The Effects of Radiation on Living Systems

3 Explain how exposure to radiation may harm or help living systems. 

Shortly after radioactivity was discovered, people thought that radiation had certain curative powers. Radium compounds were made and radium solutions were bottled and sold for drinking and bathing. That was before people knew the harmful effects of radiation exposure—and some early users of these cures paid a dear price for acquiring that knowledge. Today s medical practitioners are much wiser. They have devised sophisticated ways to use radionuclides to examine patients, diagnose their illnesses, and treat their disorders. 

The unit most commonly used to express radiation exposure is the rem. More than 600 rems in one dose is fatal. The radiation therapy used in fighting cancers gives a total dose over time in the 4000- to 7000-rem range. This radiation indeed damages healthy tissue surrounding a tumor, but healthy cells are more capable of repairing themselves than are malignant cells. 

Most of the radiation you encounter is measured not in rems, but in millkems, mrem. For example, a chest x-ray is about 25 mrem, a complete diagnostic gastrointestinal x-ray series is about 2000 mrem, and a dental x-ray is about 0.5 mrem. The federal standard for occupational exposure is 5000 mrem/year. 

Sources of radiation are everywhere. Radiation is emitted from rocks, soil, water, and even atoms in us. Although the atmosphere acts as a filter between us and the rest of the universe, we are constantly bombarded by radiation from sources outside the earth s atmosphere. Indeed, the average exposure to natural sources of radiation is 

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