科研之友
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摘要
At low densities, with decreasing temperatures, in symmetric nuclear matter alpha particles are formed, which eventually give raise to a quantum condensate with four-nucleon alpha-like correlations (quartetting). Starting with a model of alpha matter, where undistorted alpha particles interact via an effective interaction such as the Ali-Bodmer potential, the suppression of the condensate fraction at zero temperature with increasing density is considered. Using a Jastrow-Feenberg approach, it is found that the condensate fraction vanishes near saturation density. Additionally, the modification of the internal state of the alpha particle due to medium effects will further reduce the condensate. In finite systems, an enhancement of the S-state wave function of the center-of-mass orbital of alpha-particle motion is considered as the correspondence to the condensate. Wave functions have been constructed for self-conjugate 4n nuclei that describe the condensate state but are fully antisymmetrized on the nucleonic level. These condensate-like cluster wave functions have been successfully applied to describe properties of low-density states near the n alpha threshold. Comparison with orthogonality condition model calculations in (12)C and (16)O shows strong enhancement of the occupation of the S-state center-of-mass orbital of the alpha particles. This enhancement is decreasing if the baryon density increases, similar to the density-induced suppression of the condensate fraction in alpha matter. The ground states of (12)C and (16)O show no enhancement at all, thus a quartetting condensate cannot be formed at saturation densities.
- 出版日期2008-6
