Ionizing radiation units

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Radiation Measurement Units - International System (SI)

Activity of an isotope or material

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)

Radiation absorbed dose (rad)

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

conversion

1 Gy = 100 rad

1 rad = 0.01 Gy

1 roentgen (R) = 258 microcoulomb/kg (µC/kg)

1 millicoulomb/kg mC/kg = 3876 milliroentgen (mR)

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

Conversion

1 Sv = 100 rems

1 rem = 0.01 Sv

Counts per minute (CPM)

Used for alpha particles, beta particles or mixed gamma/beta, gamma/alpha, alpha/beta actual counts per minute. Counts per minute can also be useful when detector efficiency is in question. For example, when a scintillator is designed to detect the 0.013 Mev photons from Uranium 238 and one is measuring the 1.146 Mev photons from Potassium 40, the units cannot be easily converted to roentgens; CPM is a more appropriate unit under these conditions.

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 It has been superseded by the rad.

References

• Rad pro calculator
• 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"

See also

• Scintillation counter
• Geiger counter
• Radon gas
• Lucas cell
• Photomultiplier