Radioactivity and particles units
- Syllabus
- 2024
- Topic
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- Level
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Learning objectives
Choose and write radioactivity units correctly
A measurement needs a numerical value and the correct unit. In radioactivity work, choose the unit from the quantity being measured: activity, length or time.
| Quantity or context | Unit name | Symbol | Useful meaning |
|---|---|---|---|
| activity of a radioactive source | becquerel | Bq | 1 Bq means one nuclear decay per second |
| a short length, distance or thickness | centimetre | cm | 1 cm = 0.01 m |
| a long time interval | hour | h | 1 h = 60 min |
| a medium time interval | minute | min | 1 min = 60 s |
| a short time interval | second | s | the SI unit of time |
Method: first identify the measured quantity, then choose a sensible unit and convert all values to a common unit before calculating. Write the symbol after the value: for example, an activity of 450 Bq, a source-detector distance of 3.0 cm, or a counting time of 60 s. A duration of 2 h 30 min is 150 min or 9000 s.
Unit symbols are case-sensitive: write Bq with a capital B and lower-case q, but write cm, h, min and s in lower case. Symbols do not take plurals or full stops: use 20 cm, not 20 cms, and 5 min, not 5 mins. A becquerel measures activity; it is not a type of radiation or a unit of time.