ISO DIS 4037-2

Description / Abstract: This part 2 of ISO 4037 specifies the procedures for the dosimetry of X and gamma reference radiation for the calibration of radiation protection instruments over the energy range from approximately 8 keV to 1,3 MeV and from 4 MeV to 9 MeV and for air kerma rates above 1 μGy/h. The considered measuring quantities are the air kerma free in air, K_a, and the phantom related operational quantities of the International Commission on Radiation Units and Measurements (ICRU)^[2], H*(10), H_p(10), H'(3), Hp(3), H'(0,07) and H_p(0,07), together with the respective dose rates. The methods of production are given in ISO 4037-1 Ed.2.

This part 2 of ISO 4037 is also valid for the radiation qualities specified in the informative annexes A, B and C of ISO 4037-1 Ed.2.

The requirements and methods given in this standard are targeted at an overall uncertainty (k = 2) of the dose(rate) of about 6 % to 10 % for the phantom related operational quantities in the reference fields. To achieve this, two production methods of the reference fields are proposed in ISO 4037-1 Ed.2.

The first is to produce “matched reference fields”, which follow the requirements so closely that recommended conversion coefficients can be used. The existence of only a small difference in the spectral distribution of the “matched reference field” compared to the nominal reference field is validated by procedures, which are given and described in detail in in this part 2 of ISO 4037 Ed.2. For matched reference radiation fields recommended conversion coefficients are given in ISO 4037-3 Ed.2 only for specified distances between source and dosemeter, e.g., 1,0 m and 2,5 m. For other distances, the user has to decide if these conversion coefficients can be used.

The second method is to produce “characterized reference fields”. Either this is done by determining the conversion coefficients using spectrometry, or the required value is measured directly using secondary standard dosimeters. This method applies to any radiation quality, for any measuring quantity and, if applicable, for any phantom and angle of radiation incidence. The conversion coefficients can be determined for any distance, provided the air kerma rate is not below 1 μGy/h.

Both methods require charged particle equilibrium for the reference field although this is not always established in the workplace field for which the dosemeter shall be calibrated, especially at high photon energies. The meaning of high photon energies depends on the definition depth in the phantom. Electrons of energies above 65 keV, 0,75 MeV and 2,1 MeV can just penetrate 0,07 mm, 3 mm and 10 mm of ICRU tissue, respectively, and the radiation qualities with photon energies above these values are considered as high photon energies for the quantities defined in these depths.

This standard is not applicable for the dosimetry of pulsed reference fields.