AFRODITE : Gammaray Goddess of the Fairest Cape

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AFRODITE Gamma-ray Goddess of the Fairest Cape

• Simon Bongolethu Mullins
• iThemba Laboratory for Accelerator Based Sciences
• South Africa

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iThemba
L(aboratory) for
A(ccelerator)
B(ased)

S(ciences)

• Mission To provide advanced, viable,
  multidisciplinary facilities for
  training, research and services in the fields of
  nuclear science and radiation medicine for the
  pride and benefit of all the people of Africa.

Pac
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Neutron therapy treatment vault at iThemba LABS
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Proton-therapy computer-controlled treatment
set-up at iThemba LABS
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PROTON THERAPY TREATMENT PLANTypical plan for a
4-field non-coplanar proton treatment of a
pituitary adenoma.
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AFODITE at iThemba LABS
9 CLOVER detectors (9Oeph 0.017) 8 LEPS
detectors
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High resolution measurement of the 208Pb(p,g)
capture reaction

• M.Lipoglavek, R.Bark, M.Benatar, E.Gueorguieva,
  J.Kau, F.Komati, P.Kwinana, J.J. Lawrie, G.K.
  Mabala, P.Maine, S. Mukherjee, S.M. Mullins,
  S. Murray, N. J. Ncapayi, R.T. Newman,
  P. Vymers,
• iThemba Laboratory for Accelerator Based
  Sciences,
• P.O.Box 722, Somerset West 7129
• Likar, M.Vencelj, T.Vidmar
• J.Stefan Institute, 1000 Ljublijana, Slovenia

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Proton Radiative Capture into 209Bi through
Giant Resonances and Analog ResonancesK.A.Snover
, J.F.Aman, W.Hering and P.Paul, Phys.Lett. 37B,
29 (1971)

• Measured g-rays from the 208Pb(p,g)209Bi
  capture reaction with a NaI detector (energy
  resolution was 5)
• 4.4 MeV line inserted to improve fit.
• Weak peak corresponding to captures to i13/2
  state swamped by low-energy tail of strong f7/2
  peak.

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Comparison with calculations obtained from the
consistent Direct-Semi-Direct modelA.Likar and
T.Vidmar, Nucl.Phys.A 593, 69 (1995)

• Good agreement for captures to the f7/2 and
  f5/2/p3/2 states.
• Poor agreement at low proton energies for
  captures to the h9/2, and in particular, i13/2
  states.
• Need better energy resolution to investigate
  this disagreement with the consistent DSD.

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GEANT simulation for 20 MeV grays detected by
AFRODITE
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Detector and Trigger Setup

• Eight Compton-suppressed clover detectors (4 _at_
  135, 4 _at_ 90 w.r.t. beam).
• Pre-amplifiers adjusted to give positive
  polarity pulses in order to avoid saturation for
  high-energy ?-rays.
• Event trigger required the detection of at least
  one high-energy ?-ray (Eg ? 3.2 MeV) in a single
  clover-element.

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Target, Beam Data Statistics

• Target of 1mg/cm2 208Pb mounted on 5?g/cm2 C
  foil.
• Data obtained at 7 proton energies (11.3, 11.6,
  11.9, 12.6, 13.2, 14.3 and 14.8 MeV).
• Average beam intensity 40nA and 30 hours of
  data were taken at each energy.
• Energy resolution 50 keV for Eg 1019 MeV
• AFRODITE efficiency at Eg 15 MeV measured with
  66 MeV protons on a carbon target.
• ?(Eg 15 MeV) ? 9.10?4 in good agreement with
  GEANT simulations.

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Capture g-ray spectrum from the 208Pb(p,g)209Bi
reaction at Ep 11.9 MeV (AFRODITE)
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Comparison of 208Pb(p,g)209Bi spectra taken with
a NaI detector (Snover et al.) and the AFRODITE
multi-(HPGe clover)-detector array
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Level scheme for 209Bi and spectrum gated by
capture g-rays which populated
the 4418 keV state.
?
?
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Comparison with Direct-Semi-Direct Model
calculations

• Comparison of present data with those obtained
  by Snover et al.
• Calculated curves are from the
  Direct-Semi-Direct (DSD) model (A.Likar
  T.Vidmar, Nucl.Phys. A593, (1995) 69.)
• Consistent agreement found for all proton
  captures, including those to the i13/2 state.

