Ionizing radiation is a specific type of radiation that has enough energy to eject an electron from some atom. Generally speaking, the energies of alpha and beta decay particles and gamma ray photons is higher than the ionization energies of atoms and molecules. This means that instead of being absorbed, these particles ionize the matter and break molecular bonds. These resulting particles are therefore known as ionizing radiation. Ionizing radiation is important as it can produce a number of physiological side-effects, such as cancer.
The idea that radiation can be ionizing is the basis for the operation of the Geiger counter, one detector of nuclear radiation. Geiger counters only detect ionizing radiation as they rely on the products of ionization to operate.
Different forms of ionizing radiation have different uses. Radiotherapy, a cancer treatment, relies on beta decay and uses its ionizing properties to kill cancer cells. Alpha radiation also has use in the medical field, with targeted alpha therapy being used to kill cancer.
Ionizing radiation also has uses outside of the medical field. The ionizing properties of americium results in its use in smoke detectors. Inside the smoke detector alpha particles from the americium are released. This in turn ionizes the air inside the detector. Smoke in the detector absorbs this alpha radiation, so if smoke is present the ionization is altered and the alarm is triggered. Additionally, cobalt - a source of gamma ionizing radiation - is used to sterilize medical equipment and irradiate food, killing bacteria and pasteurizing the food.
The biological effects of radiation vary depending on how much exposure a person has, how long they are expose to, and what type of radiation they are exposed to. Ionizing radiation is produced when radioactive materials decay, causing damage to living tissues that cannot always be repaired. Chronic exposure to radiation can lead to cancer (as a result of damage at the cellular or molecular level) or other mutations that can be harmful to fetuses. Effects from acute exposure to ionizing radiation appear quickly, and include burns and radiation poisoning. The symptoms of radiation poisoning include nausea, weakness, hair loss, and diminished organ function and this radiation sickness can result in death if the dose is high enough.