Gamma rays will penetrate paper, skin, wood, and other substances. Like alpha and beta particles, they are also harmful if inhaled, ingested or absorbed. To protect yourself from gamma rays, you need a shield at least as thick as a concrete wall. This type of radiation causes severe damage to your internal organs. Small quantities of radioactive materials occur naturally in the air we breathe, the water we drink, the food we eat, and in our own bodies. People receive some background radiation exposure each day from the sun, from radioactive elements in soil and rocks, from household appliances such as television sets and microwave ovens, and from medical and dental x-rays. Even the human body itself emits radiation. These levels of natural and background radiation are normal. Radiation 's health effects can be mild, such as reddening of the skin, or very serious, such as cancer or early death. Radioactive materials dispersed in an urban area pose a serious health hazard. Strong sources of gamma rays can cause acute radiation poisoning or even fatalities at high doses. Long-term exposure to low levels of gamma…