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Two-proton radioactivity: an experimentalist’s view

Two-proton radioactivity: an experimentalist’s view. Catalin Borcea CEN Bordeaux-Gradignan and IFIN-HH. Two proton radioactivity – a new decay mode Two-proton emission from light nuclei Decay of 42 Cr and 49 Ni Two-proton radioactivity of 45 Fe

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Two-proton radioactivity: an experimentalist’s view

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  1. Two-proton radioactivity: an experimentalist’s view Catalin Borcea CEN Bordeaux-Gradignan and IFIN-HH • Two proton radioactivity – a new decay mode • Two-proton emission from light nuclei • Decay of 42Cr and 49Ni • Two-proton radioactivity of 45Fe • Future perspectives and developments NANUF03, Bucharest September 7-12, 2003

  2. All observed nuclei: • stable • b unstable • particle unstable Stable and b-unstable nuclei Stable nuclei Leaving the valley of stability….

  3. One-proton radioactivity Model calculations to determine single- particle level sequence • Physics topics: • test of nuclear mass models • nuclear structure beyond stability • - single particle ordering and energy • - j content of wavefunction • - shape of mean-field potential • quantum tunneling through 3D barrier

  4. Two types of 2p emission: - ground-state emission • long lived: 45Fe, 48Ni, 54Zn • short lived: 6Be, 12O, 16Ne, 19Mg - emission from excited states • β delayed: 22Al, 31Ar, … • others: 14O, 18Ne, 17Ne To be measured: • proton energies • proton-proton angle Two-proton radioactivity Sequential emission: Three-body decay: 2He emission:

  5. Two-proton radioactivity Sequential emission: Three-body decay: 2He emission: Measurement of protons and recoil

  6. Two types of experiments: • long-lived nuclei (>10ms): implantation and decay • short-lived nuclei (<1ps) : complete kinematics experiments

  7. Two proton emission from light nuclei • Mass: A = 6 – 20 • Z = 4 – 12 • low Coulomb (+ centrifugal) barrier • broad states - short half-lives T1/2 = 10-21s – 10-12s  decay already in the target complete-kinematics measurements behind production target

  8. seq. decay 2He decay 2p emission from 12O Proton-proton angle: Total decay energy: Proton-proton energy:  Data consistent with 3-body or sequential decay R.A. Kryger et al., Phys. Rev. Lett. 74 (1995) 860

  9. GANIL Experimental Procedure 24Mg fragmentation in SISSI at 95 MeV/u Selection with Alpha spectrometer : 17F, 18Ne, 20Mg Stripping reactions at entrance of SPEG

  10. 19Na 18Ne + p MUST p Target 9Be 20Mg SPEG 18Ne 19Na MUST Mass of19Na J. Cerny et al.: W. Benenson et al.: Garvey-Kelson: Pape-Antony: 12.97(7) MeV 12.93(1) MeV 12.88(20) MeV 13.30(20) MeV Mass excess: 13.09(5) MeV Reasonable agreement with experiment and predictions

  11. 18Na 17Ne + p Audi-Wapstra: Garvey-Kelson: Pape-Antony: 25.3(4) MeV 25.4(2) MeV 25.7(2) MeV First mass measurement of18Na MUST Target 9Be p 20Mg SPEG 17Ne 18Na MUST Mass excess: 24.19(5) MeV • If assumed to be ground state: • huge Thomas-Ehrman shift • 1. peak: 18Na* 17Ne* • 2. peak: 18Na  17Ne: 25.04(12)MeV • problems with theoretical calculations

  12. Theoretical calculation for18Na • Main shell-model components: • 18Na (1-): ([p(d5/2)3]3/2+[np1/2]) • ([p(d5/2)2]2+[ps1/2][np1/2]) • 18Na (2-): ([p(d5/2)3]5/2+[np1/2]) • ([p(d5/2)2]2+[ps1/2][np1/2]) • 17Ne (1/2-): ([p(d5/2)2]0+[np1/2]) • 17Ne (3/2-): ([p(d5/2)2]2+[np1/2]) Shell-model spectroscopic factors: Barrier-penetration predicts all excited states to decay to 17Ne ground state

  13. 17Ne* 16F + p 15O + 2p MUST Target 9Be p 18Ne SPEG 15O p 17Ne* MUST 18.689 18.398 18.392 18.254 18.161 17.968 17.778 17.431 16.490 17Ne 16F+p 15O+2p 2p emission from 17Ne 15O+p 15O+2p Good agreement with known separation energies and 16F

  14. 2He 2He (» 53%) Sequential / 3-body Sequential (» 47%) Sum Proton-proton angle distribution Three-body center of mass frame: 2p emission from 17Ne*

  15. Proton-proton angle distribution Three-body center of mass frame: 2p emission from 17Ne* • Agreement with MSU data : no angular correlation for Q2p =0.9 MeV states • Indication of angular correlation for higher lying states…..

  16. New search for 2p emission in 16,17Ne MUST p Target 9Be 17Ne VAMOS 14,15O SPIRAL 24 MeV/u 2*104pps 16,17Ne p MUST Mass 15F+p 16Ne 23.99 MeV Γ = 120 keV 23.89 MeV Γ = 1.2 MeV 14O+2p 19.31 MeV

  17. Conclusion: • 2p emission from 19Mg •  19Mg seems to be a good candidate • unexpected effect for 17Ne …. to be checked • determined masses of intermediate nucleus 18Na for • study of one- and two-proton emission from light proton-rich nuclei

  18. Collaborators: T. Zerguerras, Y. Blumenfeld, T. Suomijärvi, D. Beaumel, M. Fallot, I. Lhenry-Yvon, J.A. Scarpaci, A. Shrivastava IPN Orsay B. Blank, M. Chartier, J. Giovinazzo CEN Bordeaux-Gradignan W. Mittig, P. Roussel-Chomaz, H. Savajols GANIL Caen C. Jouanne, V. Lapoux DAPNIA Saclay M. Thoennessen Michigan State University

  19. Two-proton emission from medium-mass nuclei

  20. X Two-proton emission from 45Fe ground state

  21. Decay scheme for 45Fe Possibly very rich decay pattern

  22. GANIL 1999 • The observation of doubly-magic 48Ni • Study of 42Cr, 49Ni, and 45Fe

  23. Production of radioactive nuclei at GANIL • 58Ni @ 75 MeV/A on nickel target • High primary beam intensity: 3-5A

  24. Production and observation of 48Ni 10 parameters to identify: 48Ni: 4 counts 49Ni: 106 counts 45Fe: 53 counts 42Cr: 287 counts

  25. Spectroscopic studies of 42Cr: a 2p candidate Charged-particle spectrum: Two-proton ground-state emitter? Decay-time spectrum: • -decay half-life • 1.9 MeV peak too high in energy •  Most likely -delayed decay

  26. Spectroscopic studies of 49Ni: a 2p candidate Charged-particle spectrum: Decay-time spectrum: • -decay half-life predictions: • Möller et al.: 5.0 ms • Hirsch et al.: (7.3-20.4) ms • -decay half-life • 3.8 MeV peak too high in energy •  Most likely -delayed decay

  27. Spectroscopic studies of 45Fe: a 2p candidate Charged-particle spectrum: Decay-time spectrum: -decay half-life predictions: Brown: 15.5 ms Ormand: 7 ms Hirsch et al.: (3 - 7) ms Tachibana et al.: 12 ms • Too low statistics to decide between 2p emission and  decay

  28. Two-proton decay of 45Fe • Two experiments: • GANIL in July 2000 • GSI in July 2001 • GSI: • low production rate: 6 45Fe implantations in 6 days • fast data acquisition based on XIA modules • GANIL: • high production rate: 15 45Fe per day • standard data acquisition (CAMAC – VME)

  29. Detection setup: Si(Li) • 58Ni @ 75 MeV/A on nickel target • High primary beam intensity: 3-5A Two-proton decay of 45Fe: GANIL data J. Giovinazzo et al., PRL 89 (2002) 102501

  30. Two-proton radioactivity of 45Fe: GANIL data Identification of 45Fe: Identification of 22 45Fe implants J. Giovinazzo et al., PRL 89 (2002) 102501

