Edexcel iGCSE Physics -7.1 Radioactivity Units- Study Notes- New Syllabus

Radioactivity Units

In radioactivity, specific units are used to measure activity, distance, and time. Correct use of these units is essential when describing radioactive decay and carrying out calculations.

Activity – Becquerel (Bq)

Definition: The becquerel (Bq) is the unit of radioactive activity.

Meaning: One becquerel means one nuclear decay per second.

Key idea: Activity measures how quickly a radioactive source is decaying.

• High activity → many decays each second
• Low activity → few decays each second

\( \mathrm{1\ Bq = 1\ decay\ s^{-1}} \)

Time Units Used in Radioactivity

Radioactive decay is measured over time using the following units:

• second (s)
• minute (min)
• hour (h)

Key conversions:

• 1 min = 60 s
• 1 h = 60 min = 3600 s

Important: Activity is always measured per second, so time must often be converted into seconds.

Distance – Centimetre (cm)

Definition: The centimetre (cm) is used to measure distances in radioactivity experiments.

Common uses:

• Distance between a radioactive source and a detector
• Thickness of absorbing materials

Key idea: Increasing distance reduces the detected count rate.

Using Units Correctly in Radioactivity

• Activity → measured in Bq
• Time → measured in s, min, or h
• Distance → measured in cm
• Always convert time to seconds when calculating activity

Summary

• Becquerel measures radioactive activity.
• 1 Bq equals 1 decay per second.
• Time must often be converted to seconds.
• Centimetres are used for distance measurements.