Study of the #beta#-decays of "3"7Ca and "3"6Ca

The #beta#-delayed proton and #gamma#-ray emission of "3"7Ca and "3"6Ca was studied at the projectile fragment separator at GSI Darmstadt. In the "3"7Ga study, the #beta#-delayed #gamma#-decay was observed for the first time, and the half-life was redetermined, under essentially background-free conditions, as 181.1#+-#1.0 ms. The surprisingly high #GAMMA#_#gamma#/#GAMMA#_p values found for proton-unbound states in "3"7K drastically reduce former discrepancies between the Gamow-Teller strength value B(GT) measured in the "3"7Ca #beta#-decay and those deduced from the "3"7Cl(p, n)"3"7Ar mirror reaction. Our data provide evidence, on a level of 1.6 standard deviations, for isospin-mixing of the lowest T=3/2 level in "3"7K. In the "3"6Ca study, a complete #beta#-decay scheme, including the #beta#-delayed proton emission into the ground and first excited states of "3"5Ar as well as the #beta#-delayed #gamma#-decay, was measured for the first time. The "3"6Ca half-life was remeasured with improved accuracy to be 102#+-#2 ms. Our data exclude a 1"+ assignment for two near-threshold states in "3"6K that could be important resonances in "3"5Ar(p, #gamma#) reactions of astrophysical interest. The B(GT) distributions in "3"7","3"6Ca decays are compared to results obtained from large-scale sd shell-model calculations. (orig.)Available from FIZ Karlsruhe / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Double ionization of helium by fast fully stripped ions

A complete momentum-space map of the double ionisation events in the collision of 100 MeV/u C"6"+ ions with helium has been obtained. From this map the angular distribution of two ejected electrons is generated as a function of the momentum transferred by the projectile to the atom. Analysis of the angular distribution of the fragments in the plane transverse to the projectile axis (the azimuthal plane) shows a separation of events into two domains, depending on the momentum transferred by the projectile to the target. For momentum transfers smaller than 1.2 a.u., both electrons are distributed independent of the azimuthal angle. For momentum transfers larger than 1.2 a.u., the electron with larger energy is distinctly emitted along the direction of momentum transfer, and the one with smaller energy is distributed isotropically. The value of 1.2 a.u. is approximately equal to the mean value of the momenta of the bound electrons in the helium atom and demarcates indirect, soft collisions and direct, hard collisions respectively. For soft collisions, the electron angular distribution shows certain similarities with the angular distributions in photo-double ionization. (orig.)Available from TIB Hannover: RO 801(98-65) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Double ionisation of helium in fast ion collisions: the role of momentum transfer

Double ionisation of helium in the perturbative regime has been explored in a kinematically complete collision experiment using 100 MeV/u C"6"+ ions. Different ionisation mechanisms are identified by inspecting the angular distribution of the electrons as a function of the momentum transfer q to the target by the projectile. For q<1.2 a.u., both electrons are distributed uniformly in the plane perpendicular to the projectile axis, and distinct similarities with photoionisation are identified. For q>1.2 a.u., the faster electron resulting from a binary encounter with the projectile is emitted along the direction of momentum transfer, while the other electron is distributed uniformly. Experimental data are compared with various model calculations based on the Bethe-Born approximation with shake-off. Surprisingly, the effect of the final state interaction is found to depend decisively on the choice of the initial state wave function. (orig.)Available from TIB Hannover: RO 801(99-02) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Direct observation of systematic deviations from the Bethe stopping theory for relativistic heavy ions

The SIS accelerator facilities at GSI in combination with the magnetic spectrometer FRS allow the direct measurement of stopping powers for relativistic heavy ions up to uranium with high precision for the first time. Here, we report on representative results obtained for projectiles up to xenon in the energy range from (700-1000) MeV/u. Systematic deviations from the Bethe stopping-power theory are observed, whereas the data are in good agreement with theory one Mott and Bloch corrections and the Fermi density effect are included. (orig.)Part of the Ph.D. thesis of C. ScheidenbergerAvailable from TIB Hannover: RO 801(94-11) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Chemical properties of element 105 in aqueous solution: Extractions into diisobutylcarbinol

