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Chapter 12.doc

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Chapter 12: Radiation and Health:  Smoking and driving are much more dangerous then exposures to low levels of radiation.  Types of radiation:  The electromagnetic spectrum is divided into three segments with visible light in the middle.  The other two segments are referred to as ionizing and nonionizing, based on their biological activity and span a wide range of wave lengths.  The ionizing portion of the spectrum includes gamma rays and ultraviolet radiation.  Ionizing radiation is given off by decaying radioisotopes or radionuclide, typically as beta particles or gamma rays.  Ionizing radiation is genotoxic and can act as a carcinogens  Nonionizing radiation is not energetic enough to disrupt electrons and hence is not thought to be genotoxic.  The radio-frequency range of the nonionizing-radation spectrum can heat tissues.  Melatonin hypothesis postulates a reduction in the pineal gland’s nocturnal production of melatonin, which in turn could increase levels of estrogens and prolactin, reduce melatonin inhibitory effect on cell proliferation and increase susceptibility to DNA damage through a reduction in melatonin antioxidant action.  Health effects of ionizing Radiation:  What we know about radiation health effects comes principally from three sources: 1) long-term follow up of the survivors of the atomic bombings in Hiroshima and Nagasaki, which involved an acute exposure to high radiation close at high dose rates. 2) Studies of patients receiving diagnostic and therapeutic radiation, also high dose by typically intermittent. 3) Studies of occupational cohorts, typically with protracted exposures.  Ionizing radiation produces two kinds of cell injury, one immediate and other delayed. High level doseses- a term loosely designating exposures over 100rm— inevitably produces the kind of immediate, direct effects seen in the Chernobyl firegithers: skin burns, hair loss, bone marrow destruction and damage to the intestinal lining.  Scientists believe that such stochastic or probabilistic effects of radiation are also directly related to the radiation dose and that they can occur at any dose, no matter how small. This is called the linear, no-threshold hypothesis; it means that all exposure to radiation presents some risk to human health.  Exposure standards:  BEIR-V raised the estimate of cancer risk associated with low-level radiational exposure from estimates in earlier BEIR reports.  Less radiation had produced more cancer.  Atomic Bomb Survivors:  Higher risks have also been seen for leukaemia and thyroid cancer following radiation exposures in childhood compared to exposures at later ages.  Epidemiologist Problem with Cancer Studies:  Epidemiologist investigates the cause of disease in groups rather than in individual patients.  Low-level radiation is associated with increased cancer incidence, but association is
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