Application of the relativistic DV-Xα molecular orbital method to γ-uranium alloys with transition metals

The alloying behavior of 4d and 5d transition metals (TMs) in γ-phase solid uranium (U) has been investigated using the discrete-variational Dirac–Fock–Slater (DV-DFS) method. We examined the d-orbital energy (Md value) of these TMs, the orbital overlap population (OOP) between the d-orbital of these TMs and the 5f or 6d orbital of γ-U, and the effective charge on each atom of the γ-U/TM alloy, and the effect of these parameters on alloying. It was found that the maximum solid solubility (MSS) of TMs into γ-U was exponentially proportional to both the Md and the OOP (U5f–TMd and U6d–TMd), except for Ta and W elements. We found a good correlation between the MSS and Md, the effective charge, or OOP.     

Electronic structures of β-SiC containing point defects studied by DV-Xα method

The DV-Xα method was used to calculate the bond order between atoms in cubic silicon carbide (β-SiC) with a point defect. Three types of β-SiC cluster models were used: pure cluster, vacancy cluster and interstitial cluster. The bond order was influenced by the kind of defects. The bonds between C interstitial and neighboring C atoms were composed of anti-bonding type interactions, while the bonds between Si interstitial and neighboring C and Si atoms were composed of bonding type interactions. The overlap population of each molecular orbital was examined to obtain detailed information of the chemical bonding. It appeared more difficult to recombine interstitial atoms in a cluster with a C atom vacancy than in a cluster with a Si atom vacancy, due to the stronger Si–Si bonds surrounding the C atom vacancy. The C interstitial atom had C2s and C2p anti-bonding interactions with high energy levels. The Si interstitial had minimal anti-bonding interactions.     

Activity level of gross α and gross β in airborne aerosol samples around the Qinshan NPP

The monitoring results of gross α and gross β activity from 2001 to 2005 for environmental airborne aerosol samples around the Qinshan NPP base are presented in this paper. A total of 170 aerosol samples were collected from monitoring sites of Caichenmen village, Qinlian village, Xiajiawan village and Yangliucun village around the Qinshan NPP base. The measured specific activity of gross α and gross β are in the range of 0.02 - 0.38 mBq/m^3 and 0.10 - 1.81 mBq/m^3, respectively, with an average of 0.11 mBq/m^3 and 0.45mBq/m^3, respectively. They are lower than the average of 0.15 mBq/m^3 and 0.52mBq/m^3, of reference site at Hangzhou City. It is indicated that the specific activity of gross α and gross β for environmental aerosol samples around the Qinshan NPP base had not been increased in normal operating conditions of the NPP.     

Measurement of β-ray maximum energy with an HPGe detector by means of β-annihilation photons coincidence

A β⁺-ray detection system free from summation of annihilation photons has been constructed for the determination of Q_EC-values. It consists of an HPGe β-ray detector and two pairs of BaF₂ scintillation detectors for annihilation photons. A Q_EC-value of 4.83(4) MeV is obtained for ¹²⁶Cs separated with the JAERI on-line isotope separator.     

Metal location and thickness in a multilayered sheet by measuring Kα/Kβ, Lα/Lβ and Lα/Lγ X-ray ratios

When a multilayered material is analyzed by means of energy-dispersive X-ray fluorescence analysis, then the X-ray ratios of Kα/Kβ, or Lα/Lβ and Lα/Lγ, for an element in the multilayered material, depend on the composition and thickness of the layer in which the element is situated, and on the composition and thickness of the superimposed layer (or layers).Multilayered samples are common in archaeometry, for example, in the case of pigment layers in paintings, or in the case of gilded or silvered alloys. The latter situation is examined in detail in the present paper, with a specific reference to pre-Columbian alloys from various museums in the north of Peru.     

Measurement of α particle energy loss in biological tissue below 2 MeV

The energy loss of α particles crossing biological tissue at energies between 0.8 and 2.2 MeV has been measured. This energy range is very important for boron neutron capture therapy, based on the ¹⁰B(n,α)⁷Li reaction, which emits α particles with energies of 1.78 and 1.47 MeV. One of the methods used for the measurement of the boron concentration in tissue is based on the deconvolution of the α spectra obtained from neutron irradiation of thin (70 μm) tissue samples. For this technique, a knowledge of the behaviour of the energy loss of the particles in the irradiated tissue is of critical importance. In particular, the curve of the residual energy as a function of the distance travelled in the tissue must be known. In this paper, the results of an experiment carried out with an ²⁴¹Am source and a series of cryostatic sections of rat-lung tissue are presented. The experimental measurements are compared with the results of Monte Carlo calculations performed with the MCNPX code.     