  31. 1.14 MeV peak Two-proton radioactivity of 45Fe: GANIL data Decay-energy spectrum:  spectrum: Decay-time spectrum: • Q value in agreement with predictions • no b pile up for peak • half-life short enough for 2p emission • data in agreement with daughter decay • no b’s in coincidence with 1.14 MeV peak T1/2 = 16.7±7.0 ms J. Giovinazzo et al., PRL89 (2002) 102501

  32. IDENTIFICATION IN FLIGHT Br2 p/Z TOF 1,2,3 v DE  Z }  A/Z Two-proton decay of 45Fe: GSI data The FRS: Target 4 g/cm2 Be Beam current (SEETRAM) TOF 1, 2, 3 (scintillators) Implantation set-up Br1 Primary beam 650 MeV/u 58Ni Br4 Br3 DE (MUSIC) Br2 S1 degrader 3.2 g/cm2 Al S2 degrader 3.6 g/cm2 Al NaI barrel 511 keV Identified ions 511 keV Trigger, DE 300 mm Si Stack of Si detectors 7 x 300 mm M. Pfützner et al., EPJA 14 (2002) 279

  33. A/Z 0 0 1 2 3 4 5 6 Energy (MeV) Two-proton decay of 45Fe: GSI data • 5 correlated decay events: • four 2p decays • one b-delayed decay 6 implantation events identified M. Pfützner et al., EPJA14 (2002) 279

  34. ~80% ~20% Q2p = 1.14 MeV T1/2 = 3.8 ms Two-proton radioactivity of 45Fe Clear evidence of 2p radioactivity No coincident beta or gamma ray with the 1.14 MeV peak Peak width: no  pile-up Observed energy in agreement with predictions Observation of daughter decays

  35. 2.0 0.8 Experimental half-life: T1/2 = 3.8± ms Two-proton radioactivity of 45Fe: di-proton model Di-proton model half-life: 0.02 ms + SM spectroscopic factors: 0.12 ms + preformation factor ? + resonance energy ?  Lower limit for the half-life R-matrix model (Brown-Barker): S-wave p-p interaction : 4-40 ms

  36. di-proton:- - - - • 3-body: Two-proton radioactivity of 45Fe Nice agreement between exp. data and predictions for p wave protons but: f-wave protons expected….. L.V. Grigorenko et al.

  37. Conclusions • clear evidence for 2p radioactivity of 45Fe: • a new radioactivity Future studies • other candidates: 48Ni, 54Zn • decay mechanism: 2He or 3-body • setup to measure p – p angle and individual energies • g TPC

  38. First observation of 55Zn and 56Zn Expected production rate for 54Zn: 10-15 per day

  39. identification emitter Electric field protons Drift of ionisation electrons X-Y detector New setup for 2p experiments on LISE3: TPC

  40. Physics case • What information can bring the two-proton radioactivity: • masses of nuclei beyond drip line • pairing in nuclei • sequence of single-particle levels • j content of wavefunctions • deformation • complex tunneling process • …..

  41. Collaborators GSI: M. Pfützner, R. Grzywacz, Z. Janas, J. Kurcewicz University of Warsaw B. Blank, M. Chartier, J. Giovinazzo, A.-S. Lalleman, J.-C. Thomas CEN Bordeaux-Gradignan E. Badura, H. Geissel, L.V. Grigorenko, M. Hellström, C. Mazzocchi, I. Mukha, G. Münzenberg, C. Plettner, E. Roeckl, R.S. Simon GSI Darmstadt M. Stanoiu GANIL Caen C. Bingham, K.P. Rycaczewski Oak Ridge National Laboratory K. Schmidt University Of Edinburgh GSI:

  42. Collaborators GANIL: GANIL: J. Giovinazzo, B. Blank, M. Chartier, S. Czajkowski, A. Fleury, M.J. Lopez Jimenez, M.S. Pravikoff, J.-C. Thomas CEN Bordeaux-Gradignan G. de France, F. de Oliveira Santos, M. Lewitowicz, V. Maslov, M. Stanoiu GANIL Caen C. Borcea IAP Bucharest R. Grzywacz, Z. Janas, M. Pfützner University of Warsaw B.A. Brown NSCL, MSU East Lansing

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