A factory uses a radioactive source and a detector to monitor the thickness of a moving sheet of rolled steel.
The source and detector are on opposite sides of the sheet.
The table shows test results for three types of radiation. The background count rate has already been subtracted.
| Type of radiation | Corrected count rate through steel of the correct thickness in counts per minute | Corrected count rate through steel that is 2 mm thicker in counts per minute |
|---|---|---|
| alpha | 0 | 0 |
| beta | 0 | 0 |
| gamma | 3200 | 2400 |
State which type of radiation should be used in the thickness gauge.
Give two reasons why this type of radiation is suitable. Use data from the table in your answer.
The target corrected count rate is 3200 counts per minute.
During production, the corrected count rate falls to 2700 counts per minute.
State how the thickness of the steel has changed and state how the rollers should be adjusted.