Studies of Na-segregation at Ni/α-quartz interfaces

Ni/α-quartz bilayers were irradiated at 77 K with 200 keV Na⁺ ions at a fluence of 5 × 10¹⁶ ions/cm² and annealed in hydrogen up to 883 K. The Na-migration at the Ni/α-quartz interface and towards the Ni-surface, the hydrogen storage in the irradiated region, and the Ni/α-quartz interface broadening due to Na implantation and decoration were investigated via Rutherford Backscattering Spectrometry (RBS) and Resonant Nuclear Reaction Analysis (RNRA). We demonstrate that after a one hour-annealing at 833 K a large fraction of the implanted Na has been trapped at the Ni/α-quartz interface from where it is released at 883 K. The results are discussed and compared with our findings in Na-irradiated metals and silicon compounds.     

The lattice location of helium implanted in α-SiC

Methods of ion channeling analysis, employing backscattering spectrometry and the ion-induced ³He(d,p)⁴He nuclear reaction, were applied to specify a lattice site of high symmetry for helium in α-SiC. Single-crystal α-SiC, held at 300 K, was implanted with ³He⁺ at 75 keV. By considering the channeling angular distributions and the crystal structure, a probable position within the unit cell was qualitatively identified. Significant clustering and random positioning were not present. A single helium atom was centrally positioned in either a substitutional site or a tetrahedral interstitial site. Limitations upon the number of available low-index channeling directions prevented precise specification of the final lattice location. The availability of α-SiC with an orientation normal to the 0001 axis would allow the two identified possible locations for the helium to be distinguished.     

Transient thermal stresses in a composite hollow cylinder subjected to γ-ray heating

Transient temperature and thermal-stress distributions arising in an infinite long composite hollow circular cylinder subjected to internal heat generation decaying exponentially along the wall thickness resulting from γ-ray radiation are analyzed, under the thermal conditions of cooling by convection on the inner surface and insulation on the outer surface. Numerical calculations of the transient temperature and thermal-stress distributions are carried out for the case of a composite cylinder of stainless steel and carbon steel. The influence of the absorption coefficient, the Biot number and the splicing radius on the results are considered.     

Radiation damage of α-Al2O3 in the HVEM: II. Radiation damage at high temperature and high dose

The temperature dependence of the apparent displacement threshold energy has been measured for single crystal α-Al₂O₃ in a high voltage electron microscope, over the temperature range 320–1120 K. Below 570 K the threshold energy for observable damage remains constant at 390 ± 10 keV, then rises to a peak of 440 ± 20 keV at 695 K followed by a rapid fall to ~200 keV at 870 K and above. Measurement of the displacement threshold energy, using the optical absorption and luminescence of oxygen and aluminium electron irradiation induced vacancies at several temperatures, gives a value of 440 ± 25 keV for the oxygen ion and 175 ± 25 keV for the aluminium ion. These results show that oxygen and aluminium ions have widely different displacement energies, E_d, of ~75 and 18 eV respectively.     

Atomic-scale simulation of displacement cascades and amorphization in β-SiC

Molecular dynamics (MD) methods with a modified Tersoff potential have been used to simulate Si displacement cascades with energies up to 50 keV and to compare clustering behavior for Si and Au recoils in β-SiC (3C). The results show that the lifetime of the thermal spike is very short compared to that in metals, and that the surviving defects are dominated by C interstitials and vacancies for Si displacement cascades. Only 19% of the interstitial population is contained in clusters, with the largest cluster containing only four interstitial atoms for energetic Si recoils. The energy dependence of stable defect formation exhibits a power-law relationship. The high energy Si recoil generates multiple sub-cascades and forms dispersed defect configurations. These results suggest that in-cascade amorphization in SiC does not occur with any high degree of probability during the lifetime of Si cascades. On the other hand, large disordered domains are created in the cascades produced by 10 keV Au recoils. Structure analysis indicates that these highly disordered regions have amorphous characteristics. The data for the cluster spectra have been used to calculate the relative cross-sections for in-cascade amorphization (or clustering) and defect-stimulated amorphization. The ratios of these cross-sections for Si and Au are in excellent agreement with those derived from a fit of the direct-impact/defect-stimulated model to experimental data.     

A measurement of the Li(n,α) cross-section

The relative shape of the ⁶Li(n,α)/²³⁵U(n,f) cross-section ratio has been determined in the range of incident neutron energy from 2 to 800 keV. The measurements were made by the time-of-flight method using the Harwell 45 MeV linac to provide the pulsed source of neutrons. A thin ⁶Li-glass scintillator was used to register the (n,α) events, and the (n,f) events (in a metallic sample of ²³⁵U) were registered with fission neutron detectors. The shape of the ⁶Li(n,α) cross-section was obtained by combining the measured ⁶Li(n,α)/²³⁵U(tn,f) cross-section ratio with an evaluation of the ²³⁵U(n,f) cross-section. The cross-section so derived was placed on an absolute scale by normalization in the neutron energy interval 2–10 keV, where the ⁶Li(n,α) cross-section is accurately known. The cross-section at the peak of the prominent p-wave resonance near 240 keV is found to be 3.29 ± 0.12 b. The results are compared with other measurements and also with a recent theoretical calculation of the cross-section.     

