Void formation in Nickel during high temperature proton irradiation

Pure Ni foils, doped with He from 0 to 28 appm, were irradiated with protons at temperatures in the range 0.3–0.6 T_m (T_m = melting point in °K) and void formation was studied. The influence of He doping, irradiation temperature and alloying were investigated. For constant He content and proton fluence, void number density and swelling are maximum at about 400°C, while the void size increases with temperature. Most voids are octahedral in shape with no sign of truncation. Helium is required to nucleate voids, and lowering the stacking fault energy by alloying suppresses void formation completely. Present results suggest that void nucleation is inhomogeneous. Some implications of these findings are discussed.     

Quasifree proton scattering on halo nuclei as a tool for studying the neutron-halo structure

An experimental method is proposed for investigating the structure of the two-neutron halo in quasifree proton scattering on clusters of halo nuclei. This scattering process is studied in inverse kinematics by using a ⁶He beam incident to a stack of track emulsions. Preliminary data on the reaction ⁶He + p → ⁴He + p + X are compared with the results of simple kinematical calculations for quasifree proton scattering on the clusters forming the halo of the ⁶He nucleus.     

Additional production of deuterium and helium-3 by high-energy protons and antiprotons in the early Universe

The results of calculations of ³He, ³H, and D production as a result of the disintegration of primordial ⁴He by high-energy protons and anti-protons in the early Universe are reported. It is shown that for primary particle energies E _p , _p ^t- <0.2 GeV the main role in ³He, ³H, and D production is played by the secondary proton cascade that develops in the cosmological plasma and which destroys ⁴He most intensively at E~75 MeV. At the current state of the experimental data one can calculate the number of nuclei produced to within 10%, and investigation of the inelastic p ⁴He interaction channels at E~75 MeV will make it possible to improve substantially the accuracy of calculations of the additional production of light elements. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 9, 609–613 (May 1999)     

Helium/hydrogen synergistic effect in reduced activation ferritic/martensitic steel investigated by slow positron beam

Here, we investigated the irradiation defect in reduced activation ferritic/martensitic steels by slow positron beam. Three ion-irradiation experiments were carried out: (i) He²⁺ irradiation, (ii) H⁺ irradiation and (iii) He²⁺ irradiation followed by H⁺ irradiation, at temperature 450?°C. The presences of vacancy defects, represented by ?S_He+H parameter, induced by sequential irradiations was larger than the sum of defects, ?S_He parameter + ?S_H parameter, caused by single He ions and single H ions. The synergistic effect of He and H was confirmed clearly from the perspective of positron annihilation spectroscopy.     

Influence of irradiation on the thermal decomposition of lithium perchlorate

Abstract

Infrared absorption measurements were made before and after 90 °K electron irradiations of silicon samples which contained either dispersed oxygen, carbon, or carbon plus oxygen. Irradiation-produced absorption bands associated with two distinctly different defects are observed depending on the oxygen and carbon content of the silicon. One center is the well-known vacancy-oxygen A-center defect (836-cm^?1 band) and is formed on irradiation in oxygen-containing silicon with a magnitude which is independent of the carbon content. Measurements have correlated the formation of one A-center with the loss of one interstitial oxygen atom, thereby indicating that A-center formation occurs by vacancy trapping at interstitial oxygen atoms. A second center (922-and 932-cm^?1 bands) is formed only in silicon crystals which contain both oxygen and carbon. The results indicate that this center is formed by the trapping of a silicon interstitial at a carbon-oxygen complex.     

Nature of ultraviolet and Gamma ray induced damage in crystalline Uracil

Abstract

A study has been made of the damage producedin situ in dry polycrystalline uracil by irradiation with high energy 60Co photons and by low energy ultraviolet (UV) photons. The techniques of electron spin resonance, thin layer chromatography, infrared spectrometry, neutron diffraction and spectrophotometry have all been utilized to investigate effects produced by the irradiations. If was found that little lattice damage and no cis-syn cyclobutane dimers are producedin situ by irradiation of dry uracil with 60Co photons. However, following dissolution of the irradiated powder in water, radiation products are detected, and several of their characteristics have been elucidated. In contrast, following irradiation by 60Co photons of uracil in an aqueous environment, massive damage was found in the dried sample. Irradiation of dry uracil with UV photons is found to cause general lattice damage, but again negligible concentrations of cis-syn dimers are producedin situ. There is evidence for the formation of a planar, dimer-like molecular configuration.     

