Reazioni di trasferimento di due neutroni con MAGNEXstatic.sif.it › SIF › resources › public...
Transcript of Reazioni di trasferimento di due neutroni con MAGNEXstatic.sif.it › SIF › resources › public...
Studio della forza di pairing nel meccanismo di trasferimento di neutroni con lo spettrometro MAGNEX
Francesco CappuzzelloUniversity of Catania & INFN-LNS
Particle-Particle correlations in nuclei
Pairing Vibrations(p,t) and (t,p) reactions on Sn and Pb targets
Strong excitation of the 0+ ground states
Harmonic behaviour of the excitations
Eigenstates of a general harmonic oscillator in a gauge space with ∆N = ±2 and ∆L = 0
Analogy between shape and pairing vibrationsD. Bes and R.A. Broglia Nucl. Phys. 80 (1965) 289-313.
A. Bohr and B. Mottelson, Nuclear Structure, Vol. II (Benjamin, New York, 1975).
R. Middleton and D. J. Pullen, Nuclear Phys. 51 (1964) 77.
J.H. Bjerregaard et al., Phys. Lett. B 24 (1967) 568.
(t,p) ∆N=+2
(p,t) ∆N=-2
Analogy between p-h, p-p and h-h excitations
Particle-Particle correlations
Giant Resonances
Collective p-p or h-h excitations
R.A. Broglia and D. Bes PLB 69 (1977) 129-133
Giant Pairing Vibrations (GPV)
Predicted properties of the GPV (heavy nuclei)
• Excitation Energy ~ 15 – 20 MeV
• FWHM ~ 7.8 A-1/3
• Collective nature
• L = 0 angular momentum transfer
Recent theoretical studies on light nuclei
E.Khan et al., PRC 69, 014314 (2004)
B.Avez et al., PRC 78, 044318 (2008)
R. Middleton et al., Nucl. Phys. 51 (1964) 77
J.H. Bjerregaard et al., PLB 24 (1967) 568
Collective p-h excitations
Pairing vibrations
NEVER OBSERVED
GPV requires L = 0 transfer!
In transfer reactions typically large amount of linear and angular momentum is transferred
The role of the reaction mechanism
The role of the incident energy
Near the Coulomb barrier the angular momentum transfer is minimized
Drawback:
1. The angular distributions are peaked at the grazing angle and are not sensitive to the structure of the populated states
2. Q-value matching rules typically suppress the cross section at high excitation energy where the GPV is expected
At high incident energy the mechanism is characterized by a large amount of angular momentum transfer and by deep inelastic collisions
At energies between 5 and 10 times the Coulomb barrier the angular distributions are sensitive to the final populated states
N. Anyas-Weiss et al., Phys. Rep. 12 (1974) 201-272
The role of the involved nuclei
• Brink’s matching conditions D.M. Brink, Phys. Lett. B 40 (1972) 37-40
)(
/
0/)(21
0//
2121
0
22
11
21012
22110
iiffeff
eff
ZZZZQQmvk
evenlevenl
vRQRRkL
RRkk
−−=
=
=+=+
≈+−+−=∆
≈−−=∆
λλ
λλ
λλ
• The survival of a preformed pair in a transfer process is favored when the initial and final orbitals are the same
The 13C(18O,16O)15C reaction at 84MeV
18O6+ Tandem beam at Einc = 84 MeV (7.5 times above the Coulomb barrier)
13C self-supporting target 99% enriched, thickness 50 μg/cm2
16O ejectiles momentum analysed by the MAGNEX spectrometer (LNS – Catania)
Three angular settings (Ω ∼ 50 msr) θ = 3° ÷ 13°
θ = 7° ÷ 19°
θ = 13° ÷ 25°
Main features Values Maximum magnetic rigidity 1.8 T m Solid angle 50 msr Momentum acceptance ± 13% Momentum dispersion for k = -0.104 (cm/%) 3.68
First order momentum resolution
xMDRx
p ∆= 5400
ScatteringChamber Quadrupole Dipole
Focal PlaneDetector
Measured resolution
Energy ∆E/E ∼ 1/1000Angle Δθ ∼ 0.3°Mass Δm/m ∼ 1/160
Algebraic trajectory-reconstruction
MAGNEX
Particle Identification Technique
F.Cappuzzello et al. NIMA 621 (2010) 419-423
18O + 13C reaction at 84 MeV and scattering angle of θlab = 7°-19°
qpB ∝ρ
ΔE –E histogram
coun
ts
Mass (a.u.)14 15 16 17 18 19 20
inelastic
stripping pick-up
7° < θlab< 13°
Comparison of different reaction channels for18O + 13C at 84 MeV
Efficiency for the production of different chargestates estimated using the program INTENSITYJ.A.Winger et al., NIM B70(1992) 380-392
Enhancement of the two-neutron stripping channel
Relevant contribution of the direct transfer of the neutron pair
Reconstructed angle%energy
),,,,,( iiiiiii lyxX δφθ= One gets labθ Scattering angle
eccE Excitation energy
16O angle % energy spectrum
Enhancement of the known L = 0 transition (state at 3.103 MeV) and of the 11 MeV bump
13Cg.s. (1/2-) → 15Cgs (1/2+) L = 113Cg.s. (1/2-) → 15C0.74 (5/2+) L = 313Cg.s. (1/2-) → 15C3.103 (1/2-) L = 013Cg.s. (1/2-) → 15C4.22 (5/2-) L = 213Cg.s. (1/2-) → 15C4.66 (3/2-) L = 213Cg.s. (1/2-) → 15C6.84 (7/2-, 9/2-) L = 413Cg.s. (1/2-) → 15C7.35 (7/2-, 9/2-) L = 4
S.Truong and H.T.Fortune, PRC 28,977(1983)
g.s.
