### Abstract

A cylindrical γ-ray ^{60}Co source of activity α is predicted to produce an exposure rate X at a distance d in vacuum, given by X = Γ(T) (α/d^{2}), 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 language | English |
---|---|

Pages (from-to) | 867-877 |

Number of pages | 11 |

Journal | British Journal of Radiology |

Volume | 73 |

Issue number | 872 |

Publication status | Published - 2000 |

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### ASJC Scopus subject areas

- Radiology Nuclear Medicine and imaging

### Cite this

^{60}Co teletherapy source: Deviations from the inverse-square law.

*British Journal of Radiology*,

*73*(872), 867-877.

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

Research output: Contribution to journal › Article

^{60}Co teletherapy source: Deviations from the inverse-square law',

*British Journal of Radiology*, vol. 73, no. 872, pp. 867-877.

^{60}Co teletherapy source: Deviations from the inverse-square law. British Journal of Radiology. 2000;73(872):867-877.

}

TY - JOUR

T1 - Accurate measurement of exposure rate from a 60Co teletherapy source

T2 - Deviations from the inverse-square law

AU - Samat, Supian

AU - Evans, C. J.

AU - Kadni, T.

AU - Dolah, M. T.

PY - 2000

Y1 - 2000

N2 - 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.

AB - 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.

UR - http://www.scopus.com/inward/record.url?scp=0033844463&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0033844463&partnerID=8YFLogxK

M3 - Article

C2 - 11026863

AN - SCOPUS:0033844463

VL - 73

SP - 867

EP - 877

JO - British Journal of Radiology

JF - British Journal of Radiology

SN - 0007-1285

IS - 872

ER -