CTOF measurements and Monte Carlo analyses of neutron spectra for the backward direction from an iron target irradiated with 400–1200 MeV protons

A calorimetric-time-of-flight (CTOF) technique was used for real-time, high-precision measurement of the neutron spectrum at an angle of 175° from the initial proton beam direction, which hits a face plane of a cylindrical iron target of 20 cm in diameter and 25 cm thick. A comparison was performed between the neutron spectra predicted by the MARS and the MCNPX codes and that measured for 400, 600, 800, 1000 and 1200 MeV protons.     

A function to provide neutron spectrum produced from the 9Be + p reaction with protons of energy below 12 MeV

A function to give the total neutron production cross section, angular distribution, and energy spectrum via the ⁹Be + p reaction has been created by fitting experimental data to characterize compact neutron sources with thick Be targets bombarded by protons with energy below 12 MeV. To examine the suitability of the function, calculations of the angle-dependent neutron energy spectra produced in thick Be targets with 4- and 12-MeV protons using the function were compared with corresponding experiments and calculations using the nuclear data libraries of ENDF/B-VII.0 and JENDL4.0/HE. The function was in better agreement with the experiments than the calculations using the libraries except for at backward angles. The ¹¹⁵In(n,n’)^115mIn reaction rates calculated using GEANT4 with source neutrons given by both the function and ENDF/B-VII.0 were compared with that measured at the RIKEN Accelerator-Driven Compact Neutron Source to evaluate the neutron spectrum above 1 MeV. The function slightly overestimated the measurement by 14% and the calculation with ENDF/B-VII.0 underestimated by 35%. It was concluded that the function can be applied in compact neutron source designs.     

Proton inelastic mean free path in amino acids and protein over the energy range of 0.05–10 MeV

The inelastic mean free paths (MFP) of 0.05–10 MeV protons in a group of 15 amino acids and a protein have been systematically calculated. The calculations are based on the method newly derived from the Ashley’s optical-data model and from the higher-order correction terms in stopping power calculations. Especially, in this method the new and empirical Bloch correction for the inelastic MFP was given. An evaluation for the optical energy loss function is incorporated into the present calculations because of the lack of available experimental optical data for the bioorganic compounds under consideration. The proton inelastic MFPs for these 15 amino acids and the protein in the energy range from 0.05 to 10 MeV are presented here for the first time, and the combination of these inelastic MFP data and our previous data of the SP calculations for these bioorganic compounds may form a useful database for Monte Carlo track-structure studies of various radiation effects in these materials.     

Elastic scattering of 7Li + 27Al at several angles in the 7–11 MeV energy range

Elastic cross sections for the ⁷Li + ²⁷Al system were measured at laboratory energies between 7 and 11 MeV in steps of 0.25 MeV, and angles between 135° and 170° in steps of 5°. Excitation functions for the elastic scattering were measured using an array of eight Si surface-barrier detectors whereas a solid-state telescope was used to estimate and subtract background from other reactions. Contamination from α particles arising from the ⁷Li breakup process at E_lab ? 10 MeV makes the use of these energies inadvisable for RBS applications. The present results are compared with previous data obtained at 165° (E_lab ? 6 MeV), 140° and 170° (E_lab ? 8 MeV). The experimental data were analyzed in terms of the Optical Model. Two different energy-independent potentials were found. These optical potentials allow an interpolation with physical meaning to other energies and scattering angles. The experimental cross sections will be uploaded to the IBANDL database.     

