The origin of heavy elements in the solar system

1. The origin of heavy elements in the solar system (Pagel, Fig 6.8) each process contribution is a mix of many events !

2. Heavy elements in Metal Poor Halo Stars CS22892-052red (K) giantlocated in halodistance: 4.7 kpcmass ~0.8 M_sol [Fe/H]= -3.0 [Dy/Fe]= +1.7 recall:[X/Y]=log(X/Y)-log(X/Y)solar old stars - formed before Galaxy was mixedthey preserve local pollution from individual nucleosynthesis events

3. A single (or a few) r-process event(s) CS22892-052 (Sneden et al. 2003) solar r CosmoChronometer abundance log(X/H)-12 NEW:CS31082-001 with U(Cayrel et al. 2001) + Age: 16 3 Gyr(Schatz et al. 2002 ApJ 579, 626) - element number other, secondr-process to fillthis up ?(weak r-process) main r-processmatches exactly solar r-pattern conclusions ?

4. Overview heavy element nucleosynthesis

5. neutron capture timescale: ~ 0.2 ms Rapid neutroncapture b-decay Equilibrium favors“waiting point” (g,n) photodisintegration The r-process Temperature: ~1-2 GK Density: 300 g/cm3 (~60% neutrons !) Seed Proton number Neutron number

6. show movie

7. Waiting point approximation Definition: ASSUME (n,g)-(g,n) equilibrium within isotopic chain How good is the approximation ? This is a valid assumption during most of the r-process BUT: freezeout is neglected Freiburghaus et al. ApJ 516 (2999) 381 showed agreement with dynamical models Consequences During (n,g)-(g,n) equilibrium abundances within an isotopic chain are given by: • time independent • can treat whole chain as a single nucleus in network • only slow beta decays need to be calculated dynamically • neutron capture rate independent(therefore: during most of the r-process n-capture rates do not matter !)

8. Endpoint of the r-process r-process endedby n-induced fission or spontaneousfission (different pathsfor different conditions) (Goriely & Clerbaux A&A 348 (1999), 798 b-delayed fission spontaneous fission n-induced fission n-capture (DC) b- (Z,A) (Z,A) fission fission fission (Z,A+1) fission barrier (Z,A+1) (Z+1,A)

9. Consequences of fission Fission produces A~Aend/2 ~ 125 nuclei modification of abundances around A=130 peak fission products can serve as seed for the r-process - are processed again into A~250 region via r-process - fission again fission cycling ! Note: the exact endpoint of the r-process and the degree and impact of fission are unknown because: • Site conditions not known – is n/seed ratio large enough to reach fission ? (or even large enough for fission cycling ?) • Fission barriers highly uncertain • Fission fragment distributions not reliably calculated so far (for fission from excited states !)

10. Role of beta delayed neutron emission Neutron rich nuclei can emit one or more neutrons during b-decay if Sn<Qb (the more neutron rich, the lower Sn and the higher Qb) b- (Z,A) n Sn (Z+1,A-1) g (Z+1,A) If some fraction of decay goes above Sn in daughter nucleusthen some fraction Pnof the decays will emit a neutron (in addition to e-and n)(generally, neutron emission competes favorably with g-decay - strong interaction !)

11. during r-process: none as neutrons get recaptured quicklyduring freezeout : Effects: • modification of final abundance • late time neutron production (those get recaptured) Calculated r-process production of elements (Kratz et al. ApJ 403 (1993) 216): after b-decay before b-decay smoothing effect from b-delayed n emission !

12. Example: impact of Pn for 137Sb A=136 ( 99%) A=137 ( 0%) Cs (55) r-processwaiting point Xe (54) Pn=0% I (53) Te (52) Pn=99.9% Sb (51) Sn (50) In (49) Cd (48) Ag (47) r-process waiting point

13. Summary: Nuclear physics in the r-process

14. First NSCL experiment The r-process path r-process abundance distribution r-processpath RIA Reach New MSU/NSCL Reach Known (Reach for half-life)

15. National Superconducting Cyclotron Laboratory atMichigan State University New Coupled Cyclotron Facility – experiments since mid 2001 Ion Source:86Kr beam 86Kr beam140 MeV/u Tracking (=Momentum) TOF start Implant beam in detectorand observe decay 86Kr hits Be target and fragments TOF stop dE detector Separated beamof r-processnuclei Fast beam fragmentation facility – allows event by event particle identification

16. Installation of D4 steel, Jul/2000

17. First r-process experiments at new NSCL CCF facility (June 02) • Measure: • b-decay half-lives • Branchings for b-delayed n-emission • Detect: • Particle type (TOF, dE, p) • Implantation time and location • b-emission time and location • neutron-b coincidences New NSCL Neutron detectorNERO 3He + n -> t + p neutron Fast Fragment Beam Si Stack (fragment. 140 MeV/u 86Kr)

18. NSCL BCS – Beta Counting System • 4 cm x 4 cm active area • 1 mm thick • 40-strip pitch in x and y dimensions ->1600 pixels Si Si Si BCS b

19. NERO – Neutron Emission Ratio Observer BF3 Proportional Counters 3He Proportional Counters • Specifications: • 60 counters total • (16 3He , 44 BF3) • 60 cm x 60 cm x 80 cm • polyethylene block • Extensive exterior • shielding • 43% total neutron • efficiency (MCNP) Polyethylene Moderator Boron Carbide Shielding

20. June 2002 Data – preliminary results Mainz: K.-L. Kratz, B. Pfeiffer PNNL: P. Reeder Maryland/ANL: W.B. Walters, A. Woehr Notre Dame: J. Goerres, M. Wiescher NSCL:P. Hosmer, R. Clement, A. Estrade, P.F. Mantica, F. Montes, C. Morton, M. Ouellette, P. Santi, A. Stolz r-processpath 77Ni 74Co 71Fe Gated b-decay time curve(implant-decay time differences) Energy loss Time of flight Fast RIBs: • cocktail beams • no inflight decay losses • measure with low rates (>1/day)

21. Neutron Data With neutron in addition Nuclei with decay detected 420 420 Nn 370 370 DE (arb units) DE(arb units) 320 320 76Ni 76Ni 73Co 73Co 270 270 220 220 450 500 550 350 400 450 500 550 350 400 TOF (arb units) TOF (arb units) neutron detection efficiency (neutrons seen/neutrons emitted)