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 2-proton emission  experimental set-up  decay results  2p emission from 45 Fe

2-proton radioactivity. the case of Iron-45. Jérôme Giovinazzo – CEN Bordeaux-Gradignan – France PROCON’03 – Legnaro – Feb. 2003.  2-proton emission  experimental set-up  decay results  2p emission from 45 Fe  perspectives. to new decay modes. « classic » decay modes

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 2-proton emission  experimental set-up  decay results  2p emission from 45 Fe

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  1. 2-proton radioactivity the case of Iron-45 Jérôme Giovinazzo – CEN Bordeaux-Gradignan – France PROCON’03 – Legnaro – Feb. 2003  2-proton emission  experimental set-up  decay results  2p emission from 45Fe  perspectives

  2. to new decay modes « classic » decay modes beta minus, beta plus alpha emission, fission at the proton drip-line: nuclear strong interaction is not able to bound last nucleons g kept inside by Coulomb barrier  1-proton radioactivity 1981: discovered at GSI (Hoffmann et al.) ~30 known emitters, Z = 53 à 83  2-proton radioactivity due to pairing predicted in the 60’s (Goldansky)

  3. 2-proton emission from a nuclear state from an excited state b-2p decay: 22Al, 26P, 31Ar,… other cases: 14O, 17Ne, 18Ne (T. Zergueras et al.) from the ground state in light nuclei 6Be, 12O, 16Ne, 19Mg half-lives in the order of reaction times (~10-20 s) in the A~50 mass region half-lives: ~ms 45Fe, 48Ni, 54Zn, ?… séquential emission 3 bodies break-up 2He radioactivity

  4. tunneling half-life simple model: tunneling of an 2He particle through the Coulomb barrier  comparison mass models predictions  T1/2 = f(Q2P) if Q2P too high  not bound or too short T1/2 if Q2P too small  tunneling too slow: b+ dominates the decay

  5. 54Zn 49Ni 48Ni 45Fe 42Cr candidates for 2p decay mass region A~50: g Coulomb barrier high enough (Z = 20 ~ 30) g half-life: 1 ms ~ 10 ms candidates: (mass models from Cole, Brown, Ormand) 45Fe, 48Ni, 54Zn 42Cr, 49Ni  accessible in projectile fragmentation exp.

  6. experimental history 1996 GSI (Darmstadt - Germany) first observation of 42Cr, 45Fe, 49Ni no information about decay modes 1998 GANIL (Caen - France) looking for 48Ni (not successful) first observation of 55,56Zn 1999 GANIL discovery of 48Ni decay of 42Cr et 49Ni 45Fe: very low statistics (elect. trigger problems) 48Ni: no decay data 2000 GANIL – 2001 GSI 2-proton decay of 45Fe

  7. fragmentation cross sections cross sections estimates (accessibility) glow confidence… g orders of magnitudes (from exp. 1999 à GANIL) 42Cr 20~200 pb 45Fe ~0.8 pb 49Ni ~1.3 pb 48Ni ~0.04 pb

  8. GANIL/LISE3: projectile fragmentation primary beam CSS1 and CSS2 cyclotrons 58Ni @ 75 MeV / A intensity on target ~3 Ae projectile fragmentation natural Nickel target SISSI device (high acceptance) 1013 p/s transmission efficiency: 1~10 % 10-100 p/s 105 p/s LISE3 spectrometer Br selection achromatic degrader (Be) Wien filter detection set-up ions identification decay measurement

  9. identification of nuclei - light particles veto - residual energy - energy loss time of flight silicon telescope ion by ion identification of implantation events implantation: double side silicon strip detector (X-Y) 16 x 3 mm redundant measurements  background reduction - micro-channel PLATES - cyclotrons HF

  10. identification plots Blank et al. (2000) Observation of 48Ni 4 implanted nuclei experiment at GANIL 2000 22 events of 45Fe implantation identification conditions: 8 à 10 parameters  almost no background

  11. decay measurements implantation g decay pixel correlation of events  background reduction in decay energy / time distributions g b proton energy strip detector Є ~ 100 % coincidence with b particles neighbour silicon Є ~ 30 % germanium detectors array detailed spectroscopy b-g, b-p-g P

  12. delayed proton vs 2-proton

  13. spectroscopy: the case of Iron-47 less exotic a higher production rate g proton-gamma coincidences g some identified transitions g mass estimates (IMME) comparison with theoretical predictions shell model (nuclear structure, interactions)

  14. Chromium-43: daughter of Iron-45 after 2p emission

  15. Chromium-42: candidate for 2p radioactivity EP ~ 1.9 MeV a T1/2 ~ 10-12 s measured half-life: 13.4 ms a most likely b decay

  16. Nickel-49: candidate for 2p radioactivity EP ~ 3.7 MeV a T1/2 ~ 10-19 s measured half-life: 12 ms a most likely b decay

  17. 2p transition transition assignment: peak energy: 1.14 ± 0.05 MeV in the expected range for 2p emission to be observable peak width: 60 keV 30 % narrower than bp g no b pile-up half-life: 4.7 ms compatible with Q2P filiation: in agreement with bp decay of 43Cr energy and time  coherent picture of 2p emission from 45Fe ground state

  18. comparison of 45Fe and 46Fe (bp): same energy conditions: close Qb and same EP energy coincidence efficiency: 30~35 % beta-proton coincidence

  19. discussion 22 implanted nuclei of 45Fe / 12 counts in the 2p peak short half-life, acquisition dead-time 0.3~0.5 ms 3 à 4 decay events may be lost  2p branching ratio: 70~80 % competition between bp and 2p channel in agreement with GSI results very low statistics…

  20. comparison with models experiment: 1.14 ± 0.05 MeV mass models : 1.15 ± 0.09 MeV (Brown, 1991) 1.22 ± 0.05 MeV (Cole, 1996) 1.28 ± 0.18 MeV (Ormand, 1996) Q2P experiment: simple tunneling model: including spectroscopic factor: S ~ 0.20 shell model (B. Brown) half-life

  21. indép. di-proton 3-body other models R-matrix: (Barker, Brown) with p+p interaction s-wave S = 0.20 3-body calculation p-p correlation (Jacobi T)  good agreement for p-wave correl. from mirror nucleus: last two protons in f state (Grigorenko et al.) sequential emission intermediate state 44Mn Q1P = -24 à +10 keV T1/2g few hours ~ few days

  22. conclusions experiment 42Cr, 49Ni most likely b decay 45Fe 2-proton emission from ground state coherent full picture including daughter decay (43Cr) possible competition between 2p / bp data from GSI in good agreement with GANIL results comparison avec les models results depending on the model g new calculations in progress sequential emission seems excluded still open question: 3-body break-up or 2He radioactivity ?

  23. perspectives (short term) experiment (GANIL) 45Fe confirm 2p emission (reproducibility)  precise Q2P and T1/2 daughter decay, b branch 48Ni observation 1999  good conditions for 2p emission  decay mode? 54Zn observation 55,56Zn 1998  10 à 15 nuclei 54Zn / day ?

  24. identification emitting nucleus elect. field protons drift of ionisation electrons X-Ydetector perspectives (long term) purpose angular correlation measurements of emitted protons discrimination between 2He emission / other cases TPC development implantation in a gas cell 3D tracking of protons g X-Y detector g Z time projection MGWC technology (high energy physics) M. Dracos et al. integrated electronics (ASICs)

  25. Jérôme Giovinazzo – CEN Bordeaux-Gradignan – France PROCON’03 – Legnaro – Feb. 2003 research program in a more general 2p emission context g2He radioactivity g emission in light nuclei g correlated component in the b-2p decay (mainly sequential) g ... Collaborations GANIL: CENBG, GANIL, IAP Bucarest, Univ. Varsovie, NSCL / MSU GSI: Univ. Varsovie, GSI, CENBG, GANIL, ORNL, Univ. Edimbourg

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