Neutron flux distribution in the irradiation channels of Am–Be neutron source irradiation facility

Monte Carlo (MCNP-5) simulations of the neutron fluxes were performed to determine the radial and axial neutron fluxes of the two irradiation sites of the 20 Ci ²⁴¹Am–Be neutron irradiation facility at NNRI. The geometry of the ²⁴¹Am–Be source as well as the irradiator design, constituted one cylindrical neutron source at the center of a cylindrical barrel with water as moderator. In the far and the near irradiation sites that were 13.1 cm and 4.2 cm, respectively, from the source, the average thermal, epithermal and fast neutron fluxes axially increase exponentially from the bottom and peak at the center of the source 3.0 cm from the bottom of the source and decrease to a very low value at the end of the tube. The percentage of the average thermal flux increases as the distance from the source increases, while the percentages of the epithermal and fast fluxes decrease as the distance from source increases. In the far and near irradiation sites the average radial thermal neutron flux decreases at the rates of 307.02 n cm⁻² s⁻¹ and 961.54 n cm⁻² s⁻¹ per cm along the diameter, respectively. The average radial, epithermal and fast neutron fluxes were fairly uniform along the diameter in the two irradiation sites.     

Interaction of 〈1 0 0〉 loops with Carbon atoms and 〈1 0 0〉 dislocations in BCC Fe: An atomistic study

We apply atomistic simulations using the so called ‘metallic-covalent bonding’ interatomic model for the Fe–C system to study mobility of 〈1 0 0〉 interstitial dislocation loops, known to form in Fe and Fe-based ferritic alloys under irradiation, and their interaction with Carbon atoms. Carbon atoms represent an effective trap for the 〈1 0 0〉 loops with a binding energy of the order of 1 eV. The mobility of the loops is studied using the dislocation – loop drag model. From this model the activation parameters are identified and discussed.     

Stopping force and straggling of 0.6–4.7 MeV H,He and Li ions in the polyhydroxybutyrate foil

Stopping force and straggling of 0.6–3.5 MeV ¹H ions, 2.0–4.7 MeV ⁴He ions and 1.4–4.4 MeV ⁷Li ions in the polyhydroxybutyrate (PHB) foil were measured by means of a transmission technique. The measured stopping forces are in well agreement with the SRIM 2008 calculation and the ICRU Report tables, except for the lower energy region. The obtained energy loss straggling deviates from the Bohr’s value by as much as 23.6% for the energies under study. The validity of the Bragg’s rule has also been demonstrated in the stopping force and straggling for ¹H, ⁴He and ⁷Li ions in the PHB foil.     

Porous iron pellets for AMS 14C analysis of small samples down to ultra-microscale size (10–25 μgC)

We developed the use of a porous iron pellet as a catalyst for AMS ¹⁴C analysis of small samples down to ultra-microscale size (10–25 μgC). It resulted in increased and more stable beam currents through our HVEE 4130 ¹⁴C AMS system, which depend smoothly on the sample size. We find that both the expected decrease of oxalic acid standards and increase of backgrounds with decreasing sample size, due to increasing influence of contamination, are reproducible. Using a mass-dependent background correction for dead (1.0 ± 0.4 μgC) and modern (0.25 ± 0.10 μgC) contamination, we obtain reliable results for small samples down to 10 μgC and possibly smaller. Due to our low graphitization yield for ultra-small samples (increases from 40% to 80% on average with sample size), we measured graphite standards as small as 3 μgC. The standard deviation of the corrected activity is about 5% for a 10-μgC HOxII standard.Here we report the iron pellet technique, which is new to the best of our knowledge. It is generally applicable for AMS ¹⁴C laboratories that want to measure small samples down to ultra-microscale size. As an illustrative test-case, we analyze ¹⁴C data for IAEA-C5, C7 and C8 samples with masses ranging from 15 to 300 μgC.     

Stopping of ∼0.2–3.4 MeV/amu 1H+ and 4He+ ions in polyvinyl formal

The stopping powers of polyvinyl formal resin for protons and alpha particles have been measured over the energy range ～(0.2–3.4) MeV/amu with an overall relative uncertainty of less than 2.5% using the ion beam transmission method. The obtained results are discussed in comparison to scarce experimental data from the literature and to values calculated by the SRIM-2008 computer code assuming Bragg-Kleeman’s additivity rule of stopping powers. Departures from additivity attaining ～5.5% and ～3.0% for the proton and alpha particle data, respectively, are observed at moderate projectile velocities, increasingly as one evolves towards the stopping power maximum dominated by charge exchange effects. They are presumed to be mainly due to valence structure effects involving the C–H bonds of the studied polymer compound. The less pronounced deviation for alpha particles is probably due to the projectile screening effect that occurs in distant collisions tending to reduce the contribution of valence electrons in the low projectile velocity regime.     

