Recoilbeta tagging David Jenkins Oddodd NZ Fascinating laboratory

Recoil-beta tagging David Jenkins

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 Me. V in 70 Br Evidence for np-pairing in both low lying states and high spin rotational bands Beta decays important for standard model tests - CVC hypothesis

How to study odd-odd N=Z § Nuclei are difficult to produce without reactions close to 40 Ca+40 Ca 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

Recoil-decay tagging

Recoil-beta tagging

RITU+GREAT

Test case: 74 Rb

Proof-of-principle § § § nat. Ca (36 Ar, pn) 74 Rb Ebeam = 103 Me. V τ½ (74 Rb) = 65 ms β+endpoint ~ 10 Me. V σ ~ 10 μb

High energy positrons

Varying the beta gate size 1 10 Me. V 3 10 Me. V 6 10 Me. V

Identification of 74 Rb A. N. Steer, et al. , NIM A 565, 630 (2006)

74 Rb level scheme from RBT

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

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

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)

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 ke. V/J Uniform upward trend for deformed nuclei except: A=78 - flat A=70 - strongly down A=70 data from G. de Angelis, EPJ A 12, 51 (2001) and D. G. Jenkins et al. , PRC 65, 064307 (2002)

Effect of shape change 2=-0. 3 CED=-7 ke. V 2=0. 35 TRS calculations: T. Mylaeus et al. , J. Phys. G 15, L 135 (1989) 2=0. 18 2=0. 35 CED=-75 ke. V R. Sahu et al. , J. Phys. G 13, 603 (1987) Coulomb energies calculated after S. Larsson, Phys. Scri 8, 17 (1973).

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

RBT Collaboration B. S. Nara Singh 1, A. N. Steer 1, D. G. Jenkins 1, R. Wadsworth 1, P. Davies 1, R. Glover 1, N. S. Pattabiraman 1, T. Grahn 2, P. T. Greenlees 2, P. Jones 2, R. Julin 2, M. Leino 2, M. Nyman 2, J. Pakarinen 2, P. Rahkila 2, C. Scholey 2, J. Sorri 2, J. Uusitalo 2, P. A. Butler 3, M. Dimmock 3, R. D. Herzberg 3, D. T. Joss 3, R. D. Page 3, J. Thomson 3, R. Lemmon 4, J. Simpson 4, B. Blank 5, B. Cederwall 6, B. Hadinia 6, M. Sandzelius 6 Department of Physics, University of York, Heslington, York YO 10 5 DD, UK Department of Physics, University of Jyväskylä, P. O. Box 35, FIN-40351, Jyväskylä, Finland Oliver Lodge Laboratory, University of Liverpool, Liverpool L 69 7 ZE, UK CCLRC Daresbury Laboratory, Keswick Lane, Warrington WA 4 4 AD, UK Centre d’Etudes Nuclèaires de Bordeaux-Gradignan, F-33175 Gradignan Cedex, France Royal Institute of Technology, Roslagstullsbacken 21, S-106 91 Stockholm, Sweden.