Bertram Blank – CENBG, Bordeaux, France Joint LIA COLL ‐ AGAIN, COPIGAL, and POLITA Workshop Catania, Italy, April 2016 Two-proton radioactivity - a new tool for nuclear structure beyond the drip line  What is two-proton radioactivity ?  Discovery Experiments  TPC experiments  Recent experimental results from RIKEN

Predicted by Goldansky in the 60’s Exotic radioactivities 1960 : V. Goldansky predicts exotic decay modes for nuclei at the proton drip-line : 1p radioactivity for odd Z nuclei 2p radioactivity for even Z nuclei Discovered in 2002 Discovered in 1981

What is two-proton radioacitivy?  Definition Spontaneous and simultaneous emission of two protons from the ground state of a radioactive nucleus  Process Pairing effect + Coulomb barrier effect  Decay observables Observation conditions: T 1/2 ~ ms Q 2p ~ 1-2 MeV branching ratios correlations  Candidates From mass model predictions : A ~ p p (A,Z) even Z (A-2,Z-2) + 2p (A-1,Z-1) + p S p > 0 S 2p < 0

 Decay observables (T 1/2, Q 2p, BR)  Individual proton energies  Angular distribution of the protons  Masses of nuclei beyond drip line  Tunnelling process  p-p pairing in the nucleus  Sequence of single-particle levels  Composition of wave function  Theoretical model validation (3-body model of Grigorenko et al.) (shell model of Brown et al.) Why? How? Emitted protons are the messengers from the nuclear interior! Why and how study 2p?

2002: discovery of 2p radioactivity at GANIL and at GSI J. Giovinazzo et al., Phys. Rev. Lett. 89, (2002) M. Pfützner et al., Eur. Phys. J. A14, 279 (2002)

Primary Beam: MeV/A Production Target : nat Ni 200 mg/cm 2 LISE3 Spectrometer Detection Set-up Discovery of 2p GANIL/LISE3

2p decay of 45 Fe at GANIL/LISE3 Transition assigments: Q 2p, T 1/2 no  coincidence no  E  pile-up identification of the daughter decay E DSSD = E P1+P2 E DSSD = E P +  E  P P   P P P P

M. Pfützner et al., Eur. Phys. J. A14, 279 (2002) 2p decay of 45 Fe at FRS/GSI identification: 6 implantations of 45 Fe A/Z Z decay of 45 Fe Energy (MeV) four 2p decay events

 2004 : Decay of 54 Zn and 48 Ni at GANIL with the same set-up 2p radioactivity of 54 Zn and possibly of 48 Ni 48 Ni 54 Zn B. Blank et al., Phys. Rev. Lett. 94, (2005) C. Dossat et al, Phys. Rev. C 75, (2005)

Brown and Barker R-matrix model with p-p resonance good structure description poor dynamics Grigorenko et al. 3-body model good dynamical description poor structure Rotureau et al. Shell Model Embedded in the Continuum good structure description poor dynamics Comparison with theory B.A. Brown and F.C. Barker, Phys. Rev. C 67, 2003 L.V. Grigorenko et al, Phys. Rev. Lett. 85, 2000 J. Rotureau et al, Phys. Rev. Lett. 95, 2005 similar results fo 48 Ni and 54 Zn  agreement with 3-body model, SMEC, and R-matrix model with p-p resonance 45 Fe  first results for nuclear structure

However, only total decay energy, half-life, BR no individual energies no proton-proton angle TPC

TPC detector  Gas ionisation  Drift of electrons  Detection on the X-Y plan ion identification drift of ionisation electrons emitter protons X-Y detector électric field  Tracking in 3D ! Energy signals Track particle in 2D + Time signals Z component B. Blank et al, Nucl. Instr. Meth. A 613, 65 (2010)

GANIL experiments with the TPC

Energy spectra analysis Y strip numberX strip number Energy signal (a.u.) X proton2 proton1 beam Y Z Energy signal (a.u.) Y strip number X strip number Energy signal (a.u.) Implantation: Decay:

Projection of proton tracks

45 Fe two-proton event in TPC L. Audirac et al.

45 Fe two-proton event in TPC

L. Audirac et al. 45 Fe two-proton event in TPC

L. Audirac et al. 45 Fe two-proton event in TPC

Angular distribution of the two protons L. Audirac et al, EPJA 48 (2012) 179 relative decay probabilities: P(s 2 ) = 0.59 P(p 2 ) = 0.33 P(f 2 ) = 0.08

45 Fefirst and most studied case  since 2002 (GANIL / GSI)  first direct observation (2006, TPC CENBG/GANIL)  angular correlation  structure (2007, OTPC Warsaw/MSU) K. Miernik et al. 48 Nifew counts only  first indication: only 1 event (2004, DSSSD, LISE3/GANIL)  four events (2011, OTPC Warsaw/MSU) 54 Znlow statistics, decay scheme well established  observation (2004, GANIL)  limited angular distribution (2011, CENBG TPC / GANIL) M. Pomorski et al. P. Ascher et al.  exploratory experiments with silicon detectors  tracking experiments with TPCs  good agreement with theory Experimental status: 3 known 2p emitters 54 Zn

Comparison of 54 Zn half-life with theory “Shell model corrected three-body half-lives” T 1/2 (p 2 ) = 0.91/ = 1.9 ms T 1/2 (f 2 ) = 45/ = 230 ms 1/T 1/2 = 1/T 1/2 (p 2 ) + 1/T 1/2 (f 2 ) A = A (f 2 ) + A (p 2 ) T 1/2 = 1.6 ms In excellent agreement with experiment: B.A.Brown, private communication Grigorenko: three-body model  good dynamics Half-lives: T 1/2 = 0.91 ms for pure p 2 T 1/2 = 45 ms for pure f 2 Brown: shell model  good structure 2-proton removal amplitudes: for pure p for pure f 2  indication that nuclear structure i.e. single particle content of wave function correct

