Intermediate Energy Region Research Articles

Low- and intermediate-energy stopping power of protons and antiprotons in solid targets

In this work we propose a non-perturbative approximation to the electronic stopping power based on the central screened potential of a projectile moving in a free electron gas, by Nagy and Apagyi. We used this model to evaluate the energy loss of protons and antiprotons in ten solid targets: Cr, C, Ni, Be, Ti, Si, Al, Ge, Pb, Li and Rb. They were chosen as canonicals because they have reliable values of the Seitz radio, rS=1.48-5.31 a.u., which cover most of the possible metallic solids. Present low velocity results agree well with the experimental data for both proton and antiproton impact. Our formalism describes the binary collision of the projectile and one electron of the free electron gas. It does not include the collective or plasmon excitations, which are important in the intermediate to high velocity regime. The distinguishing feature of this contribution is that by using the present model for low to intermediate energies (below the appearance of plasmon excitations), the Lindhard dielectric formalism (including plasmons) for intermediate to high energies, and the shellwise local plasma approximation to account for the inner shell contribution, then a good full-theoretical description of the available experimental data is obtained in an extensive energy range, covering the low, intermediate and high energy region.

Assessment of radio-protective properties of some anti-inflammatory drugs

When ionizing radiations are exposed to humans, numerous deleterious health effects including cancer may occur. Recently, radioprotective agents with a novel mode of action have drawn strong interest. Radioprotective agents are able to palliate, to prevent, or to handle radio-induced side-effects. In this study, in the parliamentary procedure to investigate the radioprotective effects of some pharmacological compounds, we have estimated the effective atomic number (Zeff) and electron density (Ne) of six analgesic and anti-inflammatory drugs for total photon interaction in the energy range of 1 keV–100 MeV using WinXCom. In addition, and by Geometric-Progression (G-P) method, the energy absorption (EABF) and exposure buildup factors (EBF) for incident photon energy 0.015 MeV to 15 MeV up to penetration depths of 40 mean free paths (mfp) were estimated. It has been observed that EABF and EBF posses maximum values in the intermediate energy region, where Compton scattering is the dominant photon interaction process. Among the selected compounds, Etodolac (ET) has the largest EABF and EBF, while the minimal values of EABF and EBF were recorded for Meloxicam (ME). The present work could be useful to develop novel pharmacological compounds used in radioprotection, medical diagnostics, and radiation therapy.

A Photonuclear Reaction Model Based on IQMD in Intermediate-Energy Region**Supported by the National Natural Science Foundation of China under Grant Nos 11421505 and 11220101005, the National Basic Research Program of China under Grant No 2014CB845401, and the Strategic Priority Research Program of the Chinese Academy of Sciences under Grant No XDB16.

A photonuclear reaction transport model based on an isospin-dependent quantum molecular dynamics model (IQMD) is presented in the intermediate energy region, which is named as GiQMD in this study. Methodology to simulate the course of the photonuclear reaction within the IQMD frame is described to study the photo-absorption cross section and π meson production, and the simulation results are compared with some available experimental data as well as the Giessen Boltzmann–Uehling–Uhlenbeck model.

On the search for a (n,f) cross-section reference at intermediate energies

The (n,f) cross-sections proposed as references by the IAEA for 235U, 238U and 209Bi are compared with a new analysis that combines the measurements performed at CERN-n_TOF of their cross-section ratios with new calculations done using Monte Carlo codes based on phenomenological models INCL+ +, GEMINI+ +, and ABLA07. The calculations are cross-checked with those for the (p,f) reactions, where experimental values are available. We have evaluated in this way the (n,f) cross sections for 238U, 235U and 209Bi, in the intermediate energy region going from 190 MeV to 2 GeV. Our results definitively discard the JENDL/HE-2007 evaluations above 300 MeV, falling inside the confidence corridor proposed by IAEA but for the points around 300–400 MeV where a discrepancy is to be noticed.

