two-proton radioactivity discovery of two-proton radioactivity experimental results with TPC s future studies

Transcription

1 two-proton radioactivity discovery of two-proton radioactivity experimental results with TPC s future studies Bertram Blank CEN Bordeaux-Gradignan EPS European Nuclear Physics Conference 2009 Spring meeting of the DPG Division Hadronic and Nuclear Physics March 16-20, 2009

2 alpha emission of 4 He 2 protons + 2 neutrons fission break-up of nucleus two light nuclei beta + proton neutron + light particles beta - neutron proton + light particles Gamma nuclear rearrangement + gamma ray

3 V. Goldanskii.1960 One-proton radioactivity nucleus proton + nucleus - 1 Two-proton radioactivity nucleus two protons + nucleus - 2

4 Sequential emission: Three-body decay: 2 He emission: 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: individual proton energies proton-proton angle

5 X

6 Coulomb barrier odd-z nucleus Z = proton strong interaction even-z nucleus paired protons free protons 2-protons

7 masses of nuclei beyond drip line: measurement of decay Q value pairing in nuclei: emission pattern sequence of single-particle levels: angular distribution of protons composition of wave function: angular distribution of protons tunneling process: change of deformation

8 Primary beam: MeV/A intensity: 3-4 µae SISSI target: nat Ni 200 mg/cm 2 spectrometer LISE3 : degrader Be (50 µm) Wien filter detection setup silicon telescope identification of implanted fragments DSSSD (X-Y): 2 x 16 x 3 mm - veto for light particles - residual energy, x-y position - energy loss - time of flight: micro-channel plate detectors RF cyclotron

9 Giovinazzo et al., 2002

10 45 Fe 54 Zn data taken with silicon (strip) detectors 48 Ni

11 beam intensity (SEETRAM) primary beam 650 MeV/u 58 Ni target 4 g/cm 2 Be S1 degrader 3.2 g/cm 2 Al Bρ 1 TOF 1, 2, 3 (scintillators) Bρ4 Bρ 2 Bρ ΔE 3 (MUSIC) implantation in flight identification S2 degrader 3.6 g/cm 2 Al identified ions NaI barrel 511 kev Bρ 2 p/z ToF 1,2,3 v ΔE Z } A / Z trigger, ΔE 300 µm Si 511 kev Si-telescope 7 x 300 µm M. Pfützner et al. (2002)

12 identification: 6 implantations of 45 Fe T 1/ 2. 4 = 3 +! ms Q p = ( ) 2 ± MeV decay of 45 Fe Z four 2p decay events 1 A/Z Energy (MeV) M. Pfützner et al., 2002

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15 agreement with 3-body model, SMEC, and R-matrix model with p-p resonance 54 Zn 45 Fe Grigorenko et al. Brown and Barker Rotureau et al.

16 48 Ni agreement with 3-body Model, SMEC, and R-matrix model with p-p resonance Grigorenko et al. Brown and Barker Rotureau et al.

17 However: - only total decay energy, half-life, no beta, daughter decay - no individual energies - no proton-proton angle TPC

18 aim measurement of individual proton energies and proton-proton angle distinction between correlated 2 He or uncorrelated 3-body decay principle of detection implantation in gas volume 2p emitter traces in 3D of protons X-Y detector Z from time projection technology: MGMS + GEMs electronics: ASICs electric field drift of ionisation electrons protons identification of implanted isotopes X-Y detector

19 1500 electronics channels cathode beam GEM: Gas electron multiplier 2D detector Hybrid boards Hybrid boards Daughter boards Daughter boards

20 Time projection chamber TPC Drift volume Hybrid card Mount of electronics GEM strip-strip detector d = 70µm d = 200µm Experiments in september 2006 and july 2008

21 43 Cr: β2p X Y 45 Fe: 2p X Y X Y J. Giovinazzo et al.

22 X implantation decay decay Y implantation decay

23 X implantation decay Y implantation decay

24 X implantation decay Y implantation decay

25 Energy sharing between the two protons average = 50% Sigma = 7,2 % perfect energy sharing between the two protons still to come: angle between two protons energy fraction (%)

26 technology: CCD camera + PM K. Miernik et al.

27 M. Pfützner et al. Daughter decay 45 Fe 2p 2p 2p Daughter decay 45 Fe

28 M. Pfützner et al.

29 TPC modifications for 54 Zn study entrance at the corner increased height of active volume flash-adc on GEMs X Y July 2008

30 implantation 2p decay of 54 Zn decay energy drift time

31 implantation 2p decay of 54 Zn decay energy drift time

32 implantation 2p decay of 54 Zn decay energy drift time

33 implantation 2p decay of 54 Zn decay energy drift time

34 implantation 2p decay of 54 Zn decay energy drift time.more events

35 two-proton radioactivity is discovered: - data for 45 Fe, 54 Zn, and most likely 48 Ni first direct observation of two protons in 2p radioactivity - GANIL data on 45 Fe, MSU data on 45 Fe, GANIL data on 54 Zn need for microscopic interpretation new candidates exist, but are they sufficiently 2p unbound??? - 59 Ge, 63 Se, 67 Kr

36 CEN Bordeaux-Gradignan (France) GANIL Caen (France) IAP Bucharest (Romania) Warsaw University (Poland) NSCL-MSU (USA) University of Santiago di Compostella (Spain) IPN Orsay (France) LPC Caen (France) KU Leuven (Belgium) Warsaw University (Poland), GSI Darmstadt (Allemagne), CEN Bordeaux-Gradignan (France), GANIL Caen (France), ORNL (Tennessee / USA), Edinburg University (UK) Warsaw University (Poland), MSU (USA), ORNL (Tennessee / USA), University of Tennessee (USA)