2.1.1 Nuclear Physics Introduction
Created October 6, 1995
22.214.171.124 Nuclear Physics Introduction
A nucleus is comprised of neutrons and protons. The number of neutrons in a nucleus is given by N. The number of protons, the atomic number, is given by Z. The combination of N and Z defines each nuclide uniquely. The sum (N+Z) is A, the atomic mass number, the total number of nucleons.
The number of protons Z defines the element uniquely. Each element has a two-letter symbol. The symbol used for each nuclide is the combination of the element symbol and the atomic mass number A:
For example: H-3 is the hydrogen nucleus with one proton (since it's hydrogen) and 2 neutrons (since N = A-Z = 3-1). Another way of expressing each nuclide is to redundantly list the atomic number (redundant since the element symbol tells us the atomic number:
126.96.36.199 Nuclide Nomenclature
A nuclide is a specified combination of neutrons and protons. Nuclides different energy states of the same nucleus are also separate nuclides (e.g, Tc-99m and Tc-99). Nuclides are often referred to as ISOTOPES, although stricktly speaking this is not technically correct. We will now define isotopes and related terms which refer to different groupings of nuclides
- nuclides having identical "A" values, or mass numbers. N-14 and C-14 are isobars. Isobars are important in beta decay, positron decay, and electron capture transitions since the "A" value is uneffected by these decays although the Z value does undergo change. These decays are known therefore as "isobaric transitions" and follow "isobaric" lines on the chart of the nuclides.
- isomer; isomeric state (also metastable state)
- A nuclide in an excited energy state, the decay time of this higher energy state being observable, i.e. greater than about 10**-12 s. An isomeric state of a nuclide has the same Z, N, and A as the nuclide but a differing energy level.
- nuclides having identical "N" values, or numbers of neutrons. O-15 and N-14 both have N=7 and are therefore isotones. A mnemonic is to allow the "n" in isotone to stand for a fixed Neutron number.
- nuclides of the same element, i.e. nuclides that have the same Z-value. This is remembered by assigning the "p" in isotopes to the number of Protons. For example, C-14 is an isotope of carbon. However, C-7 is not an isotope of carbon, since this nuclide with only one neutron does not exist and cannot be produced. A mnemonic is to allow the "p" in isotope to stand for a fixed "proton" number.
- either a neutron or a proton; the constituents of the atomic nucleus.
- a nucleus which has a specified number of protons (Z), and a specified number of neutrons (N). For example, C-14 has 6 protons (which define it as carbon) and 8 neutrons (which define the final value of the mass number A=Z+N or 14=6+8.) The nuclide symbol uniquely identifies each nuclide: C-14 (also writen with the A-value in a superscripted position preceeding the element symbol) tells you that we have a Z of 6 (since it is carbon) and an N value of 8 (since 14-6=8).
- a nuclide that exhibits radioactivity
188.8.131.52 Particles of Interest in this Course
A summary of the particles which comprise the atoms and nuclei and which are involved in interactions between these particles are summarized in the following table:
Return to Main Table of Contents
Return to Section 2 Table of Contents
Proceed to 2.1.2 - Line of Stability
Douglas J. Wagenaar, Ph.D., email@example.com