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Radiotherapy services

X-ray air kerma and absorbed dose to water calibration

Traceable calibration of a therapy-level dosemeter  

The service is available for thimble chambers or thin-window chambers, and offered in the Spring or Autumn (subject to demand) of each year.

Thimble Chambers

Air kerma (low + medium energy X-rays + 60Co) and absorbed dose

  • For instruments intended to be used as secondary standards or others required for measurements of the greatest accuracy
  • Calibration of an ionisation chamber with or without an electrometer
  • Ionisation chambers of type 2561, 2611, 2571, and other Farmer type chambers with a graphite wall and aluminum central electrode will be accepted after confirmation with NPL
  • Batch calibrations are undertaken between February and April each year

Absorbed dose to water

  • Calibration against NPL reference standards in terms of absorbed dose to water
  • Primary standard is the NPL graphite microcalorimeter
  • For 60Co γ-rays and X-rays generated between 4 MV and 25 MV, quality index (TPR) between 0.568 and 0.800
  • Beam qualities similar to those used for high energy photon radiotherapy.
  • Calibration conforms to IPSM Code of Practice (1990)

Air kerma

  • Calibration directly against the NPL air kerma primary standards
  • Calibration for X-rays generated between 50 kV and 280 kV and for 60Co γ-rays
  • Beam qualities similar to those used for radiotherapy treatments
  • Calibration conforms to IPEMB Code of Practice (1996)

Thin-Window Chambers

Air kerma - very low energy X-rays

  • For instruments intended to be used as secondary standards or others required for measurements of the greatest accuracy
  • PTW 23342, 0.02 cc, PTW 23344, 0.2 cc and other similar chambers are accepted after confirmation from NPL
  • Calibration of an ionisation chamber with or without an electrometer
  • Batch calibrations are undertaken between February and April each year

Air kerma

  • Calibration directly against the NPL 50 kV air kerma primary standar.
  • Calibration for X-rays generated between 8.5 kV and 50 kV
  • Beam qualities similar to those used for radiotherapy treatments 
  • Calibration conforms to IPEMB Code of Practice (1996)

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