Shipley, D R; Duane, S
(1994)
*Corrections to air kerme rate measurements of 125I brachytherapy sources to free space conditions.*
NPL Report.
RSA(EXT) 51

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## Abstract

Air kerma rate measurements have been made between 40 cm and 100 cm from one of a set of 125I reference sources within the facilities of Amersham International Plc. Monte Carlo techniques have been used to calculate the air kerma rate components over the same range of distances from this source. After comparing the calculated data with measurements, the compliance of the data with the inverse square law was investigated, and corrections were derived to obtain the air kerma rate at 1 m in free space from each source.

Simulations of the experimental setup with an isotropic monoenergetic point source close to the effective energy of 125I were found to reproduce the air kerma I rate measurements reasonably accurately, and indicated that the contribution due to scattered photons was significant. The overall correction (which is defined as the product of individual corrections for chamber size effect, air attenuation and radiation scatter) required to the inverse square law to obtain the air kerma rate at 1 m in free space was found to be 0.981, 0.984 and 0.980, respectively, for air kerma rate measurements at 40 cm, 60 cm and 100 cm from the 125I reference source. The total uncertainty in these corrections was estimated to be 0.88% at the 1s level.

Item Type: | Report/Guide (NPL Report) |
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NPL Report No.: | RSA(EXT) 51 |

Subjects: | Ionising Radiation Ionising Radiation > Dosimetry |

Last Modified: | 02 Feb 2018 13:19 |

URI: | http://eprintspublications.npl.co.uk/id/eprint/91 |

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