Terra incognita Pair transfer – Direct reactions to probe pairin Pair transfer - link between reaction mechanism and structure - Experimental methodology with RIB Ongoing studies of n-p pairing at GANIL Ongoing studies of n-n pairing at GANIL Conclusion and Outlooks D. Beaumel, IPN Orsay ESNT meeting, October 13-15 th , 2008
Pair transfer – Direct reactions to probe pairing. D. Beaumel, IPN Orsay. Terra incognita. Pair transfer - link between reaction mechanism and structure - Experimental methodology with RIB Ongoing studies of n-p pairing at GANIL Ongoing studies of n-n pairing at GANIL - PowerPoint PPT Presentation
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Terra incognita
Pair transfer – Direct reactions to probe pairing
Pair transfer - link between reaction mechanism and structure- Experimental methodology with RIB
Ongoing studies of n-p pairing at GANIL Ongoing studies of n-n pairing at GANIL Conclusion and Outlooks
D. Beaumel, IPN Orsay
ESNT meeting, October 13-15th, 2008
2-neutron (and 2-proton) transfer have been used to probe pairingEX: Early work by Broglia, Hansen, Riedel, 1973
What are the dynamical implications of pairing correlations ? Similarity between pairing field and 2-body transfer operator
→ use (p,t) and (t,p) reactions (L=0,S=0,T=1 transfer) “pairing model”
• Deuteron-like transfer reaction : enhanced transfer probabilities 0+ → 1+ levels
Neutron-proton pairing
Ongoing n-p pairing studies at GANIL
Spiral 2 will provide beams of N=Z nuclei with higher rate than SPIRAL technique :• fusion-evaporation reaction with high intensity stable beams and thick target• re-acceleration using CIME
First proposed experiment: 48Cr(p,3He) (d,) Experimental setup : MUST2 + EXOGAM + VAMOS Unfortunately delayed due to SISSI device failure…
Plan to propose similar experiment on 28 < N=Z < 50 nuclei (ideally mid g9/2 shell) at SPIRAL2
(p,t) reaction recently studied using MUST2 for spectroscopy purpose at GANIL
8He(p,t) X. Mougeot, PhD. Thesis (SphN CEA) 14O(p,t) H. Iwasaki (IPNO/Koeln) et al.
No specific experiment on pairing
Development of cryogenic helium adapted to transfer reaction studies
Could be used to study the (,6He) reaction
Evolution when going far from stability ?
Neutron-neutron pairing
Possible transfer reactions• (p,t), (t,p) • (, 6He)
0+ states
CM (deg)
2+ states
CM (deg)
208Pb(,6He) at ~ 27 MeV/u
The (,6He) reaction
Could be complementary to (p,t)
Surface-peaked reactionProbe pairing in neutron skin ?
Already studied with stable beams10 ~ 50 MeV/u energy
Cross-section much lower than (p,t)
Sequential transfer
p p 22Ne beam
CryogenicHe target
MUST II
Si annulartelescope
Test experiment @ GANIL: 22Ne + at 30 MeV/u
22Ne(,6He)20O 30 MeV/u22Ne(, 6Be)20O
Using cryogenic He gas target made for missing mass measurements
He 20O
20Ne
Ø 16 mm, 3mm thickHavar windowsT = 8.5 KP = 1 bar
22Ne + at 30 MeV/u
RESULTS - 22Ne(6He) at 30 MeV/u
Recoil PID Ejectile PID
2+
2-,3- 2+,3-,4+
Ex in 20Ne (MeV)
15 hours counting~ 106 pps beam
6He
22Ne
Located near closed-shellsFluctuations of the pairing field → collective oscillationsBasic modes : pair addition/removal phonons
Region around 208Pb (=0)
Pairing vibrations
Model predictions: Harmonic spectrum Stripping N0→N0+2→N0+4… have enhanced GS transitions with 1:2:3… ratios Same for pickup 2-phonon at 2xEg.s. 2-phonon state with GS/P.V. intensity ratio ~ 1
Good agreement with data
Observables : G.S. energies G.S. → G.S. transfer G.S. → second 0+ transfer
Study near 132Sn at SPIRAL2
EXP
Harmonic vib model
large GS→GS cross-sections Energies well reproduced by linear + quadratic term relative in agreement with the model
Comparison expnt / Pairing Model
Sn : large at mid-shell, strong pairing correlations→ Static distortion of the pairing field
I ↔ N → Strong transitions between members of superfluid band
Pairing rotations : case of Sn isotopes
Observables : G.S. energies G.S. → G.S. transfer
EXP
Conclusions/questions/outlooks
2-nucleon transfer can be used to investigate pairing far from stability
Variety of pairing-related phenomena in 2n transfer reactions
Sensitivity of the observables to pairing changes ? Ambiguities ?
Role of the coupling to continuum ?
Methodology for studying 2n transfer reactions established
At SPIRAL2 d-transfer from g9/2 shell for the study of p-n pairing
Dynamical aspects of nn pairing can be studied in new regions
Implementation of triton target (e.g. ti t2 at Munich)
GAmma SPectroscopy and PArticle DetectionPROJECT for
Integrated 4 (particle) + 4 ()
Energy resolution with SPIRAL2 beams Thicker targets
Multireaction capab.
Improve PID for low E particles
Modularity Coupling with other devices (neutron, AGATA,..)