A radioactive source has a half-life of 6 hours and an initial activity of 800 Bq. What is its activity after 18 hours?

Answer and explanation

Correct answer: B. 100 Bq

  1. Step 1: 18 hours is 18 / 6 = 3 half-lives.
  2. Step 2: 800 halves three times: 400, 200, 100.
Answer
100 Bq.
Why not the others: 400 Bq is after one half-life, 200 Bq is after two and 267 Bq divides by 3 as if the decay were linear.

Practise more Atomic Physics Space and Magnetism.

Free questions with an explanation for every one, and full timed UK GCSE mock tests.

All Atomic Physics Space and Magnetism questionsTake a mock test

More Atomic Physics Space and Magnetism questions