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Decay studies of r-process nuclei

Decay studies of r-process nuclei. s n g. T 1/2. S n. P n. . Karl-Ludwig Kratz. Max-Planck-Institut für Chemie, Mainz, Germany Department of Physics, Univ. of Notre Dame, USA. HRIBF 2006. R-process observables. Historically, nuclear astrophysics has always been concerned with

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Decay studies of r-process nuclei

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  1. Decay studies of r-process nuclei sng T1/2 Sn Pn  Karl-Ludwig Kratz • Max-Planck-Institut für Chemie, Mainz, Germany • Department of Physics, Univ. of Notre Dame, USA HRIBF 2006

  2. R-process observables • 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). Solar system isotopic abundances, Nr, T9=1.35; nn=1020 - 1028 , Bi r-process observables CS 22892-052 abundances isotopic composition Ca, Ti, Cr, Zr, Mo, Ru, Nd, Sm, Dy ↷ r-enhanced scaled solar r-process ALLENDE INCLUSION EK-1-4-1 scaled theoretical solar r-process Zr Pt Os Pb Cd Ru Ba d [‰] Nd Sn Sr Ga Pd Dy Mo Gd Er Ge Sm Ce Yb Ir Hf Y Rh La Nb Ag Ho Eu Pr Tb Au Lu Th Tm U Mass number Elemental abundances in UMP halo stars “FUN-anomalies” in meteoritic samples

  3. b-decay freeze-out Nuclear-data needs for the classical r-process • b-decay properties T1/2r-process progenitor abundances, Nr,prog Pn  smoothing Nr,prog Nr,final (Nr,) • nuclear masses Sn-values  r-process path Qb, Sn-values  theoretical b-decay properties, n-capture rates • neutron capture rates sRC + sDC  smoothing Nr,prog during freeze-out • fission modes SF, bdf, n- and n-induced fission  “fission (re-) cycling”; r-chronometers • nuclear structure development • level systematics • “understanding” b-decay properties • - short-range extrapolation into unknown regions

  4. History and progress in measuring r-process nuclei Definition: r-process isotopes lyingin the process path at freeze-out ↷ when r-process falls out of (n,g)-(g,n) equilibrium even-neutron isotopes↷“waiting points” important nuclear-physics property T1/2 odd-neutron isotopes ↷connecting the waiting points important nuclear-physics property Snsn.g In 1986 a new r-process astrophysics era started: at the ISOL facilities OSIRIS,TRISTAN and SC-ISOLDE T1/2 ofN=50“waiting-point” isotope80Zn50 (top of A80 Nr, peak; “weak” r-process) T1/2 ofN=82“waiting-point” isotope130Cd82 (top of A130 Nr, peak; “main” r-process) In 2006, altogether more than 50 r-process nucleihave been measured, which lie in the process path at freeze-out. • These r-process isotopes range from 68Fe to 139Sb. The large majority of these exotic nuclei was identified at CERN/ISOLDE via the decay mode of b–delayed neutron emission.

  5. What we knew already in 1986 ... Shell-model (QRPA; Nilsson/BCS) prediction 1+ 1.0 Q = 8.0 MeV T1/2 = 230 ms 1+ IKMz – 155R(1986) 6.0 1+ T1/2 = (195 ± 35) ms 1+ 5.0 1+ 1+ 4.0 1+ K.-L. Kratz et al (Z. Physik A325; 1986) 3.0 g7/2, g9/2 Exp. at old SC-ISOLDE with plasma ion-source quartz transfer line and dn counting 1+ 4.1 2.0 T1/2(GT) = 0.3 s Problems: high background from -surface ionized 130In, 130Cs -molecular ions [40Ca90Br]+ 1.0 1- 0 Request:SELECTIVITY !