A comprehensive study of the energy absorption and exposure buildup factors of different bricks for gamma-rays shielding

The present investigation has been performed on different bricks for the purpose of gamma-ray shielding. The values of the mass attenuation coefficient (µ/ρ), energy absorption buildup factor (EABF) and exposure buildup factor (EBF) were determined and utilized to assess the shielding effectiveness of the bricks under investigation. The mass attenuation coefficients of the selected bricks were calculated theoretically using WinXcom program and compared with MCNPX code. Good agreement between WinXcom and MCNPX results was observed. Furthermore, the EABF and EBF have been discussed as functions of the incident photon energy and penetration depth. It has been found that the EABF and EBF values are very large in the intermediate energy region. The steel slag showed good shielding properties, consequently, this brick is eco-friendly and feasible compared with other types of bricks used for construction. The results in this work should be useful in the construction of effectual shielding against hazardous gamma-rays.

Measurements of K-shell ionization cross sections of Al and L-shell x-ray production cross sections of Se by intermediate-energy electron impact

The K-shell ionization cross sections of Al (Z = 13) and the total L-shell x-ray production cross sections of Se (Z = 34) from electron impacts with kinetic energies ranging from several keV to several tenths of keV have been measured by using an improved experimental setup. An Al target of monoatomic and grid carbon substrate, which consisted of ultrathin Al film (∼3 nm) deposited onto grid carbon substrate (∼200 nm) with a layer of monoatomic carbon between the film and the grid substrate, was first proposed and measured. In addition, targets of Al film (∼3 nm) and Se film (∼7.8 nm) deposited respectively onto thick carbon substrate (∼2 mm) were also measured. Our experimental results are compared with the distorted-wave Born approximation (DWBA) theory and experimental data from the literature. It has been observed that within the uncertainties, the DWBA agrees with our experimental measurements of K-shell ionization cross sections of Al and the total L-shell x-ray production cross sections of Se, and our measured data of Al K-shell ionization cross sections are consistent with the available experimental data. This is the first time that experimental data of Se-L-shell x-ray production cross sections in the intermediate-energy region have been published.

Electron interaction with dimethyl disulfide in the low- and intermediate-energy range

We report a joint theoretical-experimental investigation on elastic electron scattering by dimethyl disulfide in the low- and intermediate-energy regions. Experimental angular distributions of the elastically scattered electrons were measured in the 10--800 eV and ${5}^{\ensuremath{\circ}}$--${130}^{\ensuremath{\circ}}$ ranges using a crossed electron beam--molecular beam geometry. The absolute values of the differential cross sections were obtained using the relative-flow technique. Also, integral and momentum-transfer cross sections were derived from the experimental differential cross sections via a numerical integration procedure. Theoretically, differential, integral, momentum-transfer, grand-total, and total absorption cross sections are reported in the 1--500 eV range. In our calculations, a complex optical potential was used to represent the collision dynamics and a single-center expansion method combined with the Pad\'e approximation was used to solve the scattering equations. Our experimental data are in good agreement with the present calculated data. Comparisons with other theoretical results are also made.

Variation of energy absorption and exposure buildup factors with incident photon energy and penetration depth for boro-tellurite (B2O3-TeO2) glasses

The gamma ray energy absorption (EABF) and exposure buildup factors (EBF) of (100-x)TeO2-xB2O3 glass systems (where x=5, 10, 15, 20, 22.5 and 25mol%) have been calculated in the energy region 0.015–15MeV up to a penetration depth of 40 mfp (mean free path). The five parameters (G-P) fitting method has been used to estimate both EABF and EBF values. Variations of EABF and EBF with incident photon energy and penetration depth have been studied. It was found that EABF and EBF values were higher in the intermediate energy region, for all the glass systems. Furthermore, boro-tellurite glass with 5mol% B2O3, was found to present the lowest EABF and EBF values, hence it is superior gamma-ray shielding material. The results indicate that the boro-tellurite glasses can be used as radiation shielding materials.

Measuring electron-impact cross sections of water: elastic scattering and electronic excitation of the ã3B1 and Ã1B1 states

Here, we report elastic differential cross sections (DCSs) for electron scattering from water in the incident energy range of 2−100 eV. Furthermore, we present a complete study on the electronic excitation of the a3B1 and A1B1 states at electron impact energies of 15, 20, and 30 eV and in the scattering angle range of 10° − 130°. Integral cross sections (ICSs) are determined from the DCSs. Measuring elastic DCSs in various experimental conditions confirmed the reproducibility of the data. The present results agree with the data previously obtained from a conventional collimating tube gas source. Ambiguities associated with the unfolding procedure of the electron energy loss (EEL) spectra for the electronic excitations have been reduced by comparison against the EEL spectrum at high electron impact energy and for small scattering angle. The reliability of the extracted DCSs is improved significantly for optically forbidden contributions from the overlap of the a3B1 and A1B1 electronic states. The BEf-scaling model is also confirmed to produce the integral cross section for the optical allowed transition of the A1B1 state in the intermediate electron energy region above 15 eV.

