89 research outputs found
Collective T=0 pairing in N=Z nuclei? Pairing vibrations around 56Ni revisited
We present a new analysis of the pairing vibrations around 56Ni, with
emphasis on odd-odd nuclei. This analysis of the experimental excitation
energies is based on the subtraction of average properties that include the
full symmetry energy together with volume, surface and Coulomb terms. The
results clearly indicate a collective behavior of the isovector pairing
vibrations and do not support any appreciable collectivity in the isoscalar
channel.Comment: RevTeX, two-column, 5 pages, 4 figure
NLSEmagic: Nonlinear Schr\"odinger Equation Multidimensional Matlab-based GPU-accelerated Integrators using Compact High-order Schemes
We present a simple to use, yet powerful code package called NLSEmagic to
numerically integrate the nonlinear Schr\"odinger equation in one, two, and
three dimensions. NLSEmagic is a high-order finite-difference code package
which utilizes graphic processing unit (GPU) parallel architectures. The codes
running on the GPU are many times faster than their serial counterparts, and
are much cheaper to run than on standard parallel clusters. The codes are
developed with usability and portability in mind, and therefore are written to
interface with MATLAB utilizing custom GPU-enabled C codes with the
MEX-compiler interface. The packages are freely distributed, including user
manuals and set-up files.Comment: 37 pages, 13 figure
Negative time delay for wave reflection from a one-dimensional semi-harmonic well
It is reported that the phase time of particles which are reflected by a
one-dimensional semi-harmonic well includes a time delay term which is negative
for definite intervals of the incoming energy. In this interval, the absolute
value of the negative time delay becomes larger as the incident energy becomes
smaller. The model is a rectangular well with zero potential energy at its
right and a harmonic-like interaction at its left.Comment: 6 pages, 5 eps figures. Talk presented at the XXX Workshop on
Geometric Methods in Physics, Bialowieza, Poland, 201
Search for Oscillation of the Electron-Capture Decay Probability of Pm
We have searched for time modulation of the electron capture decay
probability of Pm in an attempt to confirm a recent claim from a group
at the Gesellschaft f\"{u}r Schwerionenforschung (GSI). We produced Pm
via the Sn(Na, 5n)Pm reaction at the Berkeley 88-Inch
Cyclotron with a bombardment time short compared to the reported modulation
period. Isotope selection by the Berkeley Gas-filled Separator is followed by
implantation and a long period of monitoring the Nd K x-rays
from the daughter. The decay time spectrum of the x-rays is well-described by a
simple exponential and the measured half-life of 40.68(53) seconds is
consistent with the accepted value. We observed no oscillatory modulation at
the proposed frequency at a level 31 times smaller than that reported by
Litvinov {\it et al.} (Phys. Lett. B 664 (2008) 162; arXiv:0801.2079
[nucl-ex]). A literature search for previous experiments that might have been
sensitive to the reported modulation uncovered another example in Eu
electron-capture decay. A reanalysis of the published data shows no oscillatory
behavior.Comment: 12 pages (double-spaced), 6 figure
Band structure of 235 U
Over a period of several years we have performed three separate experiments at Lawrence Berkeley National Laboratory's 88-Inch Cyclotron in which 235U (thick target) was Coulomb-excited. The program involved stand-alone experiments with Gammmasphere and with the 8pi Spectrometer using 136Xe beams at 720 MeV, and a CHICO-Gammasphere experiment with a 40Ca beam at 184 MeV. In addition to extending the known negative-parity bands to high spin, we have assigned levels in some seven positive-parity bands which are in some cases (e.g., [631]1/2, [624]7/2, and [622]5/2) strongly populated by E3 excitation. The CHICO data have been analyzed to extract E2 and E3 matrix elements from the observed yields. Additionally, many M1 matrix elements could be extracted from the Îł-ray branching ratios. A number of new features have emerged, including the unexpected attenuation of magnetic transitions between states of the same Nilsson multiplet, the breakdown of Coriolis staggering at high spin, and the effect of E3 collectivity on Coriolis interactions
High-spin isomers and three-neutron valence configurations in 211Pb
Deep-inelastic reactions between a beam of 1360 MeV 208Pb ions and a thick 238U target have been used to populate the neutron-rich nucleus 211Pb. The observation of its Îł decay has allowed identification of excited states up to the highest spin which can be formed from the three valence neutrons, including identification of three high-spin isomers. Level energies and transition strengths are compared to shell-model calculations with empirical interactions and predictions are made for the expected behaviour of more neutron-rich lead isotopes. The evidence for a possible increase in the neutron effective charge moving away from the N=126 shell gap is evaluated
Fragmentation of the two-phonon octupole vibrational states in 208Pb
An experiment designed to populate two-phonon vibrational states in 208Pb by Coulomb excitation was
performed with a 136Xe beam at a bombarding energy of 650 MeV. The g rays from the decay of the excited
states were measured with Gammasphere and scattered particles were detected in the compact heavy-ion
counter CHICO. We have not been able to observe any state close to the expected harmonic energy of 5.2
MeV. However, we were able to extract the B(E3,31
2!61
1) value for the lowest known 61 state at 4.424 MeV
based on measured g-ray intensities. About 20% of the expected total E3 strength can be found in this state,
suggesting a large fragmentation of this second octupole phonon state in 208Pb. Upper limits for the B(E3)
strength were determined for higher-lying, but unseen, 61 states ranging from 15% of the harmonic value at
5.2 MeV to 100% at 6.0 MeV
Test of ΔI = 2 staggering in the superdeformed bands of 194Hg
The presence of ΔI= 2 staggering in the three known superdeformed (SD) bands of 194Hg has been reexamined in a new experiment with Gammasphere. A relative precision of better than 60 eV was achieved for most transition energies. Staggering plots were extracted and their statistical significance was analyzed. No clear evidence was found for an extended regular ΔI = 2 staggering in the three SD bands of 194Hg. However, statistically significant deviations from a smooth reference were observed in the two excited SD bands. Different scenarios are discussed but no firm conclusion about the origin of the observed deviations can be drawn
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