Investigation of the CoreHalo Structure of the NeutronRich Nuclei 6He and 8He by IntermediateEnergy

1
Measurement of the 6He ? ? d e- ?-
branching ratio
Farouk Aksouh et al.Brussels Meeting December
15 - 16, 2003
1 - Introduction Motivation 2 - Experimental
Setup 3 - Data Analysis and results 4 -
Conclusion Perspectives
2
1 - Introduction motivation

• 6He ? 6Li(g.s.) e- ?- Branch 1 ?
  99.999 Half-life 0.807 sec
• 6He ? 6Li ? ? d e- ?- Branch 2 ?
  10-3-10-4 (Q 2.033 MeV) 1

• Specific case of 6He among exotic n-rich halo
  nuclei e. g. 11Li interaction cross section,
  breakup cross section, nuclear magnetic moment,
  momentum distribution of fragments, elastic cross
  sections (protons, ?)

• 6He is a cluster of an ? core (internal part) and
  two valence neutrons forming the halo (external
  part)
• Measurement of the ?-delayed (?d) emission ?
  probe of the halo w.f. up to large distances 2

3
Present knowledge
4
Experimental setupPH196 Experiment at CRC
Beam line at CRC
6He Beam at 8 MeV implanted at the middle of the
detectorReduced intensity (5000 pps) and
uniformly distributed on the detector active
areaPeriodic Implantation 1 sec beam ON and 2
sec beam OFF (for 100 implanted nuclei, 60
registered decays)Beam suppression factor of 5.5
X 10-4 (all E) 3.7 X 10-7 (E lt 2 MeV)?-
spectrum end-point at 3.508 MeV 18Ne Beam at
10 MeV Periodic Implantation 1 sec beam ON
and 1 sec beam OFF ? spectrum end-point at
3.424 MeV
5
Double Sided Silicon Strip Detector( Micron
Semiconductor )
Active area 16mm X 16mm Thickness 78um Front
face 48 p strips horizontal Back face 48 n
strips vertical Strip width 300 um Strip pitch
335 um
Energy Resolution (5805 keV ? line of
244Cm) Front face 25 keV Back face 30 keV
Si wafer
Connector for 48 strips
Printed circuit board
Front View
6
Data Analysis
6He
Normalized spectra of 6He and 18Ne
18Ne
Number of implantationsN(6He) 1.86 X
109N(18Ne) 1.31 X 109
7
Experimental results
Preliminary
Branching ratio ()B 1.0(2) X 10-6
() Only statistical uncertainties are shown
8
CONCLUSION PERSPECTIVES
Validity of the experimental methodSeparation of
the very weak decay channel from the main decay
modeThe branching ratio value is closer to 10-6
Experimental discrepancy (Borge93 Anthony02)
is solvedImportance of the region at low
energyUse of a more sensitive electronics at low
E new measurementMore statistics improve the
shape of the transition probability distribution
9
COLLABORATORS
F. Aksouh, D. Smirnov, S. Dean, H. de Witte, J.
Gentens, I. Mukha, M. Huyse, O. Ivanov, P. Mayet,
R. Raabe, J.-C. Thomas, P. Van den Bergh, K. Van
de Vel, J. Van de Walle, P. Van Duppen C.
Angulo, J. Cabrera, A. Ninane, P. Demaret T.
Davinson
Institut voor Kern- en Stralingsfysica, Catholic
University of Leuven, Leuven, Belgium
Institut de Physique Nucléaire, Université
Catholique de Louvain, LLN, Belgium
Department of Physics Astronomy, The University
of Edinburgh, Edinburgh, UK