A scientist investigates how the activity of a radioactive isotope changes over time.
The table below shows the measured activity recorded by a detector.
Time / hoursMeasured activity / counts per second04201.52203.01204.5706.045 \begin{array}{|c|c|} \hline \text{Time / hours} & \text{Measured activity / counts per second} \\ \hline 0 & 420 \\ 1.5 & 220 \\ 3.0 & 120 \\ 4.5 & 70 \\ 6.0 & 45 \\ \hline \end{array} Time / hours01.53.04.56.0Measured activity / counts per second4202201207045The half-life of the isotope is known to be exactly 1.5 hours1.5\text{ hours}1.5 hours.
Why is each consecutive measured activity value after every 1.5 hours1.5\text{ hours}1.5 hours always greater than half of the preceding value?
Radioactive decay is a random process.
There is background radiation present in the laboratory.
The detector is positioned extremely close to the radioactive source.
The isotope undergoes multiple stages of decay.
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.