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Proton and Two-Proton Decay of a High-Spin Isomer in 94 Ag

Proton and Two-Proton Decay of a High-Spin Isomer in 94 Ag. Ernst ROECKL GSI Darmstadt and Warsaw University. Experimental Techniques. Fusion-evaporation reactions 58 Ni( 40 Ca,p3n) 94 Ag Isotope separation on-line Detectors: Silicon strip detectors: ß particles, protons

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Proton and Two-Proton Decay of a High-Spin Isomer in 94 Ag

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  1. Proton and Two-Proton Decay of a High-Spin Isomer in 94Ag Ernst ROECKL GSI Darmstadt and Warsaw University

  2. Experimental Techniques • Fusion-evaporation reactions 58Ni(40Ca,p3n)94Ag • Isotope separation on-line • Detectors: • Silicon strip detectors: ß particles,protons • Germanium detectors:γ rays

  3. Properties of the (21+) isomer of 94Agdeduced from - and -proton studies C. Plettner et al., Nucl. Phys.A 733, 20 (2004) I. Mukha et al., Phys. Rev. C 70, 044311 (2004) I = (21+) T1/2 = 0.39(4) s E* = 6.7(5) MeV fusion-evaporation = 350 pb *) *) Further parameters characterizing the experiment: 40Ca intensity 75 particle-nA, 58Ni-target thickness 3 mg/cm2, ion-source efficiency 10%, intensity of the 94Ag (21+) beam 10 atoms/min, measuring time 80 h

  4. (21+) isomer in 94Ag: What was known by end of 2003 0.39(4) s Comparison with shell-model predictions (up to 4p-4h excitations): inversion of 17+ and 21+ levels in 94Ag ! 0.61(2) s N=Z=47 Beta and -delayed proton emission studied byusing a multiple -ray trigger ! Population 0+ ground-state of 94Ag (T1/2 ~ 29 ms, A. Stolz, Ph D Thesis (2000)): not observed in fusion-evaporation reactions !

  5. One-proton decay of the (21+) isomer of 94Ag Search by measuring coincidences between charged particles and  -  cascades in 93Pd Experiment: I. Mukha et al., Phys. Rev. Lett. 95, 022501 (2005) Theory: WKB estimate of proton widths à la Gamow

  6. Si-- coincidence,  gates on 93Pd lines *) 0.79(3) MeV 1.01(3) MeV Si singles spectrum scaled down by a factor 240 *) 93Pd -rays identified by C. Rusu et al., Phys. Rev. C 69, 024307 (2004)

  7. Data on the one-proton decayof the (21+) isomer of 94Ag Ep (MeV) ______ 0.79(3) 1.01(3) Intensity per 100 decays _______ 1.9(3) 2.2(4) T1/2(exp) (s) ______ 21(6) 18(4) Ii If __________ (21+)  (33/2+) (21+)  (33/2–,35/2–) L ___ (4) (3,5) T1/2(WKB) /T1/2(exp) _______________ 110-6 (L=4) 310-7 (L=5) Deformation effect?

  8. Two-proton decay of the (21+) isomer of 94Ag Search by measuring coincidences between charged particles and  -  cascades in 92Rh Experiment: I. Mukha et al., accepted for publication in Nature Theory: Three-body breakup model, L. Grigorenko et al., Phys. Rev. C 68, 054005 (2003)

  9. 1.88(9) MeV Si-Si-- coincidence,  gates on 92Rh lines *) Si-Si-- coincidence,  gates “shifted off” the 92Rh lines *) 92Rh -rays identified by D. Kast et al., Z. Phys. 356, 363 (1997)

  10. Experimental data on the two-proton decayof the (21+) isomer of 94Ag E2p = 1.88(9) MeV I = 0.5(3) % per decay T1/2 = 0.39(4)/0.5(3)% = 80(50) s Ii If: (21+)  (13+,15+) L = (6,8) … and correlation data ...

  11. Relative energy spectra ... … for proton-proton correlations Expected for sequential 2p decay Expected for isotropic 2p decay Experiment … for proton-92Rh correlations Predictions of the break-up model

  12. Simultaneous emission of 2 protons Simultaneous emission of 2 protons Di-proton (2He) emission a = (long-to-short axis ratio)-1/2

  13. Summary and Outlook • The proton decay of the (21+) isomer of 94Ag has unprecedented features including • discovery of one- and two-proton radioactivity from one and the same nuclear state, • unambiguous identification of one- and two-proton by measuring coincidences with characteristic  rays, • new kind of emission of protons from the poles of a prolate-deformed nucleus, tentatively deduced from correlation data. It is mandatory to try to improve the proton-proton correlation data with respect to statistics and angular resolution: Where can such a measurement be done ?

  14. Si-Si-- coincidence,  gates on 93Pd lines *) All  spectra gated by 93Pd - rays *) 0.79(3) MeV 1.01(3) MeV Singles spectrum scaled down by a factor 240 “ gate” *) 93Pd -rays identified by C. Rusu et al., Phys. Rev. C 69, 024307 (2004)

  15. L=(4) L=(3,5)

  16. Si-Si-- coincidence,  gates on 92Rh lines *) 1.88(9) MeV ESi1+ESi2gates: 94Pd 1.4 - 1.6 MeV 92Rh 1.8 - 1.95 MeV Si-Si-- coincidence,  gates “shifted off” the 92Rh lines *) 92Rh -rays identified by D. Kast et al., Z. Phys. 356, 363 (1997)

  17. Estimated by extrapolating systematical trends (G. Audi et al., Nucl. Phys. A 729, 337 (2003)) This work

  18. What this talk is about 1. In the odd-odd nucleus 94Ag an isomer has been observed to have the following unique properties: • excitation energy of 6.7 MeV, • tentative spin/parity assignment of (21+), • half-life of 0.4 s, • one-proton and two-proton radioactivity 2. The one-proton decay is strongly hindered. 3. The two-proton decay is strongly enhanced.

  19. Array of three silicon-strip detectors – High resolution and low energy-threshold for detecting charged particles (positrons, protons)– High granularity*)  position informationI. Mukha et al., Nucl. Phys. A 745, 9285 (2004)*) Only 2 segments per detector used in this work

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