Department of Physics
Associate Professor Paul Barker
BA (Oxford), PhD (Manchester)
Superallowed 0+→ 0+ nuclear beta decay depends uniquely on the vector part of the weak interaction. Between T=1 analogue states, the decay strength, or Ft value, when precisely measured, can be used to determine one of Nature's fundamental constants, GV, which plays the same role for the Weak Interaction as the charge on the electron, e, does for the Electromagnetic Interaction. From this one obtains Vud , the largest element of the CKM matrix, and this enables one of the most exacting tests of the Standard Model of particle physics to be made; namely a check on the Unitarity of the first row. At this time, the test fails by more than two standard deviations.
Of the possible decays which can be studied, nine have yielded Ft values with high precision. Each requires careful measurement of the decay energy, its halflife and the branching ratio. The Auckland group has made a strong contribution to this data base, originally in our home laboratory AURA2, and now transferred to the ANU Nuclear Physics Laboratory in Canberra, where the facilities are world class.
At ANU, Professor Aidan Byrne and I are currently (March 2009) studying the positron decay of22Mg, which we make with the 20Ne(3He,n) reaction using gaseous targets of isotopically separated 20Ne, with a view to measuring the halflife with high precision. Considerable effort is being put into avoiding the effects of pileup in the analogue systems, a feature which has bedevilled previous measurements.
- P.H.Barker, K.K.H.Leung and A.P.Byrne, 2009, "Half-life of the superallowed positron emitter10C", Phys.Rev. C79, 024311
- P.H.Barker and A.P.Byrne, 2006, "Half-life of the superallowed positron emitter 50Mn", Phys.Rev.C73, 064306
- P.H.Barker and A.P.Byrne, 2004, "Measurement of the Lifetime of 14O and its Ft Value", International Conference on Nuclear and Particle Physics, Gothenburg.
Lifetime of the superallowed positron decay of 14O
- P.H.Barker, I.C.Barnett, G.J.Baxter and A.P.Byrne, 2004, "Half-life of the superallowed positron emitter 14O", Phys.Rev. C70, 24302