2.1.1 Nuclear Physics Introduction

Created October 6, 1995

2.1.1.1 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:

2.1.1.2 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

isobar
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.
isotones
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.
isotopes
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.
nucleon
either a neutron or a proton; the constituents of the atomic nucleus.
nuclide
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).
radionuclide
a nuclide that exhibits radioactivity

2.1.1.3 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:

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Douglas J. Wagenaar, Ph.D., wagenaar@nucmed.bih.harvard.edu