RNB7 2006Cortina d’Ampezzo, July 3th – 7th 2006

Elisa Rapisarda Università degli studi di Catania

E.Rapisarda for the Diproton collaboration

18 *

Two proton radioactivity is a very exotic decay mode

predicted since 1960 Goldansky Nucl. Phys. 19 (1960)

N

It is expected in Z-even 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, 94Ag 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

Medium-mass proton drip-line nuclei are very promising (45Fe, 48Ni, 54Zn and 94Ag)

First evidence of two-proton radioactivity in the decay of

45Fe Phys. Rev. Lett. 89 (2002)102501

GSI GANIL

4 decays 12

decays

NO identification of individual protons

NO measurements of their energies

NO relative emission angle

18Ne* a good candidate for the observation of diproton decay from excited level

Search of 18Ne* two proton 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 *

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?

35 MeV/A 18Ne beam will interact on a heavy thick target

The 6.15 MeV level should be populated by Coulomb excitation (E1

transition)

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

18

RIBs detected at RIBs detected at the final focusthe final focus

Tra

nsm

issio

n %

20Ne+9Be 45AMeV

21Na20Ne19Ne18N

e

Ciclope beam line

20 degrees beam line

I = 10 enA

9% of 18Ne over the total produced RIBs rate

98% of transmission along the beam line

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)

Secondary Target

(ΔE,ToF)

(x,y)

(A,Z), E

Secondary Ion

Si-Strip 1616

Tagged Ion

22Na21Na21Ne

20Ne19Ne

18Ne19F

18F17F

16O 15O15N14N

13C13N

12C 11C11B

17O

Si-Strip X-Y Position

88 THREE-FOLD TELESCOPES

ARRAY50m-300m-CsI

4.5°16.5°

81 TWO-FOLD TELESCOPES

ARRAY 300m-CsI4.5°4.5°

21Na21Ne20Ne

19Ne18Ne18F

17F16O 15O14N

13C12C 11C11B

Identification can be checked

looking to the E-E 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

9.84 2+

9.58 1-

11.52 2+

12.43 1- 14.93 2+

16.2 1-

Energy level of 16O

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)Around 100 F+p and 20

O+p+p events analyzed up to now

E1

E2

Gomez del Campo et al. PRL 86(2001)43

Details of the three O+p+p events in the 6 MeV region

E*=6.01MeV Ep1=.56 MeV Ep2=.88MeV 1=124° 2=106° 1=-42° 2 =-6° o

=36°

E*=6.14MeV Ep1=1.3 MeV Ep2=.18MeV 1=50° 2=94° 1 =90

E*=6.51MeV Ep1=1.66 MeV Ep2=.22MeV 1=144° 2=114° 1 =82° 2 =44°

o =65°

5.11 2+

6.15 1-

7.59 (1-,2+)

8.5 (1-,2+)

A B C

Possible new levels in 18Ne

A. 9.9 0.25 (1-,2+)

B. 10.8 0.5 (1-,2+)

C. 13.2 0.5 (1-,2+)

We are able to identify E1 and E2 resonances (resolution of about 1 MeV in the excitation energy measurement)The observation of 3 events O+2p in the good excitation energy range notwithstanding the not perfect efficiency tell us that the branching ratio of the 2p decay is not too small Observation of three new possible higher energy levels in 18Ne First example of measurements with exotic beam at intermediate energy at LNS

STATISTICS Better reconstruction of the reaction kinematics