Measurement and analysis of the energy–angular distribution of secondary neutrons for Be at 5.9 and 6.4 MeV incident neutrons

The energy-angle double-differential neutron emission cross-sections of beryllium have been measured using the time of flight technique for 5.9 and 6.4 MeV incident neutrons, respectively, at 10 laboratory angles between 25° and 150°. The measured results are compared with model calculations based on the LUNF code and those of other authors and the ENDF/B-VII data. The estimation of the inelastic scattering neutron cross-sections leaving ⁹Be^∗ at the low-lying level states are also theoretically analyzed by the LUNF code. The experimental and calculated results indicated that the lowest (1.68 MeV) level still contributes to the (n, 2n) reaction with cross-sections of several 10 mb. The angular distributions and the angle-integrated elastic scattering cross-sections are also presented in comparison with other ones, these being in good agreement with the ENDF/B-VII data.     

溴化镧探测器在1–10MeV能区的能量刻度

溴化镧(铈)(LaBr3(Ce))闪烁探测器具有较高的能量分辨和较高的探测效率,在中子质询非破坏性检测爆炸物、违禁品及地雷等研究领域发挥了重要作用。本文提出了中子场中LaBr3(Ce)探测器宽能范围的刻度方法:分别测量中子诱发NH4Cl和三聚氰胺(C3H6N6)的瞬发能谱,对比后确定了各核素的特征峰,获得了1–10MeV能区的能量刻度曲线。采用二次多项式及三次多项式拟合,能较好地区分被测特征核素。     

Influence of microstructural inhomogeneities on the fracture toughness of modified 9Cr–1Mo steel at 298–823 K

Quasistatic fracture behaviour of two heats of modified 9Cr–1Mo steel for steam generator applications have been assessed at 298, 653 and 823 K. J–R curves were established and the elastic–plastic fracture toughness values at 0.2 mm crack extension (J_0.2) were determined. The fracture mechanisms were entirely different for the two steels at 298 K, with brittle fracture controlled by cleavage crack initiation in one and ductile fracture in the other by void nucleation and growth. At 653 and 823 K, fracture in both materials was by ductile crack growth. The difference in behaviour between the two steels at 298 K was attributed to the differences in microstructure, distribution and density of inclusions as well as phosphorous contents.     

Experimental stopping powers of Al,Mg, F and O ions in ZrO2 in the 0.1–0.6 MeV/u energy range

The study of the stopping and range of heavy ions (Z > 3) in matter isdsc cfddc of both fundamental and practical interest as heavy ions find increasing usage in a wide range of ion beam based techniques. While semi-empirical formulations like the widely used SRIM code can predict the stopping powers of hydrogen and helium in many elemental and compound targets over a wide range of energies quite well, their predictive accuracy for heavy ions is not as good. This is mainly due to the lack of heavy ion experimental stopping power data on which such codes are based. We present results of measurements performed using a Time of Flight–Energy spectrometer to determine the stopping powers of O, F, Mg and Al ions in the oxide ceramic ZrO₂ within the 0.1–0.6 MeV/u energy range. Possible SRIM correction (or correlation) factors for F, Mg and Al ions were extracted from quantitative comparisons of experimental and predicted stopping power values.     

Design and testing of a 5 GHz TE10–TE30 mode converter mock-up for the lower hybrid antenna proposed for ITER

The design and overall dimensions of a 5 GHz TE₁₀–TE₃₀ mode converter are presented. This mode converter is a RF element of a 20 MW CW lower hybrid system proposed for ITER. A low power mock-up of this device has been manufactured at CEA/IRFM and measured at low power. RF measurements indicate a return loss of 40 dB and a transmission loss of 4.78 dB ± 0.03 dB for the three outputs. The forward conversion efficiency from TE₁₀ mode to TE₃₀ has been measured from electric field probing to 99.9%. The good RF performances obtained validate the RF design of this element.     

