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

« 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  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 )

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

simple model: tunneling of an 2 He particle through the Coulomb barrier  comparison mass models predictions  T 1/2 = f(Q 2P ) if Q 2P too high  not bound or too short T 1/2 if Q 2P too small  tunneling too slow:  + dominates the decay

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

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

cross sections estimates (accessibility)   low confidence…  orders of magnitudes (from exp à GANIL) 42 Cr20~200 pb 45 Fe~0.8 pb 49 Ni~1.3 pb 48 Ni~0.04 pb

projectile fragmentation natural Nickel target SISSI device (high acceptance) projectile fragmentation natural Nickel target SISSI device (high acceptance) LISE3 spectrometer B  selection achromatic degrader (Be) Wien filter LISE3 spectrometer B  selection achromatic degrader (Be) Wien filter detection set-up ions identification decay measurement detection set-up ions identification decay measurement primary beam CSS1 and CSS2 cyclotrons MeV / A intensity on target ~3  Ae primary beam CSS1 and CSS2 cyclotrons MeV / A intensity on target ~3  Ae 10 5 p/s p/s p/s transmission efficiency: 1~10 %

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 time of flight - micro-channel PLATES - cyclotrons HF -light particles veto - residual energy -energy loss

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

P P     implantation  decay pixel correlation of events  background reduction in decay energy / time distributions proton energy strip detectorЄ ~ 100 % coincidence with  particles neighbour siliconЄ ~ 30 % germanium detectors array detailed spectroscopy  - ,  -p- 

comparison with theoretical predictions shell model (nuclear structure, interactions) less exotic  higher production rate  proton-gamma coincidences  some identified transitions  mass estimates (IMME)

E P ~ 1.9 MeV  T 1/2 ~ s measured half-life: 13.4 ms  most likely  decay

E P ~ 3.7 MeV  T 1/2 ~ s measured half-life: 12 ms  most likely  decay

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  p  no  pile-up half-life:4.7 ms compatible with Q 2P filiation: in agreement with  p decay of 43 Cr energy and time  coherent picture of 2p emission from 45 Fe ground state

comparison of 45 Fe and 46 Fe (  p): same energy conditions: close Q  and same E P energy coincidence efficiency: 30~35 %

22 implanted nuclei of 45 Fe / 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  p and 2p channel in agreement with GSI results very low statistics…

experiment: simple tunneling model: including spectroscopic factor: S ~ 0.20 shell model (B. Brown) 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) Q 2P half-life

R-matrix: (Barker, Brown) with p+p interaction s-wave S = 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 44 MnQ 1P = -24 à +10 keV T 1/2  few hours ~ few days di-proton 3-body indép.

experiment 42 Cr, 49 Nimost likely  decay 45 Fe2-proton emission from ground state coherent full picture including daughter decay ( 43 Cr) possible competition between 2p /  p data from GSI in good agreement with GANIL results experiment 42 Cr, 49 Nimost likely  decay 45 Fe2-proton emission from ground state coherent full picture including daughter decay ( 43 Cr) possible competition between 2p /  p data from GSI in good agreement with GANIL results comparison avec les models results depending on the model  new calculations in progress sequential emission seems excluded still open question: 3-body break-up or 2 He radioactivity ? comparison avec les models results depending on the model  new calculations in progress sequential emission seems excluded still open question: 3-body break-up or 2 He radioactivity ?

experiment (GANIL) 45 Feconfirm 2p emission (reproducibility)  precise Q 2P and T 1/2 daughter decay,  branch 48 Niobservation 1999  good conditions for 2p emission  decay mode? 54 Znobservation 55,56 Zn 1998  10 à 15 nuclei 54 Zn / day experiment (GANIL) 45 Feconfirm 2p emission (reproducibility)  precise Q 2P and T 1/2 daughter decay,  branch 48 Niobservation 1999  good conditions for 2p emission  decay mode? 54 Znobservation 55,56 Zn 1998  10 à 15 nuclei 54 Zn / day ?

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

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