Electrical resistivity and length variations of iron and nickel during low temperature electron irradiations

Abstract

Low concentrations of Frenkel pairs are produced in polycrystalline iron and nickel targets during irradiations with 1.9 to 2.5 MeV electrons at 5 or 20 K. During irradiation (and subsequent thermal annealing for the nickel target) we simultaneously measure on the targets the changes of electrical resistivity, and of length with two different linear systems: a capacitive and an inductive device.

The measured ratios of relative length to electrical resistivity increases are [(Δl/l)/Δρ]_Fc = and [(Δl/l)/Δρ]_Nj = 1020 ±120(Ωcm)^?1. Values of Frenkel pair formation volumes of ν _Fc = 1.35 ± 0.25 and ν _Ni = 2.06 ± 0.30 atomic volumes are proposed.     

Effect of initial texture on texture evolution in cold-rolled AA 5182 aluminium alloy

AA 5182 aluminium alloy with a strong cube texture was cold rolled to different reductions along the following directions: firstly, the original rolling direction; secondly, at angles of 22.5 and 45° to the original rolling direction. The evolution of texture in the cold-rolled samples with different initial textures was then investigated by X-ray diffraction. The texture evolution was quantified by mathematical formulae of texture volume fractions and rolling true strain. The results show that initial texture has a strong influence on the evolution of rolling texture. AA 5182 aluminium alloy with an initial rotated-cube (r-cube) (45° normal direction r-cube) texture exhibits the fastest rate of formation of the β fibre. The rate of formation of the β fibre decreases as the initial texture changes from the r-cube texture to the cube texture. The relationship between the rate of formation of the β fibre (k _β value in the mathematical formula for the volume fraction of the β fibre) and the initial texture (M _cube and M _r-cube: the volume fractions of the cube and r-cube components respectively) can be expressed as k _β ?=?0.37???0.03(M _cube /5.41???M _r???cube /5.64).     

Proton and triton momentum distributions from4He fragmentation at relativistic energies

The 0° differential cross sections of the¹²C(⁴He,p) and¹²C(⁴He,t) reactions have been measured at beam momenta of 4.52 and 2.69 GeV/c/nucleon, respectively. The proton and triton momentum distributions in⁴He are extracted from the cross sections using a relativistic impulse approximation. Some theoretical models based on realisticN-N potentials are examined for our data.     

Chemical ionization of hydrogen halide molecules in collision with metastable helium atoms

An anomaly of the temperature dependence of the cross section for chemical ionization of HBr molecules by metastable helium atoms He*(2³ S ₁) is discovered. It is shown that the interaction anisotropy induced by rotation of the HBr molecule has a significant influence on the formation of the anomaly. Zh. Tekh. Fiz. 68, 13–15 (February 1998)     

Transport and relaxation properties of isotopomeric hydrogen–helium binary mixtures. II. HD,D2, T2–He mixtures

The comprehensive comparison between calculated bulk non-equilibrium properties of hydrogen–helium isotopomeric mixtures and experiment that has previously been carried out for H₂–helium mixtures [2004, Molec. Phys., submitted] has been extended to mixtures of HD, D₂ and T₂ with ³He and ⁴He. For HD–⁴He mixtures, comparison is also made, where possible, with previous calculations of Köhler and Schaefer [1983, Physica A, 120, 185]. The phenomena examined herein include low temperature interaction second virial coefficients, binary diffusion and thermal conductivity coefficients, rotational relaxation, transport property field effects and flow birefringence. Scattering calculations have been carried out for the HD–He PES of Schaefer and Köhler [1985, Physica A, 129, 469], and for both the Köhler–Schaefer and Tao [1994, J. chem. Phys., 100, 4947] potential surfaces for the D₂–He and T₂–He interactions. Comparisons between calculated and experimental results for HD, D₂, T₂–He mixtures confirm the conclusion, reached earlier from the H₂–He comparisons, that these potential surfaces are very close to the correct one for the hydrogen–helium interaction, and that the small differences between them cannot be distinguished readily by measurements of bulk gas phenomena unless the attendant experimental uncertainties are better than ±0.3%.     

