Nuclear Chemistry Nuclear chemistry is the study of the properties and reactions of atomic nuclei. Radioactivity- the spontaneous emission of radiation from a nucleus. Every element in the periodic table has at least one radioactive isotope, or radioisotope. Radioactivity is the result of atoms having unstable nuclei.

Radiation is emitted when an unstable radioactive nucleus, or radionuclide spontaneously changes into a more stable one. The stability of an atom’s nucleus depends on the number and type of nuclear particles, called nucleons (nucleon is a general term for both protons and neutrons).

RADIOACTIVITY involves the emission of energy and particles from the nucleus as an atom decays into a more stable form. The emissions are known as RADIATION.

Main Types of Radiation

Ionizing Radiation High energy radiation of all kinds is often grouped together under the name IONIZING RADIATION. This include not only alpha particles, beta particles and gamma rays, but also X-rays and cosmic rays. X-rays are like gamma rays. They have no mass and consist of high energy electromagnetic radiation, however, the energy of X-rays are less than that of gamma rays. Cosmic rays are not rays, but a mixture of high energy particles that shower the Earth from outer space. They consist primarily of protons, along with some alpha and beta particles.

The interaction of any kind of ionizing radiation with a molecule knocks out an electron, converting the atom or molecule into an extremely reactive ion (a highly unstable radical). This reactive ion can react with other molecules nearby, creating still other fragments that can in turn cause further reactions.

A small dose of ionizing radiation may not cause visible symptoms, but can be dangerous if it strikes a cell nucleus and damages the genetic machinery inside. The resultant changes might lead to a genetic mutation, to cancer, or to cell death. The nuclei of rapidly dividing cells, such as those in bone marrow, the lymph system, the lining of the intestinal tract, or an embryo, are the most rapidly damaged. It is because of the susceptibility of rapidly dividing cells to radiation effects that ionizing radiation is able to selectively destroy cancer cells.

Half-Life The rate of radioactive decay varies greatly from one radioisotope to another. Some radioisotopes such as uranium- 235 decay slowly over billions of years, while others, such as carbon-17, decay within thousandths of a second. Rates of nuclear decay are measured in units of half-life (t1/2), defined as the amount of time required for one half of the radioactive sample to decay.

Fraction of original sample remaining = (1/2)n where n = the number of half-lives.