Accurate measurement of exposure rate from a 60Co teletherapy source

Deviations from the inverse-square law

Supian Samat, C. J. Evans, T. Kadni, M. T. Dolah

Research output: Contribution to journalArticle

5 Citations (Scopus)

Abstract

A cylindrical γ-ray 60Co source of activity α is predicted to produce an exposure rate X at a distance d in vacuum, given by X = Γ(T) (α/d2), where Γ(T) is the specific γ-ray constant. It has been documented that this formula may be used to approximate X with an accuracy of 1% from a source of length l, provided that d/l ≥ 5. It is shown that the formula is accurate to 0.1% under these conditions, provided that the distance is measured from the centre of the source. When absorption in the source and scattering in the collimator are considered, the position of the origin d = 0 can shift by a distance of the order of centimetres. Absorption in air between the source and the ionization chamber adds an exponential factor to the formula. It is shown that even when these modifications are included the discrepancy in the results, although generally less than 1%, is still large compared with the measurement errors. Some suggestions are made for the origin of this discrepancy.

Original languageEnglish
Pages (from-to)867-877
Number of pages11
JournalBritish Journal of Radiology
Volume73
Issue number872
Publication statusPublished - 2000

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ASJC Scopus subject areas

  • Radiology Nuclear Medicine and imaging

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Accurate measurement of exposure rate from a 60Co teletherapy source : Deviations from the inverse-square law. / Samat, Supian; Evans, C. J.; Kadni, T.; Dolah, M. T.

In: British Journal of Radiology, Vol. 73, No. 872, 2000, p. 867-877.

Research output: Contribution to journalArticle

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