Two-proton radioactivity: an experimentalist’s view Catalin Borcea CEN Bordeaux-Gradignan and IFIN-HH NANUF03, Bucharest September 7-12, 2003 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 Future perspectives and developments

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

One-proton radioactivity 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 Model calculations to determine single- particle level sequence

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

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

Two types of experiments: - long-lived nuclei  s)  implantation and decay - short-lived nuclei  ps) : complete kinematics experiments

Two proton emission from light nuclei Mass: A = 6 – 20  Z = 4 – 12  low Coulomb (+ centrifugal) barrier  broad states - short half-lives T 1/2 = s – s  decay already in the target  complete-kinematics measurements behind production target

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

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

Mass of 19 Na 19Na19Na 18 Ne + p Reasonable agreement with experiment and predictions 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 MUST SPEG Target 9 Be 20 Mg 19Na19Na 18 Ne p

First mass measurement of 18 Na MUST SPEG Target 9 Be 20 Mg 18Na18Na 17 Ne p 18Na18Na 17 Ne + p If assumed to be ground state: - huge Thomas-Ehrman shift 1. peak: 18 Na *  17 Ne * 2. peak: 18 Na  17 Ne: 25.04(12)MeV - problems with theoretical calculations Mass excess: 24.19(5) MeV Audi-Wapstra: Garvey-Kelson: Pape-Antony: 25.3(4) MeV 25.4(2) MeV 25.7(2) MeV

Theoretical calculation for 18 Na Main shell-model components: 18 Na (1 - ): ([  (d 5/2 ) 3 ] 3/2+ [ p 1/2 ]) ([  (d 5/2 ) 2 ] 2+ [  s 1/2 ][ p 1/2 ]) 18 Na (2 - ): ([  (d 5/2 ) 3 ] 5/2+ [ p 1/2 ]) ([  (d 5/2 ) 2 ] 2+ [  s 1/2 ][ p 1/2 ]) 17 Ne (1/2 - ): ([  (d 5/2 ) 2 ] 0+ [ p 1/2 ]) 17 Ne (3/2 - ): ([  (d 5/2 ) 2 ] 2+ [ p 1/2 ]) Barrier-penetration predicts all excited states to decay to 17 Ne ground state Shell-model spectroscopic factors:

2p emission from 17 Ne 15 O+p 15 O+2p Good agreement with known separation energies and 16 F F+p 17 Ne 15 O+2p Ne *16 F + p 15 O + 2p MUST SPEG Target 9 Be 18 Ne 15 O p p 17 Ne *

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

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

New search for 2p emission in 16,17 Ne MUST VAMOS Target 9 Be 17 Ne 16,17 Ne Mass 15 F+p 14 O+2p 14,15 O p p SPIRAL 24 MeV/u 2*10 4 pps 16 Ne MeV Γ = 120 keV MeV Γ = 1.2 MeV MeV

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

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

Two-proton emission from medium-mass nuclei

Two-proton emission from 45 Fe ground state X

Decay scheme for 45 Fe  Possibly very rich decay pattern

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

Production of radioactive nuclei at GANIL MeV/A on nickel target High primary beam intensity: 3-5  A

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

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

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

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

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

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

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

Decay-time spectrum: Two-proton radioactivity of 45 Fe: GANIL data Decay-energy spectrum:  spectrum: T 1/2 = 16.7±7.0 ms 1.14 MeV peak J. Giovinazzo et al., PRL89 (2002)  Q value in agreement with predictions  no  pile up for peak   half-life short enough for 2p emission  data in agreement with daughter decay  no  ’s in coincidence with 1.14 MeV peak

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

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

Two-proton radioactivity of 45 Fe Q 2p = 1.14 MeV T 1/2 = 3.8 ms   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

Two-proton radioactivity of 45 Fe: di- proton model Experimental half-life: T 1/2 = 3.8± ms 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

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

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

First observation of 55 Zn and 56 Zn Expected production rate for 54 Zn: per day

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

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 ….. Physics case

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:

Collaborators 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 GANIL: