RNB7 2006 Cortina d’Ampezzo, July 3th – 7th 2006 Elisa Rapisarda Università degli studi di...
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Transcript of RNB7 2006 Cortina d’Ampezzo, July 3th – 7th 2006 Elisa Rapisarda Università degli studi di...
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