0.74
6.84
7.35
3.10
34.
22
4.66
15C excitation energy (MeV)
13C(18O,16O)15C9 < θlab < 12
15C excitation energy (MeV)
Cou
nts
Cou
nts
g.s.
0.74
6.84
7.35
3.10
34.
22
4.66
13C(18O,16O)15C4.5 < θlab < 7
?
?
Good candidate for GPV?
Preliminary spectra of 15C
1E+0
1E+1
1E+2
1E+3
1E+4
10 20 30 40 50
dσ/dω
[µb/
sr]
θCM [°]
13C(18O,16O)15C at 84 MeV, θsc = 7° ÷ 18°
6.84 MeV L = 4
12.9 MeV
x10
Comparison of the angular distributions
State at Ex = 11 MeV13CGS (1/2-) (18O ,16O)15C3.103 (1/2-) L = 0
13CGS (1/2-) (18O ,16O)15Cgs (1/2+) L = 1
13CGS (1/2-) (18O ,16O)15C6.84 (7/2-÷9/2-) L = 4
1E+0
1E+1
1E+2
1E+3
1E+4
10 20 30 40 50
dσ/dω
[µb/
sr]
θCM [°]
13C(18O,16O)15C at 84 MeV, θsc = 7° ÷ 18°
g.s. MeV L = 1
12.9 MeV
1E+0
1E+1
1E+2
1E+3
1E+4
10 20 30 40 50
dσ/dω
[µb/
sr]
θCM [°]
13C(18O,16O)15C at 84 MeV, θsc = 7° ÷ 18°
3.1 MeV L = 0
12.9 MeV
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Transfer experiments on different targets
9Be, 11B, 12,13C, 28Si, 58,64Ni, 128Sn, 208Pb
Absolute horizontal position calibration of the FPD
Relative calibration of the pads for the horizontal position measurement
Absolute vertical calibration (drift time)
Relative calibration of the silicon detectors energy
Identification of 16O8+ ions at the FPD
Representation in the focal plane parameters (Xfoc, θfoc, Yfoc, φfoc)
Construction of the spectrometer transport matrix
Preliminary spectrum of 11Be
18O beam 84 MeV
9Be target 114µg/cm2 + collodion 6 µg/cm2
g.s
+ 0.
32 +
14C
.
1.78
9Be(18O,16O)11Be12C(18O,16O)14CΘlab = 8°
g.s.
+ 0
.32
1.78
2.69
3.89
+ 3
.96
5.24
6.72
11Be excitation energy (MeV)
Cou
nts ?
12C target
9Be target
Preliminary spectrum of 13B
11B(18O,16O)13BΘlab = 8.5°
g.s.
18O
4.13
5.39
6.17
+ 6
.43
13B excitation energy (MeV)
Cou
nts
?
18O beam 84 MeV
11B target 33µg/cm2 + Formvar 4 µg/cm2
12C target 50 µg/cm2
Contribution due to carbon impurities subtracted
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64Ni(18O,16O)66Ni
Xfoc (m)
12° < Θlab < 24°
Θfo
c(r
ad)
Xfoc (m)
coun
ts
64Ni(18O,16O)66NiEbeam = 84 MeVΘlab ≈ 18°Max E* 28 MeV
g.s.
1.42
14C
14C
PRELIMINARY
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MAGNEX + EDEN MAGNEX to measure high resolution energy spectra for well identified reaction products
EDEN to study the decaying neutrons emitted by the observed resonances with good efficiency and energy resolution
Unique facility to study the resonant states of neutron rich nuclei (low separation
energy)
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MAGNEX + EDEN
Memorandum Of Understanding
INFN -LNS
IN2P3 – IPN Orsay
Proposal at the LNS PACfor the commissioning
12C(18O,17O)13C
16O(18O,17O)17O
To setup electronics and study efficiency and resolution
13C(18O,16O)15C 2 neutron coincidences
Conclusions and outlooks
A broad resonance observed in 15C spectrum populated via (18O,16O)
at 84 MeV
Compatible with GPV?
Analysis of the angular distributions in progress
Break-Up calculations will be done to study the continuum
background (TDSE)
Different targets (9Be, 11B, 28Si, 58Ni, 66Ni, 120Sn, 208Pb) explored via
(18O,16O), data analysis in progress
Working group
F.Cappuzzello1,2, D.Carbone1,2, M.Cavallaro2, A.Cunsolo1,2,A.Foti1,3, M.Bondì1,2, G.Santagati1,2, G.Taranto1,2, R.Linares4,R.Chen1,5
1. Dipartimento di Fisica e Astronomia, Università degli Studi di Catania, Italy2. Istituto Nazionale di Fisica Nucleare – Laboratori Nazionali del Sud, Italy3. Istituto Nazionale di Fisica Nucleare – Sezione Catania, Italy4. University of Sao Paulo, Institute of Nuclear Physics, Sao Paulo, Brazil5. Institute of Modern Physics, CAS, PRC
F. Azaiez, S.Franchoo, M.Niikura, J.A.Scarpaci
CNRS - IN2P3 – Institut de Physique Nucléaire d’Orsay, France