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 …