Nuclear Spectroscopy of Very Neutron-rich rich Ag and Cd Isotopes

Transcription

1 132 Nuclear Spectroscopy of Very Neutron-rich rich Ag and Cd Isotopes Iris Dillmann*,# for the Mainz- Maryland- Oslo- CERN/ ISOLDE- Collaboration * Institut für Kernchemie, Universität Mainz (Germany) # Departement Physik und Astronomie, Universität Basel (Switzerland)

2 The r-process r at the N=82 shell 130 Te 130 Sb 130 Cd is the most important nucleus before the break-out out of the magic N=82 shell build-up of the solar r-abundance peak at 130 Te N= Sn 131 Sn 132 Sn 133 Sn 134 Sn 135 Sn 136 Sn 130 In 131 In 132 In 133 In 129 Cd 130 Cd 131 Cd 132 Cd 133 Cd 126 Ag 127 Ag 128 Ag 129 Ag 130 Ag 123 Pd 125 Rh 127 Pd 128 Pd 121 Rh (n ) (n ) 126 Rh 127 Rh n, r-process boulevard for T 9 =1.35 and n n =10 24 cm -3

3 What we already knew in 1986 identification of the first two r-process waiting-points : 80 Zn 50 (at TRISTAN and OSIRIS) 130 Cd 82 (at the old SC-ISOLDE) Q = 8.0 MeV IKMz 155R(1986) Problem: use of a plasma ion-source High background of [ 40 Ca 90 Br] + ( dn) surface-ionized 130 In, 130 Cs Too high isobaric background to perform -spectroscopy! R.L. Gill et al., Phys. Rev. Lett. 56 (1986) 1874 E. Lund et al., Phys. Scr. 34 (1986) 614 K.-L. Kratz et al., Z. Phys. A 325 (1986) 489 g 7/2 g 9/ Shell-model (QRPA; Nilsson/BCS) prediction T 1/2 (GT) = 0.3 s

4 Neutron-rich rich beams at CERN/ ISOLDE Mass separator: GPS/ HRS Technical improvements To the beamlines 1: Neutron converter 2: Laser Ion Source 3: High Resolution Separator Primary beam: GeV protons, Intensity: ca p/pulse ISOLDE Laser System: 3 copper vapor lasers 2 dye lasers (cw, frequency tripling by two BBO cristals UV) Transfer line (Nb) ~2200 K UC 2 -C- Target Converter (Ta or W)

5 UC 2 -C Target #208: W-surface with W- converter target Technical improvements 1: Neutron converter 2: Laser Ion Source 3: High Resolution Separator converter one Cu-vapor-laser as oscillator two dye-laser are pumped with 511 or 578 nm frequency-tripling by two BBO-cristals to get UV-radiation

6 The MOPSBALL* -detector setup The Mainz dn-detector detector setup *engl. pug-ball Beam Moving Tape Collector 64 3 He long counters in three rings (~ 33% efficiency) -Telescope HPGe (efficiency 55-70%) beam -detector paraffine

7 Laser ON vs. Laser OFF mode -singles spectrum T 1/2 by multiscaling of dn 130 Cd 1669 kev Cd 1732 kev 130 Sb 1749 kev Counts 100 Laser ON 10 Laser on Laser OFF 1 Laser off Difference Energy [kev] Time [ms] Laser OFF: only surface-ionized elements with low ionization potentials (e.g. Cs, In) Laser ON: surface-ionized elements + laser-ionized Ag & Cd

8 Spectroscopy of neutron-rich rich even-mass Ag isotopes 126 Ag 95 ms Cd OXBASH 128 Ag 58 ms Cd OXBASH 130 Ag 35 ms (2+) 1395 (2+) ? 130 Cd OXBASH Reduced transition probability B(E2) ~ 1/E(2 + ) Larger quadrupole polarizability up to N= Cd 130 Cd?

9 129g Cd 129 Cd dn emission 129m Cd h 11/2 Q GT (9/2,11/2,13/2) - high l n S n 128 In 1 - (3 + ) d 3/2 h 11/2 (Q +x) GT (1/2,3/2,5/2) + low l n S n 128 In 1 - (3 + ) 129 In 129 In hard dn-spectrum mainly outer 3 He ring of the long counter soft dn-spectrum mainly inner 3 He ring 100 Counts 10 1 T 1/2 ( 129m Cd) = 104 (6) ms (d 3/2 isomer) T 1/2 ( 129g Cd) = 242 (8) ms (h 11/2 ground state) Time [ms] O. Arndt (Diploma Thesis; Universität Mainz, 2003)

10 129 Cd -decay 4 -lines identified incl. 8.5 s 334 kev transition (Genevey et al., Grenoble) different placement of s-isomer with our data possible >30 new -lines up to 4 MeV coincidence data analysis in progress 15 coincidence relationships, [experimental Q -value (theor kev)] J. Genevey et al., Phys. Rev. C67 (2003)

11 Half-lives lives for 130 Cd Cd T 1/2 ( 130 Cd)= 162 (7) ms T 1/2 ( 131 Cd)= 68 (3) ms T 1/2 ( 132 Cd)= 97 (10) ms T 1/2 ( 133 Cd)= 55 (20) ms M. Hannawald et al. (Nucl. Phys. A688; 2001) O. Arndt (Diploma Thesis; Universität Mainz, 2003) Counts T 1/2 ( 133 Cd)= 55 (20) ms T 1/2 ( 132 In) = 206 ms 0, Time [ms]