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Conclusions

• High-resolution measurement of the
  208Pb(p,g)209Bi capture reaction with the
  AFRODITE HPGe array up to Eg 19 MeV.
• More than factor of 10 improvement in energy
  resolution c.f. NaI data of Snover et al.
• Capture g-rays associated with i13/2 state in
  209Bi clearly resolved, and improved data for the
  h9/2 state too.
• Good agreement with consistent DSD model for all
  captures, including those to the i13/2 state.
• Published in Phys. Lett. B 593, 61 (2004).

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Search for tetrahedral shapes in Yb nuclei
J.Dudek, A.Gozdz, N.Schunck M.Miskiewicz, PRL
25, 252502 (2002)
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• Oblate
• Prolate
• Oblate
• Prolate

J.Dudek, A.Gozdz, N.Schunck M.Miskiewicz, ibid
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Schematic E vs I plot depicting isomeric
tetrahedral states and their associated bands
relative to the yrast line.
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Total projection of clover-clover matrix
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Level scheme for 160Yb
Data analysis almost complete have also studied
?-decay of 160Lu Any evidence for tetrahedral
shapes?! Jury is out! Plan to Coulex 160Yb beam
at ISAC-2 (TRIUMF)
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Tetrahedral Magic Numbers

• From a WS potential
• 20, 32, 40, 56-58, 64, 70, 90, 100, 112,
• Existence of Td magic numbers independent of the
  realization of the mean-field
  Universality

Yb isotopes
Zr isotopes
Best candidates proton-rich or neutron-rich
nuclei
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AFRODITE 154Sm(?,4n)154Gd
?
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DIAMANTHungarian-South African agreement
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ATOMKI Chessboard 24 CsI crystals coupled to
photo-diodes
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13C 170Er ? 176Hf ?3n _at_ 80MeV
? Rays (CsI)
Protons
Deuterons
? particles
? Rays (PIN-diode)
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Ratio of Hf/W in ungated matrix 8
evaporation codes predict 1 Ratio of Hf in
gated/ungated ? ? efficiency 15
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Intensities are consistent with complete break-up
of 13C into ?-?-?-n
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New ECR ion sources
Berlin HMI Waiting for water cooling (by end of
July) Commissioned for continuous running by end
of year
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GTS ion sourceStill no vacuum equipmentNo
dedicated power suppliesMiddle of Next Year
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Opportunities Provided by the New
ECR Ion Source

• Reactions in inverse kinematics
• Deep Inelastic
• Neutron Rich
• Lifetimes
• Radioactive beams
• (Projectile Fragmentation)

Low cross-sections High recoil velocities! v/c
gt 10 !
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RIBS at iThemba ? Beam Intensities
Remember, a typical stable particle beam
experiment uses a few pnA, and 1 pnA 1010
pps

Typical intensities at present day radioactive
beam facilities 104 107 pps
Get 3 orders of magnitude back with the addition
of 8 tracking detectors
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What can be done with 107 pps, and a Tracking
AFRODITE ?
What can be done with 106 pps, and a Tracking
AFRODITE ?
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TIGRESS 32-Fold Segmented HPGe Clover Detector
Four 40 n-type HPGe crystals close-packed in a
four-leaf clover geometry. 32-fold segmentation
of the outer contacts provide position
resolution.
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Improvement of AFRODITEwith TIGRESS type CLOVERs
AFRODITE
2 TIGRESS clovers
4 TIGRESS clovers
6 TIGRESS clovers
8 TIGRESS clovers
Costs R4M per TIGRESS CLOVER
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Background reduction with triples
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PROTEA
Photopeak Reconstruction Omnipurpose Tracking
Energy Array
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Thanks to the iTL accelerator operations group
for delivering the beams and technical support.
Thanks in particular to Rob Bark, Matej
Lipoglavek and John Sharpey-Schafer for allowing
me to show their data, and to all the other
members of the iTL Physics Group who contributed
to the measurements.
Happy Birthday wishes from the Fairest Cape!