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Phys. Rev. C 68, 034311 (2003) [6 pages]

Free energy and criticality in the nucleon pair breaking process

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M. Guttormsen*, R. Chankova, M. Hjorth-Jensen, J. Rekstad, and S. Siem
Department of Physics, University of Oslo, N-0316 Oslo, Norway

A. Schiller
Lawrence Livermore National Laboratory, L-414, 7000 East Avenue, Livermore, California 94551, USA

D. J. Dean
Physics Division, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, Tennessee 37831, USA

Received 19 September 2002; published 16 September 2003

Experimental level densities for 171,172Yb, 166,167Er, 161,162Dy, and 148,149Sm are analyzed within the microcanonical ensemble. In the even isotopes at excitation energies E<2MeV, the Helmholtz free energy F signals the transition from zero to two quasiparticles. For E>2MeV, the odd and even isotopes reveal a surprisingly constant F at a critical temperature Tc∼0.5MeV, indicating the continuous melting of nucleon Cooper pairs as function of excitation energy.

© 2003 The American Physical Society

URL:
http://link.aps.org/doi/10.1103/PhysRevC.68.034311
DOI:
10.1103/PhysRevC.68.034311
PACS:
21.10.Ma, 24.10.Pa, 25.55.Hp, 27.70.+q

*Electronic address: magne.guttormsen@fys.uio.no

 
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