Yoshihisa Wakuta

Fission of U and Th by Gamma Rays from 200 MeV to 1150 MeV

Measurements of the photofission cross section, fragment angular distribution and fragment single kinetic energy distribution for 238 U and 232 Th over an energy range from 200 MeV to 1150 MeV are described. Semiconductor detectros were used for the measurements. It is found from a photon difference method that the photofission cross section shows a resonance at a photon energy of about 330 MeV and 350 MeV with a peak value of ∼120 mb and ∼40 mb for U and Th respectively. It is evident that this resonance can be attributed to the well known (3, 3) resonance in the pion photoproduction from a free nucleon. Furthermore, the result of the photofission cross section measurements was analyzed, by assuming that nuclear excitation resulting from the reabsorption of the created pions and the quasi-deuteron absorption within a nucleus induces the photofission in the heavy nucleus. From this analysis it is shown that these assumptions explain qualitatively the general properties of the photofission in the energy re...

Design chart of gas-cooled current leads made of copper of different RRR values

Abstract The generalized pressure drop of the cooling gas of current leads is obtained using the effective friction factor λ p = 0.0715 , which has been obtained in experiments on spiral-fin current leads. The design chart of current leads made of RRR = 92.5 copper is improved with respect to the generalized pressure drop of the cooling gas. For various copper materials with different values of RRR approximate expressions are considered to evaluate the electrical resistivity and the thermal conductivity as a function of temperature. The generalized characteristics of current leads made of copper of several RRR values are summarized in the design chart.

Spin polarization effect on ignition access condition for D-T and D-3He Tokamak fusion reactors

In this paper, ignition characteristics in deuterium-tritium(D-T) and D-{sup 3}He tokamak reactors with spin-polarized fuels are presented by using the ignition access condition based on the generalized saddle point in the representation of ({bar P}{sub ht}{tau}{sup 2}{sub E}, n{tau}{sub E}, T). Enhancement of the D-T fusion cross section due to parallel spin polarization with respect to the magnetic field can reduce the confinement enhancement factor required for reaching ignition by {approximately} 20% if fusion particle loss is not induced by the anisotropic fusion particle distribution. Spin polarization is this effective when a D-T reactor is marginal for ignition. In D-{sup 3}He fusion, it is more advantageous to use spin-polarized fuel in the heating phase than in the case of D-T fusion. The auxiliary heating power to reach ignition, which is rather large for D-{sup 3}He fusion, can be reduced by a factor of 2 to 3 compared with the unpolarized case. The deuterium-deuterium fusion suppression effect, it is exists, does not alter the ignition condition much. Various problems related to the spin polarization scheme are also discussed.

A fast neutron time-of-flight spectrometer with neutron-gamma ray discrimination

Abstract A fast neutron time-of-flight spectrometer with neutron-gamma ray discrimination based on the method developed by Alexander et al. is described. A combination of a 5″ dia. NE213 liquid scintillator and a 5″ dia. XP1040 photomultiplier is used both for neutron-gamma discrimination and neutron energy measurements. This spectrometer has a time resolution less than 2.0 nsec and is used at a counting rate as high as 4 × 104 pps.

Effect of dissociator nozzle temperature on polarized atomic hydrogen beam intensities

Abstract An overall effect of cooling the dissociator nozzle on the polarized beam intensities is described. Emphases are placed on the considerations of the atomic beam transmission through the sextupole separation magnet for different pole piece configurations and a comparison with the Kyushu University polarized ion source has been made.

Operational performance of spiral-fin current leads

Abstract The profile of the pressure drop of cooling gas was measured in operational tests of 7 and 10 kA current leads. The current leads have spiral-shaped fins which permit both high heat exchange efficiency and reliability against thermal runaway. A general design chart was employed to determine the geometrical dimensions and to estimate the operational performance of the leads. The spiral-fin current leads exhibited good performances in the operational tests. The heat flow from the cold end of the 7 and 10 kA leads was 7.47 and 10.4 W, respectively, in the self-sustained condition. A constant friction factor of 0.0715 was found to reproduce the experimental pressure drop profile along the cooling path. This friction factor can be employed to estimate the pressure drop of the cooling gas of current leads in general designs.

Permanent sextupole magnets

Abstract Compact but very strong sextupole permanent magnets have been assembled for use in a newly developed cold atomic beam polarized ion source. The sextupole magnetic field characteristics have been found to be satisfactory.

Characteristics of σ-transitions in an atomic-beam polarized deuteron source

Abstract Quantum mechanical calculations of the degree of polarization after inducing σ -transitions in an atomic-beam polarized deuteron source have been done. Four parameters are found to be important for characterizing the performance of rf transitions. These are the strength of the rf oscillating magnetic field, the field gradient of the static magnetic field, the separation efficiency of atomic states and the temperature of atomic gas. It is shown that the degree of polarization can conveniently be evaluated by an “adiabatic field factor” which is defined by the first two of these four parameters irrespective of the kind of σ -transition. Some applications of the present results are also discussed.

Large area mosaic solid-state detectors for low yield fission study

Abstract A number of silicon surface barrier detectors has been arrayed in mosaic structure to increase the sensitive area by an order of magnitude. It has been used as a remote detector at the end of the flight tube in the double-energy single-time-of-flight measurements of 252 Cf spontaneous fission fragments and found to be as good in performance as a small detector ordinarily used.

Production of high-energy polarized gamma-rays from an electron synchrotron with amorphous radiator

Abstract It has been tried to obtain high-energy polarized gamma-rays from a synchrotron with an amorphous radiator. As a radiator a nylon mono-filament, 60 μm in dia., was used. The polarization of the photon beam was determined by comparing the angular distribution of the pair electrons produced by the polarized photon beam with that produced by the unpolarized one. The angular distribution of the pair electrons were observed with a wire spark chamber. The degree of the photon polarization was measured at various incident electron- and photon-energies and the emission angles of the photon beam, and for different accelerating rf conditions of the synchrotron.