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Beta-decay studies of neutron-rich Fe, Co and Ni isotopes at LISOL using the MINIBALL detector

Beta-decay studies of neutron-rich Fe, Co and Ni isotopes at LISOL using the MINIBALL detector. Dieter Pauwels, Oleg V. Ivanov, Maria Sawicka, Mark Huyse, Piet Van Duppen, Thomas E. Cocolios, Yuri Kudryavtsev, Johnny Gentens, Paul Van den Bergh, Irina Stefanescu, Jarno Van de Walle,

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Beta-decay studies of neutron-rich Fe, Co and Ni isotopes at LISOL using the MINIBALL detector

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  1. Beta-decay studies of neutron-rich Fe, Co and Ni isotopes at LISOL using the MINIBALL detector Dieter Pauwels, Oleg V. Ivanov, Maria Sawicka, Mark Huyse, Piet Van Duppen, Thomas E. Cocolios, Yuri Kudryavtsev, Johnny Gentens, Paul Van den Bergh, Irina Stefanescu, Jarno Van de Walle, and MINIBALL Collaboration Katholieke Universiteit Leuven, Instituut voor Kern- & Stralingsfysica

  2. 68Ni  (-1 +1) 68Ni  (+1) 68Ni  (+1+1) g9/2 g9/2 ng9/2 J.Van Roosbroeck,Phys.Rev.C 692004 J.Van Roosbroeck,Phys.Rev.C 692004 S.Franchoo Ph.D.Thesis, Leuven 1999 f5/2 n-1 n+1 N=40 65Fe 69Cu 67Co 67Ni 68Ni 68Co 66Co 70Cu 65Co 66Fe 67Fe 68Fe 68Cu 69Ni 1+ 5/2- 5/2- 1/2- 9/2+ 2- 1+ 1980 1110 2553 1214 842 694 369 p1/2 p1/2p1/2-1 f5/2 ng9/2 p3/2 np1/2 -1 (ng9/2)+2 2+ 84 p+1 1+ 242 1+ 0 3/2- 0 6- 0 p3/2p1/2-1 p3/2 p3/2 ng9/2 68Ni  n-1 68Ni  n+1 Z=28 np3/2 -1 (ng9/2 )+2 p-1 ng9/2 (np1/2 )-2 W.F. Mueller,Phys.Rev.Lett. 83,1999 5/2- 3/2- 1/2- 9/2+ 1007 1400 915 321 nf5/2 -1 (ng9/2 )+2 L. Weissman,Phys.Rev.C 591999 nf5/2 -1 ? ? ? np1/2 -1 (ng9/2 )+2 1/2- 0 9/2+ 0 np1/2 -1 ng9/2 Almost nothing is known about nuclear structure of 65,66,67,68Co Nuclear Structure around semi-doubly magic 68Ni To probe N=40 subshell gap we can look for levels interpreted as particle(hole) 68Ni

  3. Leuven Isotope Separator-On-Line Cyclotron 30 MeV Proton Beam Mass Separator Laser-ionized reaction products Buffer Gas 238U Targets (10 mg/cm2) Ion Guide (SPIG) Data-acquisition System XIA DGF-4C Gas Cell A+ + e- Lasers IGOR A* b-g Detection Set-up A Experimental set-up

  4. 6-fold segmented MINIBALL Clusters Beam 3 Plastic DE b-detectors Detection set-up

  5. Analysis of b-gated g events (data 2005) 67Fe 189 keV 67Fe 2080 keV 67Fe 2054 keV 67Fe 2087 keV 67Co 694 keV 67Fe 1251 keV Lasers ON Fe Lasers OFF

  6. T1/2=411(32) ms b- 67Fe 2054 2080 2087 1251 1251 572 189 67Co 67Fe decay scheme after bg analysis T1/2=425(20) ms Lasers on Co L. Weissman et al. PRC59 (1999) 2004 b- 67Co (5/2-) 2155 (9/2+) 313 (5/2-) 694 (1/2-) 67Ni

  7. 694 keV 491 keV Single g spectrum: welcome 491 keV! (data 2005) Lasers ON Fe Lasers OFF Similar half-lives No b coincidences No g coincidences COMPLETE ANSWER: b-g-g CORRELATIONS

  8. b- 491 ? 67Fe 189 b- 67Co 694 67Ni … t (ms) -200 0 200 … … ttrig Cycle structure LISOL and Correlations (data 2006) Activity@tape t Beam ON Beam OFF 1 macro-cycle

  9. Random subtracted Correlations Random events Result: single g’s before (-200 – 0 ms) a b-694 keV trigger Correlated events 491 keV 511 keV 694 keV Control random events!

