Session DA: Recent Progress in Nuclear Astrophysics

Experimental studies of photonuclear reactions relevant to astrophysical nucleosynthesis

Nuclear reactions and transitions caused by the electromagnetic interaction are considered to play important roles in various processes occurring in stars and in the early universe, and therefore precise data of the photonuclear reactions as well as their inverse radiative capture reactions are indispensable for quantitative studies of astrophysical nucleosynthesis. Photonuclear reactions are also useful to probe the analogous neutrino-induced nuclear reactions by weak neutral current, which are supposed to play critical roles in the dynamics of Type-II supernova explosions and in accompanying neutrino-induced nucleosynthesis. Recently developed $\gamma $-ray sources based on the Compton backscattering of laser photons with relativistic electrons are expected to provide a powerful tool for high-precision experiments on photonuclear reactions at astrophysically important energies, because they have nice features such as quasi-monochromatic and tunable energy, little background, high polarization, small angular spread, and so on. In this contribution the current status of the backscattered $\gamma $-ray facilities in the intermediate energy regions will be introduced, and some topics on nuclear astrophysics studies at those facilities will be presented.   

The r-Process in Supernovae and Galactic Chemical Evolution

I will discuss the recent progress of r-process issues relevant to the neutrino-driven outflows of core-collapse supernovae. Main topics include 1) r-process in neutrino winds, which is based on the semi-analytic wind solutions with taking the effect of termination shock into account, 2) nucleosynthesis in electron-capture supernovae (or AGB supernovae, ONeMg supernovae), which is based on a recent collaborative work with the Munich hydro group, and 3) Galactic chemical evolution of r-process elements, which is based on the evolution model of the Galactic halo with the spectroscopic data of metal-poor stars collected at the SUBARU telescope.   

Direct Measurements of Radiative Capture and Charged Particle Reactions of Astrophysical Importance Using Radioactive Beams

This decade has seen the growth of facilities such as TRIUMF-ISAC, and methods enabling the direct measurement of nuclear reactions considered to have astrophysical importance using radioactive ion beams. Many challenges exist in developing the intense radioactive ISOL beams needed, and the sensitive and precise detectors required, to make these measurements, which are crucial inputs to astrophysical models of explosive scenarios such as novae and x-ray bursts enabling direct comparison with astronomical data such as those from orbiting gamma ray observatories. With emphasis on the radiative capture reaction measurements made at the DRAGON facility using radioactive beams in the last decade for classical novae, I will discuss these direct measurements and their role in certain stellar environments, as well as the technical challenges involved in these difficult experimental measurements. Where relevant I will also refer to connected auxiliary indirect measurements at TRIUMF-ISAC and other laboratories, or similar stable beam measurements. I will present the results of the first direct measurement of the $^{23}$Mg(p,$\gamma$)$^{24}$Al reaction at DRAGON, and discuss it in its context of explosive hydrogen burning in classical novae.