Search for bp-decay from 11Be K Riisager on behalf of A.Becerrill, M.J.G. Borge, J.A. Briz, O. Forstner, L.M. Fraile, H.O.U. Fynbo, J.S. Johansen, B. Jonson, G.T. Koldste, K.L. Laursen, M.V. Lund, T. Nilsson, G. Nyman, P. Steier, O. Tengblad CSIC University of Vienna Universidad Complutense Aarhus University Chalmers Tekniska Högskola

Why look for beta-p in 11Be ? Only possible due to the low neutron separation energy: Similar to beta-delayed deuteron emission from (halo nuclei) 6He and 11Li If occuring: coupled to the neutron halo in 11Be According to theory the decay mechanism is also dynamically coupled to the halo structure: decay directly to continuum This needs experimental proof Qbp = mn – mH – Sn (Z,N) = 0.782 – Sn MeV = 0.280 MeV

Predicted beta-p spectrum D. Baye, E.M. Tursonov, Phys.Lett. B696 (2011) 464 - b(11Be) = 3 10-8 Simple models: “emit before decay”, direct to continuum, sequential decay

Earlier experiment – IS374 Proposal in 1998 (including other ABe decay studies) 11Be sample (5 1011 atoms) collected in 2001 10Be content determined by AMS (Uppsala, 2008), upper limit of 106 atoms Limit of order 2 10-6 on beta-p branching ratio Why a new attempt now? New theoretical calculation points to 10-8 range AMS technical improvements at VERA Have now experience in producing pure sample Aim for a 11Be sample of more than 1012 atoms – need AMS to be sensitive down to about 104 10Be atoms

VERA – Vienna environmental research acc. Dissolve sample in acid Precipitate BeOH Add 9Be (known) Negative ion source 1 Accelerate BeO- Foil stripper Measure 9/10 ratio Overall efficiency: 5 10-4

Proposed set-up Collect on Cu-foils AMS needs: no 9Be, 10Be, 10B

Determination of #(11Be) 1) Monitor the gamma spectrum from 11Be, in particular the 2124 keV line 2) Measure current on collection foil 2001 collection: 5 1011 atoms Yield improved factor 3 since then (RILIS)

Contamination from 11Li ? Problem: 11Li decays produce 10Be (85% beta-n decay branch) Use HRS to separate 11Li from 11Be (factor 10-3) Primary yield down by factor 2000 or more Delay collection until 11Li yield is down (e.g. 150 ms) Conclusion: this contamination is under control Take advantage of 10Be produced from 11Li: Collect known source of 10Be at the end, to cross-check AMS efficiency (not feasible with direct 10Be)

Contamination from 10Be ? Problem: 103 more 10Be than 11Be, i.e. need suppression by factor 10-11 Tail of the 10Be peak extending to A=11 ? Unlikely, but cross-check with 8Li and 11Be profiles (scan in A) 10Be appearing as 10Be1H molecule ? Would be on top of 11Be, so dangerous Unlikely with surface ionization (limit from 2001 result) Can check via a separate laser-off collection

Summary and beam request We ask for 15 shifts (UCx or Ta, RILIS): 2 shifts set-up of HRS (NB! Need 60 kV) 10 shifts 11Be (main sample: 6, BeH: 3, resolution:1) 2 shifts 8Li (HRS resolution) 1 shift 11Li (known sample of 10Be)