1. 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

2. 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) = – Sn MeV
= MeV

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

4. Earlier experiment – IS374
Proposal in 1998 (including other ABe decay studies)
11Be sample ( atoms) collected in 2001
10Be content determined by AMS (Uppsala, 2008), upper limit of 106 atoms
Limit of order 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 Be atoms

5. 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

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

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

8. 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)

9. 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

10. 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)