Radiobiology

Summary

Radiation is energy in the form of waves and particles that are emitted from a source.
- It comes in many forms.
- It is not necessarily a dangerous thing.
Visible light divides the electromagnetic spectrum into general regions.
- infrared and below — non-ionizing radiation
- visible light — able to excite electrons in normal atoms
- ultraviolet and above — ionizing radiation
The forms of radiation that are especially dangerous to living things are those with energy sufficient to penetrate tissues and then ionize the atoms they pass along the way.
- They generally have energies on the order of 1 MeV.
- They damage tissues by disrupting normal cellular chemistry.
- They are mutagenic (can damage genes) and carcinogenic (can cause cancer).
The absorbed dose (D) is the energy absorbed from a source of radiation by some material per kilogram.
- It only provides a first approximation of the radiobiological damage in a human.
- The SI unit of absorbed dose is the gray, which is equal to a joule per kilogram [Gy = J/kg].
The equivalent dose (H) is the absorbed dose multiplied by the radiation weighting factor (Q) — a number that varies according to the type of radiation.
- It relates the absorbed dose to the equivalent radiobiological damage in a human.
- The SI unit of equivalent dose is the sievert, which is equal to a joule per kilogram [Sv = J/kg].
The effective dose (H) is the equivalent dose multiplied by the tissue weighting factor (Q) — a number that varies according to the organ or tissue exposed.
- It relates the equivalent dose to the effective radiobiological damage in a human.
- The SI unit of effective dose is the sievert, which is equal to a joule per kilogram [Sv = J/kg].
In symbolic form, the relation between H the equivalent or effective dose, D the absorbed dose, and Q the weighting factor is …

H = QD
Dose Units Summarized
- The SI unit of absorbed dose is the gray [Gy].
- The SI unit of equivalent effective dose is the sievert [Sv].
- The gray and the sievert are each equal to a joule per kilogram, but they are not equal to each other.
- The weighting factors are unitless.

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