NS08 MSU, June 3rd – 6th 2008 Elisa Rapisarda Università degli studi di Catania E.Rapisarda 18 2
ü Two proton radioactivity is a very exotic decay mode predicted since 1960 Goldansky Nucl. Phys. 19 (1960) N ü It is expected in PROTON RICH NUCLEI in the vicinity or beyond the proton drip line Mass of nuclei beyond the drip line Pairing in nuclei Sequence of single particle levels Deformation Tunneling process
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 Sequential emission Three body decay 2 He emission The mass of the Z-even two-proton emitter smaller than the mass of the odd-Z one-proton daughter In two-proton emitter the one- proton emission must be forbidden
First evidence of two-proton radioactivity in the decay of 45 Fe Phys. Rev. Lett. 89 (2002) Eur. Phys. J. A14 (2002) 279 Ground-state 2p-radioactivity is DEFINITELY established as a nuclear decay mode Phys. Rev. Lett. 89 (2002) (C. Dossat et al, 2005 ) (B. Blank et al, 2005 ) ü Medium-mass proton drip-line nuclei are very promising ( 45 Fe, 48 Ni and 54 Zn) ü Short-lived nuclear resonances: interpretation of experimental results by sequential emission 19 Mg 16 Ne I. Mukha et al, Phys. Rev. Lett. Vol.99, (2007)
18 Ne* a good candidate for the observation of diproton decay from excited level Search of 18 Ne* two proton decay has been already performed Gomez del Campo PRL 86(2001)43 using the fusion reaction 17 F+H at 44 MeV
The measured angular distributions cannot discriminate between direct or two step emission of 2p or 2 He emission 18 * Laboratory reference system
Search for DI-PROTON DECAY of excited states of 18 Ne 208 Pb 18 Ne 18 Ne* 16 O 2 He 208 Pb 18 Ne 18 Ne* 16 O Proton energy and angle correlations di-proton emission? ü 18 Ne beam produced at 35MeV/u by projectile fragmentation ü The 6.15 MeV level populated by Coulomb excitation (E1 transition) by interaction on lead target
20 Ne + 9 Be(500 m) at 45 AMeV Degrader Q 1 Q 2 Q 3 Q 4 Q 5 Q 6 Q 7 Q 8 Q 9 D1D1 D2D2 Production Target. Fragment Separator Production Target Q 1,2 18 = 4msr p/p = +/- 1% Max B = 2.7 Tm See Poster N. 37: Tagged RIBs at intermediate energies
Secondary Target (ΔE,ToF) (x,y) (A,Z), E Secondary Ion Si-Strip 1616 Tagged Ion Si-Strip X-Y Position
250 enA of primary beam current 60 kHz of secondary beam on the tagging detector 5 kHz of 18 Ne (9% of the total secondary beam)
88 THREE-FOLD TELESCOPES ARRAY 4.5° 16.5° 81 TWO-FOLD TELESCOPES ARRAY 4.5° 4.5° Angular range: 0° - 20° Solid Angle: 0,34 str Geometrical efficiency: 72 %
3body detection efficiency 16 O+p+p 16% 16 O+ 2 He 16 O+p+p: 14 % 17 F+p 16 O+p+p 11% At Excitation Energies < 7 MeV: 18 Ne 16 O+p+p 25% 16 O+ 2 He 16 O+p+p: 30 % Lost events
Identification can be checked looking to the E-ToF scatter plot in forward detectors
The procedure have been checked for the 16 O 16 v lab v cm E* = E cm + Q val 16 O 12 C + alpha Q val = MeV Energy level of 16 O
Known levels in 18 Ne 6.15 (1 - ), 7.06, 7.35, 7.71, 7.91, 8.09, 8.5 Possible new levels in 18 Ne 10.7 0.25 (1 -,2 + ) 12.7 0.5 (1 -,2 + ) 13.7 0.5 (1 -,2 + )
CENTER OF MASS REFERENCE SYSTEM 16 O p pp 18 Ne 2 He p Relative momentum Relative angle (66 9)% direct three-body (3 2)% virtual sequential (31 7)% 2 He decay * 5.9<E<6.5
B.R. (6.15) 80 %B.R. (7.059) 40 %
(64 7)% direct three-body (30 4)% true sequential (6 2)% 2 He decay E <E<6.5
We are able to excite several 18 Ne levels through Coulomb excitation at incident energy of 35 MeV/u The excitation energy spectrum of 18 Ne was kinematically reconstructed from the fully measured decaying products: several levels of 18 Ne have been recognized, many of them still unknown The correlation function of the two decaying protons of 18 Ne 16 O + 2p was calculated Coulomb excitation cross section measurements Same analysis for other proton-rich nuclei 19 Ne, 17 F, … In progress …