Final answer:
The two main sources of ionizing radiation are natural sources, such as cosmic rays and radioactive materials like radon, and human-made sources, including medical procedures and nuclear accidents. Ionizing radiation is harmful because it can cause cellular damage and lead to health issues.
Step-by-step explanation:
The two main sources of ionizing radiation are natural sources and human-made sources. Natural sources include cosmic rays from space and radiation released from the ground, such as radon gas and other radioactive material naturally present in the earth's crust. Human-made sources include medical procedures, like cancer radiotherapy and diagnostic imaging, and the aftereffects of nuclear accidents.
Ionizing radiation is particularly harmful because it has enough energy to ionize atoms and molecules, which can lead to DNA damage, cancer, and other health problems. Using devices such as Geiger counters and dosimeters can help measure and monitor exposure to these sources. To reduce the risk, one can take measures to block or shield the radiation, move farther from the source, or limit the time of exposure.