Variation of energy absorption build-up factor with penetration depth for some titanium compounds

The buildup factor is an important characteristic that need to be studied and determined prior to using a material clinically in radiation treatment and protection. Energy absorption buildup factors for some titanium compounds like Titanium dioxide (TiO 2 ), Titanium Carbide (TiC), Titanium Nitride (TiN) and Titanium Silicate (TiSi 2 ) has been calculated using the G.P. fitting technique upto penetration depth of 40 mean free path (mfp) and in an energy range from 0.015 to 15.0 MeV. The variation of absorption buildup factors with penetration depth for the selected compounds of titanium has been studied. It has been found that the maximum value of energy absorption buildup factors shifts to the intermediate incident photon energy regions with the increase in penetration depth of the selected compounds of titanium.

Mineralogical composition of hardsetting soils and its effect on the radiation attenuation characteristics

One important group of soils that has not been well studied yet belongs to the hardsetting horizons. These soils have been characterized through basic physical property measurements (porosity, bulk density, particle size distribution). XRD and XRF analytical techniques and the interaction of radiation (X and γ-rays) through the soil can also be interesting tools for a better understanding of the properties of these soils. This work presents the chemical and mineralogical properties of Brazilian hardsetting soils and their effects on the radiation attenuation characteristics. The mass attenuation coefficient (μm) of hardsetting soils was calculated by using the XCOM computer code based on the chemical composition of the soils. Soil samples derived from different regions of Brazil were collected in the hardsetting horizons. Each sample was mashed, sieved, and submitted to dispersion and physical fractioning process by sedimentation. Semi-quantitative elemental analysis of the soils was accomplished through EDXRF. Based on the soil chemical composition analyses, the contribution of the photoelectric absorption and incoherent and coherent scatterings were investigated. The mineralogical composition was determined through the Rietveld method combined with X-ray diffraction (RM-XRD) data. The soil mass attenuation coefficient decreased increasing the photon energy as expected. A great decrease was observed in the low photon energy region, where the contribution of the photoelectric absorption was dominant. Regarding the intermediate photon energy region, where the contribution of the incoherent scattering was dominant, only a slight decrease was observed in μm with photon energy. Strong positive and moderate negative linear correlations were found between μm and Fe2O3 and SiO2 oxides. The highest mineral percentages found for the hardsetting soils were quartz, kaolinite, and halloysite. Strong positive (photoelectric absorption) and negative (coherent and incoherent scatterings) correlations were found for goethite. Increase in the percentage of goethite and kaolinite influences increase in μm. The same behavior could be observed in relation to the contribution of the photoelectric absorption to μm. On the other hand, an increase in the amount of these two minerals presented a decrease in the contribution of the coherent and incoherent scatterings to μm. Therefore, in the absence of XRF analyses, the mineralogical soil measurements carried out through RM-XRD might be an interesting tool to infer the radiation attenuation characteristics of hardsetting soils. Such results bring a new insight into the radiation interaction through soils due to the analysis of the influence of the minerals in the photon attenuation.

The optical conductivity in double and three layer graphene systems

Abstract We investigate the longitudinal optical conductivity in few-layer monolayer graphene systems, which is different from the bilayer or trilayer graphene structures analytically and numerically. Here, few isolated parallel two-dimensional (2D) monolayer graphene are separated by a distance d with no interlayer tunneling, where the finite width thickness has to be taken into account. The carrier׳s energy structure and states for each layer are unaffected by the others. The carrier density in each layer is assumed to be tuned by the corresponding gate voltage. The optical conductivity depends on the electron density, the number of layer, and the broadening width at low temperature. However, analytical and numerical results show that the optical conductivity has little dependence on the distance between the adjacent layers. It is found that two intra- and inter-band transition channels for optical transition via absorption scattering in each layer can be observed. When the optical energy is larger than two times the kinetic energy at the Fermi energy, the optical conductivity is proportional to the layer numbers of monolayer graphene that can determine the number of the monolayer graphene layer. In sharp contrast to the bilayer or trilayer graphene systems, several turning points can be observed. Increasing the broadening width, the turning area becomes gradual. The main difference on the optical conductivity for double layer graphene and bilayer graphene is in the intermediate energy region where the threshold structure is observed.

