The Physics
Hypertextbook
Opus in profectus

## 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 of the ionizing radiation (E) absorbed by some object per mass (m).
• 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].  D = E m
• The equivalent dose (H) is the absorbed dose (D) multiplied by the radiation weighting factor (wR) — a number that varies according to the type of radiation.  H = wRD
• 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 (E) is the equivalent dose (H) multiplied by the tissue weighting factor (wT) — a number that varies according to the organ or tissue exposed.  E = wTH
• 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].
• Dose units summarized
• The SI unit of absorbed dose is the gray [Gy].
• The SI unit of equivalent dose and 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 gray was named in honor of the English physicist Louis Gray (1905–1965) who developed the concept of relative biological effectiveness, which was later quantified as the weighting factor
• The sievert was named in honor of the Swedish physicist Rolf Sievert (1898–1966) who developed the basic techniques for measuring absorbed dose
• The weighting factors are unitless.