Some students set up an experiment to measure the count rate for a radioactive source.
First, they measure the radioactive background count rate in the laboratory by taking three measurements. Each measurement is taken over a 5-minute period.
The table shows their results.
| Measurement | Number of counts in 5 minutes |
|---|---|
| First measurement | 112 |
| Second measurement | 118 |
| Third measurement | 115 |
Next, the students measure the counts near the radioactive source. This count rate is measured as 856 counts per minute.
What is the corrected count rate for the source?
833 counts per minute
741 counts per minute
511 counts per minute
148 counts per minute
484 exam-style questions on CIE IGCSE Physics 5.2 Radioactivity, covering 5.2.1 Background radiation and measuring count rate, 5.2.2a Alpha, beta and gamma emission, 5.2.2b Deflection and ionising effects of nuclear radiation, 5.2.3a Radioactive decay, 5.2.3b Effects of decay on the nucleus and decay equations, 5.2.4a Half-life, 5.2.4b Choosing isotopes for applications, and 5.2.5 Effects of ionising radiation and safety precautions. Each one has a worked solution and a mark scheme showing where the marks go.