Saburo Takamura

Computer simulation of damage depth profiles for 2–7.5 MeV/amu heavy ions incident on pure metals with experimental comparisons

Abstract A computer code EDEP-1 was extended to a high energy region using currently reliable stopping powers. The damage depth profiles calculated for pure metals for Al, Fe, Ni, Cu, Ag, and Ta irradiated with 2–7.5 MeV/amu heavy ions of C, Cl and Cr show that the extended code gives nearly similar profiles and depths of peak damage to those obtained by a Monte Carlo calculation code, TRIM85. The discrepancies from the experimental peak depths are less than 15%. The damage stragglings around the peak are calculated to be much smaller than the experimental values.

Effect of low temperature irradiation on insulators and other materials for superconducting magnets

Abstract Insulators, stabilizers and superconductors for superconducting magnets were irradiated in a fission reactor at about 5K. For insulators, the mechanical properties of Mylar, polyimide, epoxy resins and fibre reinforced epoxies(FRP) were measured in liquid helium and in liquid nitrogen without warm up after irradiation. The breaking stress of epoxy resins decreased by ~40%, that of FRP decreased by about 15% and the yield stress of polyimide exhibited a slight decrease after a dose of 1.1 × 10 9 rad at about 5K. For the stabilizers Cu and Al, the effects of deformation prior to irradiation and after irradiation on the change of electrical resistivity were investigated. For superconductors, the change in critical current after neutron irradiation at low temperature is also reported.

Recovery of copper alloys after neutron irradiation at low temperatures

Abstract The effects of fast neutron irradiation near 4.2°K on dilute Cu, Cu3Au, α-CuZn, β-CuZn and CuNi alloys were studied by electrical resistivity measurements. For Cu3Au, the recovery stage at ∼ 100°K becomes more distinct with increasing long-range order, and is attributed to migration of interstitials. The ratio of the number of replacements to the number of displacements (C R /C F ) is estimated to be about 50 for neutron irradiation, in contrast to the previously reported value of ∼2 for electron irradiation. For α-CuZn, a large recovery stage at ∼150°K is found and attributed to annihilation of interstitids whose migration produces ordering. For β-CuZn, migration of interstitials also produces ordering. It is also suggested that in β-CuZn, the ratio C R /C F is larger for neutron irradiation than for electron irradiation as in the case of Cu3Au. The results on CuNi alloys are presented without explanation.

Electrical Resistivity Measurements of F.C.C. Metals Deformed at 4.2°K

The recovery of the electrical resistivity of polycrystalline 99.999% Au, Cu and Al, deformed at liquid helium temperature by elongation, was studied in the temperature range of 4.2° to 200°K. Initial recovery was followed in general by the large recovery stage for the three metals. The initial recovery stage was attributable to the dislocation rearrangement. The latter was considered to be due to annihilation of interstitial type defects. The results are discussed on the basis of current theories.

Production of an intense slow positron beam by using an electron LINAC and its applications

Abstract An image of reemitted positrons has been produced in a proto-type positron transmission-type reemission microscope by using the electrostatic intense slow positron beam from an electron LINAC. RHEPD experiments have then been performed on H-terminated Si(111).

Brightness enhanced intense slow positron beam produced using an electron linac

An intense pulsed slow positron beam was produced from a 100 MeV electron linac of the Japan Atomic Energy Research Institute and was extracted using solenoid transport tubes. The intensity of the obtained slow positron beam was 2–3×107 e+/s at 110 of the full power operation (at 10 μA average electron beam current). In order to use the beam for positron scattering, diffraction and microscope experiments, it was transferred from the solenoid magnetic field to a field-free region, and was then brightness-enhanced. The final beam size was reduced from 10 mm o in the solenoid magnetic field to 0.5 mm o after two stages of remoderation.

Recovery of Fast Neutron Irradiated Niobium and Vanadium at Low Temperature

The recovery structures of Nb and V after fast neutron irradiation near liquid helium temperature are determined. The effects of radiation doping, impurity doping and deformation before the low temperature irradiation on the recovery stages are investigated. Impurities appear to suppress the recovery stage at 45 K (the 45 K stage) and enhance the 70 K stage for Nb and similarly suppress the 50 K stage and enhance the 72 K stage for V. The enhancement of stage I by radiation doping at room temperature was observed in Mo and W in the previous experiments, but it is not seen in Nb and V. These results suggest the following temperature ranges for the recovery stages: stage I (below 50 K) and stage III (∼220 K) for Nb, and stage I (below 60 K) and stage III (∼170 K) for V.

Recovery of Fast Neutron Irradiated Copper and Gold at Low-Temperatures

The recovery of the electrical resistivity of 99.999% purity Cu and Au and Au-0.1% Cu alloy was studied after fast neutron irradiation at liquid He temperature. The damage production rate decreased by cold work and alloying in Au, but it increased by cold work in Cu. Cold work enhanced the recovery above 150°K in Cu and above 50°K in Au. In Au, the stage III recovery shifted by about 30°K toward lower temperature for cold worked specimens.

Recovery of Fast Neutron Irradiated Iron at Low Temperatures

The isochronal annealing studies of electrical resistivity of Fe after fast neutron irradiation at liquid helium temperature were performed. Recovery spectra of annealed, cold worked and as-received specimens were compared. The main peak in stage I was divided into two substages and stages II and III recovery seemed to be influenced by interstitial impurities.

Damage distribution of heavy-ion irradiation in metals studied by electrical resistivity measurement

Abstract The stacked thin foil samples were irradiated by heavy-ions of C, Cl and Br with energies of 90–160 MeV at a low temperature below liquid nitrogen temperature, and the depth profiles of damage were obtained from the electrical resistivity change by isochronal annealing in the foils of pure Al, Fe, Ni, Cu, Ag and Ta set at various depths from an ion bombarded surface. The difference between the experimental damage peak depth and the theoretical one calculated by the modified EDEP-1 and TRIM codes is studied in terms of atomic number of irradiated metals. The half-value width of the damage distribution obtained from the experiment is larger than the calculated half-value width in the samples irradiated with C, Cl and Br ions.