Nuclear Data Needs for r-Process Calculations

1. Nuclear Data Needs for r-Process Calculations Bradley Meyer Clemson University

2. Four Requirements for Meaningful Measurements for Astrophysics (The et al. 1998) • An appropriate astrophysical model of events significant for nucleosynthesis . (“Appropriate” does not necessarily = “correct”!) • An observable from the nucleosynthesis process, usually an abundance result that is either known or measurable. • The dependency of the value of the observable on the value of a nuclear cross section. • An experimental strategy for measuring that cross section, or at least of using measurable data to better calculate it.

6. R-Process Observables • Production of heavy elements: • Neutron-to-seed ratio (~100) • Dependent on nuclear reactions at T9 > 4 • Details of final abundance distribution • Peaks • Freezeout abundances—smoothing • Dependent on nuclear reactions for T9<3

7. Appropriate Model? Which regime? • Low-entropy r-process • High-entropy r-process • High-entropy, fast expansion r-process

8. Production of heavy nuclei in the first place (n/s~100) • Depends on weak interaction physics—electron capture rates, neutrino-nucleus interaction rates • Quasi-equilibrium: nuclear masses and partition functions • Three-body reaction rates (α+α+α12C, α+α+n9Be and 9Be+α12C+n • Charged-particle reactions on proton-rich isotopes for the high-entropy, fast expansion regime

9. Meyer and Wang (2007)

10. Production of 4He from n, p (T9 = 10 – 8)

11. Production of 4He from n, p (T9 < 8) Too few heavy nucleineutrons and protons don’t assemble into alpha particles and heavier speciesmany free neutrons and protons around to bombard the few heavy nuclei present

12. Meyer and Wang (2007)

13. Details of the Final R-Process Abundances • Depends on: • Nuclear masses • Neutron-capture cross sections • Beta-decay rates • Spins and partition functions • Fission yields

14. Reference calculation

15. Neutron-capture cross sections

16. Beta-decay rates

17. Spins and Partition Functions

19. Four Requirements for Meaningful Measurements for Astrophysics (The et al. 1998) • An appropriate astrophysical model of events significant for nucleosynthesis . (“Appropriate” does not necessarily = “correct”!) • An observable from the nucleosynthesis process, usually an abundance result that is either known or measurable. • The dependency of the value of the observable on the value of a nuclear cross section or other nuclear property. • An experimental strategy for measuring that cross section, or at least of using measurable data to better calculate it.

20. What is libnucnet? • A C toolkit for storing and managing nuclear reaction network. • Built on top of libxml (the gnome XML parser and toolkit) and gsl (the GNU scientific library). • Released under the GNU General Public License.

21. History of libnucnet • Original goal—online nucleosynthesis tool • Problem—input over the web • Solution—XML (eXtensible Markup Language) • Libxml as input and output • Libxml has powerful built-in data structures (lists, hashes, trees, etc.)—build new nucleosynthesis code on top of libxml • Hashes provide easy access to data—particularly useful for experimentalists

22. Features of libnucnet • Intrinsically 3-d • Easily handles arbitrary nuclear network (bbn to r-process), including (any number of) isomeric states • Reactions are handled the way humans think about them: “c12 + he4  o16 + gamma” or “o15  n15 + positron + neutrino_e” • Hierarchically structured • Naturally uses xml as input (allows for schemas, stylesheets, xpath selection, etc.) • Read and validate data across the web • Allows for user-supplied screening and NSE correction factor functions.