12 131 Cd -decay Prediction QRPA (pure GT, Folded-Yukawa potential, Lipkin-Nogami pairing, low Q from FRDM): T 1/2 (GT)= 943 ms, P n (GT)= 99% Experiment (Hannawald et al.): T 1/2 = 68 ms, P n = 3.4% modified QRPA calculation (GT+ff, Nilsson potential with 0.7*l²-term, Lipkin-Nogami pairing, high Q from ETFSI-Q): T 1/2 (GT+ff)= 95 ms, P n (GT+ff)= 3% 2-3 possible -lines (low statistics): kev, 4484 kev and 4576 kev no coincidence data b/c of low yields M. Hannawald et al., Phys. Rev. C62, (2000) B. Pfeiffer et al., Nucl. Phys. A693, 282 (2001)

13 131 Cd -decay predictions

14 130 Cd -decay 21 new -lines up to 6 MeV 2 -coincidences (possibly 2 more indications) Q -value measured decay scheme incl. 15 transitions I. Dillmann et al., Phys. Rev. Lett. 91, (2003)

15 130 Cd decay scheme Surprises high [ g 7/2 g 9/2 ] 1 + state 389 kev level ( s-isomer confirmed; GSI) high Q -value weakening of the g 7/2 - g 9/2 residual interaction OXBASH (B.A. Brown, Oct. 2003) (new) (old) reduction of the TBME (1+) by 800 kev In 81

16 Level systematics for the lowest 1 + state in neutron-rich rich even-mass In isotopes Experimental OXBASH (B.A. Brown, Oct. 2003) (new) kev kev kev kev (old) Reduction of the TBME (1+) by 800 kev 124 In In In In In 81 Konfiguration 3+: d 3/2 g 9/2 Konfiguration 1+: g 7/2 g 9/2 Konfiguration 1-: h 11/2 g 9/2 Difference between 3+ and 1+ gives level space between d 3/2 and g 7/2

17 Comparison of experimental values for 130 Cd and input parameters from OXBASH -decay T 1/2 Q -value Experimental OXBASH (Oct. 2003) 162 ms 233 ms 8344 kev 8753 kev characteristics of the lowest 1 + -level: -feeding I log ft-value E(1+) 70% 100% kev 2181 kev Good agreement, BUT only with reduction of the TBME of the 1 + state by 800 kev (no explanation for this!)

18 Q -value of of 130 Cd 130 Cd Way-Wood diagram Z=50 and N=82 shell closures visible High Q -value is a clear signature for an N=82 shell quenching below 132 Sn 50 Mass model predictions Hilf et al. (GTNM, 1976) Möller et al. (FRDM, 1995): Aboussir et al. (ETFSI, 1995): Duflo & Zuker (1995) Dobaczewski et al. (HFB/SkP, 1996): Pearson et al. (ETFSI-Q, 1996): Audi & Wapstra (Mass Eval., 1997): Goriely et al. (HFBCS, 2001) Samyn et al. (HFB-2, 2002) Brown et al. (local OXBASH, 2003): Q 7.57 MeV 7.43 MeV 7.87 MeV 7.56 MeV 8.93 MeV 8.30 MeV 8.50 MeV 7.00 MeV 7.64 MeV 8.75 MeV

19 Normalized mass deviations of 50 Sn and 48 Cd isotopes Comparison to mass model predictions with shell quenching HFB/SkP ETFSI-Q HFB-2 and Audi & Wapstra Evaluation (AMDC, 2003) relative to the unquenched FRDM Different behavior beyond N=82 in Cd chain Only ETFSI-Q with right trend! Need for experimental masses of 129 Cd, 131 Cd, 132 Cd I. Dillmann et al., Phys. Rev. Lett. 91, (2003)

20 Nuclear structure consequences... a number of recent nuclear structure surprises in the 132 Sn region, e.g. trend of low E(2+) larger quadropole polarizability in n-rich Cd isotopes up to N=80 low T 1/2 and P n in N= Cd importance of ff-strength high E(1 + ) and high Q in N= Cd decay weakening of the g 7/2 - g 9/2 residual interaction best agreement with experimental masses is given by quenched models (ETFSI-Q, HFB-SkP) evidence for N=82 shell quenching Shell structure around 132 Sn is not yet fully understood!

21 Astrophysical consequences (I) Dynamic r-process calculations (T 1/2,P n from exp. + QRPA S n,q from AMDC + ETFSI-Q) 128 Pd Classical waiting-point concept T 1/2 (N=82)~N r, too simple! 132 Sn apart from T 1/2 (N=82) also effect from S n (N=83) on N r,prog N r, 131 In 129 Ag 130 Cd N(mag.) r-progenitors act as waiting points for different n n - ranges

22 Astrophysical consequences (II)...mainly resulting from new nuclear structure information: weakening of the TBME: half-lives of so far unknown N=82 waiting-point nuclei ( 128 Pd, 127 Rh, 126 Ru and 125 Tc) will become longer than predicted by recent shellmodels better understanding of formation and shape of, as well as r-process matter flow through 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) 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)

23 MOPSBALL Productions would like to thank the following persons: Karl-Ludwig Kratz, Andreas Wöhr (Notre Dame), William B. Walters (Maryland), Oliver Arndt, Alex Brown (MSU), Michael Hannawald, Per Hoff (Oslo), Thomas Kautzsch, Ulli Köster (CERN), Peter Möller (LANL), Bernd Pfeiffer, Darek Seweryniak (Argonne), Jason Shergur (Argonne), Friedel Thielemann (Basel) and the CERN/ ISOLDE Collaboration