Nuclear data on unstable nuclei for astrophysics

Nuclear data on unstable nuclei for astrophysics

Nuclear Physics A 746 (2004) 569c–572c Nuclear data on unstable nuclei for astrophysics Michael S. Smitha , Richard A. Meyerb , Daniel W. Bardayana ,...

395KB Sizes 22 Downloads 19 Views

Nuclear Physics A 746 (2004) 569c–572c

Nuclear data on unstable nuclei for astrophysics Michael S. Smitha , Richard A. Meyerb , Daniel W. Bardayana , Jeffery C. Blackmona , Kyungyuk Chaec,a , Michael W. Guidryc,a , W. Raphael Hixc,a , R. L. Kozubd , Eric J. Lingerfeltc,a , Zhanwen Mac,a , Jason P. Scottc,a a

Physics Division, Oak Ridge National Laboratory, Oak Ridge, TN RAME’ Inc., Teaticket, MA c Dept. of Physics and Astronomy, Univ. of Tennessee, Knoxville, TN d Physics Dept., Tennessee Technological Univ., Cookeville, TN b

Recent measurements with radioactive beams at ORNL’s Holifield Radioactive Ion Beam Facility (HRIBF) have prompted the evaluation of a number of reactions involving unstable nuclei needed for stellar explosion studies. We discuss these evaluations, as well as the development of a new computational infrastructure to enable the rapid incorporation of the latest nuclear physics results in astrophysics models. This infrastructure includes programs that simplify the generation of reaction rates, manage rate databases, and visualize reaction rates, all hosted at a new website www.nucastrodata.org. 1. NUCLEAR DATA EVALUATIONS FOR STELLAR EXPLOSION STUDIES Thousands of different isotopes of neutron-rich nuclei are believed to be synthesized in supernova explosions. To simulate these cataclysmic events, a knowledge of the structure of neutron-rich nuclei and the reactions involving them is essential. Similarly, information on proton-rich unstable nuclei is needed to understand nova explosions occurring on the surface of white dwarf stars and X-ray bursts on the surface of neutron stars. Recent measurements with radioactive beams at ORNL’s Holifield Radioactive Ion Beam Facility (HRIBF)[1] have prompted the evaluation of a number of reactions involving unstable nuclei, and the associated level structures, that are necessary to probe the details of these spectacular astrophysical explosions. A number of reactions are also being investigated to prepare for possible future measurements at HRIBF. The results of our evaluations – new cross sections and level schemes – will be converted into new thermonuclear reaction rates using software tools discussed below. Recent reactions and nuclei being assessed at ORNL include: •

18



14

F(p,α)15 O and 18 F(p,γ)19 Ne and the level structure of 19 Ne above the threshold; this work is illustrated in Fig. 1 and discussed below

18

F + p

O(α,p)17 F and the level structure of 18 Ne above the 14 O + α and 17 F + p thresholds; R-matrix fits to the measurements of four different reaction yields are currently being made[2]

0375-9474/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.nuclphysa.2004.09.092

570c

Rate / Present

M.S. Smith et al. / Nuclear Physics A 746 (2004) 569c–572c

10

1

10

0

10

-1

10

-2 18

18

10

19

F(p,γ) Ne

15

F(p,α) O

-3

0.03

0.1

0.5

1

0.1

0.5

1

3

Temperature (T9) Figure 1. The ratio of the 18 F+p reaction rates to the present nominal rate. The solid lines correspond to the low and high rates in the present study, and the shaded regions are the rates in Ref. [4].



33,34



30

Cl(p,γ)34,35 Ar and the level structure of 34,35 Ar above the 33,34 Cl + p thresholds, for a future HRIBF measurement

P(p,γ)31 S and the level structure of 31 S above the 30 S + p threshold; this work includes results from a recent HRIBF measurement of 32 S(p,d)31 S

The highlights of our first evaluation of the 18 F(p,α)15 O and 18 F(p,γ)19 Ne reactions and the level structure of 19 Ne above the 18 F + p threshold are given in Shu et al. [3], and a longer paper updated with recent results from a 18 F(d,p)19 F measurement is in progress. Our new thermonuclear reaction rates based on this evaluation are shown in Fig. 1, where the “low” and “high” rates were calculated by varying the contribution of each of 21 resonances within their uncertainty and adding the resultant deviation in quadrature. Our updated rate is consistent with the rates in Ref. [4] within uncertainties, except at temperatures of 2–3 GK and near 0.3 GK. The difference near 0.3 GK results from a smaller value of the strength of the 330-keV 19 Ne resonance in the present work. At 2–3 GK, our rate is larger by ∼ 20–60% primarily because of the contributions of higher energy resonances included in the present work. The uncertainty in our (p,α) rate is smaller than in Ref. [4] primarily because of the precision of the newer measurements

