People have been trying to figure out what the basic stuff of the material world is for thousands of years. An ancient Greek named Democritus said around 460 BC that there were tiny indivisible things he called atoms that made up all material objects. After that there were a lot of other ideas proposed that were not as advanced.
In the early 19th Century, John Dalton built on earlier work to propose that chemical elements were made up of a single type of unique tiny objects or atoms. These elements combined in various ways to make up compounds. Elements and compounds constitute all material substances and objects.
In the mid 19th Century, Dmitri Mendeleev developed the periodic table which arrayed all the elements in a grid based on increasing numbers of atoms which make up a particular element. The elements in each column shared similar chemical properties. The gaps in the grid have been steadily filled in until today we have a complete table containing elements with up to118 atoms.
In the early 20th Century, it was discovered that the "indivisible" atoms were actually made up of smaller units. These were call electrons, protons and neutrons. It turned out that atoms were mostly empty space with a cloud of electrons surrounding a tiny nucleus containing protons and neutrons. The electrons carry a negative charge, the protons carry a positive charge and neutrons are neutral. (Actually neutrons are composed of an electron and a proton.) The number of protons in the nucleus of an atom uniquely identifies that atom as a particular element.
While the number of protons in the atoms of a particular element is a fixed number, the number of neutrons can vary. An atom of a particular element that contains a specific number of neutrons is referred to as an isotope of that element. The term nuclide is often used in place of isotope when the focus is on the behavior of the nucleus in nuclear chemistry as opposed to the behavior of the element in conventional chemistry. The neutron number can have a big influence on nuclear properties but has very little effect on the chemical properties of an element.
Elements are identified by their atomic number which corresponds to the number of protons in their nucleus. The combination of the protons and neutrons in a nucleus is referred to as the mass number. So a particular element will always have the same atomic number but the isotopes or nuclides of a particular element will have different mass numbers.
Some isotopes are radioactive and are referred to as radioisotopes or radionuclides. This means that they can decay. There are several different types of decay including spontaneous fission, alpha decay and double beta decay. The time it takes for half of the atoms of an isotope to decay is known as the half-life of that isotope. Half-lives can vary from nanoseconds to trillions of years. Many of the naturally occurring isotopes are considered to be stable and to never undergo any type of decay. Other naturally occurring isotopes have estimated half-lives longer than the estimated life span of the universe. I will be primarily concerned with naturally occurring and man-made isotopes which have half-lives from nanoseconds to millions of years.
The particles of energy and matter emitted by an isotope when it undergoes decay are the types of radiation that I will be discussing in this blog.