Nuclear Physics课件.ppt

Chapter 12;Summary to the last lecture;2. The characteristics of laser Good directionality High brightness and high intensity. Good monochromatic Good coherence (time spatial 相干性) Good polarization (偏振);12.1 The basic properties of nucleus ;It is well known that an atom has a nucleus in the center of the atom. The most obvious feature of the atomic nucleus is its size, of the order of 20,000 to 200,000 times smaller than the atom itself. Although the “surface” of a nucleus is not a sharp boundary, experiments determined an approximate radius for each nucleus. The radius is found to depend on the mass, which in turn depends on the total number A of neutrons and protons, usually called mass number.;12.1.1 the structures of nucleus (核子);Nuclear masses: Mass of an atom includes the mass of electrons and the mass of nucleus. ;Atomic mass number ;12.1.2 Nuclear properties;Where m is the mass of a nuclear such as proton or neutron which is given as 1.67 ? 10-27kg. So the density of the nucleus is ;2. Nuclear forces and nuclear energy levels: The force of making the protons and neutrons together is obviously not electromagnetic force as neutrons are charge free and it is not the gravitational force either. Experiments show that such a force is a special interaction force which is called nuclear force. ; Nuclear force properties: (1). It is a “short distance force” as its effective distance is about 10-15m and out of this range it reduces to zero sharply; (2). The force is the strongest force we have observed so far; (3) the force has a feature of saturation, the nucleus can interact only with its nearest neighbor; ;(4) the interaction of nuclear force does not depend on charged condition of nuclei. That is that interaction forces from n-n, n-p and p-p are almost the same. ;12.1.3. Nuclear binding energy and mass defect (亏损）;;Where;Brief Review to the last lecture;12.2 The decay types of the atomic nucleus;? decay The heavy nucleus with its mass number A209 could emit