1 Decay studies of r-process nuclei Karl-Ludwig Kratz - Max-Planck-Institut für Chemie, Mainz, Germany - Department of Physics, Univ. of Notre Dame, USA T 1/2 PnPn SnSn nn  HRIBF 2006

2 scaled theoretical solar r-process scaled solar r-process Nb Zr Y Sr Mo Ru Rh Pd Ag Ba La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Hf Os Ir Pt Au Pb Th U Ga Ge Cd Sn Elemental abundances in UMP halo stars r-process observables Solar system isotopic abundances, N r,  “FUN-anomalies” in meteoritic samples isotopic composition Ca, Ti, Cr, Zr, Mo, Ru, Nd, Sm, Dy ↷ r-enhanced Historically, nuclear astrophysics has always been concerned with interpretation of the origin of the chemical elements from astrophysical and cosmochemical observations description in terms of specific nucleosynthesis processes (already B²FH, 1957).  [‰] ALLENDE INCLUSION EK Mass number CS abundances T 9 =1.35; n n = R-process observables, Bi

3 Nuclear-data needs for the classical r-process  nuclear masses S n -values  r-process path Q , S n -values  theoretical  -decay properties, n-capture rates   -decay properties  neutron capture rates  fission modes T 1/2  r-process progenitor abundances, N r,prog P n  smoothing N r,prog N r,final (N r,  )  RC +  DC  smoothing N r,prog during freeze-out SF,  df, n- and -induced fission  “fission (re-) cycling”; r-chronometers  -decay freeze-out  nuclear structure development - level systematics - “understanding”  -decay properties - short-range extrapolation into unknown regions

4 History and progress in measuring r -process nuclei Definition: r-process isotopes lying in the process path at freeze-out ↷ when r-process falls out of (n,  )-( ,n) equilibrium even-neutron isotopes ↷ “waiting points” important nuclear-physics property T 1/2 odd-neutron isotopes ↷ connecting the waiting points important nuclear-physics property S n   n.  In 1986 a new r-process astrophysics era started: at the ISOL facilities OSIRIS, TRISTAN and SC-ISOLDE T 1/2 of N=50 “waiting-point” isotope 80 Zn 50 (top of A  80 N r,  peak; “weak” r-process) T 1/2 of N=82 “waiting-point” isotope 130 Cd 82 (top of A  130 N r,  peak; “main” r-process) In 2006, altogether more than 50 r-process nuclei have been measured, which lie in the process path at freeze-out. These r-process isotopes range from 68 Fe to 139 Sb. The large majority of these exotic nuclei was identified at CERN/ISOLDE via the decay mode of  –delayed neutron emission.

5 What we knew already in K.-L. Kratz et al (Z. Physik A325; 1986) Exp. at old SC-ISOLDE with plasma ion-source quartz transfer line and  dn counting Problems: high background from -surface ionized 130 In, 130 Cs -molecular ions [ 40 Ca 90 Br] + Request: SELECTIVITY ! Shell-model (QRPA; Nilsson/BCS) prediction 1.0 T 1/2 (GT) = 0.3 s g 7/2,  g 9/2 Q  = 8.0 MeV IKMz – 155R(1986) T 1/2 = 230 ms T 1/2 = (195 ± 35) ms

6 The r-process “waiting-point“ nucleus 130 Cd QQ QP 4QP J  =1 + { g 7/2,  g 9/2 } SnSn T 1/2, Q , E(1 + ), I  (1 + ), log ft obtain a physically consistent picture! “free choice” of combinations : low E(1 + ) with low Q  high E(1 + ) with low Q  low E(1 + ) with high Q  high E(1 + ) with high Q  T 1/2 (GT) 233 ms 1130 ms 76 ms 246 ms (log ft=4.1)

7 Ag CdIn Cs Sn SbTeIXe Improvements since 1993 at PS-Booster ISOLDE Fast UC x target Neutron converter Laser ion-source Hyperfine splitting Isobar separation Repeller Chemical separation Multi-coincidence setup Request: Selectivity ! >10 5 the Ag “needle” in the Cs “haystack” Why ? How?

