What is the rem threshold indicating immediate danger from radiation exposure at 30 cm from a source?

The rem threshold indicating immediate danger from radiation exposure is recognized as 100 rem. This value is significant because it represents a level of exposure where acute radiation effects may start to manifest, and the risk of injury increases dramatically. At 100 rem, individuals may experience symptoms consistent with radiation sickness, including nausea, vomiting, and increased probability of long-term health effects such as cancer.

Understanding the implications of radiation exposure at such levels is crucial for radiation safety practices. It highlights the necessity for effective monitoring and protective measures to limit exposure to as low as reasonably achievable, particularly in medical and industrial settings where radiation sources are prevalent.

Lower thresholds like 5 and 10 rem are considered significantly less risky, representing levels that are generally regarded as safe and often permissible in occupational settings. The threshold of 500 rem is far above levels typically associated with immediate danger and signifies an extremely hazardous environment where serious health outcomes are almost guaranteed without intervention.