well as the maximum residual dose rates on the surface of the production target and the beam dump are 3.93 × 107μSv/h and 9.58 × 107μSv/h, respectively, after one month of continuous irradiation. Furthermore, the radiation shielding design is completed using the Q235 steel compact shielding together with the ordinary concrete and sand soil, based on the Monte Carlo simulations and the relevant dose limits. Finally, the radiation effects under this shielding scheme are analyzed. The results show that the shielding design meets the relevant design goals and can provide reliable radiation protection for the environment, public and personnel.

Improving the accuracy of GIPAW chemical shielding calculations with cluster and fragment corrections

Ab initio methods for predicting NMR parameters in the solid state are an essential tool for assigning experimental spectra and play an increasingly important role in structural characterizations. Recently, a molecular correction (MC) technique has been developed which combines the strengths of plane-wave methods (GIPAW) with single molecule calculations employing Gaussian basis sets. The GIPAW + MC method relies on a periodic calculation performed at a lower level of theory to model the crystalline environment. The GIPAW result is then corrected using a single molecule calculation performed at a higher level of theory. The success of the GIPAW + MC method in predicting a range of NMR parameters is a result of the highly local character of the tensors underlying the NMR observable. However, in applications involving strong intermolecular interactions we find that expanding the region treated at the higher level of theory more accurately captures local many-body contributions to the N15 NMR chemical shielding (CS) tensor. We propose alternative corrections to GIPAW which capture interactions between adjacent molecules at a higher level of theory using either fragment or cluster-based calculations. Benchmark calculations performed on N15 and C13 data sets show that these advanced GIPAW-corrected calculations improve the accuracy of chemical shielding tensor predictions relative to existing methods. Specifically, cluster-based N15 corrections show a 24% and 17% reduction in RMS error relative to GIPAW and GIPAW + MC calculations, respectively. Comparing the benchmark data sets using multiple computational models demonstrates that N15 CS tensor calculations are significantly more sensitive to intermolecular interactions relative to C13. However, fragment and cluster-based corrections that include direct hydrogen bond partners are sufficient for optimizing the accuracy of GIPAW-corrected methods. Finally, GIPAW-corrected methods are applied to the particularly challenging NMR spectral assignment of guanosine dihydrate which contains two guanosine molecules in the asymmetric unit.

A Monte Carlo simulation model to determine the effective concrete materials for fast neutron shielding

Concretes are popularly used as shielding materials in nuclear radiation facilities. Special concrete features are employed in the facilities where Fast neutrons, including corresponding ‘prompt gamma’ rays, are prevalent. The conventional shielding calculations for fast neutrons are complicated and constrained with energy-limited formulas. In this research work, a concrete bunker model has been developed with a variety of compositions and densities. Eleven following appropriate composite materials were used in this case; G4_C (2.3), Ordinary (2.5), Barytes BA-a (3.5), Magnetite M-a (3.55), Ilmenite I-Ia (3.5), Limonite with Steel Punch LS-a (4.54), (80%G4_C+20%Fe+10%B) Mix-1 (2.9), (80%G4_C+20%B4C) Mix-2 (2.35), (80%G4_C+20%BaSO4) Mix-3 (2.74), Serpentine (3) and Serpentine (3.3). Depth-dose profiles for each concrete composition were investigated by Monte Carlo simulation, subjected against an 18.5 MeV neutron source. Shielding properties, like Relaxation lengths, Half Value Layers, and Tenth Value Layers have been deduced harnessing these data. The most efficient materials for shielding fast neutrons regarding half value layers found for the two physics lists, QGSP_BERT_HP and Shielding, successively are, 5.78 and 12.48 cm for Serpentine (3.3), 14.88 and 9.18 cm for Ilmenite I-Ia (3.5), 14.28 and 25.18 cm for Limonite with Steel Punch LS-a (4.54), and 13.58 and 13.48 cm for (80%G4_C+20%Fe+10%B) Mix-1 (2.9). This model could be used to determine the radiation shielding parameters made of any kind of materials and composites using different sources of radiation.

Ammonia: The molecule for establishing 14N and 15N absolute shielding scales and a source of information on nuclear magnetic moments.

Multinuclear Nuclear Magnetic Resonance (NMR) studies of the gaseous mixtures 3He/14NH3 and 3He/15NH3 are reported. Precise analysis of the 3He, 14N, 15N, and 1H resonance frequencies show a linear dependence on the gas density. Extrapolation of these results to the zero-pressure limit gives ν0(1H), ν0(14N), and ν0(15N) resonance frequencies of the isolated ammonia molecule at 300K. The analogous value for 3He atoms in gaseous mixtures ν0(3He) was measured as well. The application of a new scheme to introduce the most important electronic effects on NMR shieldings, together with highly accurate quantum chemical shielding calculations, allows the 14/15N and 1H shielding of the isolated ammonia molecule to be obtained with the greatest accuracy and precision. For the first time, these studies were carried out on ammonia within the so-called four-component relativistic framework. The NMR frequency comparison method provides an approach for determining the 14N and 15N nuclear magnetic moments. The new shielding parameters in ammonia were used for re-evaluation of the entire nitrogen absolute shielding scale. Additionally, the absolute shielding values of several gaseous compounds and secondary reference substances in liquids were presented. It was established that 14N and 15N absolute shielding constants in 14NH3 and 15NH3 are very similar and only differ by less than 0.01 ppm, which is not usually measurable in NMR experiments. Precise calculations of 14N and 15N dipole moments were also made from these accurate shielding values.

The Multi-PN angular discretization method of the neutral-particle transport equation for radiation shielding calculations

The well-known Discrete Ordinates (SN) approximation is little effective in multidimensional radiation shielding calculations. In the presence of geometrically large and low-scattering media, discrete-ordinates solutions are generally affected by the ray effect and an adequate refinement of the angular discretization is sometimes prohibitive in terms of calculation cost. The Multi-PN method (MPN) is an angular discretization technique leading to SN-like transport equations but less affected by ray effect. It relies on a solid angle expansion of the interface fluxes, allowing for a local coupling between different angular degrees of freedom within the same solid angle. This coupling enables to solve the equation by means of a standard sweeping algorithm. Furthermore, flux angular moments are directly integrated without any use of quadrature rules. The MPN measured error convergence rate with respect to the number of angular degrees of freedom is significantly larger than the one measured with SN.