A materials laboratory carries out two trials using gamma-emitting material and ceramic test pieces P and Q.
In the trial with P, the gamma-emitting material remains inside a sealed source capsule. In the trial with Q, the test piece is placed in a closed processing chamber in which unsealed gamma-emitting material has been used.
After each trial, every source capsule and the remaining unsealed material are moved to a shielded store. The detector is held at the same distance from each test piece. Each reading lasts one minute.
| Measurement | Count |
|---|---|
| Background away from the apparatus | 24 |
| Near P before the trial | 25 |
| Near P while the sealed source is beside it | 612 |
| Near P after the sealed source is moved to the store | 22 |
| Near Q before the trial | 23 |
| Near Q after all sources and materials are moved to the store | 284 |
| Near Q after it is moved 5 m from the processing chamber | 276 |
Explain what the readings show about what happened to test pieces P and Q.
Test piece Q is placed inside an intact sealed bag. The bag is positioned 10 cm from a clean steel plate without touching it. The bag is then moved away.
| Measurement near the steel plate | Count |
|---|---|
| While the bag containing Q is 10 cm away | 176 |
| After the bag containing Q is moved away | 23 |
A student concludes that the steel plate became contaminated because the count increased while Q was nearby.
Evaluate the student's conclusion.