" " "
TO BASICS
Do you know anyone who ' d like to learn a bit more about radiation ? These pull-out sheets are for this purpose
RADIOACTIVITY UNITS AND HALF-LIFE
Radioactivity The nucleus of a radioactive atom is unstable and energetic . It releases its energy by radioactive decay .
The basic unit of radioactivity is the Becquerel ( named after Henri Becquerel ) and is 1 disintegration per second . This is a very small unit and for the amounts of radioactivity commonly encountered , it is necessary to use prefixes that represent multiples . For example , there are about 4 kBq of naturally occurring potassium-40 in our bodies : whilst activity levels commonly found in industrial , medical and research uses range from MBq to TBq .
18
EBq ( Exa ) = 10 Bq
Half-Life Radioactive atoms decay independently of each other and whether an individual atom decays is a matter of probability or chance . However , when a group of radioactive atoms
Radiation Protection Today Summer 2021
are observed collectively , they follow the trend shown in the graph ; this is known as exponential decay . The activity reduces over time . The time taken for half of the atoms to decay is always the same for a specific radioisotope .
See our website for our recent video recorded for The Edinburgh Science Festival - a demonstration of exponential decay .
This is called the half-life and is shown graphically for Tellurium-131m , which has a half life of 30 hours . Half-lives range from less than a second to millions of years . The list shows the half-lives for some of the commonly used radionuclides .
Radionuclide |
Symbol |
Half-life |
Sodium-24 |
24
Na
|
15 hours |
Phosphorous-32 |
32
P
|
14 days |
Iridium-192 |
192
Ir
|
74 days |
Promethium-147 |
147
Pm
|
3 years |
Cobalt-60 |
60
Co
|
5 years |
Caesium-137 |
137
Cs
|
30 years |
Americium-241 |
241
Am
|
433 years |
Use of a particular radionuclide is often determined ( amongst other radiation properties ) by the half-life . For example , for medical diagnostic imaging , short half life sources , eg Technetium-99m ( with a half-life of about 6 hours ), are used because they decay quickly and minimise exposure to the body .
Simple explanations of basic principles of radiation ( from SRP ’ s posters for schools . See more at srp-uk . org / public-andschools / resources-for-students ).
35