Masaru Yasuno

Energy Gap in Nuclear Matter

An equation for the energy of the one particle mode and the energy gap of nuclear matter is directly solved in the momentum space for the realistic soft- core potentials without introducing ambiguities entering in the transformation to the configuration space. (C.E.S.)

Effective Interaction in Nuclear Many-Body Problem

General treatment of nuclear many-body problem will be given in terms of Green functions and the correlation property of nucleus will be exhibited by correlation factor. Effective interaction certifying the independent particle motion is introduced and proved to identify with Brueckners K-matrix. And on the basis of this point, applying the method of the particle-hole pair to the system, a collective mode will be derived and the effective interaction contributing to collective motion will be studied. It will also be shown that this effective interaction has the property very different from electron plasma case.

Spontaneous Fission Half-lives

A dynamical theory of nuclear distortion leading fission, is presented. This theory is based on_ the unified model (the collective model). But, since the spontaneous fission is, so to speak, an irreversible process, the present theory is treated reflecting this speciality. Starting from this dynamical theory, a semi-empirical formula of spontaneous fission half.lives of even-even nuclei is derived. This formula can well reproduce the general tendency of spontaneous fission half-lives of even-even nuclei. The essential features which affect half-lives are discussed. Finally, a reasoning for the asymmetry character of fission and the orientation in calculating the difference of half-lives between even-even and even-odd nuclei are given.

Remarks on Interacting Many-Fermion System

Dynamic correlation behavior of nuclear matter is considered. The two-particle scattering mode, including hole motion, is discussed. A definite phase shift is found in the wave function, indicating effects due to the attractive interaction, in turn due to the Pauli principle. This is true even though the original interaction consisted only of a repulsive core. The mode of the independent particle motion under the conditions may not be certified in the Fermi sea except in the neighborhood of the Fermi surface.

Effect of the Particle-Hole Pair Interactions in Nuclear Many-Body Problem

The dynamical aspects of nuclear particle-hole pairs are studied in many- body nuclear systems. The method used is adapted from plasma particle-hole pair interaction methods. It is shown that the particle-hole pair interaction screens the Fourier oonaponent of the Coulomb forces so that the probability of low- momentam-transfer interactions is increased. It is concluded that the pair interaction increases the range of nuclear interactions. (T.F.H.)

Interpretation of the Optical Model in Nuclear Reactions

The theoretical basis of the nuclear optical model is investigated for the elastic scattering of neutrons at low energies. It is argued in connection with statistical mechanics of irreversible processes that the characteristic feature of the optical model can be revealed by means of wave packets whose energy spread is wide enough to cover many compound levels. The giant resonance of the Lorentzian shape is found to result owing to fluctuations in the interaction potential which is experienced by an incident nucleon in a target nucleus. The imaginary part of the optical potential or the half width of a giant resonance is expressed by the product of the second moment and the correlation time. The latter is closely related to the concept of portee introduced by Bloch, with whom we share the same opinion in many respects. The correlation time is shown by our method to reveal a feature of the fluctuations and can be evaluated, if the fourth moment is known. (auth)