240 research outputs found
Effect of electron irradiation on vortex dynamics in YBa_2Cu_3O_{7-x} single crystals
We report on drastic change of vortex dynamics with increase of quenched
disorder: for rather weak disorder we found a single vortex creep regime, which
we attribute to a Bragg-glass phase, while for enhanced disorder we found an
increase of both the depinning current and activation energy with magnetic
field, which we attribute to entangled vortex phase. We also found that
introduction of additional defects always increases the depinning current, but
it increases activation energy only for elastic vortex creep, while it
decreases activation energy for plastic vortex creep.Comment: 4 pages, 3 figures, submited to Phys. Rev.
On the origin of the anomalous behaviour of 2+ excitation energies in the neutron-rich Cd isotopes
Recent experimental results obtained using decay and isomer
spectroscopy indicate an unusual behaviour of the energies of the first excited
2 states in neutron-rich Cd isotopes approaching the N=82 shell closure.
To explain the unexpected trend, changes of the nuclear structure far-off
stability have been suggested, namely a quenching of the N=82 shell gap already
in Cd, only two proton holes away from doubly magic Sn. We
study the behaviour of the 2 energies in the Cd isotopes from N=50 to N=82,
i.e. across the entire span of a major neutron shell using modern beyond mean
field techniques and the Gogny force. We demonstrate that the observed low
2 excitation energy in Cd close to the N=82 shell closure is a
consequence of the doubly magic character of this nucleus for oblate
deformation favoring thereby prolate configurations rather than spherical ones.Comment: 10 pages, 4 figures, to be publised in Phys. Lett.
Position-sensitive ion detection in precision Penning trap mass spectrometry
A commercial, position-sensitive ion detector was used for the first time for
the time-of-flight ion-cyclotron resonance detection technique in Penning trap
mass spectrometry. In this work, the characteristics of the detector and its
implementation in a Penning trap mass spectrometer will be presented. In
addition, simulations and experimental studies concerning the observation of
ions ejected from a Penning trap are described. This will allow for a precise
monitoring of the state of ion motion in the trap.Comment: 20 pages, 13 figure
Restoration of the N=82 Shell Gap from Direct Mass Measurements of Sn
A high-precision direct Penning trap mass measurement has revealed a 0.5-MeV deviation of the binding energy of Sn from the currently accepted value. The corrected mass assignment of this neutron-rich nuclide restores the neutron-shell gap at N=82, previously considered to be a case of âshell quenching.â In fact, the new shell gap value for the short-lived Sn is larger than that of the doubly-magic Ca which is stable. The N=82 shell gap has considerable impact on fission recycling during the process. More generally, the new finding has important consequences for microscopic mean-field theories which systematically deviate from the measured binding energies of closed-shell nuclides
Magnetic field stabilization for high-accuracy mass measurements on exotic nuclides
The magnetic-field stability of a mass spectrometer plays a crucial role in
precision mass measurements. In the case of mass determination of short-lived
nuclides with a Penning trap, major causes of instabilities are temperature
fluctuations in the vicinity of the trap and pressure fluctuations in the
liquid helium cryostat of the superconducting magnet. Thus systems for the
temperature and pressure stabilization of the Penning trap mass spectrometer
ISOLTRAP at the ISOLDE facility at CERN have been installed. A reduction of the
fluctuations by at least one order of magnitude downto dT=+/-5mK and
dp=+/-50mtorr has been achieved, which corresponds to a relative frequency
change of 2.7x10^{-9} and 1.5x10^{-10}, respectively. With this stabilization
the frequency determination with the Penning trap only shows a linear temporal
drift over several hours on the 10 ppb level due to the finite resistance of
the superconducting magnet coils.Comment: 23 pages, 13 figure
Mass measurements beyond the major r-process waiting point 80Zn
High-precision mass measurements on neutron-rich zinc isotopes 71m,72-81Zn
have been performed with the Penning trap mass spectrometer ISOLTRAP. For the
first time the mass of 81Zn has been experimentally determined. This makes 80Zn
the first of the few major waiting points along the path of the astrophysical
rapid neutron capture process where neutron separation energy and neutron
capture Q-value are determined experimentally. As a consequence, the
astrophysical conditions required for this waiting point and its associated
abundance signatures to occur in r-process models can now be mapped precisely.
The measurements also confirm the robustness of the N = 50 shell closure for Z
= 30 farther from stability.Comment: 4 pages, 3 figure
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