ISO 4037-2:2019 pdf free download – Radiological protection一X and gamma reference radiation for calibrating dosemeters and doserate meters and for determining their response as a function of photon energy一 Part 2: Dosimetry for radiation protection over the energy ranges from 8 keV to 1,3 MeV and 4 MeV to 9 MeV.
6 Direct calibration of the reference field in terms of the required phantom related measuring quantity. A direct calibration is required for characterized reference fields if spectrometry shall be avoided. The instrument to be used for the measurement of the reference radiation shall either be a secondary standard or another appropriate instrument, which is traceably calibrated to a primary standard. Generally, this comprises an ionization chamber assembly and a measuring assembly. Several different types of instruments for the measuring quantities H*(10), H(10), H’(3), H(3) H’(0,07) and H(0,O7) and for the appropriate phantoms are required for the direct calibration. The standard instrument shall follow the requirements given in Clause 4, shall be operated as described in Annex A. and the procedures in Clause 7 shall be followed. The calibration shall be performed for each calibration distance for which the reference field is intended to be used.
7 Measurement procedures applicable to ionization chambers
7.1 Geometrical conditions
The cross-sectional area of the reference-radiation beam should be sufficient to irradiate the standard chamber or the device to be calibrated, whichever is the larger. The variation of kerma rate over the useful beam area shall be less than 5 %, and the contribution of scattered radiation to the total kerma rate shall be less than 5 % (see ISO 4037-1). Corrections shall be applied if considered necessary.
The finite size of the chamber may affect the measurement of the radiation at small source-chamber distances, see Reference [11], e.g., due to divergence of the beam.
7.2 Chamber support and stem scatter
The structure supporting the standard chamber in the beam shall be designed to contribute a minimum of scattered radiation. Since the effect of stem scatter and radiation-induced currents in the stem under the calibration conditions is included in the calibration factor for the standard instrument, no correction factor for these effects should be applied unless the beam area is significantly different from that used to calibrate the standard.
The effect of stem scatter may be found from measurements with and without a replicate stem in appropriate geometrical conditions.
NOTE Stem scatter is a function of the reference radiation quality and the beam area. However, the effect of scattered radiation on subsequent use of the beams to calibrate instruments is dependent on the type of instrument and the method of its support unless the standard and the instrument are identical.
7.3 Location and orientation of the standard chamber
The standard chamber shall be set up as specified by the calibration laboratory on the axis of the reference radiation beam at the desired distance from the source to the reference point of the chamber and its reference orientation to the beam shall be as stated by the manufacturer.
7.4 Measurement corrections
7.4.1 General
The indication of the standard instrument shall be corrected, where necessary, for the effects described in Annex A to determine the result of a measurement.
NOTE Some types of instrument have automatic temperature and/or pressure compensation, obviating the need for further correction, provided that the compensation is to the same reference calibration conditions as given above.
The above corrections do not consider the attenuation of the photon radiation due to the air path from the source to the point of measurement. This needs only to be considered for low X-ray energies generated by a potential of 30 kV or less. For the correction, see ISO 4037-4.