pdf 4.1 absorbed and equivalent dose

7/28/2019 PDF 4.1 Absorbed and Equivalent Dose

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A Look at NuclearScience and Technology

Larry Foulke

Radiation and Realism

4.1 Absorbed and Equivalent Dose



Nuclear Engineering Program

Relevant Reading Assignments

• Chapter 3 of “ Nuclear Engineering: Theory and Technology of Commercial Nuclear Power,” Knief, 2nd edition, AmericanNuclear Society (1992, reprint by ANS 2008)

• Chapters 9 & 10 of “ Introduction to Nuclear Engineering,”

Lamarsh and Baratta, 3rd edition, Prentice-Hall (2001)

• DOE Handbook, Radiological Worker Training,http://www.hss.doe.gov/nuclearsafety/techstds/docs/handbook/hdbk-1130-07.pdf , December 2007

• Chapter 2 of “Radiation and Modern Life” Alan Waltar,Prometheus Books, 2004

• “The Nuclear Energy Option,” Bernard Cohen, Plenum Press,1990 available on the web at http://www.phyast.pitt.edu/~blc/book/BOOK.html

http://www.hss.doe.gov/nuclearsafety/techstds/docs/handbook/hdbk-1130-07.pdf


http://www.phyast.pitt.edu/~blc/book/BOOK.html

http://www.phyast.pitt.edu/~blc/book/BOOK.html






Overview • Previous Module

– Types of radiation interactions

– Calculation of reaction rates

– Fission

• This module

– Radiation dose and damage

– Calculation of radiation exposure

– Radiation protection




Radiation Exposure

• We have already established that radiation damageis related to the amount of energy deposited in amaterial.

• The energy deposition is proportional to– The rate at which radiation enters the material.

– The energy content of each radiation particle.

– The probability that a radiation particle will interact within thematerial.

– The length of time that the material is exposed to the radiationfield.




Radiation Exposure• The first attempt to quantify radiation effects

resulted in a unit called the Roentgen (R)

– 1 Roentgen = the amount of radiation required toproduce an electric charge density of 2.58×10-4

coulombs per kilogram due to ionizations in air atstandard temperature and pressure.

• The Roentgen provides a good measure of the amount of radiation directed at a

material, material referred to as exposure.• Meaningful measurements for radiation

exposure were restricted to X and γ-Rays,usually with energies < 3 MeV.

Image Source: See Note 1




Absorbed Dose• The Roentgen does not provide any information on the

probability of radiation interactions in materials other thanair.

• A more meaningful measurement is the total amount of

radiation energy deposited per mass of a given material,referred to as the absorbed dose.

• In 1956 the ICRU adopted a standard unit for radiationenergy deposition in a material

– 1 rad = the absorption of 10-2 joules of radiation energy per kilogramof material. (100 erg/gm)

– rad stands for “radiation absorbed dose”

– For biological tissue 1 R exposure produces ≈0.95 rad


http://slidepdf.com/reader/full/pdf-41-absorbed-and-equivalent-dose 7/13Nuclear Engineering Program

Biological Effect• For biological damage, concentrations of ionizations

within a single cell are more damaging than the samenumber of ionizations spread over many cells.

• Therefore, biological damage is proportional to boththe absorbed dose of radiation, as well as the LET forthe type and energy of radiation.

Typical cell size

Gamma ray, low LET

Alpha particle, high LET



Biological Effectiveness

• In order to have a common basis for comparing biological effects due to different types of radiation, we define a relative biological effectiveness (RBE):

• The RBE is highly dependent on the type and energy of radiation.

RBE =

Reference Dose of radiation to produce a given effect

Dose of specific radiation to give the same effect



Equivalent Dose• The upper limit of the RBE for a specific type of

radiation is called the quality factor (Q) for theradiation.

• Multiplying absorbed dose by the quality factor for thetype of radiation gives the effective or equivalent dose.

• Equivalent dose in rem (Roentgen Equivalent Man) is acommon unit of measurement for comparing uniqueexposure events.

equivalent dose (rem) = Q× absorbed dose (rad)




Equivalent Dose

• Because the quality factor is an upper limit, equivalent

dose is considered a measure of the potential damagefrom radiation exposure.

• Simultaneous doses from multiple types of radiation areadditive.

F r o m

1 0 C F R 2 0 . 1

0 0 4




SI Units

• Dose units rad and rem are in [cJ/kg].

• SI base units require [J/kg], giving us new SIstandards for dose:

• Absorbed dose

– 1 Gray (Gy) = 100 rad

– 1 rad = 1 cGy

• Equivalent dose– 1 Sievert (Sv) = 100 rem

– 1 rem = 1 cSv

Rolf SievertImage Source: See Note 2




The BananaEquivalent Dose

• Bananas contain a small amount of

radioactivity in the form of Potassium-40 (40K)

• A typical banana has about a half of agram of potassium, or an activity of

about 31 Bequerels

• One BED is the dose one gets by eating one banana.

Image Source: See Note 3



1. Public domain:http://www.nlm.nih.gov/visibleproofs/galleries/technologies/radiology.html

2. Public domain:http://en.wikipedia.org/wiki/File:Rolf_Sievert_1896-1966.jpg

3. Creative Commons Attribution-ShareAlike2.5 Generic:http://en.wikipedia.org/wiki/File:Bananen_Frucht.jpg

Image Source Notes

http://www.nlm.nih.gov/visibleproofs/galleries/technologies/radiology.html


http://en.wikipedia.org/wiki/File:Rolf_Sievert_1896-1966.jpg


http://creativecommons.org/licenses/by-sa/2.5/deed.en


http://en.wikipedia.org/wiki/File:Bananen_Frucht.jpg










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