Nuclear phase transitions

A substantial simplification of the systematics in nuclear phase transition regions is obtained if the data are plotted against the product, Np Nn, of the number of valence protons and neutrons instead of against N, Z, or A as is usually done. Such a scheme leads to a unified view of nuclear transition regions and to a simplified scheme for collective model calculations. 

Particle-in-cell simulation, 154 Phonon stiffening, 36 Phonon-magnon coupled mode, 39 Photo-absorption cross section, 156 Photo-induced phase transitions, 42 Photo-nuclear activation, 173 PIC, 135... 

The equation of state (EOS), the composition and the possible occurrence of phase transitions in nuclear matter are widely discussed topics not only in nuclear theory, but are also of great interest in astrophysics and cosmology. Experiments on heavy ion collisions, performed over the last decades, gave new insight into the behavior of nuclear systems in a broad range of densities and temperatures. The observed cluster abundances, their spectral distribution... 

The inclusion of both three and four-particle correlations in nuclear matter allows not only to describe the abundances oft, h, a but also their influence on the equation of state and phase transitions. In contrast to the mean-field treatment of the superfluid phase, also higher-order correlations will arise in the quantum condensate. 

One important condition is constituted by the fact that certainly in symmetric nuclear matter no phase transition is observed below 3po- In fact some theoretical interpretation of the heavy ion experiments performed at the CERN SPS [30] points to a possible phase transition at a critical density pc ss 6po ss 1/fm3. We will in the following take this value for granted and use an extended MIT bag model [31] (requiring a density dependent bag constant ) that is compatible with this condition. 

Concerning the quark matter EOS, we found that a density dependent bag parameter B p) is necessary in order to be compatible with the CERN-SPS findings on the phase transition from hadronic to quark matter. Joining the corresponding EOS with the baryonic one, maximum masses of about 1.6 M are reached, in line with other recent calculations of neutron star properties employing various phenomenological RMF nuclear EOS together with either effective mass bag model [39] or Nambu-Jona-Lasinio model [40] EOS for quark matter. 

The value of the maximum mass of neutron stars obtained according to our analysis appears rather robust with respect to the uncertainties of the nuclear and the quark matter EOS. Therefore, the experimental observation of a very heavy (M > 1.6M ) neutron star, as claimed recently by some groups [41] (M ss 2.2 M ), if confirmed, would suggest that either serious problems are present for the current theoretical modelling of the high-density phase of nuclear matter, or that the assumptions about the phase transition between hadron and quark phase are substantially wrong. In both cases, one can expect a well defined hint on the high density nuclear matter EOS. 

First-order phase transition from a nucleonic matter to the strange quark state with a transition parameter A > 3/2 that occurs in superdense nuclear matter generally gives rise to a toothlike kink on the stable branch of the dependence of stellar mass on central pressure. Based on the extensive set of calculated realistic equations of state of superdense matter, we revealed a new stable branch of superdense configurations. The new branch emerges for some of our models with the transition parameter A > 3/2 and a small quark core (.Mcore 0.004 A- 0.03M ) on the M(PC) curve, with Mmax 0.08M and A 0.82M for different equations of state. Stable equilibrium layered... 

At nonzero temperatures the mass gap decreases as a function of the chemical potential already in the phase with broken chiral symmetry. Hence the model here gives unphysical low-density excitations of quasi-free quarks. A systematic improvement of this situation should be obtained by including the phase transition construction to hadronic matter. However, in the present work we circumvent the confinement problem by considering the quark matter phase only for densities above the nuclear saturation density no, i.e. ub > 0.5 no. 

According to Quantum Chromodynamics (QCD) a phase transition from hadronic matter to a deconfined quark phase should occur at a density of a few times nuclear matter saturation density. Consequently, the core of the more massive neutron stars is one of the best candidates in the Universe where such deconfined phase of quark matter (QM) could be found. Since /3-stable hadronic matter posses two conserved charges (i.e., electric charge and baryon... 

Figure 1. Comparison of the considered nuclear EoS. The hybrid EoS (dashed curve) has a phase transition region (1.8po < p < 3.5/9o) where adiabatic indices are substantially lower, followed by a quark phase which is has a similar stiffness as the nuclear matter at those densities.

In a first approximation the 70 years of Ya.B. s life can be divided into four periods 1914-1930 — childhood and high school 1931-1947 — the Institute of Chemical Physics, the study of adsorption, catalysis, phase transitions, hydrodynamics, and, most importantly, the theory of combustion and detonation with application to rocket ballistics, and the first papers on nuclear chain reactions 1947-1963 — work on the creation of a new technology, nuclear physics and elementary particle physics, and a textbook, Higher Mathematics for Beginners 1964-1987 — astronomy, including application of the general theory of relativity, and cosmology. 

Iwayanagi, S. and Miura, J. Nuclear magnetic resonance study of solid phase transition of trans- 1,4-polybutadiene, Rept. Progr. Polymer Phys. Japan 8, 303 (1965)... 

Knowledge of the mode of crystn of TNT is essential because it underlies the widespread practice of melt-pouring employed in the preparation of the commonly-used composite expls, such as Composition B. Samples of TNT obtained by sublimation onto a condensing surface held at a temp (78°) close to the mp, or by freezing melts at temps close to the mp, consist solely of the simple monoclinic form (Ref 26). Crystn from solvents at room temp, or from strongly supercooled melts, yields primarily monoclinic variant forms. Orthorhombic TNT is formed by crystn from solvents at low temps. At least seven morphological types of TNT have been identified (Ref 48). Two types have been identified by nuclear quadripole resonance (NQR) (Ref 66) a phase transition was noted at... 

Abstract Existing data on 63Cu-nuclear spin relaxation reveal two independent relaxation processes the one that is temperature independent we link to incommensurate peaks seen by neutrons, while the "universal temperature dependent contribution coincides with 1/6371 (1/ ) for two-chain YBCO 124. We argue that this new result substitutes for a "pseudogap regime in a broad class of high-Tc cuprates and stems from the 1st order phase transition that starts well above the superconductivity Tc but becomes frustrated because of broken electroneutrality in the CuC>2 plane. 

We attempt below to put the results in the context of a phase separation [4]. The decomposition of l/63l/ i(T, x) into two terms, as it will be discussed below in more details, manifests itself in a broad temperature interval above Tc. It is limited from above by a T that depends on the concentration, x. We consider T defined in this way as a temperature of a 1st order phase transition, which, however, cannot complete itself in spatial coexistence of two phases because of the electroneutrality condition [5]. It was already argued in [4] that such a frustrated 1st order phase transition may actually bear a dynamical character. The fact that a single resonant frequency for the 63Cu nuclear spin is observed in the NMR experiments, confirms this suggestion. Although in what follows, we use the notions of the lattice model [4, 5], even purely electronic models [6-9] for cuprates may reveal a tendency to phase separation. 

Thermal analysis is capable of providing accurate information on the phase transition temperatures, degradation temperatures, heat capacity, and enthalpy of transition of polymers using comparatively simple DTA, DSC, and TG instruments. The measurement time is short compared with other techniques, such as viscoelastic measurement and nuclear magnetic resonance spectroscopy. Moreover, any kind of material, e.g., powders, flakes, films, fibers, and liquids, may be used. The required amount of sample is small, normally in the range of several milligrams. 

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