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 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 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.E-03

 

0.000001

micro (µ)

1.E-06

 

0.000000001

nano (n)

1.E-09

 

0.000000000001

pico (p)

1.E-12