The discoveries of uranium 237 and symmetric fission — From the archival papers of Nishina and Kimura

Shortly before the Second World War time, Nishina reported on a series of prominent nuclear physical and radiochemical studies in collaboration with Kimura. They artificially produced 231Th, a member of the natural actinium series of nuclides, by bombarding thorium with fast neutrons. This resulted in the discovery of 237U, a new isotope of uranium, by bombarding uranium with fast neutrons, and confirmed that 237U disintegrates into element 93 with a mass number of 237. They also identified the isotopes of several middle-weighted elements produced by the symmetric fission of uranium. In this review article, the highlights of their work are briefly summarized along with some explanatory commentaries

Near-Edge Spontaneous Photoluminescence in GaSe_<1-x>S_x(Physics)

Photoluminescence spectra of GaSe_S_x (0≦x≦0.2) are investigated at 4.2 K by the time resolving method. The shift in the photon energies of the luminescence lines with respect to the chemical composition x may be understood without any quantitative contradiction if one employs the empirical model that the direct conduction band edge lies 5 meV below the indirect one, whereas the ground state of the direct exciton lies 13 meV above that of the indirect one in ε, γ-GaSe at 4.2 K. The direct-indirect gap reversal occurs near x=1×10^

Nonlinear Photomagnetoelectric (PME) Effect in Bi by Laser Irradiation

The transverse (nonoscillatory) and longitudinal (oscillatory) photomagnetoelectric effects have been measured with single crystals of Bi under pulsed illumination by a Q-switched Nd-laser (wavelenghth : 1.06μ) with its peak intensity range from 10^3 to 10^6 W/cm.^2 The superlinearity in the PME voltage is observed for the Faraday configuration for the beam intensity above 1.4×10^5 W/cm.^

Phonon-Assisted Stimulated Emission in 2H Type PbI_2(Physics)

The stimulated emission in 2H type PbI_2 crystals has been observed under N_2 laser beam excitation at 4.2 K. The analysis of its gain spectrum shows that the emission is induced by the recombination of free exciton assisted by the emission of one longitudinal optical phonon. At a higher level of excitation, the gain spectrum peak shifts to lower energy side. Possible mechanisms of this spectral change are discussed