RTS&T-2014 code status

The paper describes the main features of newest version of the RTS&T code system. The RTS&T [1] code (Radiation Transport Simulation and Isotopes Transmutation Calculation) was assigned for detailed Monte Carlo simulation of many particle types (γ, e±, p, n, π±, K±, LL0, antinucleons, muons, ions and etc.) transport in a complex 3D geometry's with composite materials in the energy range from a fraction eV to 20TeV and calculation of particle fluences, radiation field functionals and isotopes transmutation problem as well. A direct using of evaluated nuclear data libraries (ENDF/B-VI.8/VII.1, ROSFOND, JENDL, BROND etc.) to particle transport and isotopes transmutation modeling in low and intermediate energy regions is the general idea of the RTS&T code. It is possible to use the RTS&T code to simulate of reactors, detectors, spacecraft, radiotherapy treatment planning, criticality calculation and radiation safety analysis. The comparison between calculated and measured data is presented.

Neutron shielding qualities and gamma ray buildup factors of concretes containing limonite ore

Neutron dose transmissions for fast neutrons produced by 5.486MeV alpha particles on beryllium are measured in concrete samples with and without limonite ore to investigate their neutron shielding qualities. Using measured values, macroscopic removal cross-sections (ΣR, cm−1) have been determined experimentally and also ΣRvalues have been calculated theoretically using the elemental composition of the concrete mixes. The best neutron shielding property of concrete sample containing 100% limonite ore (FCL: fine and coarse limonite) was found. Additionally, energy absorption buildup factor (EABF) and exposure buildup factor (EBF) of concrete sample were calculated using the five-parameter Geometric Progression (G-P) approximation in the energy range of 0.015–15MeV for penetration depths up to 40 mean free path (mfp). The incident photon energy and penetration depth dependence of buildup factors were examined. Finally, we observed that concrete samples have maximum values of buildup factors in the intermediate energy region around 0.1–0.3MeV. FCL has the minimum values of both of the buildup factors. FCL has the excellent gamma shielding properties compared to the concrete samples.

Spent fuel interrogation using delayed fast neutron spectrum at Missouri University of Science and Technology Reactor

Interrogation of nuclear fuel and Plutonium (Pu) and Uranium (U) discrimination was performed using Missouri University of Science and Technology Reactor (MSTR) fuel by non-destructive (NDA) method. Post-irradiated delayed fast neutron spectra were obtained for two pairs of burnt and fresh fuels. Burnup and 239Pu conversions were calculated based on neutron emission intensity ratios. After 100 kW high power runs, all fuel elements showed three distinct regions of neutron spectra; a distinct low energy peak followed by intermediate energy region without distinct peak but a wide hump, followed by a high energy peak with a long tail. At 10 kW low powers, intermediate energy hump and low energy peak seems to merge together while the high energy peak still remains distinct. Based on data from 10 kW power runs, the burnup values of F1 and F2 fuel elements were estimated to be 149 MWD/T and 196 MWD/T, respectively. 239Pu conversion since 1992 for low enriched (19.75%) fuel elements was calculated as 0.24 g for F1 and 0.32 g for F2. Results based on high power runs of 100 kW provided comparable burnup of 217 MWD/T for F2. However the results for F1 were approximately 10 times higher perhaps due to unique burnup history and consequently high poison buildup. These experimental burnup results compare well with the reactor burnup calculation as reported to the Nuclear Regulatory Commission (NRC).