8 Request: Selectivity ! Laser ion-source (RILIS) Chemically selective, three-step laser ionisation of Cd into continuum 130 Cd 1669 keV 130 Cd 1732 keV Laser ON Laser OFF 130 Sb 1749 keV Energy [keV]  -singles spectrum Laser ON Laser OFF Comparison of Laser ON to Laser OFF spectra Properties of the laser system: Efficiency ≈ 10% Selectivity ≈ s 2 1 S 0 5s 5p 1 P 1 5s 5d 1 D nm nm 228.8nm Cd

9 Mass scan at HRS (ISOLDE) in 2002; efficiency corrected in reality, „on a good day…“  M/M ≈ 1/4000 DM/M=7.5*10 -5 HRS design  ≥ 1/10 4 Request: Selectivity ! Isobar separation In Cs Cd Cd In with HRS !

10 Request: Selectivity ! Chemistry in the transfer line between target and ion-source ↷ thermochromatography Deposition of Zn, Rb, Ag, In, Cd and Cs in a quartz tube with a temperature gradient  separation Cd, from Cs, In Prototype UC x target at CERN/ISOLDE with temperature-controlled quartz transfer-line  Oct Diploma thesis C. Jost (2005)

11 Surprises high [ g 7/2  g 9/2 ] 1 + state weakening of the g 7/2 -  g 9/2 residual interaction high Q  -value 130 In 81 OXBASH (B.A. Brown, Oct. 2003) (old) (new) reduction of the TBME (1+) by 800 keV Full spectroscopy 130 Cd decay

Fe Co Ni Cu Zn Ga Ge As Se Br Kr Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Z N Sb Te I Xe Cs Ba Snapshots: r-process paths for different neutron densities heaviest isotopes with measured T 1/2 g 9/2 d 5/2 s 1/2 g 7/2 d 3/2 h 11/2 g 9/2 p 1/2 p 3/2 f 5/2 f 7/2

Fe Co Ni Cu Zn Ga Ge As Se Br Kr Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Z N Sb Te I Xe Cs Ba R-process path for n n =10 20 „waiting-point“ isotopes at n n =10 20 freeze-out n n =10 20

Fe Co Ni Cu Zn Ga Ge As Se Br Kr Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Z N Sb Te I Xe Cs Ba „waiting-point“ isotopes at n n =10 23 freeze-out R-process paths for n n =10 20 and (T 1/2 exp. : 28 Ni – 31 Ga, 36 Kr, 37 Rb, 47 Ag – 51 Sb) n n =10 23 n n =10 20

Fe Co Ni Cu Zn Ga Ge As Se Br Kr Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Z N Sb Te I Xe Cs Ba (T 1/2 exp. : 28 Ni, 29 Cu, 47 Ag – 50 Sn) boulevard R-process boulevard for n n =10 20, and „waiting-point“ isotopes at n n =10 26 freeze-out n n =10 23 n n =10 26 n n =10 20

16... resulting from new experimental and theoretical nuclear structure information: better understanding of shape of and matter flow through the major r-process bottle-neck at the A  130 N r,  peak no justification to question waiting-point concept (Langanke et al., PRL 83, 199; Nucl. Phys. News 10, 2000) no need to request sizeable effects from -induced reactions (Qian et al., PRC 55, 1997) Astrophysical consequences  r-process abundances in the Solar System and in UMP Halo stars......are governed by nuclear structure! Nuclear masses from AMDC, 2003 ETFSI-Q Normalized to N r,  ( 130 Te) Longer T 1/2 ! „short“ T 1/2 „long“ T 1/2

17 Abundance clues and constraints Observations versus calculations - solar system - UMP halo stars Conditions for „main“ and „weak“ r-process - n-densities - entropies Split between the two r-processes I (Wasserburg et al.) - below N=82 R-process chronometric pairs - Th/Eu, Th/U - new: Th/Hf Ages of UMP stars, Galaxy and Universe Suggestions on r-process sites Galactic chemical evolution (Un-) importance of fission recycling

18 Conclusion nuclear-physics data for explosive nucleosynthesis calculations still unsatisfactory !  better global models for all nuclear shapes (spherical, prolate, oblate, triaxial, tetrahedral,…) and all nuclear types (even-even, odd-particle, odd-odd)  more measurements masses ! gross  -decay properties level systematics full spectroscopy of selected key“ waiting-point isotopes Despite impressive experimental and theoretical progress, situation of with sufficiently large SP model space,