ann-cecilie larsen workshop on level density and gamma strength in continuum oslo, may 21-24, 2007
DESCRIPTION
Experimental level densities and -ray strength functions in the f 7/2 nuclei 44,45 Sc and 50,51 V. Ann-Cecilie Larsen Workshop on Level Density and Gamma Strength in Continuum Oslo, May 21-24, 2007. DEPARTMENT OF PHYSICS UNIVERSITY OF OSLO. Overview. Motivation - why study Sc and V? - PowerPoint PPT PresentationTRANSCRIPT
Experimental level densities and -ray strength functions in
the f7/2 nuclei 44,45Sc and 50,51V
Ann-Cecilie LarsenWorkshop on Level Density
and Gamma Strength in Continuum
Oslo, May 21-24, 2007
DEPARTMENT OF PHYSICSUNIVERSITY OF OSLO
Overview• Motivation - why study Sc and V?• Some experimental details• The Oslo method• Level densities• Gamma-ray strength functions• Summary
Motivation• Nuclei with A~40-50• Shell effects, Z=20, N=28 shell gap• Upbend structure in strength functions?
(previously seen in 56,57Fe, 93-98Mo)
Where are we? (I)
44,45Sc, 44Sc, 45Sc,
d3/2
f7/2
p3/2
f5/2
d3/2
f7/2
p3/2
f5/2
d3/2
f7/2
p3/2
f5/2
Where are we? (II)
50,51V,
d3/2
f7/2
p3/2
f5/2
50V,
d3/2
f7/2
p3/2
f5/2
51V,
d3/2
f7/2
p3/2
f5/2
Experimental details (I)
3He beam, 30 MeV on 51Vand 38 MeV on 45Sc.Reactions:
Inelastic scattering (3He,3He’)Pick-up (3He,)
Experimental details (II)• Particle- coincidences
45o
NaI(Tl)
Si E-E telescope
3He
Target nucleus
The Oslo method• Unfold all spectra †
• Apply the first-generation method ††
• Ansatz: first-gen. matrix (E-E)T(E) †††
† : M. Guttormsen et al., NIM A374 (1996) 371†† : M. Guttormsen et al., NIM A255 (1987) 518††† : A. Schiller et al., NIM A447 (2000) 498
Normalizing the first-generation matrix
E (MeV)
0
4
8
40 8
E (MeV)
50V
E,min = 1.7 MeV
Emin = 3.3 MeV
Emax = 9.2 MeV
Extraction of level density and -ray transmission coefficient
The primary -ray matrix P(E, E)is factorized according to
Theoretical approach:
Iteration methodMinimize
E
Input matrixP(E, E), 50V
E
The resultingPth(E, E), 50V
E
E
Quality of the iteration procedure
50V 44Sc
Normalizing the level density
• Low E: known, discrete levels
• At Bn (or Bp): data from neutron (proton) resonance experiments
Uncertainties in normalization
• Calculation of (Un/p), spin cutoff parameter
1)
2)
3)
Spin distributions, 44Sc
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+BCSDemetriou and Goriely, Nucl. Phys. A695 (2001) 95
1)
2)
3)
Level densities of 44,45Sc
Level densities of 50,51V
Constant-temperaturemodel
Model to calculate the level density
• Combining all possible proton and neutron configurations
• Nilsson energy scheme• BCS quasiparticlesSingle q.p energy:
Total energy due to q.p. excitations:
Nilsson levels, 45ScModel parameters:
= 0.066 = 0.32
[D.C.S. White et al., Nucl. Phys. A 260, 189 (1976)]
= 0.23[In agreement with
P. Bednarczyk et al., Phys. Lett. B 393, 285 (1997)]
Calculated level densities, 44,45Sc
Average number of broken pairs
Parity asymmetry
Defining the parity asymmetry as
[U. Agvaanluvsan, G.E. Mitchell,J.F. Shriner Jr., Phys. Rev. C 67, 064608 (2003)]
~0.02for (J=1/2, J=3/2)
The -ray transmission coefficient
Assuming dominanceof dipole radiation (E1 and M1)
Normalizing the -ray strength functions of 44,45Sc
Data from J. Kopecky and M. Uhl:
fE1 = 1.61(59)·10-8 MeV-3
fM1 = 1.17(59)·10-8 MeV-3
Comparing with other data and theory
45Sc(,n)44Sc
46Ti(,p)45Sc
The -ray strength functions of 50,51V
Kadmenskij, Markushev and Furman:
Lorentzian, spin-flip:
Summary• Extraction of and T from first-
generation spectra• Level densities of 44,45Sc and 50,51V• New model to calculate , Nqp, • Gamma-ray strength functions of 44,45Sc
and 50,51V
Collaborators• Oslo: M. Guttormsen, S. Messelt, F.
Ingebretsen, J. Rekstad, S. Siem and N.U.H. Syed
• Åbo Akademi, Finland: T. Lönnroth• NSCL/MSU, USA: A. Schiller• Ohio University, USA: A. Voinov