Diapositive 1

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Pair transfer reactions Experimental perspectives
D. Beaumel, IPNO
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Pairing in Exotic Nuclei

• Neutronrich effect of Density Dependence
• Ex - Increase of the pairing gap with
  neutron excess
• - A neutron skin favours pairing
  phenomena
• Proton-rich side Interplay between T0 and
  T1 pairing
• At Drip line New effects due to low binding ?
• Strong effects due to the coupling to the
  continuum expected

Possible tool Pair transfer reactions Ex
pairing rotation J ? N (pair)
Enhanced L0 pair transfer

• GANIL/SPIRAL Energy regime well adapted to
  transfer reactions
• Angular distributions sensitive to transferred-l
• limited BU effects
• Cross-sections mb/sr (for 1nucleon
  transfer)
• A large number of transfer measurements have been
  performed

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Experimental Method

• The MUST array
• (IPNO-Saclay-Bruyères)
• 8 Telescopes surface 6x6cm2
• DS Strip 60X60Y (300 mm)
• Si(Li) 3mm
• CsI

• Investigated
• 6He(p,t)
• 8He(p,d) (p,t)
• 8He(d,p) (d,3He) (d,6Li)
• 10Be(d,p)
• 11Be(p,d) (d,3He)
• 44,46Ar(d,p)

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Results for 46Ar (d,p) 47Ar at SPIRAL
47Ar
46Ar rate few 104 pps
L. Gaudefroy (PhD), O. Sorlin, et al.
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Going to pair transfer
4 among 7 experiments proposed by
IPN/SACLAY/GANIL collaboration are pair
transfer measurements !

• Expected difficulties
• Lower cross-sections (fact 10-100)
• Analysis
• - in 1nucleon transfer
• For 2n transfer, amplitudes add coherently
• Reaction mechanisms
• sequential, multistep, continuum effects
• CRC mandatory

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Study of n-p pairing correlations in nuclei

• In nuclei
• 4 types of Cooper pairs
• largest when strong spatial correlation
• same valence shell (NZ)
• Extra binding for NZ Wigner energy
• np additionnal correlations ?
• Isovector nn and pp pairing well-understood
• little is known for T0

• Several approaches
• Mass differences
• Coriolis destruction of pairs
• jp jn aligned in T0 pairs

(p, 3He), (3He,p) DT0,1 (d,a), (a,d)
DT0 (a, 6Li), (6Li,a) DT0

• Deuteron-like transfer reaction
• enhanced transfer probabilities
• 0 ? 1 levels
• proposed experiment 48Cr(p,3He) (d,a)

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Experimental Setup A big step compared to
previous experiments !
SPAGA
ExoGam
48Cr 56Ni 30MeV/u
CATS2
VAMOS
Spokes Y. Blumenfeld, R.C. Lemmon A. Ramus,
PhD. Thesis
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The Array
Collaboration IPNO,SPhN/Saclay,GANIL

• MUST2 a major upgrade of MUST
• Increase angular coverage
• Better efficiency
• Measure several reactions in one shot
• Increase granularity (multiparticle events)
• New electronics to handle the increase of
  channels

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Analyse des spectres à poursuivre 4n, 3n, 2n
Autres données à etudier 9He, 8He, 7He, 7H
Informations sur interaction nn
Intensité du faisceau (?)
Cible mince deutérium pure (?)
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Study of n-p pairing using deuteron transfer
experiments

• To analyze the data
• We need microscopic form-factors with np pairing
  !
• to be injected in a reaction code to calculate
  cross-section

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Pairing vibrations

• Low-lying pairing vibration excited by 2-neutron
  transfer reactions
• near closed shells
• studied extensively near 208Pb

cQRPA response for 2n transfer on 22O
Predictions exist for a Giant Pairing Vibration
(GPV) Ex 15-20 MeV Never observed Accepted
proposal at Ithemba (E. Khan) Sn(p,t) at 50 MeV
GPV
HFB
Probability of excitation expected to be
enhanced with weakly bound probes Ex 116Sn(
6He,4He) at 40 MeV cross-section 1 mb
! (Fortunato et al., EPJA 14 (2002)
E. Khan et al, PRC69(2004)
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Perspectives _at_ SPIRAL2

• SPIRAL2 will provide heavier with higher
  intensities
• EX A good region to study np pairing
  mid g9/2 NZ nuclei
• (P.Van Isacker et al., PRL 94
  (2005))
• NZ Beams produced by
  fusion-evaporation reaction
• with high intensity primary beams
• Design of a new detection system for the study
  of Direct Reactions
• Improved capability for Heavier ions
• 4p particles 4p gamma
• A LoI will be submitted to the Scientific
  Advisory Committee of GANIL