Transient effects in fission evidenced from new experimental signatures

A new experimental approach is introduced to investigate the relaxation of the nuclear deformation degrees of freedom. Highly excited fissioning systems with compact shapes and low angular momenta are produced in peripheral relativistic heavy-ion collisions. Both fission fragments are identified in atomic number. Fission cross sections and fission-fragment element distributions are determined as a function of the fissioning element. From the comparison of these new observables with a nuclear-reaction code a value for the transient time is deduced.Comment: 6 pages, 2 figures, background information at http://www-w2k.gsi.de/kschmidt

Primary-residue production cross sections and kinetic energies in A GeV "2"0"8Pb on deuteron reactions

The production cross sections and the kinematical properties of primary residual nuclei have been studied in the reaction "2"0"8Pb (1 A GeV) + d. Isotopic distributions were measured for all elements from titanium (Z=22) to lead (Z=82). The measured kinematical properties of the residues were also used to disentangle the relevant reaction mechanisms, spallation-evaporation and spallation-fission. The fragment separator FRS at GSI, Darmstadt, was used to separate and identify the reaction products. The measured quantities are important for the design and planning of future radioactive-beam facilities and accelerator-driven systems. The measured data of the present work are comprehensively compared with the experimental data from the reaction "2"0"8Pb (1 A GeV) + p. (orig.)Available from TIB Hannover: RO 901(2001-29) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Isotopic production cross sections of fission residues in "1"9"7Au-on-proton collisions at 800 A MeV

Interactions of "1"9"7Au projectiles at 800 A MeV with protons leading to fission are investigated. We measured the production cross sections and velocities of all fission residues which are fully identified in atomic and mass number by using the in-flight separator FRS at GSI. The new data are compared with partial measurements of the characteristics of fission in similar reactions. Both the production cross sections and the recoil energies are relevant for a better understanding of spallation reactions. (orig.)Available from TIB Hannover: RO 801(2000-05) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

New approach to determine the angular transmission in zero-degree magnetic spectrometers

A new method to estimate the angular transmission in zero-degree magnetic spectrometers is presented. This method is based on a parameterisation of the angular aperture of the spectrometer for any possible value of the magnetic rigidity of the transmitted particles. This parameterisation of the angular aperture together with a description of the kinematics of the reaction mechanism allows to determine the angular transmission analytically, avoiding tedious Monte-Carlo calculations. The analytical solutions are implemented for residual nuclei produced in fission, projectile-fragmentation and fusion-evaporation reactions. (orig.)Available from TIB Hannover: RO 801(2000-37) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Light nuclides observed in the fission and fragmentation of "2"3"8U

Light nuclides produced in collisions of 1 A.GeV "2"3"8U with protons and titanium have been fully identified with a high-resolution forward magnetic spectrometer, the fragment separator (FRS), at GSI, and for each nuclide an extremely precise determination of the velocity has been performed. The so-obtained information on the velocity shows that the very asymmetric fission of uranium, in the "2"3"8U + p reaction, produces neutron-rich isotopes of elements down to around charge 10. New important features of the fragmentation of "2"3"8U, concerning the velocity and the N/Z-ratio of these light fragments, and a peculiar even-odd structure in N=Z nuclei, have also been observed. (orig.)SIGLEAvailable from TIB Hannover: RO 801(2001-08) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Model calculations of a two-step reaction scheme for the production of neutron-rich secondary beams

A two-step reaction scheme for the production of extremely neutron-rich radioactive beams, fission followed by cold fragmentation, is considered. The cross sections of the second step, the cold fragmentation of neutron-rich fission fragments, are estimated with different computer codes. Discrepancies between an empirical systematics and nuclear-reaction codes are found. (orig.)Available from TIB Hannover: RO 801(2000-41) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Time evolution of the fission-decay width under the influence of dissipation

Different analytical approximations to the time-dependent fission-decay width used to extract the influence of dissipation on the fission process are critically examined. Calculations with a new, highly realistic analytical approximation to the exact solution of the Fokker-Planck equation sheds doubts on previous conclusions on the dissipation strength made on the basis of less realistic approximations. (orig.)Available from TIB Hannover: RO 801(2002-33) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Production of neutron-rich isotopes by cold fragmentation in the reaction "1"9"7Au + Be at 950 A MeV

The production cross sections and longitudinal-momentum distributions of very neutron-rich isotopes have been investigated in the fragmentation of a 950 A MeV "1"7"9Au beam in a beryllium target. Seven new isotopes ("1"9"3Re, "1"9"4Re, "1"9"1W, "1"9"2W, "1"8"9Ta, "1"8"7Hf and "1"8"8Hf) and the five-proton-removal channel were observed for the first time. The reaction mechanism leading to the formation of these very neutron-rich isotopes is explained in terms of the cold-fragmentation process. An analytical model describing this reaction mechanism is presented. (orig.)Available from TIB Hannover: RO 801(99-35) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

#beta#-decay of "4"0Ti

The #beta#-decay of "4"0Ti was studied. The Fermi and Gamow-Teller strength function was deduced from the observed #beta#-delayed emission of protons and #gamma#-rays and from the measured half-life of 55(2) ms. The results are compared to shell-model predictions and are used to estimate the neutrino-capture rate of the solar-neutrino detector ICARUS. (orig.)Available from FIZ Karlsruhe / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Possibilities for the production of non-stable isotopes

The production of neutron-rich isotopes is discussed in terms of the two main reaction mechanisms leading to the formation of these nuclei, projectile fragmentation and fission. Production cross sections are calculated for cold-fragmentation and fission. The expected yields are estimated taking into account different technical approaches actually discussed for the production of radioactive beams. (orig.)Contribution to th 37. Int. Winter Meeting on Nuclear Physics, Bormio (IT), Feb. 1999, 25 refs.Available from TIB Hannover: RO 801(99-14) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman