A nucleon model of nuclei

A nucleus possesses an internal structure. It consists of many elementary particles— nucleons—the main of which are protons and neutrons. They move in the field of nuclear forces and continuously change their state from that of charged particle (proton) to neutral particle (neutron) and back. However, on an average in a given nucleus, a certain number 

The symbol is used to identify a nucleus, where Z is the chemical symbol of a given element. Mass number A defines the mass of a nucleus. Thus, there are 92 protons and 143 neutrons in the uranium nucleus 092. The number of nucleons Z is often omitted because the relevant information is contained in its chemical symbol. Thus, is the usual symbol. In the text below, a proton mass is marked by ntp. Mass can be measured in kilograms ( ip=1673X10 kg), or can be denominated in atomic units of mass (1 a.m.u. = 1.66X10 kg). It is sometimes also expressed in eneigy units ( ip=938.2 MeV). 

Each nucleon possesses its own angular momentum, i.e., spin. The quantum numbers of neutron and proton spins are the same as an electron spin, i.e., 1/2. In general, a complex nucleus also possesses a spin angular momentum. As a result of the partial or complete compensation of nucleonic spins, the total spin can have values of 0, 1/2, 1, 3/2, etc. Herewith, in full analogy with the electronic shell, the angular moment (mechanical moment) of a nucleus is  

Analogously with electron characteristics, the projection Lj on the selected axis z can have the values  

Since in nuclear physics the mutual orientation of the angular and magnetic moments can be both parallel or antiparallel, the gyromagnetic ratio can also be positive (parallel orientation of these two vectors) and negative (antiparallel orientation as for orbital electron state). Therefore, the nuclear g-factor (g ) (in units e/2 jp) can have both positive and negative signs. They cannot be calculated but are defined from experiment only. Therefore, one can see that the sign is historically casual. For proton gp is +5.5851, for neutron gj,=-1.9103. 

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