Variations in the photofission cross section near ''threshold'' with initial kind of nucleus were investigated for seven spheroidal nuclei in the region of atomic numbers 90, 92, 93. The photofission cross sections at the two discrete energies 6.14 and 7.0 Mev were determined for the following even-even nuclide . Th/sup 232/, U/sup 234/, U/;sup 236/, and U/sup 238/; and also the odd- A nuclides. U/sup 233/, U/sup 235/ and Np/sup 237/. Nuclear excitation of the target nuclei was achieved via gamma rays from nuclear capture of protons on fluorine. Protons of 1.380- and 3.645-Mev energy impinged on a thick CaF/sub 2/ target. The highenergy quanta of 5.14, 6.91, and 7.12 Mev so obtained represent the well-known ground state transitions in O/sup 16/, whose relative intensities change with bombarding energy of the proton. The fission counting was done in a double-region ionization chamber of 2 pi geometry. The heavy-element samples were nearly uniform oxide deposits of about one mg/cm/sup 2/, on platinum. Employing the known thick target relative gamma-ray intensity ratio, I(6.91 + 7.12)/I(6.14), plus the measured gamma flux and fission counting yield at each of the two above proton energies, the ( gamma , fission) cross sections at 6.14 snd …

Purified, degassed samples of cis- and trans-1,2dichloroethylene were irradiated in glass cells with 48Mev helium ions at energy inputs up to 10/sup 21/ ev/cc. The principal volatile radiolysis products are acetylene, hydrogen chloride, chloroacetylene, vinyl chloride, hydrogen, and dichloroacetylene, in order of decreasing yield. The use of a mass spectrometer in conjunction with gas chromatography made possible the identification of several higher-boiling, or ''polymer,'' products as tetrachloroethane, tetrachlorobutene, and pentachlorobutene isomers. However, about half of the higher-boiling material proved to have too low a vapor pressure (b.p.> 300 deg ) at the highest praticable column temperature for these techniques to yield any clues to its nature. Hence these products were characterized only by yield, average molecular weight, and average composition. The effect on product yields of the variation of certain kinetic parameters --total dose, density of initial excitation, and temperature --was determined in survey experiments. These included irradiation with helium ions at 80 deg and at room temperature, irradiation with electrons of differing energy distribution provided by a microwave linear accelerator and by a Van de Graaff machine and irradiation with Co/sup 60/ gamma rays. There are no significant differences in the radiolytic behavior of the cis- and trans- isomers …

ABS>An accurate measurement of the differential cross section for the photoproduction of positive pions was made at the Berkeley synchrotron, for photon energies of 280 and 290 Mev. The mesons were produced in a thin-walled liquid hydrogen target, and the meson detection apparatus utilized the characteristic pi -- mu decay of the meson. The measurements were done in two steps, from 0 to 50 deg with equipment specifically designed to reduce a very high positron background, and from 30 to 160 deg with equipment whose efficiency and solid angle could be accurately determined. The experimental results in the small-angle region definitely show the effects of ''photoelectric'' production of pions from the cloud surrounding the nucleon, which are characterized by an abrupt flattening of the cross section in the region forward of 40 deg (c. m.). The results are compared to the theory of photoproduction derived from the dispersion relations, and the sgreement is satisfactory within the limitations of the theory. (auth)

in which the nuclear interactions of the incoming and outgoing particles are considered. Two different formal expressions that give the transition amplitude are derived, and the wave functions in this amplitude are approximated by an optical-model procedure in which it is assumed that the initial- and final- state particles scatter elastically in the nucleus. The inelasticscattering effects are shown to be small. Several closed forms for these optical-model wave functions are derived on the hsis of a WKB approximation for a complex square- well scattering potential. The use of these wave functions, along with an approximation that gives the form of the transition amplitude in terms of Gaussian functions, allows a closed-form solution for the differential cross section. lt is found tht the elastic scattering processes are not negligible, since they affect considerably the magnitude and the shape of the differential cross section. By comparing the theory with recent pickup experiments on C/sup 12/ at 95 and 145 Mev, one obtains a nuclear-momentum distribution that, unlike the Born approximation analysis, is in good agreement with the results of other determinations of momentum distributions. It is found tht a neutron number of from 4 to 7 neutrons and a momentum distribution …