Akira Katase

Elastic scattering of electrons by water molecules over the range 100-1000 eV

Relative values of differential cross sections (DCS) are measured by the crossed-beam method. Two cylindrical-mirror energy analysers are employed. One of them is moved to detect scattered electrons at every angle, and the other is fixed at an angle to monitor the elastic scattering events. The effects of target gas distributions in a molecular beam flowing out from a multicapillary array are taken account of to correct the relative values. The DCS are also measured at an angle for water molecules and helium atoms by using gas chamber. On the basis of the absolute DCS for He measured by Jansen et al. (1976), the relative DCS for water molecules are converted into absolute values. In addition, the DCS are calculated by the partial-wave method for the double Yukawa potential. The values of its three adjustable parameters are determined by comparison with the experimental DCS. A spherically symmetric realistic potential is also inferred without adjustable parameters from the charge distribution that was derived from molecular-orbital theory. The DCS calculated for this potential reproduce the experimental values fairly well.

Indoor concentrations of 220Rn and its decay products.

The distribution of 220Rn atoms in a room was derived from the diffusion equation. The activity concentrations of 212Pb and 212Bi were obtained in relation to 220Rn exhalation rate from a concrete wall. Near the surface of the concrete wall, the radiation exposure due to inhalation of 220Rn decay products may be significant in some cases.

Elastic Scattering of Protons from B¹¹, Al, P, Co and Cu from 6 to 7.4 MeV

The energy dependence of the angular distributions of protons elastically scattered by the odd nuclei, B 11 , Al, P, Co and Cu, was measured in the energy range from 6 to 7.4 MeV by using the 105 cm Kyoto University Cyclotron. No remarkable energy dependence of the pattern of the angular distributions was found in all the energy and angular ranges studied. It may be concluded that a less energy dependence of the angular distributions of protons elastically scattered by the odd nuclei is due to a less contribution of the compound elastic scattering and moreover a less energy dependence of the compound elastic scattering.

Optimization method for superconducting magnet current leads

Abstract Current leads for superconducting magnets are studied to simplify the design into a single chart. A new parameter, obtainable with a brief calculation, is introduced. Characteristics of a wide variety of current leads, namely geometric dimension, heat flow into liquid helium and pressure drop of the cooling gas flow are represented in the form of a single design chart by using this parameter. Current leads can be optimized without explicit consideration of quantities such as cross-sectional area and length of conductor, heat transfer coefficient and cooling perimeter. As the burn-out of current leads is expected to occur with the accidental decrease or stoppage of cooling gas flow, this serious situation must be taken into account in the design. An adiabatic approximation is used to estimate the temperature rise. Further improvement of the performance can be obtained if the cross-sectional area decreases along the length of the conductor.

Characteristics of Nb-based Josephson junctions at a temperature below 1 K

A lithographic technique for Josephson LSI (large scale integrated) circuits was applied to the production of a superconducting tunnel junction for radiation detection. Nb-Al/aluminum oxide/Nb tunnel junctions with different junction sizes and barrier oxidation times have been fabricated. The current-voltage curves were measured in the temperature range from 4.2 to 0.45 K. The junctions showed some amounts of leakage current, which remained below 2 K. The behavior of the leakage current was successfully understood from its experimental dependence on the junction size. >

Propagation velocity of normal zones in a SC braid

Abstract Propagation velocities of normal zones are obtained experimentally in a superconducting (SC) braid which is wound into a coil to simulate the SC pulsed dipole magnet for a synchrotron from the viewpoint of cooling. A numerical calculation to determine this velocity is carried out by using a modified thermal conduction equation. The equation eliminates a troublesome problem on the boundary condition reported previously by defining a new variable of the square of the heat flux along the conductor. A velocity dependent correction factor is used for cooling to take account of the transient effect. The values calculated are a representation of the experimental dependence of the velocity on both current and magnetic field and this indicates that the correction factor is applicable to the winding of the braid if modified properly. Discussion is also made on the transient cooling in the coil.

Thermal stability of high current density magnets

Abstract The stabilization theories hitherto proposed for superconducting (SC) magnets are not fully developed for application to high current density magnets such as pulsed dipole magnets for a synchrotron. Hence, thermal stability in such high current density magnets is studied by obtaining a minimum energy of thermal disturbances which barely leads a magnet to quench. To find the minimum energy by calculation a dynamic simulation of temperature distribution along a conductor is carried out following an application of the disturbances on the conductor. The minimum energy is found to depend largely on time duration and spatial length of the disturbances. The values of the minimum energy given by calculation agree almost with the experimental results obtained for a coil which simulates a pulsed dipole magnet from the viewpoint of cooling. Discussion is also made in relation to the minimum energy on the performance of a pancake type solenoid magnet which has the same cooling as in the simulating coil.

Variation of Intensity of Environmental Gamma-Rays Measured with Ge(Li) Spectrometer

The variation of the intensity of environmental γ-rays has been studied with a Ge(Li) spectrometer. The 12 γ-rays were selected to be examined and typical characteristics of variations were obtained for each γ-rays. The intensity of γ-rays of 214Pb and 211Bi which are 222Rn daughter nuclei increases on rainy days to the severalfold value of the average in the case of no precipitation. These variations were observed to be roughly proportional to rainfall rate in a sequence of precipitation. The γ-rays intensity of nuclides of the thorium series and 137Cs is nearly constant within about 3% regardless of the weather. Its variation is about equal to the statistical fluctuation of the present measurements. The mean diurnal variations of f-ray intensity were obtained on days without precipitation. The intensity of 214Pb and 214Bi j-rays fluctuates nearly sinusoidally with an amplitude of about 6% of the average value and the maximum in the early morning.

Three-Point-Charge Model for Ternary Fission

Trajectories of three point charges are computed two-dimensionally to analyze the experimental data of ternary fission. In the case of a fission accompanied by a long-range alpha particle (LRA fission), the final value of emission angle of the alpha particle is found to depend mainly on the values of the fragment mass ratio and the ratio x , where x = D a (distance between emission point and light fragment)/ D f (distance of two fragments at scission). The final alpha particle energy E A is represented by the equation \begin{aligned} E_{A}=\left(a+\frac{b}{{D_{f}}^{c}}\right)(x-x_{0})^{2}+\left(d+\frac{f}{{D_{f}}^{e}}\right){E_{\alpha}}^{g(D_{f-h})^{1/2}}, \end{aligned} where E α is an initial kinetic energy. The values of parameters a , b , c , d , e , f , g , h and x 0 are determined for some values of the mass ratio and the total kinetic energy in LRA fission of 236 U and 252 Cf. The distributions of E α , D f and the initial total kinetic energy of two fission fragments are obtained for LRA fission of...

Protons from 40Ca bombarded with 14.1 MeV neutrons

Abstract Energy spectra and angular distributions were measured for protons emitted from 40 Ca bombarded with 14.1 MeV neutrons. The constant-nuclear-temperature formula for level density fits the energy distribution for backward angles and yields a nuclear temperature of 1.34 ± 0.04 MeV for 40 K. The angular distributions of the protons emitted through compound process are nearly symmetric around 90°. The spin cut-off parameter is estimated to be about 2.0 from the angular distribution of protons emitted by the (n, p) reaction. The cross sections for the (n, p) and (n, np) reactions through compound process are 471 ± 21 mb and 180 ± 32 mb, respectively. The direct (n, p) reactions has a cross section of about 11 mb.