  6. The r-process “waiting-point“ nucleus 130Cd ...obtain a physically consistent picture! T1/2, Q, E(1+), I(1+), log ft Q Sn 7.0 8.9 J=1+ {g7/2, g9/2} 2QP 4QP 1.2 2.9 “free choice” of combinations: T1/2(GT) 233 ms 1130 ms 76 ms 246 ms low E(1+) with low Qb high E(1+) with low Qb low E(1+) with high Qb high E(1+) with high Qb (log ft=4.1)

  7. Request: Selectivity ! Sb Te I Xe Sn Cd In Ag Cs Why ? the Ag “needle” in the Cs “haystack” How? Improvements since 1993 at PS-Booster ISOLDE • Fast UCx target • Neutron converter • Laser ion-source • Hyperfine splitting • Isobar separation • Repeller • Chemical separation • Multi-coincidence setup 50 800 >105

  8. Request: Selectivity ! 130Cd 1669 keV 130Sb 1749 keV 130Cd 1732 keV Laser ON Laser OFF Energy [keV] Laser ion-source (RILIS) Laser ON 510.6nm Comparison of Laser ON to Laser OFF spectra 5s 5d1D2 643.8nm 5s 5p1P1 Laser OFF 228.8nm 5s2 1S0 Cd g-singles spectrum Chemically selective, three-step laser ionisation of Cd into continuum Properties of the laser system: Efficiency ≈ 10% Selectivity ≈ 103

  9. Request: Selectivity ! Isobar separation HRS design DM/M ≥ 1/104 in reality, „on a good day…“ DM/M ≈ 1/4000 In Cd 2.000 ! DM/M=7.5*10-5 In 17.000 Cs Cd with HRS Mass scan at HRS (ISOLDE) in 2002; efficiency corrected

  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 UCx target at CERN/ISOLDE with temperature-controlled quartz transfer-line Oct. 2005 Diploma thesis C. Jost (2005)

  11. Full spectroscopy 130Cd decay • Surprises • high [ng7/2pg9/2] 1+ state • weakening of the ng7/2 - pg9/2 • residual interaction • high Qb-value OXBASH (B.A. Brown, Oct. 2003) 2598 1- 2515 0- 1+ 2181 (new) reduction of the TBME (1+) by 800 keV 1906 1- 1441 1- 1+ 1382 (old) 0- 895 473 3+ 1- 0 130In81

  12. Z N Snapshots: r-process paths for different neutron densities 82 84 86 88 90 92 94 Ba Cs Xe heaviest isotopes with measured T1/2 I Te Sb Sn In Cd Ag g9/2 Pd Rh Ru Tc Mo Nb Zr p1/2 Y Sr Rb p3/2 Kr Br Se As f5/2 Ge Ga Zn Cu Ni f7/2 Co Fe 42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 8082 h11/2 d3/2 g9/2 d5/2 g7/2 s1/2

  13. nn=1020 Z N R-process path for nn=1020 82 84 86 88 90 92 94 Ba Cs Xe I Te Sb Sn In Cd Ag Pd Rh Ru Tc Mo Nb Zr Y Sr Rb Kr Br Se As Ge Ga Zn Cu Ni Co Fe 42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 8082 „waiting-point“ isotopes at nn=1020 freeze-out

  14. nn=1020 nn=1023 Z N R-process paths for nn=1020 and 1023 82 84 86 88 90 92 94 Ba Cs Xe I Te Sb Sn In Cd Ag Pd Rh Ru Tc Mo Nb Zr Y Sr Rb Kr Br Se As Ge Ga Zn Cu Ni Co Fe 42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 8082 „waiting-point“ isotopes at nn=1023 freeze-out (T1/2 exp. : 28Ni – 31Ga, 36Kr, 37Rb,47Ag – 51Sb)

  15. nn=1020 nn=1023 nn=1026 Z N R-process boulevard for nn=1020, 1023 and 1026 82 84 86 88 90 92 94 Ba Cs Xe I Te Sb Sn In Cd Ag Pd Rh Ru Tc Mo Nb Zr Y Sr Rb Kr Br Se As Ge Ga Zn Cu Ni Co Fe 42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 8082 „waiting-point“ isotopes at nn=1026 freeze-out (T1/2 exp. : 28Ni, 29Cu, 47Ag – 50Sn)

  16. Astrophysical consequences Longer T1/2! • ... 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 Nr, 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 n-induced reactions • (Qian et al., PRC 55, 1997)  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 Nr,(130Te) „short“ T1/2 „long“ T1/2

  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 - 129I (Wasserburg et al.) • - below N=82 • (Un-) importance of fission recycling • Suggestions on r-process sites • Galactic chemical evolution • R-process chronometric pairs - Th/Eu, Th/U • - new: Th/Hf • Ages of UMP stars, Galaxy and Universe

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

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