Investigation of the characteristics of an e, φ scintillation spectrometer with a BGO crystal for energies of 0.5–100 MeV

Conclusions The measurements have shown that a BGO crystal with a diameter of 5 cm can be used to build relatively compact, highly efficient spectrometers for electrons and quanta; the resolution is 15–5% for energies of 0.5–6 MeV and 40% for 20–100 MeV; the characteristic of the spectrometer is linear in this entire range.Translated from Atomaya Énergiya, Vol. 69, No. 4, pp. 246–248, October, 1990.     

Bremsstrahlung energy spectra from electrons with kinetic energy 1 keV–10 GeV incident on screened nuclei and orbital electrons of neutral atoms with Z = 1–100

A comprehensive set of bremsstrahlung cross sections (differential in the energy of the emitted photons) is tabulated. The set includes results for electrons with energies from 1 keV to 10 GeV incident on neutral atoms with atomic numbers Z = 1 to 100. For bremsstrahlung in the Coulomb field of the atomic nucleus, use was made of (a) results of Pratt, Tseng, and collaborators based on numerical phase-shift calculations for the screened Coulomb potential at energies below 2 MeV; and (b) the analytical high-energy theory (with Coulomb corrections) of Davies, Bethe, Maximon, and Olsen at energies above 50 MeV, supplemented by the Elwert Coulomb correction factor and the theory of the high-frequency limit given by Jabbur and Pratt. In the high-energy region, the effect of screening was included by the use of Hartree-Fock atomic form factors. A numerical interpolation scheme, applied to suitably scaled cross sections, was used to bridge the gap between the low-energy and high-energy theoretical results, and thus to obtain improved cross sections in the intermediate-energy region 2 to 50 MeV. Bremsstrahlung in the field of the atomic electrons was calculated according to the theory of Haug, combined with screening corrections derived from Hartree-Fock incoherent scattering factors.     

Void reactivity coefficient benchmark results for a 10 × 10 BWR assembly in the full 0–100% void fraction range

A boiling water reactor SVEA-96+ fresh fuel lattice has been used as the basis for a benchmark study of the void reactivity coefficient at assembly level in the full voidage range. Results have been obtained using the deterministic codes CASMO-4, HELIOS, PHOENIX, BOXER and the probabilistic code MCNP4C, combined for almost all cases with different cross section libraries. A statistical analysis of the results obtained showed that the void reactivity coefficient tends to become less negative beyond 80% void and that the discrepancies between codes tend to increase from less than 15% at voidages lower than 40% to more than 25% at voidages higher than 70%. The void reactivity coefficient results and the corresponding differences between codes were isotopically decomposed to interpret discrepancies. The isotopic decomposition shows that the minimum observed in the void reactivity coefficient between 80% and 90% void is largely due to the decrease in the relative importance of the ¹⁵⁷Gd(n, γ) rate with increasing voidage, and that the fundamental discrepancies between codes or libraries are mainly governed by the different predictions of the ²³⁸U(n, γ) variation with voidage.     

Annealing of ion implanted 4H–SiC in the temperature range of 100–800 °C analysed by ion beam techniques

Ion implantation induced damage formation and subsequent annealing in 4H–SiC in the temperature range of 100–800 °C has been investigated. Silicon Carbide was implanted at room temperature with 200 keV ⁴⁰Ar ions with two implantation fluences of 4 × 10¹⁴ and 2 × 10¹⁵ ions/cm². The samples were characterized by Rutherford backscattering and nuclear reaction analysis techniques in channeling mode using 2.00 and 4.30 MeV ⁴He ion beams for damage buildup and recovery in the Si and C sublattices, respectively. At low ion fluence, the restoration of the Si sublattice is evident already at 200 °C and a considerable annealing step occurs between 300 and 400 °C. Similar results have been obtained for the C sublattice using the nuclear resonance reaction for carbon, ¹²C(α,α)¹²C at 4.26 MeV. For samples implanted with the higher ion fluence, no significant recovery is observed at these temperatures.