W. M. Howard

Some nuclear data needs in astrophysics

In this paper we discuss a number of astrophysical environments and how improved nuclear data could facilitate a better understanding of them. One area of interest includes proton and alpha-particle reactions with unstable nuclei which are necessary for understanding the nucleosynthesis and energy generation in hot hydrogen-burning environments. Efforts underway at LLNL and elsewhere to develop the technology for the measurement of these reaction rates are discussed. Heavy-element nucleosynthesis in the late stages of red-giant stars and supernovae requires a complete network of neutron capture rates and beta-decay rates for nuclei near and far from stability. Experimental and theoretical efforts at LLNL to supply the input data and to model the nucleosynthetic environments will be outlined. Suggestions are made as to which nuclear data are most critical for the various scenarios. 42 refs., 11 figs., 1 tab.

Dynamic stellar neutron capture nucleosynthesis: The need for more nuclear data for the s‐process

We summarize results from a detailed parameter study of the s‐process in models which produce an exponential distribution of exposures by sequential irradiations and dredge up in the stellar environment. The calculations are based on a complete network of measured and calculated neutron capture and beta‐decay rates as well as estimates for their temperature dependence. In the framework of these models we identify and systematically vary the astrophysical variables which affect the observed solar‐system σN (cross section times abundance) curve. Constraints are placed on the s‐process neutron exposure and flux as well as the temperatures, densities, neutron pulse shape and inter‐pulse period. The results also highlight important needs for better nuclear data in various mass regions.

Nuclear information needs for the astrophysical s-process

The astrophysical s-process is a sequence of neutron-capture and beta-decay reactions on a slow time scale compared to beta-decay lifetimes near the line of stability. We systematically study this detailed sequence of neutron capture, continuum and bound-state beta decay, positron decay, and electron-capture reactions that comprise the s-process for a broad range of astrophysical environments. Our results are then compared with the solar-system abundances of heavy elements to determine the range of physical conditions responsible for their nucleosynthesis. The nuclear data needs are extensive but have begun to be precise enough to allow for a consistent interpretation of the astrophysical site for the s-process.

A parametric study of dynamic s‐process neutron‐capture nucleosyntheses: nuclear data needs

We summarize the stellar parameters which characterize the s‐process σN curve in the framework of models which produce an exponential distribution of exposures by periodic time‐dependent neutron irradiations. The optimum parameter space, defined by the best fit to the solar‐system σN curve, is distinctively different than the classical smooth monotonically decreasing curve. Constraints are placed on the s‐process environment. The needs for better neutron‐capture data in various mass regions are highlighted.