Forces nuclear

Besides particles, the forces of nature play also a key role. In the past century four fundamental forces were recognized the gravitational, electromagnetic, weak, and strong forces. Of these the weak and strong forces are less familiar, because they are nuclear forces and their strength rapidly diminishes over all but subatomic scales. 

H. Yukawa (Kyoto) prediction of the existence of mesons on the basis of theoretical work on nuclear forces. 

The nucleus of an atom consists of protons and neutrons that are bound together by a nuclear force. Neutrons and protons are rearranged in a nuclear reaction in a manner somewhat akin to rearrang ing atoms in a chemical reaction. The nuclear reaction liberating energy in a nuclear power plant is called nuclear fission. The word fission is derived from fissure, which means a crack or a separation. A nucleus is separated (fissioned) into two major parts by bombardment with a neutron. 

It is relatively easy to summarize how nuclear stability (and hence the attractive nuclear forces) depends upon the numbers of protons and neutrons in the nucleus. For atoms with atomic number less than 20, the most stable nuclei are those in which there are equal numbers of protons and neutrons. For atoms with atomic numbers between 20 and 83, the most stable nuclei have more neutrons than protons. For atoms of atomic number greater than 83, no nucleus can be considered stable by our definition. These... 

Electrical repulsion between protons should cause a nucleus that contains more than one proton to fly apart. In Section 2H. we describe how the third type of fundamental force, called the strong nuclear force, acts within nuclei and generates enough attraction among nuclear particles to hold nuclei together. 

As described in Chapter 2, nuclei with more than one nucleon are held together by the strong nuclear force. Energy must be provided to overcome this force and remove a nucleon from a nucleus. This energy is called the nuclear binding energy. 

Neutron capture always is exothermic, because the neutron is attracted to the nucleus by the strong nuclear force. Consequently, neutron capture generates a product nuclide in a metastable, excited state. These excited nuclei typically lose energy by emitting either y rays or protons ... 

In contrast to PIXE and RBS, where forces are respectively electromagnetic and electrostatic, this kind of microanalysis uses low range nuclear forces. The analysis is based on the detection of the y-rays emitted from nuclei that are in an excited state following a charged particle induced nuclear reaction. 

Fig. 2.7. Coulomb barrier penetration by a charged particle, a is the range of the nuclear force and b the classical turning point.

This section begins with a brief summary of the compliance approach to nuclear motions (Decius, 1963 Jones and Ryan, 1970 Swanson, 1976 Swanson and Satija, 1977). The inverse of the nuclear force constant matrix H of Equation 30.2, defined in the purely geometric g-representation,... 

Cochran, T.B., Arkin, W.M., and Hoenig, M.M., Nuclear Weapons Databook Volume I, U.S. Nuclear Forces and Capabilities, Ballinger, Cambridge, 1984. 

In 1925 physicists had known of two particles of matter, the proton and the electron. By 1947 five were known the proton, neutron, electron, muon, and neutrino. Yet another particle, the pion, was known, but it was associated with a force and it wasn t a component of matter. In 1925 they had known of two forces gravity and electromagnetism. Now there were four. The two new ones were the weak nuclear force (now called simply the weak force ) and a strong nuclear force that held nuclei together. 

The four forces are gravity, electromagnetism (electrical attraction and repulsion and magnetic forces are explained by the same theory), and the strong and weak nuclear forces. The weak force is... 

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