Level Densities and ray Strength Functions in Sm Isotopes

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Level Densities and ?-ray Strength Functions in
Sm Isotopes

• Sunniva Siem
• University of Oslo

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Spin energy diagram
In our experiments spin 2-6 h
Bn
Excitation energy
Yrast
Spin
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CACTUS- experimental setup

• Reactions (3He,?) and (3He,3He)
• Beam 30-45 MeV
• Targets Yb, Dy, Er, Sm, Nd, Si, Mo, Fe, Sn, V,
  Pb,Ti,Ni
• 8 Si particle telescopes at ? 45
• Spin 2-6 h

• CACTUS detector array (28 NaI 2Ge) has 15
  efficiency

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• Energy distribution of primary ? rays contains
  info on
• level density ?(Ef)
• -ray transmission coefficient T(E?)
• Brink-Axel
• P(Ex,E?) T(E?) ?(Ef)

Ex
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147Sm
146Sm
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Microcanonical Temperature
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148Sm strength function

• Circles our data
• Squares from photoabsorpsjon cross sections
  P.Carlos et al. NPA 225 (1974)
• Filled triangle is based on neutron capture in
  147Sm

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Radiative strength function of 57Fe
A.Voinov et al. Phys.Rev.Lett.93, 142504 (2004)
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M.Guttormsen et al. Phys.Rev.C 71,044307(2005)
?-strength functions in Mo isotopes
Filled circles (3He,a) Open circles (3He,3He)
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A workshop onLevel density and ?-strength in
continuum
21-24 May 2007 in Oslo http//ocl.uio.no
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Collaborators

• R.Chankova, M.Guttormsen, F.Ingebretsen, S.
  Messelt, J.Rekstad, A.C.Larsen, N.U.H.Syed,
  S.Ødegård, University of Oslo
• A.Voinov, Dubna, Russia
• U.Agvaanluvsan, G.Mitchell, TUNL, USA
• J.A.Becker, L.Bernstein, LLNL, USA
• A.Schiller, MSU,USA
• T.Lønnroth, Åbo,Finland
• T.Belgya, Budapest, Hungary
• E.Algin, Turkey

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Summary

• Unique technique to extract level densities and
  ?-strength function experimentally
• New Sm data show that the level density continues
  to decrease as one approaches the N82 closed
  shell
• The M1 pygmy resonance observed in several
  deformed nuclei vanishes in the Sm nuclei as one
  approaches N82
• We dont understand the large enhancement in
  strength function for low E? in Fe, Mo and V
  isotopes

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Microcanonical Temperature
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strength functions in Mo as a function of the
initial excitation energy of the nucleus.
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Strength functions as a function of the final
excitation energy feed by the decay, i.e. only
feeding 1.1 MeV or 1.8 MeV etc.