european ssaf crete, sept. 7-8, 2007 european ssaf crete, sept. 7-8, 2007 1 1 oslo cyclotron...
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European SSAF Crete, Sept. 7-8, 2007European SSAF Crete, Sept. 7-8, 2007
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Oslo Cyclotron Laboratory and the
Nuclear Physics Program
Oslo Cyclotron Laboratory and the
Nuclear Physics Program
S. SiemDepartment of Physics
University of Oslo
S. SiemDepartment of Physics
University of Oslo
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Oslo Cyclotron Laboratory (OCL)Oslo Cyclotron Laboratory (OCL)
Protons 2-35 MeVDeuterons4-18 MeV3He 6-47 MeV4He 8-35 MeV
Protons 2-35 MeVDeuterons4-18 MeV3He 6-47 MeV4He 8-35 MeV
European SSAF Crete, Sept. 7-8, 2007European SSAF Crete, Sept. 7-8, 2007
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Experimental set-upExperimental set-up
CACTUS:28 NaI 5”x5” and 8 Si telescopes
CACTUS:28 NaI 5”x5” and 8 Si telescopes
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The PhysicsThe PhysicsNuclear structure and decay properties in continuumNuclear structure and decay properties in continuum
Spin2 - 6 ħ
Ex
T = 1 MeV
Yrast line(no levels)
European SSAF Crete, Sept. 7-8, 2007European SSAF Crete, Sept. 7-8, 2007
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The energy distribution of primary rays contains information on the level density ρ(Ef) and gamma-ray transmission coefficient T(E)
The Brink Axel hypothesis:
The Brink Axel hypothesis:
)()(),( ρ ETEEEP fi ⋅∝
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Level densityLevel density Gamma-ray strength functionsGamma-ray strength functions
148Sm
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147Sm
146Sm
Level Densities Level Densities • Left: Comparing even-even nuclei: the nuclei closer to a closed shell and
have smaller level density, but more structure.• Right: There is a big difference between odd and even nuclei due to pairing
• Left: Comparing even-even nuclei: the nuclei closer to a closed shell and have smaller level density, but more structure.
• Right: There is a big difference between odd and even nuclei due to pairing
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Microcanonical Temperature
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Radiative strength functions for some rare earth nuclei. Roughly, the shape corresponds to the tail of the giant electric dipole resonance (GEDR). There is a significant bump superimposed on the radiative strength function, which is interpreted as scissors mode in continuum (M1).
Radiative strength functions for some rare earth nuclei. Roughly, the shape corresponds to the tail of the giant electric dipole resonance (GEDR). There is a significant bump superimposed on the radiative strength function, which is interpreted as scissors mode in continuum (M1).
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Scissors mode
€
Established M1 multipolarity of a pygmy
resonance in 172Yb at Eγ = 3.3 MeV
€
B(M1↑) =9hc
32π 2
σΓ
E
⎛
⎝ ⎜
⎞
⎠ ⎟py
= 6.5(15)μN2
€
π ν
European SSAF Crete, Sept. 7-8, 2007European SSAF Crete, Sept. 7-8, 2007
1111A.Voinov et al. Phys.Rev.Lett.93, 142504 (2004)
Radiative strength function of 57Fe
A large unexpected increase in the radiative strength function was first seen in iron. We still don’t have an explanation for what the physics behind it is.
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Features and future plansFeatures and future plans
• OCL is modern and well equipped• Continues beam time of 1-2 weeks• New Silicon Ring (SiRi) with 64
particle telescopes• Plans to replace the 28 NaI
detectors with BrilLanCe 380 crystals
• OCL is modern and well equipped• Continues beam time of 1-2 weeks• New Silicon Ring (SiRi) with 64
particle telescopes• Plans to replace the 28 NaI
detectors with BrilLanCe 380 crystals
European SSAF Crete, Sept. 7-8, 2007European SSAF Crete, Sept. 7-8, 2007
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In Oslo we now have:
2 PhD positions and
1 Postdoc position
To be filled as soon as possible.