EVS 1501 Lecture Notes - Ultraviolet, Electromagnetic Radiation, Electromagnetic Spectrum
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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
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
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
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:
Epidemiologist investigates the cause of disease in groups rather than in