Angular distribution Conclusions and perspectives Conclusions  Observation of 2p radioactivity in the decay of 45 Fe, 48 Ni and 54 Zn  Correlations of the protons determined for 45 Fe and 54 Zn  However: very few data Perspectives  Future similar experiments with higher statistics  New possible emitters ( 59 Ge, 63 Se, 67 Kr) : experiment at RIKEN  ACTAR - TPC / GET (General Electronics for TPC) Pads Sampled signals on each pad Dead time reduced Micromegas technology

Angular distribution After these experiments: Future perspectives

Implantation set-up  WAS3ABI DSSSD set-up  EURICA  -ray array New 2p search experiment at BigRIPS of RIKEN: Kr at 345 MeV/A with 250 pnA

known cases new candidates BigRIPS (+ZDS) 78 Kr at 345 MeV/A – 250 pnA setting on 51 Ni setting on 65 Br setting on 62 Se BigRIPS ZDS WAS3ABI 3 DSSSD β veto + EURICA (Ge array) New 2p search experiment at BigRIPS of RIKEN

B. Blank, T. Goigoux et al. known cases new candidates observed production (preliminary): BigRIPS (F7) ZDS (F11) WAS3ABI 59 Ge Se Kr Search experiment for new candidates 67 Kr, 63 Se and 68 Kr: new isotopes  three candidates for 2p radioactivity Production rates: x 200 compared to e.g. NSCL/MSU

T 1/2 = 13.2(17) ms mainly β-delayed proton(s) emitter if 2p:  very weak  B.R. < 0.2% Decay of 59 Ge Gross theory  -decay half-life prediction: 10.9 ms 59 Ge is not a 2p emitter!

T 1/2 = 13.8(38) ms mainly β-delayed proton(s) emitter if 2p:  very weak  B.R. < 0.5% Decay of 63 Se Gross theory  -decay half-life prediction: 13.4 ms 63 Se is not a 2p emitter!

T 1/2 = 8.9(30) ms all decay events after 67 Kr implantation E = MeV (8 counts) T. Goigoux et al. Decay of 67 Kr: energy and half-life Gross theory  -decay half-life prediction: 11.1 ms

all decay events first event after implantation p β ε β  53, 92, 51 % (from 61 Ge decay)  P(β)  5.5* DSSSD β veto T. Goigoux et al.  no β signal with peak events Decay of 67 Kr: absense of  -particles

coincidence with - 67 Kr decay (except peak) - 61 Ge decay (βp) coincidence with peak in 67 Kr decay  no signal ! p β T. Goigoux et al. Decay of 67 Kr: coincident  -particles in neighbouring detectors 67 Kr is a new 2p emitter!

Decay of 67 Kr: results 67 Kr is a new two-proton emitter! Q 2P = 1.685(22) MeV T 1/2 = 8.9(30) ms BR = 36(14) %

T. Goigoux et al., PRL to be submitted Decay of 67 Kr: summary

Two-proton radioactivity is established as new decay mode First discovery experiments with Silicon detector arrays  good agreement with models Followed by TPC-type experiments to visualised protons  good agreement with dynamical three-body model New 2p emitter 67 Kr discovered at BigRIPS 59 Ge and 63 Se no (or very weak) 2p branch Unprecedented intensities at BigRIPS (factor of 200 more) Future: 48 Ni or 54 Zn at LISE3 with ACTAR TPC (ERC milestone) 67 Kr at BigRIPS/RIKEN with ACTAR TPC Conclusions

J. Giovinazzo collection plane  256 x 64 pads (2 x 2 mm 2 )  pixels  micromegas amplification (CERN) GET electronics  analog time sampling (1-100 MHz)  up to 512 samples / channel (most likely 256 in this case)  very short decay mode (not required) active gas volume  P5 / P10 gas (Ar-CH 4 )  750 mbar (implantation depth vs track length) 512 mm 128 mm  200 mm GET front-end (AsAd) active volume beam detector status  demonstrator prototypes tested in exp. campaigns 2048 channels (32x64 pads) (D. Suzuki et al., IPN Orsay 2015)  final detector construction: end 2016 ACTAR TPC

Thank you for your attention Gracie per la vostra attenzione

P. Ascher, B. Blank, M. Gerbaux, T. Goigoux, J. Giovinazzo, S. Grévy, T. Kurtukian Nieto, C. Magron, CEN Bordeaux-Gradignan J.Agramunt, A. Algora, V. Guadilla, A. Montaner-Piza, A. I. Morales, S.E.A. Orrigo, B. Rubio, W. Gelletly, IFIC Valencia D.S. Ahn, P. Doornenbal, N. Fukuda, N. Inabe, G.G. Kiss, T. Kubo, S. Kubono, S. Nishimura, H. Sakurai, Y. Shimizu, P.A. Söderström, T. Sumikama, H. Suzuki, H. Takeda, P. Vi, J. Wu, RIKEN Y. Fujita, M. Tanaka, RNCP Osaka P. Aguilera, F. Molina, Santiago de Chile F. Diel, University Köln D. Lubos, TU Munich G. de Angelis, D. Napoli, INFN Legnaro C. Borcea, IAP Bucarest A. Boso, INFN Padova R.B. Cakirli, E.Ganioglu, Istanbul University J. Chiba, D. Nishimura, H. Oikawa, Y. Takei, S. Yagi, Tokyo University of Science K. Wimmer, Dep. Physics, University of Tokyo G. de France, GANIL Caen S. Go, University of Tennessee B.A. Brown, NSCL-MSU Participants in RIKEN experiment