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  3. Radiation occurs from three natural sources: radioactive material in the environment such as in soil, rock, or building material

Radiation occurs from three natural sources: radioactive material in the environment such as in soil, rock, or building material

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问题     Radiation occurs from three natural sources: radioactive material in the environment such as in soil, rock, or building materials; cosmic rays; and substances in the human body, such as radioactive potassium in bones and radioactive carbon in tissues. These natural sources account for an exposure of about 100 millirems a year for the average American.
    The Iargcst single source of man-made radiation is medical X rays, yet most scientists agree that hazards from this source are not as great as those from weapons test fallout, since strontium 90 and carbon 14 become incorporated into the body, hence delivering radiation for an entire life- time. The issue is, however, by no means uncontroversial; the last two decades have witnessed intensified examination and dispute about the effects of low-level radiation, beginning with the United Nations Scientific Committee on the Effects of Atomic Radiation, which reported in 1958: "Even the smallest amounts of radiation are liable to cause deleterious genetic and perhaps also somatic effects."
    A survey conducted in Britain confirmed that an abnormally high percentage of patients suffering from arthritis of the spine who had been treated with X rays contracted cancer. Another study revealed a high incidence of childhood cancer in eases where the mother had been given prenatal pelvic X rays. These studies have pointed to the need to reexamine the assumption that exposure to low-linear energy transfer presents only a minor risk.
    Recently, examination of the death certificates of former employees of a West Coast plant which produces plutonium for nuclear weapons revealed markedly higher rates for cancers of the pancreas, lung, bone marrow, and lymph systems than would have been expected in a normal population.
    While the National Academy of Sciences Committee attributes this difference to chemical or other environmental causes rather than radiation, other scientists maintain that any radiation expo- sure, no matter how small, leads to an increase in cancer risk. It is believed by some that a dose of one rem, if sustained over many generations, would lead to an increase of 1 percent in the number of serious genetic defects at birth, a possible increase of 1,000 disorders per million births.
    In the meantime, regulatory efforts have been disorganized, fragmented, inconsistent, and characterized by internecine strife and bureaucratic delays. A Senate report concluded that coordination of regulation among involved departments and agencies was not possible because of jurisdictional disputes and confusion. One federal agency has been unsuccessful in its efforts to obtain sufficient funding and manpower for the enforcement of existing radiation laws, and the chairperson of a panel especially created to develop a coordinated federal program has resigned.
Natural sources of radiation are______.
选项 A、radioactive potassium in bones, strontium 90, uranium ore
B、carbon 14 in tissues, cosmic rays, X rays
C、cosmic rays, radioactive potassium in bones, radioactive carbon in tissues
D、X rays, carbon 14, plutonium
答案C
解析
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