  10. b- 67Fe 189 b- 67Co 694 491 keV after b-189 keV! 67Ni 491 keV in 67Co! b- 67Fe 189 483 (56) ms 499 (24) ms 512 (43) ms 491 b- 67Co 694 67Ni Random substracted results (I) 491 keV events coming before b-694 keV 491 keV events coming after b-189 keV T1/2: 329 (28) ms T1/2: 483 (56) ms 329 (28) ms 425 (20) ms PRC 59 2004 491 ?

  11. Grand-daughter correlations!!! • Branching ratios (preliminary) 491 0.98 (5) 67Co 189 0.05 (15) 491 0.95 (15) 67Co Random substracted results (II) • Placing isomer • T1/2 isomeric and ground state from direct correlations

  12. 50 1g9/2 2p1/2 1f5/2 2p3/2 28 1f7/2 20 1d3/2 2s1/2 1d5/2 Speculative interpretation 411 (32) ms [440]1/2+ ?? b- 50% 2054 2080 2087 50% 189 499 (24) ms [321]1/2- ?? 491 [303]7/2- 329 (28) ms 7/2-p-1 b- [321]1/2- 694

  13. Conclusions and outlook • 67Co level scheme fully analyzed • Isomerism in 67Co • Isomer @ 491 keV and g.s. 67Co fully characterized thanks to bgg correlations • Placement, T1/2, Branching • Correlations in seconds domain thanks to • Pure beams from laser ionization • Read-out on a event-on-event basis • Segmentation of MINIBALL clusters: Multiplicity 1 491 keV g events • need for SM calculations with 48Ca core: • Allow for proton excitations across the Z=28 gap • Interpretation of the isomer • New beam time @ LISOL is granted for a 64-66Fe b-decay campaign in July 2007: onset of deformation?

  14. Limitations correlations Simulation

  15. No correlation! Correlation! Random subtracted results 694 keV events coming before b-694 keV 491 keV events coming before b-694 keV

  16. Randoms: strategy Step 1: A dataset of single g, b and b-g histograms Hi in steps of 5 ms. Step 2: Scan the trigger distribution in steps of 5 ms to know the number of triggers Ntr. Step 3: Build the random (b-)g’s from the dataset and normalize to Ntr. 5 ms 200 0 tcorr (ms) tcorr=Ntr*5 ms trandom=Dtmeas/tcycle*5 ms ttrig tcycle

  17. Neutron-induced events during the proton beam ON! 85 ms 115 ms Neutron-induced background (data 2006) Macro-cycle: 10s/0s/1 Micro-cycle: 100ms/100ms Singleg events during and 15 ms after proton beam ON are rejected.

  18. b- 67Fe 189 b- 67Co 694 67Ni Result: e.g. single g’s before (-200 – 0 ms) or after (0 - 200 ms) a b-694 keV trigger BEFORE 491 keV 511 keV 694 keV Count-rate g’s: ~35 Hz # triggers:6353 DT/histogram/trigger:85 ms # randoms/histogram: ~19000 491 ? AFTER In 67Co!!

  19. 50 E 50 1g9/2 40 40 2p1/2 1f5/2 2p3/2 28 28 1f7/2 n-1 n+1 N=40 p n p+1 Z=28 p-1 70Co 69Co 68Cu 69Cu 70Cu 71Cu 72Cu 66Ni 67Ni 68Ni 69Ni 69Fe 67Fe 65Co 66Co 67Co 68Co 70Ni 67Cu 68Fe 66Fe 65Fe 64Fe 71Ni 67Fe situated on the chart of nuclides Experiments: 1. Nov. 2005 2. June 2006 Z N

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