Radioactivity and the Decay of Nuclei


Radioactivity is a property of a number of elements in the periodic table where their nuclei break down and release particles such as alpha, beta and gamma particles.

Radioactivity is a property of a number of elements in the periodic table particularly larger elements past uranium. These particles are broken own into smaller elements but also often produce ionising radiation. Ionising radiation is called as such as when it comes into contact with another atom or molecule it can cause the loss of electrons creating ions.

This occurs when an atom begins to break down and gives off radiation in the form of alpha beta or gamma particles. Alpha radiation is when a helium nucleus is given off, two protons and neutrons. They are slow moving and can be stopped by the skin and small amounts of air/paper but are highly ionising. Beta particles are faster moving and are comprised of an electron, they can be stopped by sheets of metal and are only moderately ionising. Gamma waves are not treated as particles, instead they are waves of energy. Gamma waves can only be stopped by lead and concrete and can travel far distances, however they are weakly ionising.

Radioactive decay is the breakdown of the parent nucleus to produce two daughter nuclei. When this break down occurs very often alpha beta and gamma decay are produced. Uranium and thorium are the two best known examples of radioactive nuclei naturally occurring in the earth’s crust in compounds. This radioactive decay can be harnessed in a nuclear reactor to generate heat energy which can be harnessed to heat water and generate steam for electricity production.

Radioactive decay is linked to the concept of half life. Elements that are decay products exist before breaking down further into more stable elements. The term half life is defined as the time required for exactly half of the elements to decay on average. Some elements have long half lives for example Uranium has a half life of 4.5 billion years making it very dangerous and difficult to store. However the synthetic element Seaborgium has a half life of 2.4 minutes. These short half lives make synthetic elements very difficult to study due to their short existence and rapid decay.

A large number of later discovered elements in the periodic table in the Actinoid series were discovered using particle accelerators. Large nucleuses are combined together to create elements with a large mass, these are known as synthetic elements. These do not occur naturally but are artificial. The first example of this was Curium which was synthesised in the bombardment of plutonium using alpha particles. The work of Seaborg and Ghiorso between 1952 to the late 70’s involved the use of detecting radioactive debris from the detonation of atomic bombs. During the Cold War teams from the Soviet Union and the US were competing to discover new elements using particle accelerators.

Terms in section
Half life

Half life is a measurement of the time taken for half of the mass of a radioactive element to decay into smaller more stable elements


Glenn Seaborg was an American physicist who is credited with discovering many synthetic elements for which he was awarded the nobel prize for chemistry


Albert Ghiorso was an American scientist whose research led to the discovery of 12 chemical elements


Actinoids are elements from the atomic number 89 to 103 largely forming the F block of elements in the extended periodic table. They are mostly radioactive

Synthetic element

Synthetic elements are elements that do not occur naturally in the universe and have to be created in a lab or through nuclear experiments in a cyclotron


Nuclei is the term given to a single nucleus of an atom

Radioactive decay

Radioactive decay is when a large unstable nucleus breaks down into two smaller nuclei releasing radiation in the form of alpha beta or gamma to release energy and become more stable

Daughter nuclei

Daughter nuclei is the name given to two or more nucleuses that are formed from the a parent nucleus

Alpha particle

An alpha particle is a product of nuclear decay released by some radioactive elements. Made of two protons and two neutrons with a mass of 4. A large particle but slow moving and is easily stopped by air

Beta particle

A beta particle occurs when a neutron in an unstable nucleus turns into a proton and electron. The electron is released from the atom as the radiation

Gamma Wave

Gamma waves occur when a radioactive nuclei breaks down releasing a photon of energy as a wave. Very penetrating and can be stopped by lead and concrete but has a weak ionizing power


The electron is the smallest sub atomic particle that make up the atom. Has a negative charge and is located in shells that orbit the nucleus


Ionising is a term used to describe when an atom turns into an ion. Ionising radiation causes an atom to lose electrons


An ion forms when an atom loses or gains electrons to form a positive or negative particles due to the unbalanced number of protons


Uranium is the name of an element that is radioactive and unstable due to its high mass. it is used in the production of nuclear power


Radioactivity is a property of some elements where the nucleus breaks down and turns into smaller parts to release energy

Particle accelerator

A particle accelerator is a machine designed to speed up atoms before colliding them together to create new elements with a large mass

Parent nucleus

Parent nucleus is the term given to the original nucleus at the start of the decay


Oxidation States of Ions and Atoms


Common Groups and Periods of the Periodic Table