Ionising particles

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Radioactive emission is a chemical process which occurs when the nucleus of an unstable atom loses energy spontaneously by emitting radiation and other ionising particles. In this decay process, one atom usually called the �parent� nuclide is been transformed to a different atom after the emission and this new atom is called �daughter� nuclide.

In 1896, Henri Becquerel, who was a French scientist first discovered radioactivity when he was working on phosphorescent material. Becquerel was thoroughly conversant with Wilhelm Conrad Roentgen�s work on X-rays discovery and as a result that he focused his attention on the study of X-ray�s associated occurrence of phosphorescence and fluorescence. Becquerel accidentally made a remarkable discovery. He realised that although phosphorescence, fluorescence and X-ray had many alikeness, they had quite important differences too. He observed that while X-rays and fluorescence halted when the initiating energy source is stopped or removed, phosphorescence progressed in its emission for a while even when the energy source has been removed.

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Marie Curie and her husband Pierre who both worked in Becquerel�s lab, embarked on a further study on radioactivity and its properties. Marie and Pierre were aware of Becquerel�s notification that uranium emanations had the ability to convert air into an electric conductor. They therefore used very sensitive instruments to measure how well the emanations of several elements will induce electric conductivity.

In 1898, they tested uraninite, which is the primary ore of uranium, in order to determine it�s capability to convert air into electric conductor. Amazingly, they found out that uraninite produced a current which was 300 times more powerful the than pure uranium. They carried out the same measurement several times uraninite and always found the same shocking results. These findings made them to believe that there was an unknown substance together with uranium existed in the uraninite ore.

Radioactive emissions are of three types. These are alpha, beta and gamma emissions and these are emitted from alpha, beta, and gamma decays respectively.

In alpha emissions, an alpha particle is emitted by an unstable atomic nucleus. An alpha particle is basically a helium atom which has a mass number of 4 and proton number of 2. Therefore, after alpha emission, the �parent� atom is transferred to another atom which has a mass number four� and atomic number two less.

For example; Uranium-238 undergoes alpha decay to produce Thorium-234.

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�92 U� →�� 90Th + 2� He.

During Beta emissions, a beta particle is emitted by an unstable atomic nucleus. Beta particle are electrons or positrons which are usually high in energy and also with high speed and are always are in a form of ionising radiations.

An electron is a subatomic particle which bears a negative charge but a positron on the other hand bears a positive charge and it�s the anti-matter counterpart of an electron.

The type of beta emission in which electrons are emitted (denoted B-) occurs when an unstable atomic nucleus which has neutrons in excess have a neutron converted to an electron, proton and an electrically neutral anti-neutrino.

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However, the type of beta emission in which positrons are emitted (denoted B+) occurs when an unstable atomic nucleus which has protons in excess have a proton converted to a neutron, a positron and a neutrino.

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Gamma emissions results in the formation of gamma rays. Gamma rays production is normally accompanied by alpha and beta emissions. Mostly, the �daughter� nuclide after alpha and beta emissions are left in a high energy (excited) states. From these excited, the daughter nuclei can jump to a lower energy state and by so doing emit gamma rays.