Systematic study of the pi(-)/pi(+) ratio in heavy-ion collisions with the same neutron/proton ratio but different masses

A systematic study of the pi(-)/pi(+) ratio in heavy-ion collisions with the same neutron/proton ratio but different masses can help single out effects of the nuclear mean field on pion production. Based on simulations using the IBUU04 transport model, it is found that the pi(-)/pi(+) ratio in head-on collisions of Ca-48 + Ca-48, Sn-124 + Sn-124, and Au-197 + Au-197 at beam energies from 0.25 to 0.6 GeV/nucleon increases with increasing the system size or decreasing the beam energies. A comprehensive analysis of the dynamical isospin fractionation and the pi(-)/pi(+) ratio as well as their time evolution and spatial distributions demonstrates clearly that the pi(-)/pi(+) ratio is an effective probe of the high-density behavior of the nuclear symmetry energy.

Symmetry energy and isovector giant dipole resonance in finite nuclei

We study the relationship between the properties of the isovector giant dipole resonance of finite nuclei and the symmetry energy in the framework of the relativistic mean field theory with six different parameter sets of nonlinear effective Lagrangian. A strong linear correlation of excited energies of the dipole resonance in finite nuclei and symmetry energy at and below the saturation density is found. This linear correlation leads to the symmetry energy at the saturation density at the interval 33.0MeV <= S(po) <= 37.0 MeV. The comparison to the present experimental data in the soft dipole mode of (132) Sn constrains approximately the symmetry energy at p = 0.1 fm(-3) at the interval 21.2MeV similar to 22.5 MeV. It is proposed that a precise measurement of the soft dipole mode in neutron rich nuclei could set up an important constraint on the equation of state for asymmetric nuclear matter.

Entrance-channel dependence of isospin effects on double n/p ratio in HIC

Within the hadronic transport model IBUU04, we investigate the effect of density-dependent symmetry energy on double neutron/proton (n/p) ratio of free nucleons in heavy ion collisions by taking four isotopic Sn+Sn reaction systems. Especially the entrance-channel asymmetry and impact-parameter dependence of the effect of symmetry energy are discussed. It is found that in both central and semi-central collisions the sensitivity of the double n/p ratio to the density-dependent symmetry energy is more pronounced in neutron-richer systems. Our results also indicate clearly that the effect of symmetry energy is stronger in central collisions than that in semi-central collisions.

Neutron-proton bremsstrahlung from intermediate energy heavy-ion reactions as a probe of the nuclear symmetry energy?

Hard photons from neutron-proton bremsstrahlung in intermediate energy heavy-ion reactions are examined as a potential probe of the nuclear symmetry energy within a transport model. Effects of the symmetry energy on the yields and spectra of hard photons are found to be generally smaller than those due to the currently existing uncertainties of both the in-medium nucleon-nucleon cross sections and the photon production probability in the elementary process pn -> pn gamma. Very interestingly, nevertheless, the ratio of hard photon spectra R-1/2(gamma) from two reactions using isotopes of the same element is not only approximately independent of these uncertainties but also quite sensitive to the symmetry energy. For the head-on reactions of Sn-132 + Sn-124 and Sn-112 + Sn-112 at E-beam/A = 50 MeV, for example, the R-1/2(gamma) displays a rise up to 15% when the symmetry energy is reduced by about 20% at rho = 1.3 rho(0) which is the maximum density reached in these reactions. (C) 2008 Elsevier B.V. All rights reserved.

Influence of in-medium nucleon-nucleon cross section on the isoscaling parameter alpha

The influence of in-medium nucleon-nucleon cross section on the isoscaling parameter a is investigated for two couples of central nuclear reactions Ca-40 + Ca-40 and Ca-60 + Ca-40; Sn-112 + Sn-112 and Sn-124 + Sn-124 within the isospin dependent quantum molecular dynamics. The calculated result shows that the influence of the in-medium nucleon-nucleon cross section on the isoscaling parameter a is mainly determined by the corresponding number of collisions, both for isospin dependent and isospin independent parameterizations. The mechanisms behind the effects of the in-medium nucleon-nucleon cross sections on the alpha are investigated in more details.

Structure of upper-g(9/2)-shell nuclei and shape effect in the Ag-94 isomeric states

Using a shell model which is capable of describing the spectra of upper g(9/2)-shell nuclei close to the N = Z line, we study the structure of two isomeric states 7(+) and 21(+) in the odd-odd N = Z nucleus Ag-94. It is found that both isomeric states exhibit a large collectivity. The 7(+) state is oblately deformed, and is suggested to be a shape isomer in nature. The 21(+) state becomes isomeric because of level inversion of the 19(+) and 21(+) states due to core excitations across the N = Z = 50 shell gap. Calculation of spectroscopic quadrupole moment indicates clearly an enhancement in these states due to the core excitations. However, the present shell model calculation that produces the 19(+)-21(+) level inversion cannot accept the large-deformation picture of Mukha et al.

Effect of entrance-channel asymmetry on the isospin dependence of nucleon emission in heavy ion collisions

Using the isospin- and momentum-dependent hadronic transport model 1BUU04, we have investigated the influence of the entrance-channel isospin asymmetry on the sensitivity of the pre-equilibrium neutron/proton ratio to symmetry energy in central heavy-ion collisions induced by high-energy radioactive beams. Our analysis and discussion are based on the dynamical simulations of the three isotopic reaction Systems Sn-132+Sn-124, Sn-124+Sn-112 and Sn-112+(112)Su which are of the same total proton number but, different isospin asymmetry. We find that, the kinetic-energy distributions of the pre-equilibrium neutron/proton ratio are quite sensitive to the density-dependence of symmetry energy at incident beam energy E/A = 400 MeV, and the sensitivity increases as the isospin asymmetry of the reaction system increases.

