IEC 61331-1-2014 pdf free download.Protective devices against diagnostic medical X-radiation – Part 1: Determination of attenuation properties of materials.
The ATTENUATION RATIO FB for a given test material (or test object) shall be measured according to the arrangement for BROAD BEAM CONDITION as shown in Figure 2. This arrangement is designed to measure the ATTENUATION of the x-ray beam if secondary photons emitted by the material sample are included in the detection of the attenuated beam. The probability that secondary photons such as fluorescence photons or Compton scattered photons from the test object reach the RADIATION DETECTOR is maximized. The distance a, from the focal spot to the radiation exit plane of the test object shall be at least three times the diameter d, of the beam limiting aperture, i.e. a  3d. The aperture diameter d shall be at least 10 times greater than the distance b, of the reference point of the RADIATION DETECTOR from the surface of the test object, i.e. d  lOb. b shall be chosen as small as possible in order to minimize the ATTENUATION of secondary photons by the amount of air between the reference point of the RADIATION DETECTOR and the point of emission of the secondary photons from the test object. The distance between the outer wall of the chamber and the surface of the test object shall not exceed 10 mm. The minimal distance of the wall or the floor from the detector (position 6 in Figure 2) in the direction of the beam shall be 700 mm.
4.3.2 AIR KERMA RATE measurements
The AIR KERMA RATE shall be measured under three different conditions with the same RADIATION DETECTOR at the same position, where:
k0 denotes the AIR KERMA RATE without the test object in the RADIATION BEAM;
k1 the AIR KERMA RATE with the test object in the RADIATION BEAM;
K8 the AIR KERMA RATE with the test object in the beam replaced by a sheet of material of the same shape with an ATTENUATION RATIO greater than io.
The same constant dose rate of the primary beam shall be used for the three measurements. If the mean dose rate of the primary beam varies by more than 0,2 % during the measurements a monitor shall be used to normalize the three measurements to the same primary beam dose rate, The dose rate of the primary beam at any point in the plane of the beam-limiting aperture shall not vary by more than 2 %.
4.3.3 RADIATION QUALITIES and RADIATION DETECTOR
The RADIATION QUALITIES given in Table 1 shall be used for the measurements. The RADIATION DETECTOR shall be calibrated in terms of AIR KERMA. The quotient K0 divided by shall be known with a relative standard uncertainty not more than 2 %. The dependence of the response of the RADIATION DETECTOR upon the direction of incidence shall be negligibly small over a hemisphere. It is recommended to use a spherical ionisation chamber.IEC 61331-1 pdf free download.