58 Radioactive Materials Safety Manual Environmental Health and Safety Appendix II - Dictionary and Glossary Absorbed Dose – the amount of energy imparted to matter by ionizing radiation per unit mass of irradiated material. The unit of absorbed dose is the rad, which is 100 ergs/gram. Absorption – the phenomenon by which radiation imparts some or all of its energy to any material through which it passes. Activation – the process of making a material radioactive by bombardment with neutrons, protons, or other nuclear radiation. Activity – the rate of disintegration or transformation or decay of radioactive material. The units of activity are the becqueral (bq) and the curie (Ci). Acute Exposure – the absorption of a relatively large amount of radiation (or intake of radioactive material) over a short period of time. Acute Health Effects – prompt radiation effects (those that would be observable within a short period of time) for which the severity of the effect varies with the dose, and for which a practical threshold exists. Agreement State – any state with which the U.S. Nuclear Regulatory Commission has entered into an effective agreement concerning the licensing of by-product material. Iowa is an agreement state and regulates the safe uses of radiation and by-product material within its boundary. ALARA (acronym for As Low As Reasonably Achievable) – making every reasonable effort to maintain exposures to radiation as far below the dose limits as is practical, consistent with the purpose for which the licensed activity is undertaken, taking into account the state of technology, the economics of improvements in relation to state of technology, the economics of improvements in relation to benefits to the public health and safety, and other societal and socioeconomic considerations, and in relation to utilization of nuclear energy and licensed materials in the public interest. Alpha Particle – a strongly ionizing particle emitted from the nucleus during radioactive decay having a mass and charge equal in magnitude to a helium nucleus, consisting of 2 protons and 2 neutrons with a double positive charge. Annual Limit on Intake (ALI) – the derived limit for the amount of radioactive material taken into the body of an adult worker by inhalation or ingestion in a year. ALI is the smaller value of intake of a given radionuclide in a year by a reference person that would result in a committed effective dose equivalent of 5 rem (0.05 Sv) or a committed effective dose equivalent of 50 rem (0.5 Sv) to any individual organ or tissue. Attenuation – the process by which a beam of radiation is reduced in intensity when passing through some material. It is the combination of absorption and scattering processes and leads to a decrease in flux density of the beam when projected through matter. Audit – the periodic examination of the radiation safety program related to the possession, use, storage, transfer, & disposal of licensed material or devices. Background Radiation – ionizing radiation arising from radioactive material other than the one directly under consideration. Background radiation due to cosmic rays and natural radioactivity is always present. There may also be background radiation due to the presence of radioactive substances in other parts of the building, in the building material itself, etc. Becquerel (Bq) – unit of activity in the SI system equal to 1 disintegration per second. 1 becquerel = 2.703 x 10-11 Ci or 2.703 x 10-8 mCi 1 mCi=3.7 x 107 Bq Beta Particle – charged particle emitted from the nucleus of an atom during radioactive decay. Anegatively charged beta particle is identical to an electron. A positively charged beta particle is called a positron.