Ionizing radiation units
Ionizing radiation units are standards for measuring ionizing radiation, including units for measuring the activity of radioactive sources, and for quantifying the amount of radiation striking other objects, particularly people. The current SI units replaces older conventional ones.
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[edit] Activity of an isotope or material
This measurement applies directly to the source and represents decay product per time unit.
Conventional unit: 1 curie = 37 billion disintegrations per second.
SI unit: 1 becquerel = 1 disintegration per second
Conversions:
1 curie (Ci) = 37 gigabecquerel (GBq)
1 gigabecquerel (GBq) = 27 millicurie (mCi)
[edit] Exposure
Exposure is a quantity that expresses the radiation delivered to a point at a certain distance.
Conversions:
1 roentgen (R) = 258 microcoulomb/kg (µC/kg)
1 millicoulomb/kg mC/kg = 3876 milliroentgen (mR)
[edit] Radiation absorbed dose (rad)
Under exposure a given material has an ability to absorb radiation. This differs with certain materials (think lead versus water) and some will absorb more or less as radiation passes through.
Conventional units: A dose of 1 rad means the absorption of 100 ergs of radiation energy per gram of absorbing material
SI units: A dose of 1 gray means the absorption of 1 joule of radiation energy per kilogram of absorbing material
Conversions:
1 Gy = 100 rad
1 rad = 0.01 Gy
[edit] Dose equivalent
The dose equivalent is a measure of biological effect for whole body irradiation. The dose equivalent is equal to the product of the absorbed dose and the Quality Factor.
The Quality Factor (Q) depends on the type of radiation:
X-ray, Gamma ray, or beta radiation: Q = 1
alpha particles: Q = 20
neutrons of unknown energy: Q = 10 (If the neutron energy is known, see more specific Q values at 10 CFR 20.1004 [1])
Conventional units: dose equivalent (rems) is the product of dose (rads) and Q
SI units: dose equivalent (sieverts) is the product of dose (grays) and Q
Conversions:
[edit] Counts per minute (CPM)
The counts per minute is an aggregate measurement that detects all decay events at a particular point. This could be alpha particles, beta particles or mixed gamma/beta, gamma/alpha, alpha/beta actual decays. This can be used with a conversion factor, knowing the type and composition of materials to convert to Roentgen or Coulomb per kilogram. Counts per minute can be useful when detector efficiency is in question.
[edit] Roentgen equivalent physical (rep)
Roentgen equivalent physical (rep) is an obsolete unit of absorbed dose of any ionizing radiation with a magnitude of 93 ergs per gram. It has been superseded by the rad.
[edit] References
- Metric units and conversion charts, A metrication handbook for engineers, technologist, and scientist. By Theodore Wildi. ISBN 0-7803-1050-0, IEEE order Number: PP4044.
- Code of Federal (US) Regulations, Title 10, Chapter 20, "Standards For Protection Against Radiation"
[edit] External links
- X-Ray Risk Radiation Risk Calculator. Calculate radiation dose and cancer risk for medical diagnostic X-rays. Designed to be usable for patients.
- Rad pro calculator More technical calculations for radiologists, physicists, and other health professionals.
- Measurement section of the online brochure "Guidance for Radiation Accident Management" at the Radiation Emergency Assistance Center/Training Site (REAC/TS) at Oak Ridge Institute for Science and Education.