A practical method for calculation of mass-attenuation coefficients of β particles

A practical method to calculate mass-attenuation coefficients of β particles has been described. This method is based upon the analytical conclusion of β emission energy spectrum and the range distribution of an individual β particles. The mass-attenuation coefficients are obtained as the slope of the semi-log plot of theoretical calculated fraction of transmission vs. the foil thicknesses. This method has been applied to obtain the mass-attenuation coefficients of β particles in aluminium, copper and gold. The results have been compared with the values given in previous works.     

Performance of multigap resistive plate chamber in a γ-ray aging test

1 Introduction MRPC is a new type of gas detector [1, 2] devel- oped in the last few decades. It has been proposed to be a substitute for the Time of Flight (TOF) detector used in conventional technology in high-energy nu- clear and particle experiments because of its properties of excellent time resolution, high efficiency, simple structure, insensitivity to magnets, and low energy dissipation. The MRPC technology has been adopted for TOF by the STAR group at Relativistic Heavy Ion C…     

Measurements of thick-target (α, n) yields from light elements

High-precision measurements of thick-target yields from (α, n) reactions on Be, BeO, BN, C, UC, UO₂, Mg, Al, Si, Fe and stainless steel are described. The measurements cover an incident α-particle energy range of 3.6–10 MeV at energy intervals of 0.2 MeV in the energy range 4–7 MeV. The accuracy achieved is between 1 and 2% in most cases. As well as monitoring the incident α-particle energy by Rutherford scattering, precautions include a check for the presence of neutron-producing impurities in the targets by examination for γ-rays from (α, nγ), (α, pγ) and (α, α'γ) reactions.Values of the yields measured here from Be, Mg, Al and Si are 8–9% higher than recent published values. The measured yields in the compounds BeO and UC, when compared with those in Be and C, respectively, are used to assess a convenient approximate method of deriving thick-target yields in compounds from the values in the constituent elements.     

Status report of the SARA IGISOL used in the study of the U(α 40 MeV, ƒ) reaction

A new ion guide isotope separator on-line (IGISOL), operating with the SARA facility, has been constructed. Using the ²³⁸U(α 40 MeV, ƒ) reaction to produce very neutron-rich radioisotopes, all mass chains from A = 96 to 122 have been scanned by conventional methods of nuclear spectroscopy. Provided the stopping volume is separated from the primary beam, it has been proved that the yield is nearly proportional to the He pressure. In addition to the usual advantages (quasi-independence from physical and chemical properties of elements), this makes IGISOL a powerful technique for high energy recoil products. During the experiments the boundary of known neutron-rich nuclei was reached such as ¹¹⁷Rh(440 ms) and several unknown activities were detected in the range A = 113–118.     

Analysis of structural modifications in γ-irradiated PbO–B2O3–SiO2 glasses by FTIR spectroscopy

The effect of γ-irradiation on the structure of lead borosilicate glasses of varying composition has been probed by FTIR spectroscopy, before and immediately after γ-irradiation. The glasses were irradiated at Calliope ⁶⁰Co plant (RC ENEA Casaccia, Rome), and the spectra were recorded after absorbed doses of 50 Gy, 500 Gy, and 4 kGy. The structural analysis have been made considering both the effect of composition and of irradiation. The experimental results clearly indicate that after irradiation a significant change in structure of borosilicate glass network is observed.     

Prediction of the performance of an ion chamber amplifier under γ radiation

The ion chamber amplifier (ICA) plays a major role in the proper functioning of a nuclear reactor as it monitors the radiations from the nuclear reactor by measuring the ionic activity inside the ion chamber. The signal conditioning circuitry of the ICA detects and conditions the weak ionic currents coming from the ion chamber dome. Degradation in the performance of the semiconductor devices used in this part of the ICA, can lead to inaccurate monitoring of the reactor operation, resulting in a possible catastrophe due to malfunction. Further, the response of the ICA under irradiation also depends upon the strength of the input signal (ionic) current it is required to handle. The active devices used in the ICA under study are operational amplifiers (Op-Amps) such as DN8500A and OPA111, instrumentation amplifier INA101, transistor 2N2920A and a voltage reference device, AD584. Since these devices may be sensitive to radiation, one must know their radiation behaviour so that the performance of the ICA can be predicted. This paper examines the performance of the ICA by characterising the radiation profiles of its vital components, viz. the Op-Amps, instrumentation amplifiers, transistors, etc. by monitoring their parametric changes on-line, i.e. when the source is on, and the devices are biased. The simulation runs involve the simulation of the entire ICA circuitry using the changed values of the vital parameters such as input bias current and input offset voltage. The main advantage of this method is that it obviates irradiating the whole ICA circuit to study its irradiation performance, and simulates an environment of radiation leakage around the ICA. Based on this study, results are presented to predict the performance of the ICA.