An environmental scientist is testing four soil samples, labeled PPP, QQQ, RRR, and SSS, collected near an old industrial site to identify potential radioactive contaminants. Using a Geiger-Müller tube and counter, the scientist records the count rates under different shielding conditions.
The average background count rate with no samples present is measured to be 22 counts per minute (cpm).
The table below shows the results of the measurements:
| Sample | No barrier (cpm) | Paper barrier (cpm) | Aluminium barrier (cpm) | Lead barrier (cpm) |
|---|---|---|---|---|
| P | 450 | 23 | 21 | 22 |
| Q | 620 | 615 | 180 | 24 |
| R | 280 | 282 | 278 | 23 |
| S | 850 | 340 | 21 | 22 |
Suggest two safety precautions the scientist should take when handling and testing these radioactive soil samples.
Identify and explain which sample: (i) emits gamma radiation only. (ii) emits alpha radiation only. (iii) could emit both beta and gamma radiation.
The recorded count rates behind the lead barrier range from 21 to 24 counts per minute. Explain why there is a variation in these readings when the average background is around 22.
The scientist decides to repeat the measurements, but records the counts over a much longer time interval for each sample. Explain why this is an improvement.