The U-like AT-vacancy production probability in 7.5-MeV/nucleon deep-inelastic 238 U4-238 U collisions has been measured for no-fission, single-fission, and double-fission exit channels. The results are interpreted using quasimolecular orbital correlations for diatomic and triatomic configurations. This leads to the determination of lower limits for the time scale for late fission of U~like products (> 8 and > 4 as) and their probability (> 77% and > 52%), at mean initial-excitation energies of -40 and -105 MeV, respectively. PACS numbers: 25.70.Lm, 21.10.Tg, 25.85.Ge, 34.50.Fa PPAC FIG. details. 1. Schematic of the experimental setup. See text for
Besides characteristic target and projectile x rays, x-ray continua and radiative-electron-capture photons are seen in collisions with relativistic heavy ions ranging in energy from 82 to 422MeV/amu and in atomic number from Xe to U. The angular distribution, centroid energy, cross section, and line shape of the broad radiative-electron-capture lines are analyzed. The observed continua are due to primary-and secondary-electron bremsstrahlung.In the projectile frame, primary bremsstrahlung is the radiative scattering of incident target electrons from the projectile nucleus.The continuum cross sections and angular distributions are calculated, and are compared with experiment. Secondary-electron bremsstrahlung, due to the radiative scattering of ionized target electrons from other target nuclei, is target-thickness dependent, and the cross section increases roughlỹ ith the square of the target atomic number. The calculated primary-electron bremsstrahlung cross sections are lower than experiment.
X-ray studies of relativistic heavy-ion-atom collisions allow the direct observation of the radiative-electron-capture photons. The angular distribution of these photons is approximately sin 2 0 lab , because of the cancellation of electron retardation effects when the cross sections are subjected to Lorentz transformation into the laboratory frame. Comparison of measured and calculated cross sections reveals the number of equilibrium projectile K vacancies present in the solid targets, which can be compared with charge-state measurements behind the target.
10Be (T1/2 = 1.5·106y) is mainly produced in the atmosphere by cosmic ray spallation reactions on nitrogen and oxygen. About 70 % of the production takes place in the stratosphere. 10Be becomes attached to aerosols within a very short time. If 10Be is produced in the stratosphere some latitudinal mixing occurs. Most of the 10Be is transferred to the troposphere during spring and early summer when, mainly at median latitudes, large stratospheric air masses enter the troposphere. Tropospheric 10Be is deposited rapidly on the earth's surface by precipitation. The mean residence time of 10Be in the atmosphere is ca 1 to 2 years. 10Be removed from the atmosphere by precipitation is either preserved in snow and ice layers, in the topsoil and the biosphere, or it enters the hydrosphere (oceans and lakes), where it is transported to the sediments.
Target E-vacancy and L-x-ray production cross sections in collisions with relativistic (82 -670-MeV/amu) heavy ions ranging from Ne to U are measured and compared with atomic theories of inner-shell ionization based on the plane-wave Born approximation. Because the counting methods used are unique in atomic physics, careful studies of experimental uncertainties are made. Corrections to the measured cross sections due to x-ray pileup and secondary interactions in the solid targets are also discussed.
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