Activity: How Much Is Present?
The size or weight of a container or shipment
does not indicate how much radioactivity is in it.
The amount of radioactivity in a quantity of
material can be determined by noting how many curies of the material are present. This
information should be found on labels and/or shipping papers.
More curies = a greater amount of radioactivity
A large amount of material can have a very small
amount of radioactivity; a very small amount of material can have a lot of radioactivity.
For example, uranium238 has 0.00015 curies of
radioactivity per pound (0.15 millicuries), while cobalt60 has nearly 518,000 curies per
pound.
In the International System of units (SI), the
becquerel (Bq) is the unit of radioactivity. One Bq is 1 disintegration per second (dps).
One curie is 37 billion Bq. Since the Bq represents such a small amount, you are likely to
see a prefix used with Bq, as shown below:
1 MBq (27 microcuries)
1 GBq (27 millicuries)
37 GBq (1 curie)
1 TBq (27 curies)
SI Units and Prefixes
The International System of Units has been given official status and
recommended for universal use by the General Conference on Weights and Measures.
Radiation Measurements

Radioactivity 
Absorbed Dose 
Dose Equivalent 
Exposure 
Common Units 
curie (Ci) 
rad 
rem 
roentgen (R) 
SI Units 
becquerel (Bq) 
gray (Gy) 
sievert (Sv) 
coulomb/kilogram (C/kg) 
Following is a list of prefixes and their
meanings that are often used in conjunction with SI units:
Multiple 
Prefix 
Symbol 
10^{12} 
tera 
T 
10^{9} 
giga 
G 
10^{6} 
mega 
M 
10^{3} 
kilo 
k 
10^{2} 
centi 
c 
10^{3} 
milli 
m 
10^{6} 
micro 
µ 
10^{9} 
nano 
n 
Conversions
Conversion Equivalence
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 
Conversion Factors
To convert from 
To 
Multiply by 
Curies (Ci) 
becquerels (Bq) 
3.7 x 10^{10} 
millicuries (mCi) 
megabecquerels (MBq) 
37 
microcuries (µCi) 
megabecquerels (MBq) 
0.037 
millirads (mrad) 
milligrays (mGy) 
0.01 
millirems (mrem) 
microsieverts (µSv) 
10 
milliroentgens (mR) 
microcoulombs/kilogram (µC/kg) 
0.258 

becquerels (Bq) 
curies (Ci) 
2.7 x 10^{11} 
megabecquerels (MBq) 
millicuries (mCi) 
0.027 
megabecquerels (MBq) 
microcuries (µCi) 
27 
milligrays (mGy) 
millirads (mrad) 
100 
microsieverts (µSv) 
millrems (mrem) 
0.1 
microcoulombs/kilogram (µC/kg) 
milliroentgens (mR) 
3.88 
