Experimental study of two-proton correlated emission from S-29 excited states

An experiment of a S-29 beam bombarding a Au-197 target at an energy of 49.2 MeV/u has been performed to study the two-proton correlated emission from S-29 excited states. Complete-kinematics measurements were carried out in the experiment. The relative momentum, opening angle, and relative energy of two protons, as well as the invariant mass of the final system, were deduced by relativistic-kinematics reconstruction. The Si-27-p-p coincident events were picked out under strict conditions and the phenomenon of p-p correlations was observed among these events. The mechanisms of two-proton emission were analyzed in a simple schematic model, in which the extreme decay modes like He-2 cluster emission, three-body phase-space decay, and two-body sequential emission were taken into account. Associated with the Monte Carlo simulations, the present results show that two protons emitted from the excited states between 9.6 MeV and 10.4 MeV exhibit the features of He-2 cluster decay with a branching ratio of 29(-11)(+10)%.

Superfluidity in dense nuclear matter

We discuss the onset of superfluidity in neutron stars, where the model of nuclear matter is realized in a high-density and asymmetry state. In particular, we present the study of the effects of microscopic three-body forces on the proton pairing in the 1S0 channel and neutron pairing in 3PF1 channel for β-stable neutron star matter. It is found that the main effects of three-body forces are to shrink the domain of existence of the 1S0 below the threshold of the direct URCA process and to stretch the density range of the 3PF1 pairing in a broad domain so to cover most part of the neutron-star core.

Single particle properties in asymmetric nuclear matter and TBF rearrangement effect

We have developed the formula and the numerical code for calculating the rearrangement contribution to the single particle (s.p.) properties in asymmetric nuclear matter induced by three-body forces within the framework of the Brueckner theory extended to include a microscopic three-body force (TBF). We have investigated systematically the TBF-induced rearrangement effect on the s.p. properties and their isospin-behavior in neutron-rich nuclear medium. It is shown that the TBF induces a repulsive rearrangement contribution to the s.p. potential in nuclear medium. The repulsion of the TBF rearrangement contribution increases rapidly as a function of density and nucleon momentum. It reduces largely the attraction of the BHF s.p. potential and enhances strongly the momentum dependence of the s.p. potential at large densities and high-momenta. The TBF rearrangement effect on symmetry potential is to enhances its repulsion (attraction) on neutrons (protons) in dense asymmetric nuclear matter.

The many-particle scattering system He++ on He: Experiment and a complete unified description

Highly differential experimental results of the scattering system He++ on He at 30 keV are presented as well as a complete unified theoretical description where excitation, transfer and ionization are treated simultaneously on an ab initio level. The agreement even for highly differential cross sections is nearly complete although no explicit correlation besides Pauli correlation is included in the calculations.

Proton and neutron S-1(0) superfluidity in asymmetric nuclear matter

The proton and neutron S-1(0), pairing gaps and their isospin dependence in isospin asymmetric nuclear matter have been studied by the isospin dependent Brueckner-Hartree-Fock approach and the BCS theory. We have focused on investigating and discussing the effect of three-body force. The calculated results indicate that as the isospin asymmetry increases, the density range of the S-1(0) neutron superfluidity is narrowed slightly and the maximum value of the neutron pairing gap increases 9 while the density domain for the proton superfluidity enlarges rapidly and the peak value of the proton gap decreases remarkably. The three-body force turns out to affect only weakly the neutron S-1(0) superfluidity and its isospin dependence, i. e., it leads to a small reduction of the neutron S-1(0) paring gap. However, the three-body force not only reduces largely the strength of the proton S-1(0) gaps at high densities in highly asymmetric nuclear matter but also suppresses strongly the density domain for the proton S-1(0) superfluidity phase.

Isospin dependence of S-1(0) proton and neutron superfluidity in asymmetric nuclear matter

We investigate the S-1(0) neutron and proton superfluidity in isospin-asymmetric nuclear matter. We have concentrated on the isospin dependence of the pairing gaps and the effect of a microscopic three-body force. It is found that as the isospin asymmetry goes higher, the neutron S-1(0) superfluid phase shrinks gradually to a smaller density domain, whereas the proton one extends rapidly to a much wider density domain. The three-body force turns out to weaken the neutron S-1(0) superfluidity slightly, but it suppresses strongly the proton S-1(0) superfluidity at high densities in nuclear matter with large isospin asymmetry.

Production cross section of Th-236 in the interaction of U-238 with 60 MeV/u O-18 ions

The neutron-rich target-like isotope Th-236 has been produced in the U-238-2p multinucleon transfer reaction between a 60 MeV/u O-18 beam and natural U-238 targets. The activities of thorium were determined after radiochemical separation of Th from the mixture of uranium and reaction products. The Th-236 isotope was identified by the characteristic gamma-rays of 642.2, 687.6 and 229.6 keV. The production cross section of Th-236 was determined to be 250 +/- 50 mu b.

Entrance channel dependence of the correlation function of IMFs in Ar-36+Sn-112,Sn-124 at 35MeV/u

The reduced velocity correlation functions of the Intermediate Mass Fragments (IMFs) were measured in the reactions of Ar-36+ Sn-112,Sn-124 at 35MeV/u. The anti-correlation at small reduced velocities is more pronounced in Ar-36+ Sn-124 system than that in Ar-36+ Sn-112 system. The difference of the correlation functions between the two reactions is mainly contributed by the particle pairs with high momenta. A three-body Coulomb repulsive trajectory code (MENEKA) is employed to calculate the emission time scale of IMFs for-the both systems. The time scale is 150fm/c in the Ar-36+ Sn-112 system and 120fm/c in the Ar-36+ Sn-124 system, respectively. A calculation based on an Isospin dependence Quantum Molecular Dynamics code (IQMD) reveals that the emission time spectrum of IMFs is shifted slightly leftwards in Ar-36+ Sn-124 compared with that in the Ar-16+ Sn-112 system, indicating a shorter emission time scale. Correspondingly, the central density of the hot nuclei decreases faster in Ar-36+ Sn-124 than in Ar-36+ Sn-112

Production cross-section of Th-236 in the interaction of U-238 with 60MeV/u O-18 Ions

The neutron-rich target-like isotope Th-236 was produced in U-238-2p multinucleon transfer reaction between a 60MeV/u O-18 beam and nature U-238 targets. The thorium activities were radiochemically separated from the mixture of uranium and reaction products. The isotope Th-236 was identified by 642.2keV, 687.6keV and 229.6keV characteristic gamma-rays. The production cross section of Th-236 has been determined to be 250 +/- 50 mu b.