Physicists have called the three types of radiations emitted by nuclei, alpha, beta and gamma, the three first letters of the greek alphabet.
This naming convention of the three types of radiation has been in use since their discovery, and still applies today. The ancient greek alphabet was familar to physicists nourished by classical culture.
Alpha radiation is the name for the emission of an alpha particle in fact an helium nuclei, beta radiation is the emission of electrons or positrons, and gamma radiation is the term used for the emission of energetic photons.
When uranium salts were found in 1896 to produce unknown emissions, two types of radiation, X-rays and cathode rays, have been just discovered. At that time, nuclei, electrons and photons were unknown. It would take decades before the origins of all these rays were properly understood, but a few years to identify their nature. Incidentally cathode rays and X-rays were found to be electrons and photons like beta and gamma radiations.
In the case of alpha radiation, the nucleus attempts to find stability by emitting an ‘alpha particle’ – identical to a helium nucleus (two protons and two neutrons).
Beta radiation involves the transformation of a neutron into a proton through the emission of an electron, or the reverse process, the transformation of a proton into a neutron through the emission of a positron (similar to an electron, but with a positive charge).
Gamma radiation is simply a loss of energy by the nucleus, a desexcitation ; much like an emission of light or X-rays by energetic atoms. Alpha and beta decays almost always leave the nucleus in an excited state. Gamma emission brings the nucleus down to a more stable energetic state.
Alpha and beta decays are often difficult to occur. They can be very slow processes. The lifetimes of some radioactive nuclei are long for the clocks of the infinitely small. They can also be for us. The lifetimes of natural radioactive alpha emitters such as uranium or thorium can extend to several billions of years.
These emissions change the composition of the nucleus, therefore the nature of the atom. Alpha and beta radioactivities do not transform lead into gold, but transmute matter like other nuclear reactions do.
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