Narrow Results

The importance of measuring Q-values in rapid proton capture process has been investigated. The microscopic optical model, derived using a nucleon–nucleon interaction and densities from relativistic mean field (RMF) calculations, has been utilized to calculate the reaction rates. It has been observed that the Q-values involved in the reactions at waiting points at A = 60 and 64 are very important in determining the final abundance of the process. Some other Q-values also play a crucial role in the final abundance of nuclei near the end point of the process.

Nuclear astrophysics is a active, rapidly developing field that addresses fundamental scientific questions. Advances in astronomy have to be matched with advances in nuclear physics to address these questions in the future. I discuss some of the major open questions and future directions, using as examples supernovae, the rapid neutron capture process, and processes on the surface of accreting neutron stars. In all cases nuclear physics is needed to interpret observations and to guide and constrain theoretical models. While a wide range of experimental facilities is required, one of the major challenges for the future is the study of unstable nuclei that play a central role in many of the major open questions. Therefore, an advanced radioactive beam facility such as the proposed Rare Isotope Accelerator (RIA) is of particular importance for the future of this field.

Recent commissioning of the Cooler Storage Ring at the Heavy Ion Research Facility in Lanzhou (HIRFL-CSR) has allowed us for direct mass measurements at the Institute of Modern Physics in Lanzhou (IMP), Chinese Academy of Sciences. A series of isochronous mass measurements have been carried out in the past few years using ⁷⁸Kr, ⁸⁶Kr, ⁵⁸Ni, and ¹¹²Sn beams. The main results and the present status are presented in this talk, and the implications of these results with respect to nuclear structures and nucleosynthesis in the rp-process of x-ray bursts are discussed.

Characterizing the nature of single-particle states outside of double shell closures is essential to a fundamental understanding of nuclear structure. This is especially true for those doubly magic nuclei that lie far from stability and where the shell closures influence nucleosynthetic pathways. The region around ¹⁰⁰Sn is one of the most important due to the proximity of the N=Z=50 magic numbers, the proton-drip line, and the end of the rp-process. However, owing to the low production rates, there is a lack of spectroscopic information and no firm spin-parity assignment for ground states of odd-A isotopes close to ¹⁰⁰Sn. Neutron knockout reaction experiments on beams of ^108,106Sn and ¹⁰⁶Cd have been performed at the NSCL. By measuring gamma rays and momentum distributions from reaction residues, the spin of ground state and first excited state for ^107,105Sn have been established. The results also show a degree of mixing in the ground states of the isotopes ^108,106Sn between the d_5/2 and g_7/2 single particle-states and they are compared to reaction calculations. Single-, double-, and triple-neutron knockout reactions on the ¹⁰⁶Cd beam have been observed. The spin-parity of ¹⁰⁵Cd is already known, therefore, the measurement of the momentum distributions of the ground and first excited states of this residue is an important validation of the technique used for the light tin isotopes.