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NS08MSU, June 3rd – 6th 2008
Elisa Rapisarda Università degli studi di Catania
E.Rapisarda
18
2
Two proton radioactivity is a very exotic decay mode
predicted since 1960 Goldansky Nucl. Phys. 19 (1960)
N
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: 45Fe, 48Ni, 54Zn • short lived: 6Be, 12O, 16Ne, 19Mg - emission from excited states • β delayed: 22Al, 31Ar, … • others: 14O, 18Ne, 17Ne To be measured: • proton energies • proton-proton angle
Sequential emissionSequential emission Three body decayThree body decay 22He emissionHe 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 45Fe Phys. Rev. Lett. 89 (2002)102501
Eur. Phys. J. A14 (2002) 279
Ground-state 2p-radioactivity is DEFINITELY established as a
nuclear decay mode
Phys. Rev. Lett. 89 (2002)102501
(C. Dossat et al, 2005 )
(B. Blank et al, 2005 )
Medium-mass proton drip-line nuclei are very promising (45Fe, 48Ni and 54Zn)
Short-lived nuclear resonances: interpretation of experimental results by sequential emission
19Mg
16Ne
I. Mukha et al, Phys. Rev. Lett. Vol.99, (2007) 182501
18Ne* a good candidate for the observation of diproton decay from excited level
Search of 18Ne* two proton decay has been
already performed
Gomez del Campo PRL 86(2001)43
using the fusion reaction
17F+H at 44 MeV
The measured angular distributions cannot
discriminate between direct or two step emission of 2p or
2He emission
18 *
Laboratory Laboratory reference systemreference system
Search for DI-PROTON DECAY of excited states of
18Ne
208Pb18Ne
18Ne*16O
2He
208Pb18Ne
18Ne*16O
Proton energy and angle correlations di-proton emission?
18Ne beam produced at 35MeV/u by projectile fragmentation
The 6.15 MeV level populated by Coulomb excitation (E1 transition) by
interaction on lead target
20Ne + 9Be(500m)
at 45 AMeV
Degrader
Q1 Q2 Q3
Q4 Q5 Q6
Q7 Q8 Q9D1
D2
Production Target.
Fragment Separator
Production Target
Production Target
Q1,2
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 18Ne (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 3body detection efficiencyefficiency
16O+p+p 16% 16O+2He 16O+p+p: 14 %17F+p 16O+p+p 11%
At Excitation Energies < 7 MeV:
18Ne 16O+p+p 25%16O+2He 16O+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 16O
16
vlab
vlab
vcm
E* = Ecm + Qval
16O 12C + alpha
Qval = 7.149 MeV
Energy level of 16O
Known levels in 18Ne
6.15 (1-), 7.06, 7.35, 7.71, 7.91, 8.09, 8.5
Possible new levels in 18Ne
10.7 0.25 (1-,2+) 12.7 0.5 (1-,2+) 13.7 0.5 (1-,2+)
CENTER OF MASS CENTER OF MASS REFERENCE SYSTEMREFERENCE SYSTEM
16O
p
pp
18Ne
2He
p
Relative momentumRelative momentum Relative angleRelative angle
(669)% direct three-body
(32)% virtual sequential
(317)% 2He decay
*
5.9<E<6.5
B.R. (6.15) 80 %B.R. (7.059) 40 %
(647)% direct three-body
(304)% true sequential
(62)% 2He decay
E
6.5
5.9<
E<
6.5
We are able to excite several 18Ne levels through Coulomb excitation at incident energy of 35 MeV/uThe excitation energy spectrum of 18Ne was kinematically reconstructed from the fully measured decaying products: several levels of 18Ne have been recognized, many of them still unknownThe correlation function of the two decaying protons of 18Ne 16O + 2p was calculated
Coulomb excitation cross section measurementsSame analysis for other proton-rich nuclei 19Ne, 17F, …
In progress …
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