Probing the high density behavior of the symmetry energy by using the free neutron-proton ratio

Based on the isospin- and momentum-dependent transport model IBUU04, the transverse momentum distributions of the free neutron-proton ratio in the Sn-132+(124) Sn reaction system at mid-central collisions with beam energies of 400/A MeV, 600/A MeV and 800/A MeV are studied by using two different symmetry energies. It is found that the free neutron-proton ratio as a function of the transverse momentum at the mid-rapidity is very sensitive to the density dependency of the symmetry energy especially at incident energies around 400/AMeV.

Probing the high density behavior of the symmetry energy by using proton elliptic flow

Based on the isospin- and momentum-dependent transport model IBUU04, we calculated the reaction of the Sn-132+Sn-124 systems in semi-central collisions at beam energies of 400/A MeV, 600/A MeV and 800/A MeV by adopting two different density dependent symmetry energies. It was found that the proton differential elliptic flow as a function of transverse momentum is quite sensitive to the density dependence of symmetry energy, especially for the considered beam energy range. Therefore the proton differential elliptic flow may be considered as a robust probe for investigating the high density behavior of symmetry energy in intermediate energy heavy ion collisions.

Production of EUV power with SECRAL

The high power EUV source is one of key issues in the development of EUV lithography which is considered to be the most promising technology among the next generation lithography. However neither DPP nor LPP seems to meet the requirements of the commercial high-volume product. Insufficiency of DPP and LPP motivate the investigation of other means to produce the EUV radiation required in lithography. ECR plasma seems to be one of the alternatives. In order to investigate the feasibility of ECR plasma as a EUV light source, the EUV power emitted by SECRAL was measured. A EUV power of 1.03W in 4 pi sr solid angle was obtained when 2000W 18GHz rf power was launched, and the corresponding CE was 0.5%. Considering that SECRAL is designed to produce very high charge state ions, this very preliminary result is inspiring. Room-temperature ECR plasma and Sn plasma are both in the planned schedule.

Beam energy dependence of the pi(-)/pi(+) ratio

Using the isopin- and momentum-dependant hadronic transport model IBUU04, the effect of symmetry energy on the pi(-)/pi(+) ratio are studied. Our investigations are based on the calculations of the Sn-132+Sn-124 semi-central collisions at beam energies of 400/ A MwV, 600/ A MeV and 800MeV. It is found that both the transverse momentum and kinetic energy distributions of the pi(-)/pi(+) ratio are rather sensitive to the symmetry energy, especially around the Colomb peaks. The position of the coulomb peak is shown to be nearly indrpendant of beam energy. The sesitivity of the pi(-)/pi(+) ratio to the symmetry ebergy decreases as the beam energy increases from 600/ A MeV to 800/ A MeV.

Probing the high density behavior of the symmetry energy by using the neutron-proton differential flow

Based on the isospin- and momentum-dependent transport model IBUU04, we investigated the neutron-proton differential flow in the (132) Sn + (124) Sn mid-central collisions at beam energies of 400MeV/A, 600MeV/A and 800MeV/A by adopting two different symmetry energies. It was found that the neutron-proton differential flow as a function of rapidity is very sensitive to the density dependence of symmetry energy, especially at incident energies around 400MeV/A

Single and double pi(-)/pi(+) ratios in heavy-ion reactions as probes of the high-density behavior of the nuclear symmetry energy

Based on the isospin- and momentum-dependent hadronic transport model IBUU04, effects of the nuclear symmetry energy on the single and double pi(-)/pi(+) ratios in central reactions of Sn-132+Sn-124 and Sn-112+Sn-112 at a beam energy of 400 MeV/nucleon are studied. It is found that around the Coulomb peak of the single pi(-)/pi(+) ratio the double pi(-)/pi(+) ratio taken from the two isotopic reactions retains about the same sensitivity to the density dependence of nuclear symmetry energy. Because the double pi(-)/pi(+) ratio can significantly reduce the systematic errors, it is thus a more effective probe for the high-density behavior of the nuclear symmetry energy.

Critical behavior of multifragmentation in finite nuclei and extraction of critical exponents

Using a phenomenological asymmetric nuclear equation of state, we obtained pressure-density isotherms of the finite nucleus Sn-112 simulated in r-space and in p-space and constructed the nuclear fragments by using the coalescence model. After correlatively analysing the fragments, the signal of critical behavior has been found and critical exponents were also extracted.

Medium effect of nucleon-nucleon cross section on the isoscaling parameter alpha

The medium effect of in-medium nucleon-nucleon cross section sigma(med)(NN) (alpha(m)) on the isoscaling parameter a is investigated for two couples of central nuclear reactions Ca-40 + Ca-48 and Ca-60 + Ca-48; Sn-112 + Sn-112 and Sn-124 + Sn-124 at beam energy region from 40 to 60 MeV/nucleon with isospin dependent quantum molecular dynamics. It is found that there is the obvious medium effect of sigma(med)(NN) (alpha(m)) on the isoscaling parameters alpha. The mechanism for the medium effect of sigma(med)(NN) (alpha(m)) on a is investigated.