Observation of composite nuclei at very high temperatures

Analysis of data collected with a 19.5 MeV/A⁴⁰Ar beam on a target of²⁷Al shows strong evidences for the formation of very excited composite nuclei. Incomplete linear momentum transfer remains small and the excitation energies per nucleon can be estimated to be close to 5 MeV.     

Antiproton annihilations in deuterium at rest into two pions: Evidence for pN bound states near threshold

The charged pion spectra in $\text{p}$d→π⁻π⁰p_s, π⁻π⁺n_s have been measured. The Doppler broadening of the pion mom entum due to the spectator neutron recoil is at least a factor of two larger than that due to the proton and in disagreement with that expected from the deuteron wave function. This effect and earlier observations on spectators are well described by assuming narrow $\text{N}$N bound states near threshold.     

Quark-gluon plasma in 4 GeV/c antiproton annihilations on nuclei

Recent data on strange particle production in 4 GeV/c antiproton annihilations on Ta can be successfully interpreted if quark-gluon plasma formation is assumed along with a simple reaction model in which antiprotons deposit energy in the forward cone of nuclear matter within the target nucleus. The observed spectra and total abundances of lambdas and kaons are consistent with the hypothesis that (super cooled) quark matter phase has been formed at a rather modest temperature T≲60 MeV. The spectra can then be successfully interpreted both with reference to their form and relative abundance.     

Cascade particles,nuclear evaporation,and residual nuclei in high energy hadron-nucleus interactions

Based on a Monte Carlo realization of the Dual Parton Model we study the production of target associated particles and of nuclear fragments in high energy hadronnucleus interactions. A formation zone intranuclear cascade of low energy secondaries inside the target nucleus is discussed. We calculate excitation energies of residual nuclei left after the intranuclear cascade process and treat their fürther disintegration by introducing models for the evaporation of protons, neutrons, and light fragments, high energy fission, and by applying a Fermi Break-up model to light nuclear fragments. The results are compared to data on target associated particle production. We fürthermore calculate cross sections for the production of nuclear fragments.     

Something,but not much follows from the quark line rule in nucleon-antinucleon annihilations

Validity and consequences of the quark line rule (QLR) in nucleon (N)— antinucleon (¯N) annihilations into two or three mesons at LEAR energies are investigated. Recent data on proton-antiproton annihilation into anη orη′ together with additional non-strange pseudoscalar or vector meson (s) is used to successfully test the rule. We find that for present data any pseudoscalar meson mixing angle Φ_PS restricted to ?26⁰<Φ_PS0 is approximately consistent with the QLR. Since the assumptions leading to this test are valid in any present-day quark model of nucleon-antinucleon annihilation, improvement of the data will be of utmost importance. If proven valid, the QLR can be used to test if quark-antiquark annihilation dominates over quark exchange inN¯N → mesons at LEAR energies or vice versa. Previously proposed tests of the quark line diagrams (annihilation or rearrangement) describing the quark flavor flux under either of these assumptions are worked out. We investigate without a definite conclusion if dominance of annihilation over rearrangement is consistent with present data onp¯p → π⁰ π⁰,ηη, π⁰ρ⁰, π⁰ω, ηρ⁰,ηω, ρ⁰ρ⁰,ωω. As a main consequence, dominance of annihilation predicts without any ambiguity equality of the proton-antiproton annihilation cross sections σ(ωω) and σ(ρ⁰ρ⁰). Further consequences of dominance of either annihilation or rearrangement diagrams for proton-antiproton annihilation into two or three mesons are also worked out. We compare the predictions of the models we discuss to the sparse present data. It is emphasized that our predictions only exploit the quark flavor flux within the quark line diagrams that are assumed to dominate. They thus are independent of gluon contributions to these diagrams.     

Chiral symmetry in nuclei and nuclear matter

We discuss a model for hadrons based on chiral symmetry, Hadronic masses are generated via spontaneous symmetry breaking. Within this model we investigate nuclear matter and finite nuclei. Since the model is SU_F(3)-symmetric we are also able to investigate hypernuclei. Numerical results in comparison with experimental data are presented.     

