Recoil-beta tagging

1. Recoil-beta tagging David Jenkins

2. Odd-odd N=Z Fascinating laboratory for studying interplay of T=0 and T=1 states Very unusual low level density for odd-odd nuclei e.g. only 1 state below 1 MeV in 70Br Evidence for np-pairing in both low lying states and high spin rotational bands Beta decays important for standard model tests - CVC hypothesis

3. How to study odd-odd N=Z • Nuclei are difficult to produce without reactions close to 40Ca+40Ca at near-barrier energies • Production cross-sections are low (<1% of total cross-section) • Residues are too slow at focal plane of separator e.g. FMA to use ion chamber to identify Z • Most measurements done with neutron detectors + charge particle detectors to select e.g. pn or pn channel

4. Recoil-decay tagging

5. Recoil-beta tagging

6. RITU+GREAT

7. Test case: 74Rb

8. natCa (36Ar, pn) 74Rb Ebeam = 103 MeV τ½ (74Rb) = 65 ms β+endpoint ~ 10 MeV σ~ 10 μb Proof-of-principle

9. High energy positrons

11. 1 10 MeV 3 10 MeV 6 10 MeV Varying the beta gate size

12. Identification of 74Rb A.N. Steer, et al., NIM A565, 630 (2006)

13. 74Rb level scheme from RBT

14. Unknown case:78Y • Nothing known about 78Y except 0+ superallowed decay and (5+) beta-decaying isomer • RBT technique applied using 40Ca(40Ca,pn)78Y reaction • Cross-section should be very similar to 74Rb • 90% of flux proceeds to low-lying isomer • Isomer is too long-lived for effective tagging

15. B.S. Nara Singh et al., Phys. Rev. C (accepted)

16. Coulomb Energy Differences Extremely sensitive to nuclear structure effects: • Rotational alignment mechanism • Correlations of pairs of particles • Changes in deformation • The evolution of nuclear radii D.D. Warner et al., Nature Physics 2, 311 (2006)

17. CEDs for A~70 CED(J)=Ex(J,T=1,Tz<)-Ex(J,T=1,Tz>) Difference in np and NN pairs gives CED rise of ~12 keV/J Uniform upward trend for deformed nuclei except: A=78 - flat A=70 - strongly down A=70 data from G. de Angelis, EPJ A12, 51 (2001) and D.G. Jenkins et al., PRC 65, 064307 (2002)

18. 2=0.18 2=0.35 2=-0.3 2=0.35 Effect of shape change CED=-7 keV TRS calculations: T. Mylaeus et al., J. Phys. G 15, L135 (1989) CED=-75 keV R. Sahu et al., J. Phys. G 13, 603 (1987) Coulomb energies calculated after S. Larsson, Phys. Scri 8, 17 (1973).

19. Plans for future measurements • Recoil-beta-tagging: • Search for Tz=-1 nuclei e.g.70Kr, 74Sr using double-beta-tagging • Study mirror symmetry in A=71 i.e. 71Kr • Search for 0+ in 74Rb and compare B(E0) with 74Kr • Use vacuum-mode recoil separator to select by mass and improve rates

20. RBT Collaboration B.S. Nara Singh1, A.N. Steer1, D.G. Jenkins1, R. Wadsworth1, P. Davies1, R. Glover1, N.S. Pattabiraman1, T. Grahn2, P.T. Greenlees2, P. Jones2, R. Julin2, M. Leino2, M. Nyman2, J. Pakarinen2, P. Rahkila2, C. Scholey2, J. Sorri2, J. Uusitalo2, P.A. Butler3, M. Dimmock3, R. D. Herzberg3, D.T. Joss3, R.D. Page3, J. Thomson3, R. Lemmon4, J. Simpson4, B. Blank5, B. Cederwall6, B. Hadinia6, M. Sandzelius6 Department of Physics, University of York, Heslington, York YO10 5DD, UK Department of Physics, University of Jyväskylä, P.O. Box 35, FIN-40351, Jyväskylä, Finland Oliver Lodge Laboratory, University of Liverpool, Liverpool L69 7ZE, UK CCLRC Daresbury Laboratory, Keswick Lane, Warrington WA4 4AD, UK Centre d’Etudes Nuclèaires de Bordeaux-Gradignan, F-33175 Gradignan Cedex, France Royal Institute of Technology, Roslagstullsbacken 21, S-106 91 Stockholm, Sweden.