Radiation measurement and units
Basic radiation measures
The activity of a radioactivec source is expressed in
becquerels Bq where 1 Bq is 1 decay per second.
Particles from different substances may be produced
in similar numbers but with very different
energies. This is taken into account by a second
unit the gray Gy which measures the energy deposited
in some object by the radiation --
the absorbed dose.
Different types of radiation cause different degrees of
biological damage even if the total energy is the same.
For example 1 Gy of alpha radiation causers 20 times as
much biological damage as 1 Gy of beta.
This potential for causing harm is expressed as
dose equivalent with units sievert Sv which is
the product of absorbed dose in Gy and a relative
biological effectiveness RBE factor.
Radiation limits for working places and the environment
is expressed in Sv.
Names definitions and units are summarised below.
| Name | Definition | Unit | Old Unit |
| activity | the rate of disintergrations | Bq | Ci (curie) |
| absorbed dose | energy deposited in object divided by mass of object | Gy | rad |
| dose equivalent | absorbed dose by RBE | Sv | rem |
| RBE | radiation type |
| 20 | alpha |
| 10 | neutron |
| 1 | beta, gamma, or X-ray |
Kym Horsell /
Kym@KymHorsell.COM
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