Spectroscopic studies of 75Rb and 76Sr

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• Spectroscopic studies of 75Rb and 76Sr
• Looking for experimental signatures of np pairing

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• Motivation
• Shape changes
• Shape coexistence
• Violation of the additivity principle
• Waiting points in the rp process
• Coulomb antipairing effect
• Isoscalar component of np pairing

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It there a signature for T0 pairing?
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• Previous work on 76Sr
• Thought to offer evidence of a delayed alignment
• Not clear that the data goes beyond the band
  crossing
• ZN2 and ZN4 show considerable variation in
  their band crossing frequencies

S.M.Fischer et.al. PRL 87 (13 2001)
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• Used the reaction 40Ca(40Ca,2p2n)76Sr _at_165MeV
• Gammasphere in conjunction with Microball.
• 350µg/cm2 Ca target flashed with 150µg/cm2 of Au
• Able to extend the known transitions up to spin
  22, beyond the band crossing region.

PJ Davies et al Phys Rev C75 011392 (2007)
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• Good agreement with theory (CRHB and CRMF)
• Crossing frequency from experiment 0.740.01MeV
• CRHB crossing frequency 0.73MeV
• CRHB includes an isorotational energy term
• Eiso T(T1)/2Jiso

Solid circles Experimental data Solid lines
CRHB calculations Dashed line CRMF calculations
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• TRS calculations produce a similar results
  h?0.75
• Band crossing smoother
• Acting like a rigid rotor (ß20.46)

RA Wyss and W Satula Acta Phys Pol B 32 2457
(2001)
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Coulomb Antipairing Effect

• 68Se and 72Kr changes in MoI at low spin
  attributed to shape effects
• Suggested that Coulomb exchange term would reduce
  the proton-proton pairing energy (M Anguiano et.
  Al. Nucl Phys A683 227 (2000))
• Expect two alignments, one for protons, one for
  neutrons

0.6 MeV gt h?crossing gt 1MeV
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• Contrasting behaviour in 73Kr and 75Rb a
  possible fingerprint of T0 pairing

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R Wyss, P Davies, W Satula, R Wadsworth Phys Rev
C75 011301 (2007) Experimental Data N Kelsall et
al Phys Rev C65 044331 (2002)
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• 73Kr appears to change form a 1qp to 3qp
  structure
• This may be attributed to T0 pair scattering.
  What causes the onset of this pair phase?
• However 75Rb appears to have a more traditional
  band crossing
• Alternatively the 73Kr case may be attributed to
  differences in how the N3 shell is populated
  compared to 75Rb

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