Investigation of gamma radiation shielding properties of various ores

Mass attenuation coefficients (μ/ρ, cm2/g) for some pellet samples produced using barite, magnetite, limonite, hematite and serpentine ores at 81, 276, 302, 356, 383 keV photons emitted from 133Ba and 121, 244, 344, 444, 778 keV photons emitted from 152Eu have been determined by using HPGe detector. Effective atomic numbers (Zeff) and electron densities (Ne) of the ores calculated in the selected energies.. The agreement of measured values of μ/ρ, Zeff and Ne with theoretical calculations is quite satisfactory. Mass attenuation coefficients were found to be highest for barite. The Zeff and Ne values for barite are maximum, for serpentine are minimum. Gamma ray energy absorption (EABF) and exposure buildup factors (EBF) were computed for ore samples using the five-parameter Geometric Progression (G-P) fitting method in the energy range 0.015–15 MeV for penetration depths up to 40 mean free path. Variations of EABF and EBF with incident photon energy and penetration depth were also investigated. It has been observed that among the selected ore samples, barite has lowest values for EABF and EBF in the intermediate energy region. Buildup of photons is more for serpentine. Exposure buildup factors (EBF) of given ores were compared with lead, steel-magnetite concrete (SM), concrete and bismuth borosilicate glass (BBS) with %20 mol Bi2O3. Barite is superior in terms of shielding properties among the other ore samples. The present study may be useful for radiation shielding applications.

The escape model for Galactic cosmic rays

The escape model explains the cosmic ray (CR) knee by energy-dependent CR leakage from the Milky Way, with an excellent fit to all existing data. We test this model calculating the trajectories of individual CRs in the Galactic magnetic field. We find that the CR escape time τesc(E) exhibits a knee-like structure around E/Z = few × 1015 eV for small coherence lengths and strengths of the turbulent magnetic field. The resulting intensities for different groups of nuclei are consistent with the ones determined by KASCADE and KASCADE-Grande, using simple power-laws as injection spectra. The transition from Galactic to extragalactic CRs happens in this model at low energies and is terminated below ≈ 3 × 1018 eV. The intermediate energy region up to the ankle is populated by CRs accelerated in starburst galaxies. This model provides a good fit to ln(A) data, while the estimated CR dipole anisotropy is close to, or below, upper limits in the energy range 1017 – 1018 eV. The phase of the dipole is expected to change between 1 × 1017 and 3 × 1018 eV.

Angular differential cross sections for double and single capture in fast ion-atom collisions

SynopsisWe investigate angular differential cross sections for double-electron and single-electron capture in ion- atom collisions for the intermediate and high energy region. We see the diffraction pattern in the spectrum of differential cross sections in the high energy range, i.e. another peak at 0.75 mrad in addition to Thomas peak at 0.47 mrad have been observed.

Total reaction cross sections in CEM and MCNP6 at intermediate energies

Accurate total reaction cross section models are important to achieving reliable predictions from spallation and transport codes. The latest version of the Cascade Exciton Model (CEM) as incorporated in the code CEM03.03, and the Monte Carlo N-Particle transport code (MCNP6), both developed at Los Alamos National Laboratory (LANL), each use such cross sections. Having accurate total reaction cross section models in the intermediate energy region (∼50MeV to ∼5GeV) is very important for different applications, including analysis of space environments, use in medical physics, and accelerator design, to name just a few. The current inverse cross sections used in the preequilibrium and evaporation stages of CEM are based on the Dostrovsky et al. model, published in 1959. Better cross section models are available now. Implementing better cross section models in CEM and MCNP6 should yield improved predictions for particle spectra and total production cross sections, among other results. Our current results indicate this is, in fact, the case.

Shielding efficiency of lead borate and nickel borate glasses for gamma rays and neutrons

Gamma ray exposure buildup factor (EBF) and neutron shielding efficiency of borate glass systems in composition (100 − x − y) Na2B4O7−xPbO−yNiO (where x and y = 0, 2, 4, 6, 8 and 10 weight percentage) were investigated in the present study. Gamma ray EBF values were computed using Geometric Progression (G-P) method for photon energy 0.015 to 15 MeV up to penetration depths of 40 mfp (mean free path). The macroscopic effective removal cross-sections (Σ R ) for fast neutron (2 to 12 MeV) were calculated. At low- and high-energy region, the EBF values were found minimum whereas maximum in the intermediate-energy regions with a sharp peak below 100 keV for oxide containing glass samples. The investigation was carried out for potential applications of borate glasses for radiation shielding.