the oslo method applied to the quasi-continuum of e xcited n uclei magne guttormsen
DESCRIPTION
The Oslo Method Applied to the Quasi-Continuum of E xcited N uclei Magne Guttormsen Department of Physics and SAFE University of Oslo. Measure particle - g coincidences Unfold spectra at each E 1) Apply the first- generation method 2) Ansatz : First- generation matrix - PowerPoint PPT PresentationTRANSCRIPT
The Oslo Method Applied to the Quasi-Continuum
of Excited Nuclei
Magne GuttormsenDepartment of Physics and SAFE
University of Oslo
Oslo Seminar, Oslo, 6 December, 2012
The Oslo Method
Oslo Seminar, Oslo, 6 December, 2012
1) M. Guttormsen et al., NIM A374 (1996) 3712) M. Guttormsen et al., NIM A255 (1987) 5183) A. Schiller et al., NIM A447 (2000) 498
Analysis of possible systematic errors of the Oslo methodA.C. Larsen et al., Phys. Rev. C 83, 034315 (2011)
• Measure particle-g coincidences• Unfold g spectra at each E 1) • Apply the first-generation
method 2)
• Ansatz: First-generation matrix P(E, Eg) (E - Eg) T(Eg) 3) • Normalization• Examples of level density
Experiments at OCL
12 MeV d on 232Th24 MeV 3He on 232Th
g3He –beam
3He, a,d,t
5”x5” NaI
M.Guttormsen, A.Bürger, T.E.Hansen, N.Lietaer, NIM A648(2011)168
∆E-E
Backwards:J = 40o – 54o
Oslo Seminar, Oslo, 6 December, 2012
∆E-E bananas
(d,d’)232Th (d,p)233Th (3He,t)232Pa (3He,d)233Pa
(3He,a)231Th
Oslo Seminar, Oslo, 6 December, 2012
Assumption for the extraction of first-generation g-spectra
Oslo Seminar, Oslo, 6 December, 2012
(d,p)
(d,p)
The g-energy distribution is the sameif the decay starts at E after g-emission orstarts after the direct reaction into E.
E
g
Gamma-multiplicity
Oslo Seminar, Oslo, 6 December, 2012
From total to primary g-ray matrix
spin2-6ħ
Ex
g
g
g
232Th(d,p) 233Th
Oslo Seminar, Oslo, 6 December, 2012
Primary g-ray matrix
P(Ex,Eg)
Level density Trans. coeff.
(Ef) T(Eg)
P(Ex,Eg)
Oslo Seminar, Oslo, 6 December, 2012
Multiplicative factors
Oslo Seminar, Oslo, 6 December, 2012
Brink hypothesis
Fermi’s golden rule
P(Ex,Eg) = (Ef) . T(Eg) ?
Oslo Seminar, Oslo, 6 December, 2012
Normalization
Oslo Seminar, Oslo, 6 December, 2012
1) A. Gilbert and A.G.W. Cameron, Can. J. Phys. 43, 1446 (1965)
2) T. von Egidy and D. Bucurescu, Phys. Rev. C 72, 044311 (2005), Phys. Rev. C 73, 049901(E) (2006)
3) S. Goriely, HF+BCS Demetriou and Goriely, Nucl. Phys. A695 (2001) 95
44ScAverage level spacings D from neutron capture:
(Ef) and T(Eg)
Oslo Seminar, Oslo, 6 December, 2012
231,232,233Th and 232,233Pa
Inverse energy-weighted sum rule:
K. Heyde, P. von Neumann-Cosel, A. Richter, Rev. Mod. Phys., 82, 2365 (2010)
Oslo Seminar, Oslo, 6 December, 2012
M. Guttormsen et al., PRL 109, 162503 (2012)
Thermal quasi-particles, the spectators of mid-shell nuclei
Oslo Seminar, Oslo, 6 December, 2012
Thermal quasi-particles create level density
Oslo Seminar, Oslo, 6 December, 2012
Cooper pair Broken pair
1 level 25 levels
A simple model for level density
Oslo Seminar, Oslo, 6 December, 2012
- Combining all possible proton and neutron configurations- Nilsson single-particle energy scheme- BCS quasi-particles
j
Nilsson level scheme
Oslo Seminar, Oslo, 6 December, 2012
Model parameters:k = 0.066m = 0.32b = 0.23
1p 1n1p 3n1p 5n1p 7n
3p 1n3p 3n3p 5n
5p 1n5p 3n
7p 1n
20
Level density and broken pairs
Oslo Seminar, Oslo, 6 December, 2012
Level densities
Number of broken pairs
Parity asymmetry
Oslo Seminar, Oslo, 6 December, 2012
U. Agvaanluvsan, G.E. Mitchell, J.F. Shriner Jr., Phys. Rev. C 67, 064608 (2003)
Titanium and tin
Oslo Seminar, Oslo, 6 December, 2012
46Ti
Summary
Oslo Seminar, Oslo, 6 December, 2012
• Simultaneous extraction of level density and g-strength function• Examples from A = 40 – 230• Number of thermal quasi-particles determines number of levels• Constant temperature level density• Fluctuations for lighter even-even nuclei
Oslo Seminar, Oslo, 6 December, 2012
http://tid.uio.no/workshop2013/