SIGLEAvailable from FIZ Karlsruhe / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Gamow-Teller strength in the beta-decay of "3"7Ca and its implications for the detection of the solar neutrino flux

We have studied the #beta#-decay of "3"7Ca at the projectile fragment separator FRS and GSI Darmstadt. The resulting Gamow-Teller strength function B(GT) which is important for determining the detection efficiency of the Homestake mine "3"7Cl detector is significantly changed by the inclusion of previously unobserved #beta#-delayed #gamma#-rays. With the new results former discrepancies between the B(GT) values measured in the "3"7Ga #beta#-decay and those extracted from "3"7Cl(p, n)"3"7Ar reactions are drastically reduced. Additionally, our data yield evidence for an isospin-forbidden Fermi transition in the #beta#-decay of "3"7Ca. (orig.)SIGLEAvailable from TIB Hannover: RO 801(94-67) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Gamow-Teller strength in the #beta#-decay of "3"6Ca

The #beta#-decay of "3"6Ca has been studied at the projectile fragment separator at GSI Darmstadt. The Gamow-Teller strength function B(GT), deduced from the observed #beta#-delayed proton- and #gamma#-emission and from the measured half-life of 102(2) ms, is compared to results obtained from large-scale sd-shell model calculations. (orig.)SIGLEAvailable from TIB Hannover: RO 801(94-84) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Fragmentation of a 500 MeV/nucleon "8"6Kr beam, investigated at the GSI projectile fragment separator

Production cross-sections and longitudinal momentum distributions have been investigated for reactions between a 500 MeV/nucleon "8"6Kr beam and beryllium, copper and tantalum targets. Fragments in a wide A/Z range were studied at the projectile-fragment separator FRS at GSI. The experimental production cross-sections have been used for testing the predictions obtained from a semi-empirical parameterization, a statistical abrasion model and an intranuclear-cascade model. The present study allows to extrapolate the production cross-sections towards very neutron-rich isotopes such as the doubly magic nucleus "7"8Ni. For fragments close to the projectile the measured longitudinal momentum distributions agrees qualitatively with a semi-empirical parameterization, which is based on the two-step picture of the fragmentation process. The momentum widths of lighter fragments, however, show deviations from this simple picture. (orig.)Available from TIB Hannover: RO 801(93-74) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Experiments with relativistic secondary beams of heavy ions at the GSI projectile fragment separator

At the GSI projectile fragment separator for the first time relativistic exotic nuclei throughout the whole periodic table of elements up to uranium were produced and isotopically separated. Systematic studies of the projectile fragmentation, complete mass- and charge distributions of fragments from fission of relativistic uranium nuclei, and first secondary-beam experiments such as the breakup of halo nuclei, the fragmentation of proton-rich secondary beams, and the fission of uranium fragments were made. In combination with the experimental heavy-ion storage ring experiments on the decay of exotic nuclei in exotic ionic charge states and direct mass measurements with stored and cooled ion beams were started. (orig.)Available from TIB Hannover: RO 801(93-53) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Longitudinal momenta and production cross-sections of isotopes formed by fragmentation of a 500 A x MeV "8"6Kr beam

At the projectile-fragment separator FRS at GSI, longitudinal momentum distributions and production cross-sections were investigated for reactions between a 500 A x MeV "8"6Kr beam and beryllium, copper and tantalum targets. Fragments in a wide A/Z range were studied. For fragments close to the projectile the measured longitudinal momentum distributions agree qualitatively with a semi-empirical parametrization. Deviations from this simple picture are found, however, for the momentum widths of light fragments and for the momentum transfer to those fragments that differ in their N/Z ratio from the most probable value. The experimental data on production cross-sections are used for testing the predictions obtained from a semi-empirical parameterization, a geometrical abrasion model and an intranuclear-cascade model. The cross-section for the formation of the doubly magic nucleus "7"8Ni in "8"6Kr fragmentation is estimated to be 17 pb. (orig.)Available from TIB Hannover: RO 801(94-29) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman