J. Giovinazzo – CENBG / IN2P3 2-proton radioactivity from theoretical prediction to experimental exploration LPSC – 14 march 2017
presentation summary nuclear landscape ○ stability and radioactivity ○ exotic decays modes at the proton drip-line ○ 2-proton radioactivity theoretical frameworks discovery experiments ○ indirect observation ○ recent results tracking experiments ○ indirect observation ○ experimental studies status ongoing developments and outlook J. Giovinazzo LPSC – 14/03/2017
nuclear physics playground atomic nucleus system of interacting fermions 2 types: protons & neutrons protons number nuclear chart 3000 observed isotopes 300 stable ones the question of “ stability ” and binding neutrons number J. Giovinazzo LPSC – 14/03/2017
“classic” radioactive decays 1896 M. Curie emission 1934 1938 β + decay protons number fission 1898 β decay neutrons number J. Giovinazzo LPSC – 14/03/2017
“exotic” radioactive decays 1982 1P radiactivity 2002 1984 protons number 2P radioactivity cluster rad. 1980 double β decay neutrons number J. Giovinazzo LPSC – 14/03/2017
a detour through nuclear stability binding energy: Bethe-Weizsäcker 𝑪 𝑩, 𝒂 = 𝒃 𝒘 ∙ 𝑩 volume 𝟑 −𝒃 𝒕 ∙ 𝑩 surface 𝟒 𝒂 𝒂−𝟐 −𝒃 𝒅 ∙ Coulomb 𝟐 𝟒 𝑩 𝑶−𝒂 𝟑 −𝒃 𝒃 ∙ symmetry 𝟐 𝟒 𝑩 𝟐 𝟑 ±𝒃 𝒒 ∙ 𝑩 − pairing + shell effects (magic numbers)… mass (excess) drip-lines binding energy B ( A , Z ) < 0 unbound / nuclear force J. Giovinazzo LPSC – 14/03/2017
proton(s) radioactivity: “beyond” the drip -line 1982 V.I. Goldanskii 1P radiactivity 2002 protons number 2P radioactivity at the proton drip-line - 1-proton for odd-Z isotopes - 2-protons for even-Z isotopes predicted in the 60’s… Zeldovich, first mention neutrons number Goldanski, first description J. Giovinazzo LPSC – 14/03/2017
towards the proton drip-line β + / EC S P ( Xb ) 𝒂 𝒀𝒃 𝑶 Q EC β and β - γ decays: - spectroscopy and γ nuclear structure - precision tests of weak 𝒂−𝟐 𝒀𝒄 𝑶+𝟐 interaction β + /EC decay energy: Q EC few MeV ( B / A 8 MeV ) proton separation: S P ( Xb ) > Q EC J. Giovinazzo LPSC – 14/03/2017
towards the proton drip-line 𝒂 𝒀𝒃 𝑶 F IAS p β + / EC Q EC γ GT 𝒂−𝟑 𝒀𝒅 (+𝒒) S P ( Xb ) 𝑶+𝟐 𝒂−𝟐 𝒀𝒄 𝑶+𝟐 β -delayed proton emission: Q EC increases - nuclear astrophysics S P ( Xb ) decreases - gamma / proton competition proton transitions : precise probe J. Giovinazzo LPSC – 14/03/2017
towards the proton drip-line β -delayed multi- proton emission: - rp -process waiting points - search for direct 2P emission 𝒂 𝒀𝒃 𝑶 F IAS 2p? β + / EC p Q EC p γ GT 𝒂−𝟒 𝒀𝒆 (+𝟑𝒒) γ 𝑶+𝟐 S 2p ( Xb ) 𝒂−𝟑 𝒀𝒅 (+𝒒) 𝑶+𝟐 𝒂−𝟐 𝒀𝒄 𝑶+𝟐 - often the only access to very exotic isotopes - complex proton emission patterns: level densities & statistical aspects J. Giovinazzo LPSC – 14/03/2017
towards the proton drip-line unbound with respect to proton(s) emission 2p 𝒂 𝒀𝒃 𝑶 1p 𝒂−𝒐 𝒀𝒄 𝒂−𝒐 𝒀𝒅 𝑶 𝑶 (+𝒒) (+𝟑𝒒) F β + / EC IAS p S P ( Xa ) < 0 GT and/or p S 2P ( Xa ) < 0 p γ 𝒂−𝟒 𝒀𝒆 (+𝟑𝒒) 𝒂−𝟐 𝒀𝒄 𝑶+𝟐 𝑶+𝟐 𝒂−𝟑 𝒀𝒅 (+𝒒) 𝑶+𝟐 J. Giovinazzo LPSC – 14/03/2017
proton(s) radioactivity J. Giovinazzo LPSC – 14/03/2017
quasi- ( un ) bound ground state proton drip line (w/r nuclear interaction) time scale of nucleons motion 10 − 20 s energy A+2,Z+2 A+1,Z+1 (+p) A,Z (+2p) J. Giovinazzo LPSC – 14/03/2017
quasi- ( un ) bound ground state Coulomb (+ centrifugal) barrier odd-Z isotope radius energy nuclear potential (strong int.) if Coulomb barrier is larger than proton separation energy metastable state energy then tunnel effect p 1-proton radioactivity A+2,Z+2 A+1,Z+1 (+p) A,Z (+2p) J. Giovinazzo LPSC – 14/03/2017
quasi- ( un ) bound ground state illustration of odd – even effect: - stable isotopes - drip-lines pairing effect D energy D A+2,Z+2 A+1,Z+1 (+p) A,Z (Z is even) (+2p) J. Giovinazzo LPSC – 14/03/2017
quasi- ( un ) bound ground state Coulomb (+ centrifugal) barrier radius energy nuclear potential (strong int.) radius energy pairing effect D energy D 2p A+2,Z+2 even-Z isotope A+1,Z+1 (+p) 1 proton emission forbidden A,Z (Z is even) (+2p) (so called “ true ” 2P radioactivity) J. Giovinazzo LPSC – 14/03/2017
physics case (motivation) ground-state 2-proton radioactivity drip-line and masses (beyond the « drip-line ») transition Q-values nuclear structure energies, half-life, levels configuration pairing correlations in energy and angle of emitted protons tunnel effect ? theoretical descriptions radius the emitted protons carry information energy on what’s going on inside the nucleus the 2-proton radioactivity mixes the structure (wave functions) and the (decay) dynamics J. Giovinazzo LPSC – 14/03/2017
predictions and theoretical frameworks J. Giovinazzo LPSC – 14/03/2017
initial predictions First calculation by V.I. Goldanskii (1960) simple potential model based on masses differences 2P orbital (mass predictions) tunnel effect barrier penetration of a 2 He particle vs. simultaneous emission of 2 protons energy sharing equal sharing between protons discussion of the splitting of 2 He into 2 protons along r axis Mass region A 50 already foreseen as the most promising J. Giovinazzo LPSC – 14/03/2017
simple 2 He tunneling model T 1/2 = f( Q 2P ) b decay dominates too short T 1/2 if Q 2P too high if Q 2P too small tunneling too slow: β + dominates the decay (B. Blank) emission too fast mass region A~50 (already foreseen by Goldanskii) Coulomb barrier high enough (Z 20 to 30) half-life 1 µs ~ 10 ms J. Giovinazzo LPSC – 14/03/2017
search for candidates: mass models candidates ( Q 2 P > 0) & ( Q 1 P < 0) local mass models microscopic IMME (B. Blank) Garvey-Kelson (J. Giovinazzo) J. Giovinazzo LPSC – 14/03/2017
theoretical models interpretation models based on nuclear structure R-matrix formalism - Barker & Brown approach - include p-p resonance - shell model wave functions shell model embedded in the continuum (SMEC) - tentative approach from Ploszajczak & Rotureau no dynamics limited comparison: T 1/2 ( Q 2P ) (with Q 2P taken from experiments !) 3-body model - core+p+p system (hyperspherical harmonics) - good dynamical description - no intrinsic structure prediction J. Giovinazzo LPSC – 14/03/2017
3-body model developed by M.V. Zhukov & L.V. Grigorenko 3-body Schrödinger equation solved in hyper-spherical harmonics basis L.V. Grigorenko prediction of distributions for - energy sharing between protons - proton-proton angular correlations sensitive to involved orbitals J. Giovinazzo LPSC – 14/03/2017
discovery experiments J. Giovinazzo LPSC – 14/03/2017
(beyond) drip-line nuclei: fragmentation experiments projectile fragmentation facilities only way to produce such exotic nuclei available facilities: GANIL, GSI, NSCL, RIKEN J. Giovinazzo LPSC – 14/03/2017
(beyond) drip-line nuclei: basic ingredients fragmentation experiments primary beam high intensity & high energy thin target projectile fragmentation facilities fragments coming out the target with only way to produce such exotic nuclei almost the projectile speed fragments separator available facilities: GANIL, GSI, NSCL, RIKEN fragments stopping in thick detectors implantation / decay correlations (J. Giovinazzo) GANIL / LISE3 facility J. Giovinazzo LPSC – 14/03/2017
fragments implantation & identification fragments energy E veto - impl. veto D E (light particles) - residual energy D E - energy losses (J. Giovinazzo) silicon telescope time of flight implantation: DSSSD (X-Y) 16 x 3 mm - micro-channel plates ion by ion identification of implanted fragments - cyclotrons HF redundant measurements (E, D E, ToF) background reduction in identification matrices J. Giovinazzo LPSC – 14/03/2017
previous attempts B. Blank et al. PRL77 (1996) 45 Fe 48 Ni B. Blank et al. PRL84 (2000) first observation of 45 Fe GSI experiment (1996) first observation of 48 Ni 3 events GANIL experiment (1999) 4 events no measurement of the decay modes… J. Giovinazzo LPSC – 14/03/2017
radioactive decay measurement decay information particle energy in g the impl. detector (protons total energy) beta coincidences (other silicon) b gamma energy (germanium array) P implantation / decay decay time (half-life) (J. Giovinazzo) pixel correlation (decay background reduction) J. Giovinazzo LPSC – 14/03/2017
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