Kerma vs Absorbed Dose

Absorbed Dose

Absorbed dose is defined as the amount of energy deposited by ionizing radiation in a substance. Absorbed dose is given the symbol D.  The absorbed dose is usually measured in a unit called the gray (Gy), which is derived from the SI system. The non-SI unit rad is sometimes also used, predominantly in the USA.

absorbed dose - definition

Absorbed doseUnits of absorbed dose:

  • Gray. A dose of one gray is equivalent to a unit of energy (joule) deposited in a kilogram of a substance.
  • RAD. A dose of one rad is equivalent to the deposition of one hundred ergs of energy in one gram of any material.

A dose of one gray is equivalent to a unit of energy (joule) deposited in a kilogram of a substance. This unit was named in honour of Louis Harold Gray, who was one of the great pioneers in radiation biology. One gray is a large amount of absorbed dose. A person who has absorbed a whole body dose of 1 Gy has absorbed one joule of energy in each kg of body tissue.

Kerma

Kerma is a measure of kinetic energy transferred from radiation to matter. It is an acronym for “kinetic energy released per unit mass”. Kerma is given the symbol K and it is measured by the SI unit, the gray. This unit was named in honour of Louis Harold Gray, who was one of the great pioneers in radiation biology. Kerma is defined by the formula:

kerma - unit - definition

Kerma vs Absorbed Dose

Kerma is related to, but not the same as absorbed dose. Absorbed dose is defined as the amount of energy deposited by ionizing radiation in a substance. Kerma is defined as the sum of the initial kinetic energies of all the charged particles liberated by uncharged ionizing radiation in a substance. At low energies, kerma approximately equals absorbed dose, since most of initial kinetic energies of all the charged particles deposit their energy in the sample. At higher energies kerma is larger than absorbed dose because some highly energetic secondary electrons and X-rays escape the region of interest before depositing their energy. The escaping energy is counted in kerma, but not in absorbed dose. Note that there are three key interaction mechanisms of gamma rays with matter.

 

References:

Radiation Protection:

  1. Knoll, Glenn F., Radiation Detection and Measurement 4th Edition, Wiley, 8/2010. ISBN-13: 978-0470131480.
  2. Stabin, Michael G., Radiation Protection and Dosimetry: An Introduction to Health Physics, Springer, 10/2010. ISBN-13: 978-1441923912.
  3. Martin, James E., Physics for Radiation Protection 3rd Edition, Wiley-VCH, 4/2013. ISBN-13: 978-3527411764.
  4. U.S.NRC, NUCLEAR REACTOR CONCEPTS
  5. U.S. Department of Energy, Nuclear Physics and Reactor Theory. DOE Fundamentals Handbook, Volume 1 and 2. January 1993.

Nuclear and Reactor Physics:

  1. J. R. Lamarsh, Introduction to Nuclear Reactor Theory, 2nd ed., Addison-Wesley, Reading, MA (1983).
  2. J. R. Lamarsh, A. J. Baratta, Introduction to Nuclear Engineering, 3d ed., Prentice-Hall, 2001, ISBN: 0-201-82498-1.
  3. W. M. Stacey, Nuclear Reactor Physics, John Wiley & Sons, 2001, ISBN: 0- 471-39127-1.
  4. Glasstone, Sesonske. Nuclear Reactor Engineering: Reactor Systems Engineering, Springer; 4th edition, 1994, ISBN: 978-0412985317
  5. W.S.C. Williams. Nuclear and Particle Physics. Clarendon Press; 1 edition, 1991, ISBN: 978-0198520467
  6. G.R.Keepin. Physics of Nuclear Kinetics. Addison-Wesley Pub. Co; 1st edition, 1965
  7. Robert Reed Burn, Introduction to Nuclear Reactor Operation, 1988.
  8. U.S. Department of Energy, Nuclear Physics and Reactor Theory. DOE Fundamentals Handbook, Volume 1 and 2. January 1993.
  9. Paul Reuss, Neutron Physics. EDP Sciences, 2008. ISBN: 978-2759800414.

See above:

Radiation Protection