Final answer:
Radiation doses below 50 rem can cause long-term health issues such as cancer or genetic changes, with doses less than 100 mrem per year being difficult to assess for risk of harm to a fetus. A lifetime risk of a genetic defect from a 1 rem exposure is estimated to be about 100 in a million. Low doses of radiation may potentially have beneficial effects through a process known as hormesis.
Step-by-step explanation:
When considering the amount of radiation that can cause harm to a fetus, it is important to understand how radiation affects rapidly dividing cells. Doses above 600 rem are typically fatal to humans, whereas a dose of 500 rem will kill half of those exposed within 30 days. Smaller doses, such as those below 50 rem, may have limited immediate health effects but can cause long-term problems like cancer or genetic changes, which can affect offspring. The potential risks associated with even smaller doses, such as those less than 100 mrem per year from artificial sources, are more challenging to assess. However, the risk of genetic defects due to radiation is thought to be about one-third that of cancer deaths, with a lifetime risk of around 100 in a million for a 1 rem exposure. Additionally, there is a hypothesis known as hormesis, which suggests low doses of radiation may have beneficial effects on cellular repair mechanisms.