ASNT Industrial Radiography Radiation Safety Practice Test

What should a survey meter display after a source is returned to the shielded position?

1. An immediate drop to zero

2. An increase in exposure rate

3. An increase in exposure followed by a decrease to zero

4. A continuous high reading

The correct answer is: An increase in exposure followed by a decrease to zero

When a radiation source is returned to its shielded position, the survey meter is expected to display a specific behavior related to the exposure rate. Initially, when the source is withdrawn from its shielded position, radiation levels may spike due to the proximity of the source. When the source is then returned to the shielded position, the exposure dose rate can be expected to immediately decrease as the radiation field is attenuated by the lead or other shielding material. The correct answer suggests that there may be a brief moment where an increase in exposure is noted before it rapidly decreases to zero. This can happen due to the detector's response time, and any residual readings could be attributed to the detector momentarily remaining sensitive to residual radiation from the surrounding area or the source itself until it stabilizes back at zero. Therefore, while the immediate expectation is a decrease in readings, the survey meter may not drop to zero instantaneously, leading to the transient spike illustrated in the chosen answer. This response accounts for the characteristics of survey meters, which detect radiation in real time but may have varying response times based on their design and the types of radiation being measured. Understanding this behavior is critical for users of survey meters in industrial radiography to ensure they can accurately interpret readings after