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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)

conventional units: A dose of 1 Rad means the absorption of 100 ergs of radiation energy per gram of material

SI units: A dose of 1 Gray means the absorption of 1 joule of radiation energy per kilogram of material

conversion

A unit of exposure to ionizing radiation. Only used by well trained personnel.

The amount of gamma or x-rays required to produce ions carrying 1 electrostatic unit of electrical charge (either positive or negative) in 1 cc of dry air under standard conditions.

1 roentgen (R) = 258 microcoulomb/kg (mC/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 aborbed dose and the Quality Factor.

The Quality Factor(Q) depends on the type of radiation:

x, gamma, or beta radiation: Q = 1

alpha paraticles: Q = 20

neutrons of unknown energy: Q = 10 (If the neutron energy is known, see more specific Q values at 10 CFR 20.1004, athttp://www.nrc.gov/reading-rm/doc-collections/cfr/part020/part020-1004.html

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 Sievert = 100 Rems

1 Rem = 0.01 Sievert

"C"ounts "P"er "M"inute (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. Like when a scintillator is designed to detect the 0.013 mev photons from 238U and one is measuring the 1.146 mev photons from 40K, The units cannot be easyly converted to roentgen's so CPM is a more appropriate unit under these conditions.

"R"oentgen "E"quivalent "P"hysical (rep)

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 It has been superseded by the rad.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

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"

ee also

* Counts per minute
* Curie
* Becquerel
* Gray (unit)
* Roentgen
* Röntgen equivalent man
* Sievert
* Alpha particles
* Scintillation counter
* Geiger counter
* Lucas cell
* Photomultiplier

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