Radiation Units

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Radiation Units
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1-Radioactivity Units

• Physical Units
• Becquerel
• Amount of radioactive sample s.t. there is 1
  atomic decay per second
• Henri Becquerel discovered radioactivity through
  experiments with uranium and other radioactive
  matter
• Curie (Ci)
• 3.71010 decays per second
• Approx. activity of 1g radium

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2-Exposure units (Roentgen(abbreviated 'R'

• The roentgen is a unit for measuring exposure. It
  is defined only for effect on air. The roentgen
  is essentially a measure of how many ion pairs
  are formed in a given volume of air when it is
  exposed to radiation. Therefore it is not a
  measure of energy absorbed, or dose. It applies
  only to gamma and x-rays. It does not relate the
  amount of exposure to biological effects of
  radiation in the human body.

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• The roentgen describes the amount of x-rays or
  gamma rays to which a target (e.g., fly, mouse,
  rat, dog, human, cow, elephant, etc.) is exposed.
  The roentgen relates to the ability of x-rays and
  gamma rays to remove electrons from atoms in one
  cm3 of air. 1 R (Roentgen) 1000 mR
  (milliRoentgen)

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3- Biological Units

• Rad (Radiation Absorbed Dose)
• The rad is a unit for measuring absorbed dose in
  any material. Absorbed dose results from energy
  being deposited by the radiation. It is defined
  for any material. It applies to all types of
  radiation. It does not take into account the
  potential effect that different types of
  radiation have on the body.

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• Therefore, it can be used as a measure of energy
  absorbed by the body, but not as a measure of the
  relative biological effect (harm or risk) to the
  body.
• 1 rad 1000 millirad (mrad)
• 1 gray 100 rad

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• The radiation absorbed dose is important for
  describing radiation effects. The absorbed dose
  relates to how much radiation energy gets put
  into a given target mass (e.g., lung, eye,
  thyroid gland).
• The absorbed dose has units of energy divided by
  mass (e.g., ergs per gram or joules per kilogram

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• Different absorbed doses can arise in different
  organs or tissue of the body for the same
  exposure in R. Thus, if a person were exposed to
  10 R of gamma rays, the eye, the thyroid, and the
  lung would have different absorbed doses. Special
  computer programs can calculate such doses.
• Units of absorbed dose often used are the rad and
  gray (an SI unit).

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• The gray unit represents 1 joule of radiation
  energy put into a kilogram mass. Thus, 1 gray
  equals 1 joule per kilogram.
• The gray and rad apply to all types of ionizing
  radiation, unlike the roentgen unit, which only
  applies to x-rays and gamma rays.

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Biological Units

• Radiation-Protection Units
• Equal doses of different types or energies of
  radiation cause different amounts of damage to
  living tissue. For example, 1 Gy of alpha
  radiation causes about 20 times damage as 1 Gy of
  x- rays. Therefore the equivalent dose was
  defined to give an approximate measure of the
  biological effect of radiation. It is calculated
  by multiplying the absorbed dose by a weighting
  factor W R which is different for each type of
  radiation
• .

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Relative Biological Effectiveness (RBE) or
weighting factor W R

• W R
• X rays, gamma rays, electrons, positrons 1
  
• Neutrons, protons (10 -100 Ke V) 10
• Neutrons, protons (less than 10 Ke V ) 5
• Alpha particles
  20

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• Law of the rem (introduced here for the first
  time to help understand its use)
• The risk of harm from 1 rem to an organ from one
  radiation source the risk of harm from 1 rem to
  that organ from any other radiation source!

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Question 1

• Enumerate the different radiation units?, their
  definition and their relationship?