Equilibration chronometry

We study neutron-proton equilibration in dynamically deformed atomic nuclei created in nuclear collisions. The two ends of the elongated nucleus are initially dissimilar in compositions and equilibrate on a sub-zeptosecond timescale following first-order kinetics. The technique of equilibration chronometry used to obtain this result enables new insight into the nuclear equation of state that governs many nuclear and astrophysical phenomena leading to the origin of the chemical elements

Using Light Charged Particles to Probe the Asymmetry Dependence of the Nuclear Caloric Curve

Recently, we observed a clear dependence of the nuclear caloric curve on neutron-proton asymmetry $\frac{N-Z}{A}$ through examination of fully reconstructed equilibrated quasi-projectile sources produced in heavy ion collisions at E/A = 35 MeV. In the present work, we extend our analysis using multiple light charged particle probes of the temperature. Temperatures are extracted with five distinct probes using a kinetic thermometer approach. Additionally, temperatures are extracted using two probes within a chemical thermometer approach (Albergo method). All seven measurements show a significant linear dependence of the source temperature on the source asymmetry. For the kinetic thermometer, the strength of the asymmetry dependence varies with the probe particle species in a way which is consistent with an average emission-time ordering.Comment: 7 pages, 4 figure

Efimov States From Triple α Resonances

The Efimov trimers in excited 12C nuclei, which no observation exists yet, are discussed by means of analyzing the experimental data of 70(64)Zn(64Ni) +70(64)Zn(64Ni )reactions at beam energy of E/A=35 MeV/nucleon. In heavy ion collisions, the αs interact with each other and can form complex systems such as 8Be and 12C. For the 3α systems, multi resonance processes give rise to excited levels of 12C. The interaction between any two of the 3α particles provides events with one, two or three 8Be. Their interfering levels are clearly seen in the minimum relative energy distributions. Events of three couple αrelative energies consistent with the ground state of 8Be are observed with the decreasing of the instrumental error at the reconstructed 7.458 MeV excitation energy of 12C, which was suggested as the (Thomas) Efimov state

Isospin dependence of collective flow in heavy-ion collisions at intermediate energies

Within the framework of an isospin-dependent Boltzmann-Uehling-Uhlenbeck (BUU) model using initial proton and neutron densities calculated from the nonlinear relativistic mean-field (RMF) theory, we compare the strength of transverse collective flow in reactions $^{48}Ca+^{58}Fe$ and $^{48}Cr+^{58}Ni$, which have the same mass number but different neutron/proton ratios. The neutron-rich system ($^{48}Ca+^{58}Fe$) is found to show significantly stronger negative deflection and consequently has a higher balance energy, especially in peripheral collisions. NOTE ADDED IN PROOF: The new phenomenon predicted in this work has just been confirmed by an experiment done by G.D. Westfall et al. using the NSCL/MSU radioactive beam facility and a spartan soccer. A paper by R. Pak et al. is submitted to PRL to report the experimental result.Comment: Latex file, 9 pages, 4 figures availabe upon request; Phys. Rev. Lett. (June 3, 1996) in pres

Women in physics in the United States: Recruitment and retention

Initiatives to increase the number, persistence, and success of women in physics in the United States reach preteen girls through senior women. Programs exist at both the local and national levels. In addition, researchers have investigated issues related to gender equity in physics and physics education. Anecdotal evidence suggests increased media coverage of the underrepresentation of women in science. All of these efforts are motivated and made more effective by the continued collection and presentation of data on the presence, persistence, and promise of women in physics

Investigation of transverse collective flow of intermediate mass fragments

The transverse flow of intermediate mass fragments (IMFs) has been investigated for the 35 MeV/u ${}^{70}\mathrm{Zn}+{}^{70}\mathrm{Zn}$, ${}^{64}\mathrm{Zn}+{}^{64}\mathrm{Zn}$, and ${}^{64}\mathrm{Ni}+{}^{64}\mathrm{Ni}$ systems. A transition from the IMF transverse flow strongly depending on the mass of the system, in the most violent collisions, to a dependence on the charge of the system, for the peripheral reactions, is shown. This transition was shown to be sensitive to the density dependence of the symmetry energy using the antisymmetrized molecular-dynamics model. The results present an observable, the IMF transverse flow, that can be used to probe the nuclear equation of state. Comparison with the simulation demonstrated a preference for a stiff density dependence of the symmetry energy

Sensitivity of intermediate mass fragment flows to the symmetry energy

The NIMROD-ISiS array was used to study the transverse flow of intermediate mass fragments in 35 MeV/nucleon ${}^{70}\mathrm{Zn}+{}^{70}\mathrm{Zn}$, ${}^{64}\mathrm{Zn}+{}^{64}\mathrm{Zn}$, and ${}^{64}\mathrm{Ni}+{}^{64}\mathrm{Ni}$ reactions. The intermediate mass fragment flow was previously shown to be sensitive to the density dependence of the symmetry energy. To explore the model dependence of the results, the antisymmetrized molecular dynamics, constrained molecular dynamics, and stochastic mean-field models were each compared to the experimental results to extract information on the form of the symmetry energy. The results demonstrate that sensitivity of the models to the nuclear equation of state can vary significantly based on the treatment of the nuclear dynamics. Despite the differences in the sensitivity, improved agreement with the experimental data is observed for each model with a stiff density dependence of the symmetry energy

Transverse collective flow and midrapidity emission of isotopically identified light charged particles

The transverse flow and relative midrapidity yield of isotopically identified light charged particles (LCPs) has been examined for the 35 MeV/nucleon ${}^{70}\mathrm{Zn}+{}^{70}\mathrm{Zn}$, ${}^{64}\mathrm{Zn}+{}^{64}\mathrm{Zn}$, and ${}^{64}\mathrm{Ni}+{}^{64}\mathrm{Ni}$ systems. A large enhancement of the midrapidity yield of the LCPs was observed relative to the yield near the projectile rapidity. In particular, this enhancement was increased for the more neutron-rich LCPs demonstrating a preference for the production of neutron-rich fragments in the midrapidity region. Additionally, the transverse flow of the LCPs was extracted, which provides insight into the average movement of the particles in the midrapidity region. Isotopic and isobaric effects were observed in the transverse flow of the fragments. In both cases, the transverse flow was shown to decrease with an increasing neutron content in the fragments. A clear inverse relationship between the transverse flow and the relative midrapidity yield is shown. The increased relative midrapidity emission produces a decreased transverse flow. The stochastic mean-field model was used for comparison to the experimental data. The results showed that the model was able to reproduce the general isotopic and isobaric trends for the midrapidity emission and transverse flow. The sensitivity of these observables to the density dependence of the symmetry energy was explored. The results indicate that the transverse flow and midrapidity emission of the LCPs are sensitive to the denisty dependence of the symmetry energy

Progress in constraining the asymmetry dependence of the nuclear caloric curve

The nuclear equation of state is a basic emergent property of nuclear material. Despite its importance in nuclear physics and astrophysics, aspects of it are still poorly constrained. Our research focuses on answering the question: How does the nuclear caloric curve depend on the neutron-proton asymmetry? We briefly describe our initial observation that increasing neutron-richness leads to lower temperatures. We then discuss the status of our recently executed experiment to independently measure the asymmetry dependence of the caloric curve