Nucleons Neutrons Protons

The decay of the neutron into the proton is an important example of decay between mirror nuclei. In the (3 decay of mirror nuclei, the transformed nucleons (neutron —> proton or proton neutron) must be in the same shell and have very similar wave functions. This gives rise to a large matrix element Mif 2 and a very small log ft value. For the (3 decay of mirror nuclei to their partners, log ft values are about 3, which is unusually small. Such transitions are called superallowed transitions. 

For a given nucleus, having nuclear charge number (atomic number) Z representing its number of nuclear protons and nucleon number (mass number) A representing its total number of nucleons (neutrons + protons), the mass excess of atom (Z, A) is defined by... 

Level I. A nucleon (neutron, proton) consists of three (valence) quarks, clearly seen on the scattering image obtained for the proton. Nobody has yet observed a free quark. 

Properties of Particles. From the research of the early part of the twentieth century, the existence of several types of particles was firmly estabhshed, and the properties were deterrnined. The particles that are involved in the decay of radioisotopes are given in Table 4. An additional type of conservation is that in all atomic and nuclear decays, the number of nucleons, ie, protons and neutrons, is conserved and the number of leptons, ie, electrons and neutrinos, is also conserved. 

The alpha particle is a helium nucleus produced from the radioactive decay of heavy metals and some nuclear reactions. Alpha decay often occurs among nuclei that have a favorable neutron/proton ratio, but contain too many nucleons for stability. The alpha particle is a massive particle consisting of an assembly of two protons and two neutrons and a resultant charge of +2. 

A 108 Pd atom has 46 protons, and 46 electrons. The atom described is neutral, hence, the number of electrons must equal the nunber of protons. Since there are 108 nucleons in the nucleus, the number of neutrons is 62 (= 108 nucleons-46 protons). 

Nucleon a proton or a neutron, the number of nucleons in an atom equals the sum of protons and neutrons in the nucleus Octet Rule general rule that states that the most stable electron configuration occurs when an atom surrounds itself with eight valence electrons... 

For example, uranium-238 has 238 nucleons. The atomic number of uranium is 92, which tells us that 92 of these 238 nucleons are protons. The remaining 146 nucleons must be neutrons ... 

All nucleons, both protons and neutrons, attract one another by the strong nuclear force. 

A considerable amount of evidence indicates that nuclear forces are charge-independent, i.e, the neutron-neutron, neutron-proton, and proton-proton forces are identical. The meson theory of nuclear forces, originated by Yukawa, postulates the atomic nucleus being held together by an exchange force in which particles, now called mesons, are exchanged between individual nucleons within the nucleus. 

In a nuclear reaction, there is conservation of the number of protons and neutrons (and thus the number of nucleons). Thus, the total number of neutrons (protons) on the left and right sides of the equations must be equal. 

Example gC, with mass number 14, has 14 nucleons (6 protons and 8 neutrons). 

Recall from Section 2.5 that an atom is characterized by its atomic number, Z, and its mass number, A. The atomic number, written as a subscript to the left of the element symbol, gives the number of protons in the nucleus. The mass number, written as a superscript to the left of the element symbol, gives the total number of nucleons, a general term for both protons (p) and neutrons (n). The most common isotope of carbon, for example, has 12 nucleons 6 protons and 6 neutrons. 

Since there are 12 nucleons (6 protons and 6 neutrons), the average binding energy per nucleon is... 

Theoreticians thought that stable heavier elements might be in prospect. The stability of a nucleus (based on a model of nuclear stability analogous to that of the Rutherford-Bohr model of electronic structure) is determined by the inter-nucleon forces (nucleons are protons and neutrons), an attractive force between all nucleons and a Coulombic repulsion force between protons, the latter becoming proportionately more important as the number of protons increases. Extra stability is associated with filled shells of nucleons, magic numbers for neutrons they are 2,8,20,28,50,82,126,184, and 196 and for protons they are 2, 8, 20, 28, 50, 82, 114, and 164. 

For most purposes the nucleus can be regarded as a collection of nucleons (neutrons and protons), and the internal structures of these particles can be ignored. Recall that the number of protons in a particular nucleus is the atomic number (Z) and that the sum of the neutrons and protons is the mass number (A). Atoms that have identical atomic numbers but different mass number values are called isotopes. The general term nuclide is applied to each unique atom and is represented by where X represents the symbol for a particular element. 

Isotopes are nuclides which I lave the same number of Ijroiuns. but different numbers of neutrons, in their nuclei. An isotope is defined by two numbe s the mass number. A, which is total number of nucleons I protons and neutrons) in the nucleus, and the atomic number, Z, which is total nunber of protons in the nucleus. The value of A is written as a. superscript and of Z as a subscript proceeding the element symbol, e.g. Mo. U, - Pu. 

Beta Decay. For some heavy nuclides and for almost all those with atomic numbers below 60, stability is achieved by a rearrangement of the nucleus in which the total number of nucleons is unchanged. In terms of the neutron-proton model of the nucleus, this rearrangement is the conversion of a neutron to a proton, or vice versa. During such conversions, the nucleus emits either a negative electron or its positive equivalent, a positron. The emission of the negative electron, named the beta ([3-) particle, is what is usually meant by the term [3-decay. 

Matter is composed of atoms. An atom consists of a nucleus containing protons (Z) and neutrons (N), collectively called nucleons, and electrons rotating around the nucleus. The sum of neutrons and protons (total number of nucleons) is the mass number denoted by A. The properties of neutrons, protons, and electrons are listed in Table 1.1. The number of electrons in an atom is equal to the number of protons (atomic number Z) in the nucleus. The electrons rotate along different energy shells designated as A -shcll, L-shell, M-shell, etc. (Fig. 1.1). Each shell further consists of subshells or orbitals, e.g., the L-shell has s orbital the L-shell has s and p orbitals the M-shell has s, p, and d orbitals, and the A-shell has s, p, d, and / orbitals. Each orbital can accommodate only a limited number of electrons. For example, the s orbital contains up to 2 electrons the p orbital, 6 electrons the d orbital, 10 electrons and the / orbital, 14 electrons. The capacity number of electrons in each orbital adds up to give the maximum number of electrons that each energy shell can hold. Thus, the L-shell contains 2 electrons the L-shell 8 electrons, the M-shell 18 electrons, and so forth. 

For the purposes of this chapter, the discussion of the fundamental particles occurring in nuclear reactions will be limited to the nucleons (the proton and neutron), the (negative) electron, and the positive electron (or positron). In Table 21-1 the masses of these particles are given in atomic mass units (Chapter 2) and their charges are expressed as multiples of the elementary charge e = 1.602 x 10 C. 

Because this nuclide has 26 protons, its atomic number, Z, is 26, identifying the element as iron, Fe. This nuclide of iron has 59 total nucleons (26 protons + 33 neutrons), so its nucleon number. A, is 59. 

All the nuclear models assume that the nucleus, like the atom, can exist only in certain discrete energy states. Depending on the model, the energy states may be assigned to the nucleons—neutrons and protons—or the nucleus as a whole. The present discussion of nuclear energy levels will be based on the second approach. 

---