143 research outputs found
Regularities and symmetries of subsets of collective 0+ states
The energies of subsets of excited 0+ states in geometric collective models
are investigated and found to exhibit intriguing regularities. In models with
an infinite square well potential, it is found that a single formula, dependent
on only the number of dimensions, describes a subset of 0+ states. The same
behavior of a subset of 0+ states is seen in the large boson number limit of
the Interacting Boson Approximation (IBA) model near the critical point of a
first order phase transition, in contrast to the fact that these 0+ state
energies exhibit a harmonic behavior in all three limiting symmetries of the
IBA. Finally, the observed regularities in 0+ energies are analyzed in terms of
the underlying group theoretical framework of the different models.Comment: 9 pages, 3 figures, added reference [38
Observations of the Optical Counterpart to XTE J1118+480 During Outburst by the ROTSE-I Telescope
The X-ray nova XTE J1118+480 exhibited two outbursts in the early part of
2000. As detected by the Rossi X-ray Timing Explorer (RXTE), the first outburst
began in early January and the second began in early March. Routine imaging of
the northern sky by the Robotic Optical Transient Search Experiment (ROTSE)
shows the optical counterpart to XTE J1118+480 during both outbursts. These
data include over 60 epochs from January to June 2000. A search of the ROTSE
data archives reveal no previous optical outbursts of this source in selected
data between April 1998 and January 2000. While the X-ray to optical flux ratio
of XTE J1118+480 was low during both outbursts, we suggest that they were full
X-ray novae and not mini-outbursts based on comparison with similar sources.
The ROTSE measurements taken during the March 2000 outburst also indicate a
rapid rise in the optical flux that preceded the X-ray emission measured by the
RXTE by approximately 10 days. Using these results, we estimate a pre-outburst
accretion disk inner truncation radius of 1.2 x 10^4 Schwarzschild radii.Comment: 9 pages, 1 table, 2 figure
Spectroscopic studies of Dy-168,170 using CLARA and PRISMA
Preliminary results from an experiment aiming at Dy-170. Submitted to the LNL
Annual Report 2008.Comment: 2 pages, 4 figures, Submitted to the LNL Annual Report 200
Observation of contemporaneous optical radiation from a gamma-ray burst
The origin of gamma-ray bursts (GRBs) has been enigmatic since their
discovery. The situation improved dramatically in 1997, when the rapid
availability of precise coordinates for the bursts allowed the detection of
faint optical and radio afterglows - optical spectra thus obtained have
demonstrated conclusively that the bursts occur at cosmological distances. But,
despite efforts by several groups, optical detection has not hitherto been
achieved during the brief duration of a burst. Here we report the detection of
bright optical emission from GRB990123 while the burst was still in progress.
Our observations begin 22 seconds after the onset of the burst and show an
increase in brightness by a factor of 14 during the first 25 seconds; the
brightness then declines by a factor of 100, at which point (700 seconds after
the burst onset) it falls below our detection threshold. The redshift of this
burst, approximately 1.6, implies a peak optical luminosity of 5 times 10^{49}
erg per second. Optical emission from gamma-ray bursts has been generally
thought to take place at the shock fronts generated by interaction of the
primary energy source with the surrounding medium, where the gamma-rays might
also be produced. The lack of a significant change in the gamma-ray light curve
when the optical emission develops suggests that the gamma-rays are not
produced at the shock front, but closer to the site of the original explosion.Comment: 10 pages, 2 figures. Accepted for publication in Nature. For
additional information see http://www.umich.edu/~rotse
Dynamics of coherently pumped lasers with linearly polarized pump and generated fields
The influence of light polarization on the dynamics of an optically pumped single-mode laser with a homogeneously broadened four-level medium is theoretically investigated in detail. Pump and laser fields with either parallel or crossed linear polarizations are considered, as are typical in far-infrared-laser experiments. Numerical simulations reveal dramatically different dynamic behaviors for these two polarization configurations. The analysis of the model equations allows us to find the physical origin of both behaviors. In particular, the crossed-polarization configuration is shown to be effective in decoupling the pump and laser fields, thus allowing for the appearance of Lorenz-type dynamics
High precision measurements of the ground state hyperfine structure interval of muonium and of the muon magnetic moment
No description supplie
\u3cem\u3eg\u3c/em\u3e Factor of the 2\u3csup\u3e+\u3c/sup\u3e\u3csub\u3e1\u3c/sub\u3e State of \u3csup\u3e170\u3c/sup\u3eHf
The g factor of the 2+1 state of 170Hf was measured by perturbed γ-γ angular correlation in a static external magnetic field. The result, g(2+1) = 0.28(5), extends the systematics of g factors of even-even Hf isotopes to N = 98 and enables a better test of theoretical models. The g(2+1) experimental values of these isotopes exhibit a remarkable constancy as a function of neutron number. This phenomenon, which was also observed for other isotopic chains in the Gd–W range, is explained in terms of a recently proposed empirical model
Enhanced Mixing of Intrinsic States in Deformed Hf Nuclei
Excited low-spin, nonyrast states in 170,172,174Hf were populated in β + /∈decay and studied through off-beam γ-ray spectroscopy. New coincidence data allowed for a substantial revision of the level schemes of Hf170,172 and a confirmation of the level scheme of 174Hf. The Hf isotopes represent a unique situation in which a crossing of collective intrinsic excitations occurs, enhancing significantly the effects of mixing. Using branching ratios from excited 2+ states, this mixing is followed and studied. The resulting mixing matrix elements are found to be ∼30 keV—an order of magnitude larger than estimated previously for nearby nuclei. In the case of 170Hf, the 2+β and 2+γlevel are shown to be completely mixed
- …