Helium effects on the microstructural evolution of reactor irradiated ferritic and austenitic steels

Abstract

Microstructural evolution in neutron irradiated austenitic stainless steels and Cr-Mo ferritic steels is reviewed. Important highlights are: (1) there is a strong correlation between precipitation and void evolution in austenitic steels; (2) helium affects precipitate evolution in austenitic steels, but observations indicate no effect on precipitation in ferritic steels; (3) helium has a pronounced effect on the cavity evolution of the two steel types. Helium effects are explained in terms of the interrelationship between microstructural evolution and point-defect annihilation processes. In stainless steel, three relative regimes of microstructural behavior for different helium generation rate-displacement rate ratios are recognized: (1) “low” He/dpa ratio, where helium effects on the radiation-induced microstructural evolution are negligible or develop slowly, (2) “medium” He/dpa ratio, where helium effects strongly enhance the microstructural changes, and (3) “high” He/dpa ratio, where helium effects are limited to the early development of a high density of fine bubbles which interfere with other radiation-induced microstructural changes, but allow enhanced thermal microstructural evolution to take place instead. The extensive data on austenitic steels fall within these regimes. Ferritic steels are known to be highly resistant to void swelling without helium. It is suggested that enhanced cavity formation due to helium in ferritic steels makes higher swelling a potential concern for fusion reactor applications.     

Vacuum effects on the radiation chemical yields in PADC films exposed to gamma rays and heavy ions

In order to understand the vacuum effects on the sensitivity of PADC detectors from the viewpoint of molecule structural modification along nuclear tracks, a series of FT-IR spectrometric studies has been made for PADC films exposed to He and C ions at energies below 6 MeV/n, as well as to gamma rays from an intense Co-60 source, under the both conditions of in air and in vacuum. The radiation chemical yields for the losses of ether and carbonate ester bonds are hardly affected by the environmental conditions in the cases of He and C ion irradiations. For gamma ray, the yields are about half in vacuum compared to those in air. The formation of OH groups is fairly suppressed in vacuum in all cases. Recombination of free radicals resulted in modified polymeric network formation would be enhanced in heavy ion irradiations rather than in that of gamma irradiations.     

Proton momentum distributions in the 7Li nucleus in a potential cluster model

Distributions of the proton momentum in the ⁷Li{αt} → p + ⁶He{αnp} fragmentation channel were, along with the corresponding widths and spectroscopic factors, calculated in the αnn model representation of wave functions of the ⁶He nucleus in the (0⁺,1) ground and (2⁺,1) excited states. The results are compared to the available theoretical calculations and experimental NIKHEF data on the ⁷Li(e,e′p)⁶He electron-induced proton knock-out process.     

Investigation of the antineutrino angular distribution in experiments on the β decay of polarized neutrons

Since the emission of γ grays unavoidably accompanies β decay, the final state after the β decay of a neutron includes a photon along with a proton, an electron, and an antineutrino, i.e., four particles, rather than three. Therefore, when only the electron and proton momenta are detected and the γ-ray momentum is not detected in an experiment, the antineutrino momentum cannot be uniquely reconstructed, and only its mean value over a γ-ray momentum distribution determined from corresponding calculations can be considered. The γ grays are significant for finding the asymmetry parameter B of the antineutrino angular distribution from experiments on the β decay of polarized neutrons, where the electron momentum p directed along the x axis and the projection of the proton momentum P _x onto the x axis are detected, and the neutron polarization vector ξ is parallel or antiparallel to x. Since the γ rays are not detected in such experiments, the antineutrino kinematics are not uniquely specified by the observables p and P _x and can be reconstructed only on the average, so that the antineutrino momentum distribution averaged over a γ-ray momentum distribution is considered. Thus, the exact value of B cannot be obtained from these experiments, but the true value of B can be estimated on the average by considering the mean (most likely) value 〈B〉 and the dispersion (rms deviation) ΔB. The unavoidable uncertainty in the estimate of B amounts to several percent and is thus significant for present-day experiments, which are intended to obtain the value of B to a very high accuracy of ∼ (0.1–1)%. If electromagnetic interactions are taken into account, measurements of the electron and proton momentum distributions can also be used to obtain g _A, i.e., the axial β-decay amplitude, to high accuracy. Zh. éksp. Teor. Fiz. 116, 1505–1522 (November 1999)     

