Discovery of Radioactivity
In 1895, Wilhelm Röntgen discovered X-rays. Later, Marie Pierre Curie isolated the components emitting the rays and identified two new elements: polonium and radium. For their work, she and her husband Pierre Curie were awarded the Nobel Peace Prize. Radioactivity is the process by which particles give off rays. These are the penetrating rays or particles emitted by a radioactive source.
Radioactivity in Chemistry
Radioactivity involves isotopes of atoms with unstable nuclei. This instability arises from having too few or too many neutrons. Radioactive decay occurs when unstable nuclei lose energy spontaneously by emitting radiation to attain more stable atomic configurations. Transmutation refers to the conversion of one atom of one element to an atom of a different element, and radioactive decay is one way this occurs. The type of decay that a radioactive isotope undergoes depends on its neutron-to-proton ratio and/or its general size.
Types of Radioactivity
There are three types of radioactivity: alpha radiation, beta radiation, and gamma radiation.
Alpha Radiation
Alpha radiation involves the emission of alpha particles, which are composed of helium nuclei. These particles have a charge of 2 and a mass of 4 atomic mass units (amu). They have low penetrating power, requiring only a paper or clothing shield for protection. An example of alpha decay can be represented by the equation: $$^{219}{92}U \rightarrow ^{214}{90}Th + ^{4}_{2}He$$
Beta Radiation
Beta radiation involves high-energy electrons, with a negative charge, that turn a neutron into a proton. They have a mass of 1837 amu and moderate penetrating power. An example of beta decay results in no change in the mass number, but an increase of 1 in the atomic number.
Gamma Radiation
Gamma radiation consists of high-energy electromagnetic radiation with no mass and no charge. They have high penetrating power and require lead or concrete shielding. Gamma decay does not result in any changes to mass or atomic numbers and usually accompanies alpha and beta radiation in nuclear equations.
Half-Life
The half-life of a radioisotope is the time required for half of its nuclei to decay into its products. This concept can be used to calculate the remaining mass of a radioisotope over time. For example, if we have 10.0g of strontium-90 with a half-life of 29 years, we can use the equation $m₂ = M₂ (0.5)^{t/29}$ to calculate the remaining mass.
Nuclear Reactions
In nuclear reactions, fission refers to the splitting of a nucleus, while fusion involves the combining of nuclei. Fission releases energy slowly if controlled, as seen in nuclear reactors, and radiation control depends on reducing the speed of neutrons and absorbing extra neutrons. On the other hand, fusion, which does not occur under standard conditions, has advantages such as being inexpensive with no radioactive waste. However, it also has disadvantages, including the need for a large amount of starting energy and being difficult to control. One example of fusion's energy output is seen in stars, as well as in nuclear power plants and hydrogen bombs.
