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 Dose 
Dose Equivalent 
Exposure 
Common Units 
curie (Ci) 
rad 
rem 
roentgen (R) 
SI (Metric) Units 
becquerel (Bq) 
gray (Gy) 
seivert (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
This table presents how to convert between common units and SI units of
measurement.
1 curie (3.7 x 10^{10 }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 Format 
SI 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.E03 

0.000001 
micro (µ) 
1.E06 

0.000000001 
nano (n) 
1.E09 

0.000000000001 
pico (p) 
1.E12 