Investigations of Ar+ implantation and proton irradiation of amorphous Fe40Ni40B20 samples by Mössbauer techniques

The effect of the implantation of 150 keV Ar⁺ ions at different doses on the surface of amorphous Fe₄₀Ni₄₀B₂₀ and the changes in the bulk properties following proton irradiations are investigated by conversion electron and transmission Mössbauer spectroscopy respectively. In the former case a correlation between the total Mössbauer absorption and the total energy deposited by incident Ar⁺ ions is established, indicating the development of certain stresses in the material, affecting the inter and intra molecular bonding in the near surface region. On the other hand, the proton irradiation seems to cause a reorientation of the atomic spins and also the formation of an additional Fe or Fe?Ni rich phase in the sample. Also the low field A.C. susceptibility is found to decrease as a function of the dose of incident protons. Possible reasons for the above behaviour are discussed.     

Optical reaction cross-sections for light projectiles

The optical reaction cross-sections forn, p,²H,³He,³He and⁴He for several global optical potentials available in the literature have been parametrized in terms of simple empirical expressions which are smooth functions of the target mass number and the projectile energy. The empirical forms are 5–10% accurate over the periodic table and energy-range upto 50 MeV. They can be conveniently used in calculations where the optical reaction cross-sections are required as input. The calculation of proton spectra in the (n, p) reaction at 14 MeV is discussed.     

Non-equilibrium dynamics in high-energy nucleus-nucleus collisions: (II). Calculation of inclusive particle spectra

We present theoretical results for proton, deuteron, triton, ³He and ⁴He inclusive particle spectra measured in 250 MeV/amu and 400 MeV/amu nucleus-nucleus reactions. The calculations are based on a multiple collision model which is derived from the relativistic Boltzmann equation and which includes composites formation through thermodynamics. The agreement with the data is reasonable to good and the remaining discrepancies are discussed.     

Proton Fluxes in the Neutral Sheet: A Case Study by the DOK2 on Interball-1

On December 3, 1996, in the time interval with low geomagnetic activity, the Interball-1 satellite crossed the neutral sheet of geomagnetic tail from north to south at the radial distance 25R _E. Characteristics of proton and electron fluxes 20 keV measured by DOK2 spectrometer are presented. High anisotropy of proton fluxes was observed. Fluxes of protons and their anisotropy are modulated by magnetic field. In a region where the total magnetic field is low and proton fluxes are high the anisotropy is lower and energy spectra of protons are harder than in another region. In the latter one (after 20:17 UT) when the total magnetic field is higher mainly due to an increase of |B _x | (B _x <0), DOK2 observes the increase of proton flux anisotropy. These fluxes have character of spikes. The detailed proton energy spectra shows that the spikes with duration of few seconds are characterised by very quick change of spectral slope. Proton spikes are accompanied by the increases of electron fluxes in the earthward direction. When B _x >0, the proton fluxes in earthward direction predominate. In the time with B _x <0 we observe the proton fluxes in the tail direction. This is in a good agreement with the measurements of bipolar fluxes on Geotail reported by Petrukovich et al. [J. Geophys. Res. 26 (1999) 2909]. We suppose that the cause of these bipolar proton fluxes is the reconnection of geomagnetic field lines during the growth phase of geomagnetic substorm.     

Microscopic three-cluster study of the low-energy 9 Be photodisintegration

The ⁹Be and ⁹B nuclei are investigated in a microscopic three-cluster model involving α + α + n (or α + α + p) configurations. The ⁸Be (0 ⁺ , 2 ⁺ ) + n and ⁵He (3/2 ^- , 1/2 ^- ) + α (or mirror) channels are included by taking account of the unstable nature of ⁸Be and ⁵He. Spectroscopic properties of ⁹Be and ⁹B are analyzed. We show that the ⁵He + α configurations cannot be neglected to derive accurate results. The ⁹Be(γ,αα)n photodisintegration cross-section is shown to be mainly determined by ⁸Be + n channels at low energies, but ⁵He + α channels become important beyond E _γ≈ 4 MeV. Received: 7 September 2001 / Accepted: 19 November 2001