226 research outputs found
Effect of differences in proton and neutron density distributions on fission barriers
The neutron and proton density distributions obtained in constrained
Hartree-Fock-Bogolyubov calculations with the Gogny force along the fission
paths of 232Th, 236U, 238U and 240Pu are analyzed.
Significant differences in the multipole deformations of neutron and proton
densities are found. The effect on potential energy surfaces and on barrier
heights of an additional constraint imposing similar spatial distributions to
neutrons and protons, as assumed in macroscopic-microscopic models, is studied.Comment: 5 pages in Latex, 4 figures in ep
Statistical fluctuations for the fission process on its decent from saddle to scission
We reconsider the importance of statistical fluctuations for fission dynamics
beyond the saddle in the light of recent evaluations of transport coefficients
for average motion. The size of these fluctuations are estimated by means of
the Kramers-Ingold solution for the inverted oscillator, which allows for an
inclusion of quantum effects.Comment: 12 pages, Latex, 5 Postscript figures; submitted to PRC e-mail:
[email protected] www home page:
http://www.physik.tu-muenchen.de/tumphy/e/T36/hofmann.htm
Evidence for the Jacobi shape transition in hot 46Ti
The gamma-rays from the decay of the GDR in 46Ti compound nucleus formed in
the 18O+28Si reaction at bombarding energy 105 MeV have been measured in an
experiment using a setup consisting of the combined EUROBALL IV, HECTOR and
EUCLIDES arrays. A comparison of the extracted GDR lineshape data with the
predictions of the thermal shape fluctuation model shows evidence for the
Jacobi shape transition in hot 46Ti. In addition to the previously found broad
structure in the GDR lineshape region at 18-27 MeV caused by large
deformations, the presence of a low energy component (around 10 MeV), due to
the Coriolis splitting in prolate well deformed shape, has been identified for
the first time.Comment: 8 pages, 4 figures, proceedings of the COMEX1 conference, June 2003,
Paris; to be published in Nucl. Phys.
A Dirac-Hartree-Bogoliubov approximation for finite nuclei
We develop a complete Dirac-Hartree-Fock-Bogoliubov approximation to the
ground state wave function and energy of finite nuclei. We apply it to
spin-zero proton-proton and neutron-neutron pairing within the
Dirac-Hartree-Bogoliubov approximation (we neglect the Fock term), using a
zero-range approximation to the relativistic pairing tensor. We study the
effects of the pairing on the properties of the even-even nuclei of the
isotopic chains of Ca, Ni and Sn (spherical) and Kr and Sr (deformed), as well
as the =28 isotonic chain, and compare our results with experimental data
and with other recent calculations.Comment: 43 pages, RevTex, 13 figure
Searching for ß-delayed protons from 11 Be
ISOLDE Workshop and Usersmeeting. Wednesday 05 December - Friday 07 December 2018 .CERN ( ISOLDE User Support. PH Departmen - CERN/CH-1211 Geneve 23). --.https://indico.cern.ch/event/736872/contributions
Magnetic moments of short-lived nuclei with part-per-million accuracy: Towards novel applications of -detected NMR in physics, chemistry and biology
We determine for the first time the magnetic dipole moment of a short-lived
nucleus with part-per-million (ppm) accuracy. To achieve this two orders of
magnitude improvement over previous studies, we implement a number of
innovations into our -detected Nuclear Magnetic Resonance (-NMR)
setup at ISOLDE/CERN. Using liquid samples as hosts we obtain narrow, sub-kHz
linewidth, resonances, while a simultaneous in-situ H NMR measurement
allows us to calibrate and stabilize the magnetic field to ppm precision, thus
eliminating the need for additional -NMR reference measurements.
Furthermore, we use ab initio calculations of NMR shielding constants to
improve the accuracy of the reference magnetic moment, thus removing a large
systematic error. We demonstrate the potential of this combined approach with
the 1.1 s half-life radioactive nucleus Na, which is relevant for
biochemical studies. Our technique can be readily extended to other isotopic
chains, providing accurate magnetic moments for many short-lived nuclei.
Furthermore, we discuss how our approach can open the path towards a wide range
of applications of the ultra-sensitive -NMR in physics, chemistry, and
biology.Comment: re-submitte
On nuclear transport at small excitations
Numerical computations of transport coefficients at low temperatures are
presented for shapes typically encountered in nuclear fission. The influence of
quantum effects of the nucleonic degrees of freedom is examined, with pair
correlations included. Consequences for global collective motion are studied
for the case of the decay rate. The range of temperatures is specified above
which this motion may be described as a quantal diffusion process.Comment: 8 pages, LaTex, 2 postscript figures; final version with small
editorial changes, Phys. Rev. Lett. 82 (1999) 4603; e-mail:
[email protected]; [email protected]
Progress on the PICOSEC-Micromegas Detector Development : Towards a precise timing, radiation hard, large-scale particle detector with segmented readout
This contribution describes the PICOSEC-Micromegas detector which achieves a time resolution below 25 ps. In this device the passage of a charged particle produces Cherenkov photons in a radiator, which then generate electrons in a photocathode and these photoelectrons enter a two-stage Micromegas with a reduced drift region and a typical anode region. The results from single-channel prototypes (demonstrating a time resolution of 24 ps for minimum ionizing particles, and 76 ps for single photoelectrons), the understanding of the detector in terms of detailed simulations and a phenomenological model, the issues of robustness and how they are tackled, and preliminary results from a multi-channel prototype are presented (demonstrating that a timing resolution similar to that of the single-channel device is feasible for all points across the area covered by a multi-channel device).Peer reviewe
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