M.S. Smith et al. / Nuclear Physics A 746 (2004) 569c–572c

571c

of the 330-keV and 665-keV resonance parameters, as well as the new upper limits on Γp for the 8, 38, and 287-keV levels in 19 Ne. 2. STRATEGIES FOR FUTURE NUCLEAR ASTROPHYSICS DATA ACTIVITIES Measurements and theoretical descriptions of nuclei and their interactions provide a foundation for sophisticated models of stellar explosions, as well as for other astrophysical systems ranging from the Big Bang to the inner workings of our own Sun. In many instances, the ability of astrophysical models to accurately describe the latest, spectacular observations of the cosmos strongly depends on the input nuclear data, and more extensive and precise nuclear data is required for advances in astrophysics. However, to be utilized for astrophysical studies, state-of-the-art nuclear measurements and theoretical calculations have to be appropriately processed for input into astrophysics simulation codes. This requires dedicated efforts in data compilation, evaluation, processing, dissemination, and coordination. Unfortunately, the current worldwide effort in nuclear astrophysics data does not meet the data needs of the astrophysics community. As a result, the latest nuclear measurements or model calculations are frequently not utilized in studies of the very astrophysical puzzles that motivated their generation. The situation is getting worse as more nuclear measurements are being made but not incorporated into reaction rate libraries and other astrophysical datasets that are in the public domain. Fortunately, there are a number of strategies that will enable a more effective utilization of nuclear physics information in astrophysics simulations. These include the development of software to facilitate the connection between the nuclear laboratory and stellar models, as well as initiatives to boost evaluation manpower in this field. For example, at ORNL we are creating a new computational infrastructure for nuclear astrophysics data. This suite of computer codes will expedite the incorporation of nuclear physics information into astrophysical simulation codes. Available on-line through a web browser, a simple point-and-click interface will guide users to convert input nuclear structure and reaction information – the products of evaluation activities – into thermonuclear reaction rates in a variety of popular formats, including that of the widely-used REACLIB library[5] which contains over 60000 rates. The interface will also enable users to easily access and manage databases – for example, to insert a new reaction rate into an online reaction rate library, as well as to create, merge, store, document, and share custom rate libraries. This functionality will hopefully make it possible for the community to replace multiple, proprietary versions of REACLIB that each have different, partial reaction rate updates with frequently updated public releases– making the intercomparison of results from different astrophysics simulations much easier. The infrastructure will also enable users to easily visualize rate libraries with Rateplotter, the first easy-to-use, interactive, platform-independent, graphical user interface to REACLIB-format rate libraries. This program, viewable through a web browser or as a stand-alone application, enables users to plot multiple rates, access rate parameters, add new rates and plot them, and create rate versus temperature tables, all through a point-and-click graphical user interface based on the chart of the nuclides. To host this new infrastructure for nuclear astrophysics data, a new website has been launched:

572c

M.S. Smith et al. / Nuclear Physics A 746 (2004) 569c–572c

www.nucastrodata.org. In addition to the components described above, this site features an extensive list of nuclear datasets (over 60 so far) important for nuclear astrophysics studies available from around the world. It is designed to help users navigate through these datasets, as well as to publicize them to the research community. This site and its new infrastructure have a strong potential to become a valuable asset for the nuclear astrophysics research community. Even with the new computational infrastructure discussed above, more manpower will still be needed for evaluations. Some of this may come from appeals for volunteer work from the nuclear astrophysics research community. Exploiting the overlap between the nuclear data and nuclear astrophysics communities[6] is another approach to increasing evaluation manpower. To make these approaches work, communication is crucial. First, the benefits of evaluations need to be clearly elucidated to enlist additional evaluators. Next, strong lines of communication between evaluators are needed, both nationally and internationally, to share expertise and to help avoid unnecessary duplications of effort. Third, a robust dialogue between evaluators and astrophysical modelers, the end users of the nuclear data, is vital to ensure that evaluations are focused on the most important reactions and nuclei. Such enhanced communications, as well as other data activities, would be greatly facilitated by the establishment of a Nuclear Astrophysics Data Coordinator, whose duties would include: maintaining and updating a central WWW site linking relevant datasets; modifying datasets for compatibility with astrophysical codes; and improving data accessibility via the creation of indices, search capabilities, graphical interfaces, bibliographies, error checking, plotting tools, and other enhancements. Other activities could include encouraging and helping coordinate evaluation activities; establishing and maintaining a nuclear astrophysics email distribution list; publicizing new nuclear astrophysics meetings, experimental results, and publications; and establishing and maintaining a priority list of important nuclear reactions and properties that require further study. It would also be beneficial for the Coordinator to maintain an active research program using nuclear astrophysics data to ensure the data activities truly fulfill the needs of data users. The establishment of a Coordinator would have a strong positive impact on nuclear astrophysics research efforts worldwide with only a modest investment. ORNL is managed by UT-Battelle, LLC, for the U.S. Dept. of Energy under contract DE-AC05-00OR22725. REFERENCES 1. 2. 3. 4. 5.

Stracener, D.W. Nucl. Inst. Meth. B204 (2003) 42. Blackmon, J.C. et al., Nucl. Phys. A718 (2003) 127. Shu, N. et al., Chin. Phys. Lett. 20 (2003) 1470. Coc, A. et al., Astron. Astrophys. 357 (2000) 561. F.-K. Thielemann et al., Adv. Nuclear Astrophysics 525 (1987) 1; http://quasar.physik.unibas.ch/∼tommy/adndt.html#reaclib. 6. M.S. Smith et al., U.S. Nuclear Data Program Astrophysics Task Force Report, unpublished (1995); http://www.phy.ornl.gov/astrophysics/data/task/taskforce report.html.