USNDP Astrophysics Task Force

April 22, 1996

There is a strong need to produce and disseminate high-quality evaluations of nuclear data for nuclear astrophysics. Specifically, more complete, precise, and up-to-date evaluated nuclear data are required for models of diverse astrophysical phenomena. This is especially true for a new generation of sophisticated models attempting to explain observations ranging from precision abundance measurements in meteorites to spectacular images from the Hubble Space Telescope and the Compton Gamma Ray Observatory.

There are many valuable resources in the nuclear data community that can be utilized to help meet data needs in nuclear astrophysics research. These resources include, for example, existing evaluations of nuclear reaction and nuclear structure data. The expertise in areas such as producing evaluations, testing and standardizing evaluations, nuclear modeling, data storage formats, and on-line information services are also valuable resources. Cooperation between the nuclear astrophysics and nuclear data communities in a nuclear data effort for astrophysics would bring new evaluation methods to bear on data products important for nuclear astrophysics, would minimize duplication of efforts, and would enhance the potential for success. Additionally, coordination of such an astrophysics data effort on a national scale would maximize the use of available resources and facilitate coordination with international efforts.

The Network Executive Committee of the U.S. Nuclear Reaction Data Network formed an Astrophysics Task Force to plan, initiate, and implement cooperative nuclear data evaluation activities involving the nuclear data community and the nuclear astrophysics community.

The Task Force has written a document, "U.S. Nuclear Data Resources for a Coordinated U.S. Effort in Nuclear Data for Nuclear Astrophysics", that details data community resources appropriate for nuclear astrophysics research.

Work in Progress

• Determination of the ¹²C(,)¹⁶O reaction rate (G.M. Hale).
• Calculation of Heavy Element Nucleosynthesis Reaction Rates from Evaluated Nuclear Data Files (N.M. Larson, D.C. Larson, M.S. Smith, R.Q. Wright, A.R. Braeutigam, R.R. Winters)
• Participation in the newly-formed Nuclear Astrophysics Data Evaluation Steering Committee. This twelve-member group, which includes G.M. Hale, M.S. Smith, and R.G. Stokstad, is chaired by P.D. Parker of Yale University. Near-future activities will include surveying the community to prioritize nuclear astrophysics evaluation projects.

Summary of the Astrophysics Task Force Meeting

M.S. Smith, ORNL
Golden, CO March 13-14, 1996

A summary of nuclear data projects relevant for nuclear astrophysics that are in progress or planned by USNRDN members was presented by M.S. Smith (ORNL) at the USNRDN Meeting in Golden, Colorado on March 13-14, 1996. These activities include projects in measurements, compilations, modeling, evaluations, (reaction rate) calculations, and data dissemination. These projects, as well as issues concerning the evaluation of nuclear reactions and dissemination of data for nuclear astrophysics, were discussed at a meeting of the Astrophysics Task Force. Members of the Task Force present included M.S. Smith (Chair), F.E. Cecil, G.M. Hale, and D.A. Resler; other USNRDN members also participated in the discussion. The Task Force made the following four recommendations:

1. Evaluation Procedures: A group of nuclear astrophysicists and nuclear data scientists should evaluate a few (2-3) nuclear reactions of astrophysical importance, and provide extremely detailed documentation of the evaluation procedures and problems. This documentation, along with a hands-on demonstration (the details of which will be determined at a later date), should assist prospective evaluators of these reactions in learning modern evaluation procedures by example.
2. Upon consultation with colleagues, the Task Force chairman will determine the reactions to be evaluated.
3. The future roles of the Task Force include the following:
   1. Contribute to the nuclear data evaluations and expertise of the Nuclear Astrophysics Data Evaluation Steering Committee.
   2. Initiate, encourage, and publicize astrophysics data activities by USNRDN members.
   3. Recruit evaluators for nuclear astrophysics data evaluations.
   4. Interface with the Steering Committee and with other nuclear data organizations.
4. The Task Force should help determine the data dissemination needs of the nuclear astrophysics community, and should encourage and publicize ongoing data dissemination efforts.

Part of the discussion at the Task Force meeting focused on a proposal by David Resler (LLNL) and Roger White (LLNL) to expand their Thermonuclear Data File (TDF) into an Astrophysics Data File (ADF). TDF, developed by White and Resler for fusion energy applications, presents users with fast, standardized, easily-updated, numerically-accurate access to the rates of the 5 plasma-burn reactions [such as t(d,n)] as a function of temperature. These rates are generated from (user-selected) files of evaluated cross sections (stored at LLNL) on a minimal temperature grid and downloaded to the users' computer along with access subroutines -- including a four-point, cubic Lagrange interpolator to generate rates at any required temperature. This method is equal in speed to analytical parameterizations of rates as functions of temperatures, and has an intrinsic uncertainty of only 0.1% -- better than analytic expressions. Modifications planned for this system include providing temperature-derivatives of reaction rates, useful for coupling nuclear reactions with stellar hydrodynamics, and the incorporation of analytic reaction rate formulae (from existing rate compilations) into ADF to enable the calculation of rates before large sets of evaluated cross sections are available. It was generally felt that ADF was an excellent proposed application of nuclear data expertise to problems of astrophysical importance. More information on ADF can be obtained from David Resler (rmwhite@llnl.gov).

For more information on the Task Force or the status of its work, please contact Michael S. Smith at msmith@orph01.phy.ornl.gov.