23. Structure of libnucnet • Libnucnet__Nuc.c/h: a collection of nuclei • Libnucnet__Species: a species • Libnucnet__Nuc: a collection of species • Libnucnet__Reac.c/h: a collection of nuclear reactions • Libnucnet__Reaction: a reaction • Libnucnet__Reac: a collection of reactions • Libnucnet.c/h: a network and a collection of zones • Libnucnet__Net: a Libnucnet__Nuc + Libnucnet__Reac • Libnucnet__Zone: a physical zone • Libnucnet: a network plus a collection of zones

24. XML Data for the nuclear collection <nuclear_data> <!--n--> <nuclide> <z>0</z> <a>1</a> <source>Tuli (2000)</source> <mass>8.071</mass> <spin>0.5</spin> <partf_table> <point> <t9>0.01</t9> <log10_partf>0</log10_partf> </point> <point> <t9>0.15</t9> <log10_partf>0</log10_partf> </point> </partf_table> </nuclide> … </nuclear_data>

25. XML Data for the nuclear collection (with states) <!--al26--> <nuclide> <z>13</z> <a>26</a> <states> <state id="g"> <source>Tuli (2000) + Gupta and Meyer (2001)</source> <mass>-12.21</mass> <spin>5</spin> <partf_table> ... </partf_table> </state> <state id="m"> <source>Tuli (2000) + Gupta and Meyer (2001)</source> <mass>-11.982</mass> <spin>0</spin> <partf_table> ,,, </partf_table> </state> </states> </nuclide>

26. XML Data for Reactions—a rate table <reaction_data> <!-- h1 + n to h2 + gamma --> <reaction> <source>Smith et al. (1993)</source> <reactant>h1</reactant><reactant>n</reactant> <product>h2</product><product>gamma</product> <rate_table> <point> <t9>0.001</t9> <rate>4.6168E+04</rate> <sef>1.000</sef> </point> … </rate_table> </reaction> …. </reaction_data>

27. XML Data for Reactions—a single rate <!-- o19 to f19 + electron + anti-neutrino_e --> <reaction> <source>Nuclear Data tables</source> <reactant>o19</reactant> <product>f19</product> <product>electron</product> <product>anti-neutrino_e</product> <single_rate>1.6251e-01</single_rate> </reaction>

28. XML Data for Reactions—a non-smoker fit • <!– ne15 + n to ne16 + gamma -> • <reaction> • <source>ADNDT (2001) 75, 1 (non-smoker)</source> • <reactant>ne15</reactant> <reactant>n</reactant> • <product>ne16</product> <product>gamma</product> • <non_smoker_fit> • <Zt> 10</Zt> • <At> 15</At> • <Zf> 10</Zf> • <Af> 16</Af> • <Q> 8.071000</Q> • <spint> 0.0000</spint> • <spinf> 0.0000</spinf> • <TlowHf>-1.0000</TlowHf> • <Tlowfit> 0.0100</Tlowfit> • <acc> 1.900000e-06</acc> • <a1> 6.225343e+00</a1> • <a2> 1.023384e-02</a2> • <a3>-1.272184e+00</a3> • <a4> 3.920127e+00</a4> • <a5>-1.966720e-01</a5> • <a6> 1.394263e-02</a6> • <a7>-1.389816e+00</a7> • <a8> 2.983430e+01</a8> • </non_smoker_fit> • </reaction>

29. Zone data <initial_mass_fractions> <multiple_zones> <zone label1="x1" label2="y1" label3="z1"> <nuclide> <z>0</z> <a>1</a> <x>0.5</x> </nuclide> <nuclide> <z>1</z> <a>1</a> <x>0.5</x> </nuclide> </zone> … </multiple_zones> </initial_mass_fractions>

30. Where we’re headed • Release of libnucnet 0.3 imminent • Put network code based on libnucnet on line this fall • My research with libnucnet • Study nuclear network equilibria (NSE, QSE, etc.) • Build a multi-zone Galactic chemical evolution network on top of libnucnet.

31. Four Requirements for Meaningful Measurements for Astrophysics (The et al. 1998) • An appropriate astrophysical model of events significant for nucleosynthesis . (“Appropriate” does not necessarily = “correct”!) • An observable from the nucleosynthesis process, usually an abundance result that is either known or measurable. • The dependency of the value of the observable on the value of a nuclear cross section or other nuclear property. • An experimental strategy for measuring that cross section, or at least of using measurable data to better calculate it.