核科学家摇篮—北京大学技术物理系的创建、发展和历史演变

20世纪的核科学是物理学发展的重要组成部分,北京大学原子核物理学科在北大物理90年发展的历程中和我国原子能事业发展中也占有重要地位.因此,对建立于1955年、专门培养核科技人才的北京大学物理研究室-原子能系-技术物理系的创建、发展和历史演变做一简要回顾是十分必要的.文章根据许多老师（包括作者本人）的亲身经历、感受和历史回忆,并查阅有关历史资料、文件档案加以归纳、整理,尽可能地再现北京大学技术物理系的46年的光辉历程,并展望21世纪学科发展的美好前景.北京大学技术物理系的创建、发展和历史演变,是与我国核工业及原子能事业的发展历程紧密相连的.     

牛顿碰撞球的解释与分析

对牛顿碰撞球的常规碰撞形式和混合联珠单球碰撞形式做了理论分析和解释.在常规碰撞时,将悬线(钓鱼线)先悬挂小球一段时间后组装仪器,可克服悬线的拉力.在混合联珠单球碰撞时,根据理论分析,选取大球和小球的质量比为27∶8时,演示效果较好.     

Zeno effect in quantum Newton's cradle

We describe a chain of quantum oscillators which behaves analogously to Newton's cradle. The energy swings between the ends of the chain with very low population in its interior. Moreover, the oscillators at the ends can entangle with each other with negligible entanglement with the intermediate oscillators that mediate the process. Up to a certain number of oscillators, the system evolves in a manner similar to two coupled oscillators. The conditions for such behavior and the characteristic periods are analyzed. When that number exceeds a threshold, the dynamical regime changes to virtually freezing. In the oscillatory regime, Zeno effect can be observed. The parallelism between the Zeno dynamics in quantum Newton's cradle and in two coupled oscillators is highlighted. Promising platforms to observe such phenomena in the laboratory are cavities in photonic-band-gap material and trapped ions.     

A remark on the saturation of nuclear forces in nuclear matter

The paper deals with the problem of saturation in nuclear matter, when the two-nucleon interaction is described by the soft core potentials acting in a limited number of orbital states. The potentials used belong to the class of the realistic potentials.     

A Hartree-Fock nuclear mass formula

We recall the main features of the recently published mass formula, HFBCS-1, based on the Hartree-Fock-BCS method, and compare its extrapolations out to the neutron drip line with those given by the fine-range droplet model. A new Hartree-Fock-Bogolyubov mass formula, HFB-1, is described: the rms error of the fit to 1888 masses is 0.766 MeV, compared with 0 .738 MeV for HFBCS-1, but there are no substantial changes in the predictions relevant to the r-process. After a critical examination of various questions relating to the effective nucleon mass and to the requirements of the relativistic mean-field theory, we conclude that the greatest remaining ambiguity concerns the nature of the pairing force. Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002 RID="a" ID="a"e-mail: pearson@lps.umontreal.ca