Hydrodynamics of a quark droplet II: Implications of a non-zero baryon chemical potential

We present an extended version of the dynamical model for a multi-quark droplet evolution described in our proceeding paper. The model includes collective expansion of the droplet, effects of the vacuum pressure and surface tension, and now a non-zero baryon number. The hadron emission from the droplet is described following Weisskopf's statistical model. We consider evolutions of droplets with different initial temperatures and net baryon number. It is found that the introduction of a non-zero net baryon number does not change the lifetime of the droplets significantly. Only when we consider an initially very baryon-rich, low-temperature droplets is the lifetime is decreased significantly. We have, furthermore, found a convergence of both baryon chemical potential and temperature toward the values $\mu_{\rm B} \approx$ 450 MeV and $T \approx 150$ MeV. This convergence is linked to the competing emission of baryons versus mesons.Comment: 15 pages, 5 figure

FISSION DYNAMICS WITH MICROSCOPIC LEVEL DENSITIES

We present a consistent framework for treating the energy and angularmomentum dependence of the shape evolution in the nuclear fission. It combines microscopically calculated level densities with the Metropolis-walk method, has no new parameters, and can elucidate the energy-dependent influence of pairing and shell effects on the dynamics of warm nuclei

Spreading width of compound states through coincidence spectra of rotational gamma-rays

Abstract The intrinsic width of (multiparticle-multihole) compound states is an elusive quantity, of difficult direct access, as it is masked by damping mechanisms which control the collective response of nuclei. Through microscopic cranked shell model calculations, it is found that the strength function associated with two-dimensional gamma-coincidence spectra arising from rotational transitions between states lying at energies > 1 MeV above the yrast line, exhibits a two-component structure controlled by the rotational (wide component) and compound (narrow component) damping width. This last component is found to be directly related to the width of the multiparticle-multihole autocorrelation function

Hydrodynamics of a quark droplet

We present a simple model of a multi-quark droplet evolution based on the hydrodynamical description. This model includes collective expansion of the droplet, effects of the vacuum pressure and surface tension. The hadron emission from the droplet is described following Weisskopf's statistical model. We have considered evolution of baryon-free droplets which have different initial temperatures and expansion rates. As a typical trend we observe an oscillating behavior of the droplet radius superimposed with a gradual shrinkage due to the hadron emission. The characteristic life time of droplets with radii 1.5-2 fm are about 9-16 fm/c.Comment: 22 pages, 12 figure

Possible Conservation of the K -Quantum Number in Excited Rotating Nuclei

The \ensuremath{\gamma} cascades feeding into low-K and high-K bands in ${}^{163}$Er are investigated analyzing variances and covariance of the spectrum fluctuations. From a large data set of 1${0}^{9}$ triple coincidences, \ensuremath{\gamma}-\ensuremath{\gamma} coincidence spectra gated by resolved low-lying rotational bands are analyzed. Low-K bands are found to be fed by a much larger effective number of cascades than high-K bands. The covariance between pairs of gated spectra shows that the cascades feeding low-K bands are different from those feeding the high-K bands. The persistence of the K-selection rules for the excited rotational bands within the angular momentum region 30\ensuremath{\Elzxh}\ensuremath{\le}I\ensuremath{\le}40\ensuremath{\Elzxh} is suggested as explanation

Collective enhancements in nuclear level densities

Contributions to the nuclear level density from a deformed core and from surface vibrations are discussed. The influence of symmetries of the nuclear shape is highlighted by quoting and discussing analytic Fermi gas level densities for irregular, deformed and spherical shapes. A thorough evaluation of the rotational enhancement factor to the level density is carried out for 17 well deformed rare-earth nuclei. Counted experimental levels are compared to levels obtained from the combinatorial level-density model, applying the Folded-Yukawa potential with BCS quasiparticle paring. It is found that the phase space of the rotating core contributes fully to the level density at the low energies where reliable information of experimental levels exists. The analysis is inspired by recent thermal Shell Model Monte Carlo results, which are also included in the comparison. The situation at the neutron excitation energy is also discussed, together with the conditions for vibrational enhancement. Experiments aimed at investigating the fade-away of collective enhancements are briefly discussed

Generation of Fragment Angular Momentum in Nuclear Fission

As a fissioning nucleus approaches scission, the angular-momentum bearing modes in the evolving dinuclear complex may be agitated by multiple transfers of individual nucleons. It is discussed how this mechanism populates the various rotational modes at different rates and leads to fragment angular momenta that are preferentially perpendicular to the fission axis but mutually largely uncorrelated. Using the fission simulation code FREYA, it is demonstrated how a measurement of the angular distribution of photons from identified collective transitions in the product nuclei can provide quantitative information on the relative importance of the twisting mode in fission