Active Standard ISO / ASTM51538 | Developed by Subcommittee: E61.02
Book of Standards Volume: 12.02
Significance and Use
4.1 The ECB dosimetry system provides a reliable means of measuring absorbed dose in materials. It is based on a process of radiolytic formation of hydrochloric acid (HCl) in aqueous ethanolic solutions of chlorobenzene by ionizing radiation (7,8).
4.2 The dosimeters are partly deoxygenated solutions of chlorobenzene (CB) in 96 volume % ethanol in an appropriate container, such as a flame-sealed glass ampoule. The irradiated solutions indicate absorbed dose by the amount of HCl formed. Anumber of analytical methods are available for measuring the amount of HCl in ethanol (9).
4.3 Effect of Irradiation Temperature:
4.3.1 The temperature dependence of dosimeter response is a complex function of dose and temperature for each concentration of chlorobenzene (that is, for each formulation). The analysis of the published data (10) shows that the temperature dependence between 20°C and 80°C at any chlorobenzene concentration can be described by a simple exponential expression: Gt 5 G0 exp[k~t 2 20!# (3) where: Gt = the radiation chemical yield in µmol J-1 at a given temperature t in °C, G0 = the radiation chemical yield in µmol J-1 at 20°C ((G0 for different ECB solutions are given in Table 1), and k = the temperature coefficient in (°C)-1 applicable at a given dose.
4.3.2 The values of k are given in Table 2.
4.3.3 Between -30°C and 50°C the temperature coefficient 0.015 kGy/°C applies at 30 kGy dose (12). Information on the temperature dependence of dosimeter response during irradiation between 20 and 80°C is found in Ref (10), and between -40 and 20°C in Ref (13).
4.4 The concentration of chlorobenzene in the solution can be varied so as to simulate a number of materials in terms of the photon mass energy-absorption coefficients (µen/r) for X and gamma radiation, and electron mass collision stopping powers (S/r), over a broad energy range from 10-2 to 100 MeV(14-17).
4.5 The absorbed dose that is determined is the dose absorbed in the water. Absorbed dose in other materials irradiated under equivalent conditions may be calculated. Procedures for making such calculations are given in ASTM Practices E 666 and E 668 and ISO/ASTM Guide 51261.
NOTE 3 - For a comprehensive discussion of various dosimetry methods applicable to the radiation types and energies discussed in this practice, see ICRU Reports 14, 17, 34, 35, and 37.
4.6 The ECB dosimetry system may be used with other radiation types, such as neutrons (18), and protons (19). Meaningful dosimetry of any radiation types and energies novel to the system’s use requires that the respective radiation chemical responses applicable under the circumstances be established in advance.
1.1 This practice covers the preparation, handling, testing, and procedure for using the ethanol-chlorobenzene dosimetry system to measure absorbed dose in materials irradiated by photons and electrons in terms of absorbed dose in water. The system consists of a dosimeter and appropriate analytical instrumentation. For simplicity, the system will be referred to as the ECB system. It is classified as a reference-standard dosimeter and is also used as a routine dosimetry system (see ISO/ASTM Guide 51261).
1.2 This practice describes the titration analysis as a standard readout procedure for the ECB dosimeter. Other applicable readout methods (spectrophotometric, oscillometric) are described in Annex A1 and Annex A2.
1.3 This practice applies only to gamma rays, X rays, and high-energy electrons.
1.4 This practice applies provided the following are satisfied:
1.4.1 The absorbed dose range shall be from 10 Gy to 2 MGy (1).
1.4.2 The absorbed dose rate does not exceed 10 6 Gy s1 (2).
1.4.3 For radionuclide gamma-ray sources, the initial photon energy shall be greater than 0.6 MeV. For bremsstrahlung photons, the initial energy of the electrons used to produce the bremsstrahlung photons shall be equal to or greater than 2 MeV. For electron beams, the initial electron energy shall be equal to or greater than 4 MeV (3) (see ICRU Reports 34 and 35).
Note 1—The lower limits of electromagnetic radiation energy given are appropriate for a cylindrical dosimeter ampoule of 12-mm diameter. Corrections for dose gradients across an ampoule of that diameter or less are not required. The ECB system may be used at energies of incident electrons lower than 4 MeV by employing thinner (in the beam direction) dosimeter containers (see ICRU Report 35). The ECB system may also be used at X-ray energies as low as 120 kVp (4). In this range of photon energies the effect caused by the wall is considerable.
1.4.4 The irradiation temperature of the dosimeter should be within the range from 40°C to 80°C.
Note 2—The temperature dependence of dosimeter response is known only in this range. For use outside this range, the dosimetry system should be calibrated for the required range of irradiation temperatures.
1.4.5 The effects of size and shape of the irradiation vessel on the response of the dosimeter can adequately be taken into account by performing the appropriate calculations using cavity theory (5).
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.