GGR374H1 Lecture Notes - Ionizing Radiation, Ultraviolet, Electromagnetic Radiation
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Chapter 12: Radiation and Health:
Smoking and driving are much more dangerous then exposures to low levels of
Types of radiation:
The electromagnetic spectrum is divided into three segments with visible light in
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
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
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.
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:
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