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Date: 23 October 2021
Diagnostic X-ray instruments
Dose and doserate meters and Ionisation chambers/detectors designed for general radiology measurements
Ionisation chambers or solid state detectors for general radiology are calibrated against a range of X-ray spectra as defined in IEC 61267:2005, Medical Diagnostic X-ray equipment – radiation conditions for use in the determination of characteristics. The air kerma rates used are all traceable to the UK primary standards facility at the National Physical Laboratory (NPL). X-ray spectra are available from 40 kV to 150 kV to measure the instrument's performance over a broad range of energies.
For detectors used to measure the input doserates to image intensifiers or automatic exposure controls an additional spectrum is provided. This measures the performance of the detector to an X-ray beam similar to one that emerges from an irradiated object, such as a patient.
Detectors used in CT applications are calibrated against higher energy CT X-ray beams.
The standard calibration also includes a linearity test across the air kerma rate working range of the detector, incorporating an important check at the minimum doserate measurable by the instrument (for some instruments this is carried out at air kerma rates down to 15 µGy/min or 0.25 µGy/sec).
The peak accelerating voltage is obtained using a reference digital voltmeter (traceable to primary standards) which is cross referenced by obtaining the peak photon energy of the X-ray spectra using a hyper pure germanium detector and appropriate software.
Multimeters for measurements of X-ray dose and kV are calibrated using the X-ray radiation qualities described above.
Adjustments to instruments
Depending upon information being made available by the manufacturer, the calibration includes the adjustment of the response to within the manufacturer's declared specification. This is undertaken routinely for instruments from major suppliers such as Radcal and Keithley.
For further information, please contact:
- General enquiries: Tracie Such
- Technical enquiries: Joanne Johnson, John Lewis
63 Melchett Road
Kings Norton Business Centre
Birmingham, B30 3HP
Telephone: 0121 371 7000