Which is a requirement when transporting radioactive sources?

Monitoring exposure rates is a crucial requirement when transporting radioactive sources. This is essential to ensure that the radiation levels remain within safe limits during transportation. Continuous monitoring allows for the detection of any potential leaks or unintended exposure, helping to protect both the transport personnel and the public. By keeping track of the exposure rates, appropriate measures can be implemented if levels rise above permissible thresholds, ensuring safety protocols are strictly adhered to during the transport process.

In contrast, the other options do not align with safety standards for transporting radioactive materials. Allowing public exposure contradicts safety measures aimed at minimizing radiation exposure to non-essential personnel and the general public. The use of an unsealed container would significantly increase the risk of contamination and radiation exposure, as sealed containers are required to prevent the release of radioactive materials. Transporting only during the day does not address the fundamental safety considerations necessary for handling radioactive sources, as the focus should instead be on consistent monitoring and adherence to safety protocols regardless of the time of day.