Shinsaku Kobayashi

A 160 cm Synchro- and Variable Energy Ordinary Cyclotron

A 160 cm cyclotron have been constructed as the first accelerator of the Institute for Nuclear Study, University of Tokyo. This cyclotron can be used as a variable energy ordinary cyclotron as well as a synchro-cyclotron by changing the dee-system and the oscillator system. As an ordinary cyclotron it can produce protons of any desired energy between 7.5 and 15 MeV, deuterons between 15 and 21 MeV, and α particles between 30 and 42 Mev. These beams are now being used for various experiments on nuclear reactions and for production of radioisotopes. As a synchro-cyclotron, it can produce protons of 57 MeV in energy and the beam is extracted with high efficiency at a radius near n =1 with an electrostatic deflector.

Nuclear spin-spin effect in the total cross section for 1 MeV polarized neutrons on polarized 59Co nuclei

Abstract Measurements of the spin-spin effect, σ ss = (σ↑↑-σ↑↓) 2 P n · p I in the total cross section for polarized neutrons on polarized 59 Co are reported at neutron energies of 1.1 and 1.4 MeV. Target polarizations from 47 ± 5% to 30 ± 3% were obtained for a polycrystalline metal of Co 0.90 -Fe 0.10 alloy at demagnetization temperatures from 0.030 to 0.048°K. The results for σ ss are −0.21 ± 0.18 b at 1.1 MeV and −0.18 ± 0.23 b at 1.4 MeV, combined with experimental asymmetries obtained at 4.2° K. If σ ss is assumed to arise from a spin-spin term in the optical potential of the form − V ss f(r) σ · I , the upper limit of the strength is obtained as | V ss | σ ss at 7.90 MeV and assuming f ( r ) as a microscopic form factor. The obtained nature of V ss is qualitatively explained by a microscopic model.

The Spin-Spin Interaction of 0.92 MeV Polarized Neutrons with Polarized 165Ho Nuclei

In order to obtain a direct measure of the strength and form of the nuclear spin-spin interaction, the transmission of 0.92 MeV polarized neutrons by polarized 165 Ho was measured. The total cross section and relative scattering angular distribution of 0.92 MeV unpolarized neutrons through unpolarized 165 Ho nuclei were also measured in order to make a parameter search of the optical potential. The experimental results are analyzed with Davies and Satchlers DWBA formalism. The results show that the effective spin-spin interaction between a free neutron and a 165 Ho nucleus, is an attraction type and its strength has the order of one MeV, and the present experimental result together with other data obtained at ORNL and Stanford, can be fitted by the DWBA approach in either case of a volume and surface type of the form factor. For the further determination of the strength and the form of the spin-spin interaction, more precise similar experiments are needed for various different neutron energies.

NEUTRON DEPOLARIZATION IN ELASTIC SCATTERING.

The depolarization parameter D (θ) in elastic scattering of 1.36 MeV neutrons was measured at θ 2 =30°, 38°, 80°, 120° and 150° for 27 Al, 59 Co, 63,65 Cu, 209 Bi and Ni nuclei. The departure of D (θ) from unity for Al, Co, Cu and Bi was observed particularly at backward angles, but not observed for Ni. This fact shows that the spin flip of incident neutrons takes place along the normal to the scattering plane in the elastic scattering process for non-zero spin targets. These results are discussed in the light of different nuclear reaction mechanisms.

Elastic Scattering of 55 MeV Protons from Heavy Nuclei

Several targets, covering the spherical, deformed and transition regions of heavy nuclei, were bombarded with 55 MeV protons and angular distributions of the elastically scattered protons were measured. The diffraction structure of them are strongly damped for the deformed nuclei, as compared with that for the spherical nuclei and this feature changes gradually for nuclei of the transition region. The optical model analysis was also performed to discuss the details of the deformation effect.

A Liquid Helium, Time of Flight Neutron Polarimeter with a Spin Rotating Solenoid

A Liquid helium time of flight neutron polarimeter with a spin rotating solenoid has been developed to measure neutron polarization for the energies as low as 800 KeV. Energy selection is accomplished by time of flight techniques and accuracy of polarization measurement is improved by a spin rotating solenoid. Measurements of the neutron polarization for the Li7(p, n0)Be7 and C12(d, n0)N13 reactions were made for the proton and deutron energies at 2.8 MeV and 1.58 MeV at laboratory angles of 52° and 70°, respectively. The polarization of the neutron for the C12(d, n0)N13 reaction is -(40.5±2.7)%.

Low Energy (p, n) Reaction on 55Mn and the Low-Lying Excited States of 55Fe

The ( p , n ) reaction on 55 Mn was studied with the emphasis upon the investigation of the low-lying states of 55 Fe. The angular distributions of each neutron groups corresponding to energy states of 55 Fe lower than 0.93 MeV were measured at ten different proton energies in the energy range from 2.3 MeV to 2.8 MeV. New levels of 55 Fe at 0.51 and 0.68 MeV reported by Kim at ORNL were not observed at least with so much intensities as he claimed. The Integrated cross section of each group corresponding to the low-lying states of 55 Fe was analyzed by means of the statistical theory due to Hauser and Feshbach. As a Consequence, the spin and parity of 0.41 MeV level were assigned as (1/2) - ; (3/2) - was excluded. This assignment is consistent with that suggested by Schiffer et al. . The measurement of The life of the first excited state at 041 MeV was tried as a testing of core-excitation model.

A MEASUREMENT OF THE SPIN CORRELATION COEFFICIENT CKP IN p-p SCATTERING AT 52 Mev

The spin correlation coefficient in proton-proton scattering at 90 deg in the center-of-mass system was measured at 52 Mev. The spin correlation coefficient is highly sensitive to the phase shift of 3 Po, and information on the character of the spin-orbit coupling force can be obtained by measurements in this energy region. The spin correlation coefficient was found to be 0.10 plus or minus 0.14. This result seems to require a rather large value for the 3 Po phase shift and indicates that the spin-orbit coupling force in this energy region is weaker than that inferred from highenergy experiments. (C.E.S.)