SafetyNet #15 - Radiation Quanitities and Units
Activity:
The curie is the unit of activity most often used in the United States and expresses the rate of radioactive disintegrations per unit time, based on the following:
|
1 curie |
(Ci) |
= |
3.7 x 1010 dps (disintegrations per second) |
|
1 millicurie |
(mCi) |
= |
3.7 x 107 dps = 1 x 10-3 Ci |
|
1 microcurie |
(µCi) |
= |
3.7 x 104 dps = 10-6 Ci |
|
1 nanocurie |
(nCi) |
= |
3.7 x 101 dps = 10-9 Ci |
|
1 picocurie |
(pCi) |
= |
3.7 x 10-2 dps = 10-12 Ci |
|
dps (dis./min) |
= |
cpm (counts/min)/efficiency of detector for specific radionuclide |
|
|
1 becquerel |
(Bq) |
= |
1 disintegration per second |
Radiation Exposure: The Roentgen (pronounced rank-kin) is the unit of radiation exposure in air and is expressed as the amount of ionization per unit mass of air due to x or gamma radiation.
|
1 Roentgen (R) |
= |
2.58 x 10-4 Coulomb/Kg air |
|
1 milliroentgen (mR) |
= |
2.58 x 10-7 Coulomb/Kg air = 10-3 R |
Absorbed Dose: Radiation absorbed dose (rad) represents the amount of energy deposited per unit mass of absorbing material.
|
1 rad |
= |
100 ergs/gram |
|
1 rad |
= |
10-2 Joule/kg |
|
1 millirad (mrad) |
= |
10-5 Joule/kg = 10-3 rad |
Dose Equivalent: The measure of the biological effect of radiation requires a variable called the quality factor (QF). The quality factor takes into account the different degrees of biological damage produced by equal doses of different types of radiation.
1 rem (Roentgen Equivalent Man) is the product of the amount of energy absorbed (rad) times the efficiency of radiation in producing biological damage (the quality factor, QF)
|
1 rem |
= |
1 rad x QF |
|
1 mrem |
= |
10-3 rem |
For X and gamma radiations and for most beta particles, the QF = 1. Therefore, 1 rem = 1 rad
Alpha radiation has a QF of 20
QF for neutrons ranges from 2 to 11
Regulatory exposure limits and dosimetry results are usually expressed in rem or mrem
S.I. System
: The S.I. system is widely used in Europe and is gradually being adopted in the United States. The traditional and S.I. units are shown below with their conversion factors.
|
Current Unit |
S.I. Units |
Conversion |
|---|---|---|
|
Curie (Ci) |
Becquerel (Bq) |
1 Ci = 3.7 x 1010 Bq |
|
rad |
Gray (Gy) |
1 rad = 10-2 Gy |
|
rem |
Sievert (Sv) |
1 rem = 10-2 Sv |
For additional information, contact your EH&S Safety Advisor, EH&S at 752-1493 or ehsdesk@ucdavis.edu.
Reviewed/Revised. 8/2008
GW