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What do all the numbers mean?

Radiation can be measured in terms of activity or exposure. This can create a lot of confusion. Measurements of activity describe how a radioactive material is physically disintegrating, but these levels cannot be directly used to evaluate whether the radiation will cause harm to someone. This table presents some common units for measuring activity and exposure.

Radiation Measurements
Unit Radioactivity Absorbed Rate Dose Equivalent Exposure
Common Units curie (Ci) rad rem roentgen (R)
SI (Metric Units) becquerel (Bq) gray (Gy) sievert (Sv) coulomb/kilogram (C/kg)
  • Curies and Becquerels - Indicate number of atoms disintegrating, but reveal little about the exposure dose or internal exposure received from a radioactive material.
  • Roentgen - Of interest only to physicists.
  • Rads and Grays - Absorbed dose, most useful for describing partial body exposures.
  • Rems and Sieverts - Equivalency unit, useful for describing whole body exposures.

The following table presents how to convert between common units and SI units of measurement.

Common Unit SI Unit
1 curie (3.7 x 1010 disintegrations per second) 1 becquerel (1 disintegration per second
1 millicurie (mCi) 37 megabecquerels (MBq)
1 rad 0.01 gray (Gy)
1 rem 0.01 sievert (Sv)
1 roentgen (R) 0.000258 coulomb/kilogram (C/kg)
1 megabecquerel (MBq) 0.027 millicuries (mCi)
1 gray (Gy) 100 rad
1 sievert (Sv) 100 rem
1 coulomb/kilogram (C/kg) 3,880 roentgens

Not only are there different units describing activity and exposure, but there are also issues of presenting information in different number formats. Everyone knows how to go from 0.1 to 1,000 by looking at the numbers written out. However, most scientific data is presented in what's called scientific notation or SI units. This table presents the different number formats.

Number formats for presenting scientific information
Number Format Units Scientific Notation
1,000,000,000,000 tera (T) 1.E+12
1,000,000,000 giga (G) 1.E+09
1,000,000 mega (M) 1.E+06
1,000 kilo (k) 1.E+03
0.001 milli (m) 1.E-03
0.000001 micro (ยต) 1.E-06
0.000000001 nano (n) 1.E-09
0.000000000001 pico (p) 1.E-12