Safety Standards for Protection against Ionizing Radiation Article 2

The terms used in the Standards are defined as follows:1.Nuclide refers to a species of atom characterized by its neutron number, proton number and nuclear energy state.2.External exposure refers to body exposure due to irradiation by ionizing radiation from outside the body.3.Internal exposure refers to exposure due to irradiation by ionizing radiation arising from the intake of radioactive material.4.Activity refers to the number of spontaneous disintegrations occurring in a certain amount of radionuclides at a given time. The special name for the unit of activity is becquerel (Bq). One (1) spontaneous disintegration per second is one (1) becquerel.5.Dose refers to the radiation energy or its equivalent absorbed by material. (1) Absorbed dose refers to the mean energy imparted by radiation per unit mass of material. The special name for the unit of absorbed dose is gray (Gy). One (1) joule imparted per kilogram of mass is one (1) gray. (2) Dose equivalent refers to the product of the absorbed dose of body tissue or organ multiplied by a quality factor.The special name for the unit of dose equivalent is sievert (Sv). The quality factors used for radiation protection are seen in Schedule I-1(1). (3) Personal dose equivalent refers to the dose equivalent in soft tissue at an appropriate depth below a specified point on the body from external exposure. The relevant depth is 10 mm for strongly penetrating radiation, 0.07 mm for weakly penetrating radiation and 3 mm for the lens of the eye. The special name for the unit of personal dose equivalent is sievert. (4) Organ dose refers to the average absorbed dose in a unit mass of the tissue or organ. The special name for the unit of organ dose is gray. (5) Equivalent dose refers to the sum of the products of organ doses and their corresponding radiation weighting factors. The special name for the unit of equivalent dose is sievert. The radiation weighting factors are seen in Table I-1 of Schedule I-1(2). (6) Committed equivalent dose refers to the integration of equivalent dose rate in a particular tissue or organ following an intake of radioactive material over a time period. The period of integration is 50 years for those of age over 17. For those 17 or younger, the integration will be taken to age 70. The special name for the unit of committed equivalent dose is sievert. (7) Effective dose refers to the sum of the products of equivalent doses and their corresponding tissue weighting factors in all the exposed tissues and organs of the body. The special name for the unit of effective dose is sievert. The tissue weighting factors are seen in Table I-2 of Schedule I-2. (8) Committed effective dose refers to the sum of the products of committed equivalent doses and their corresponding tissue weighting factors for all the exposed tissues and organs of the body. The special name for the unit of committed effective dose is sievert. (9) Collective effective dose refers to the sum of effective doses received by a specific group of population exposed to a certain radiation source. It also means the product of the total number of population exposed to a certain radiation source and the average effective dose of individuals in the population. The special name for the unit of collective effective dose is man-sievert. 6.Reference man refers to an idealized adult representing an aggregation of human physical and physiological characteristics proposed by the International Commission on Radiological Protection (ICRP) for the purpose of radiation protection assessment.7.Annual limit on intake (ALI) refers to the intake of a given radionuclide in one (1) year by the reference man that would result in (1) a committed effective dose of 50 mSv, or (2) a committed equivalent dose of 500 mSv to any tissue or organ,whichever is the smaller.8.Derived air concentration (DAC) refers to the derived concentration of a given radionuclide in a cubic meter of air. If a reference man breathes in air with such a concentration for two thousand hours (2000 h) while doing light work, the intake would amount to one (1) ALI.9.The health effects of radiation are categorized as follows: (1) Deterministic effect: referring to an effect of functional loss of the tissue or organ, whose degree of severity increases in proportion to the magnitude of the dose received. A threshold dose may exist for this type of effect. (2) Stochastic effect: referring to an effect of carcinogenesis and heredity, whose probability of occurrence increases in proportion to the magnitude of the dose received, and is independent of its severity. There is no threshold dose for the occurrence of this type of effect.10.As low as reasonably achievable (ALARA) Observing the ALARA means making every reasonable effort to maintain, in a practical way, radiation exposure far below the dose limits of the Standards. Key principles are: (1) the activity must be consistent with the original permission; (2) the present state of technology, public health improvement, the economic benefits of safety, and societal and socioeconomic factors must be taken into account; and (3) the use of radiation must be in the public interests.11.Critical group refers to a group of people (1) representing the general public; (2) who receive rather uniform exposure from a known radiation source or a group of radiation sources; and (3) whose members have received the maximum dose.12.Human body tissue equivalent sphere (ICRU sphere) refers to a sphere of 300 millimeters in diameter made of tissue equivalent material with a density of 1 mg．mm-3 and a mass composition of 76.2% oxygen, 11.1% carbon, 10.1% hydrogen and 2.6% nitrogen.Schedule I Weighting Factors used in Radiation Protection.PDFSchedule I Weighting Factors used in Radiation Protection.doc