Trung tâm Vật lý tính toán - Trung tam Vat ly tinh toan

Seminar on Theoretical and Computational Physics:
Title	Pairing in finite systems at nonzero temperature and angular momentum
Speaker	D.Sc. Nguyen Dinh Dang
Affiliation	RIKEN, Tokyo and Institute for Nuclear Science and Technique, Hanoi
Date	Friday, 09-01-2009
Time	9h30AM
Location	Institute of Physics, 10 Dao Tan, Ba Dinh, Hanoi
Abstract	In small systems such as nuclei, large thermal fluctuations smooth out the sharp transition from the superfluid phase to the normal one. Two microscopic approaches to thermal pairing in finite nuclei, which have been recently proposed by us, will be presented, namely the modified BCS (MBCS) and the BCS + self-consistent quasiparticle RPA (BCS+SCQRPA). It is shown that, in both of them the fluctuation of quasiparticle number is responsible for smoothing out the sharp superfluid-normal phase transition. As the result, the thermal pairing gap does not collapse at a critical temperature predicted by the conventional BCS theory, but has a tail extended to high temperatures. By extending the BCS+SCQRPA to finite angular momentum, the appearance of a thermally assisted pairing in hot and rotating nuclei is also predicted. As an application of the theory, I will show the role of thermal pairing in the damping of giant dipole resonances (GDR) in highly-excited nuclei, namely the pairing effect on the width of GDR at temperatures below 1.5 MeV. The theoretical prediction is compared with the experimental data for the GDR widths in tin isotopes. Finally, a novel formula for extracting the thermal gap from the odd-even mass difference of hot nuclei is proposed.

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