On nuclear stopping in asymmetric colliding nuclei

Using the isospin-dependent quantum molecular dynamics (IQMD) model, nuclear stopping is analyzed in asymmetric colliding channels by keeping the total reacting mass fixed. The calculations have been performed by varying the mass asymmetry of the colliding pairs with different neutron-proton ratios at an incident beam energy of 250 MeV/nucleon. We find sizable effects of mass asymmetry on nuclear stopping and on the equilibrium of the nuclear matter. A reasonable agreement is also observed between the experimental data and our present calculations.     

Instabilities in nuclear matter and finite nuclei

Spinodal instability in nuclear matter and finite nuclei is investigated. This instability occurs in the low-density region of the phase diagram. The thermodynamical and dynamical analysis is based on Landau theory of Fermi liquids. It is shown that asymmetric nuclear matter can be characterized by a unique spinodal region, defined by the instability against isoscalar-like fluctuation, as in symmetric nuclear matter. Everywhere in this density region the system is stable against isovector-like fluctuations related to the species separation tendency. Nevertheless, this instability in asymmetric nuclear matter induces isospin distillation leading to a more symmetric liquid phase and a more neutron-rich gas phase.     

Fragmentation of relativistic gold nuclei in nuclear emulsion

Basic data are presented on the parameters of fragmentation, multiplicities and angular spectra of low energetic targed associated particles in the interction of ¹⁹⁷Au nuclei of 10.7A GeV.     

Shell structure in deformed nuclei and nuclear fission

Some new aspects in the theory of heavy nuclei emerging from studies of nuclear shell structure in the nuclear-fission process are described. Specific subjects cover general understanding of shell structure, the significance of macroscopic modes and the droplet model.     

Deuterium transport and isotope effects in type 316L stainless steel at high temperatures for nuclear fusion and nuclear hydrogen technology applications

We present the first complete data set for the permeability, diffusivity, and solubility of both deuterium and hydrogen in 316L stainless steel (316L SS) obtained over a wide temperature range of 350–850 °C that accommodates both nuclear fusion and nuclear hydrogen technology applications. The deuterium results were also compared with the hydrogen results to estimate the isotope effect. The isotope effect ratio for diffusivity was different from the classical prediction. Furthermore, some of our results were compared with the results previously reported for 316 SS. Results and discussion are presented with an emphasis on the deuterium permeation and isotope effects.     

The symmetry energy in nuclei and in nuclear matter

We discuss to what extent information on ground-state properties of finite nuclei (energies and radii) can be used to obtain constraints on the symmetry energy in nuclear matter and its dependence on the density. The starting point is a generalized Weizs?cker formula for ground-state energies. In particular, effects from the Wigner energy and shell structure on the symmetry energy are investigated. Strong correlations in the parameter space prevent a clear isolation of the surface contribution. Use of neutron skin information improves the situation. The result of the analysis appears consistent with a rather soft density dependence of the symmetry energy in nuclear matter.     

Evidence for a nuclear phase transition in target nuclei after relativistic nuclear interactions

The degree of excitation of the emulsion target nuclei due to nuclear interactions of oxygen and sulfur projectiles at 200 GeV/nucleon incident energy has been investigated. Using the plausible assumption that the numberN _b of slow particles emitted from the struck target nucleus can be interpreted as a measure of the temperatureT of the residual nucleus, we have found that there exists a critical temperatureT _c of the excited target nucleus. For Ag and Br target nuclei this temperature corresponds to <N _b>≌12 and it is attained when the impact parameters are less than about 4 fm.     

Interpretation of correlations between nuclear observables in rare-earth nuclei

We have recently obtained the optimal core-cluster decompositions for an extensive set of heavy even-even nuclei in the rare-earth region. The core-cluster charge products thus deduced are found to be closely correlated with the corresponding B(E2) values. We investigate here the strong resemblance of these correlations to the corresponding Casten plots, and find that the cluster model also predicts a further correlation between core-cluster charge products and the nuclear excitation energies, suggesting a new form of Casten plot for these energies.     

Muon induced fission in high threshold nuclei

Muon captures by nucleon pairs via meson-exchange currents produce a high energy excitation tail in heavy nuclei. The muon induced fission by these excitations is calculated in several subactinide nuclei with high threshold fission barriers. The probability for delayed fission ranges from 4×10^?5 to 4×10^?3 for the isotopes considered.