【国外标准】 Standard Practice for Use of the Ethanol-Chlorobenzene Dosimetry System

4.1 The ECB dosimetry system provides a reliable means of measuring absorbed dose to water. It is based on a process of radiolytic formation of hydrochloric acid (HCl) in aqueous ethanolic solutions of chlorobenzene by ionizing radiation ((7, 8) , ICRU 80).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. Radiation chemical yields (G) for the formation of HCl in typical ECB solution formulations are given in Table 1.(A) The ratio of the photon mass energy-absorption coefficients for water and the dosimeter solution at 60Co gamma ray energy:(B) Radiation chemical yield of HCl in the dose range from 100 Gy to 100 kGy.(C) Upper dose range 20 kGy.(D) Lower dose range 1 kGy. This formulation also contained 0.04 % acetone and 0.04 % benzene.4.3 The irradiated solutions indicate absorbed dose by the amount of HCl formed. A number of analytical methods are available for measuring the amount of HCl in ethanol (10) .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/ρ) for X- and gamma radiation, and electron mass collision stopping powers (S/ρ), over a broad energy range from 10−2 to 100 MeV (11-14).4.5 The ECB dosimetry system may be used with other radiation types, such as neutrons (15) , and protons (16). 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 (ECB) dosimetry system to measure absorbed dose to water when exposed to ionizing radiation. The system consists of a dosimeter and appropriate analytical instrumentation. For simplicity, the system will be referred to as the ECB system. The ECB dosimeter is classified as a type I dosimeter on the basis of the effect of influence quantities. The ECB dosimetry system may be used as a reference standard dosimetry system or as a routine dosimetry system.1.2 This document is one of a set of standards that provides recommendations for properly implementing dosimetry in radiation processing, and describes a means of achieving compliance with the requirements of ISO/ASTM Practice 52628 for the ECB system. It is intended to be read in conjunction with ISO/ASTM Practice 52628.1.3 This practice describes the mercurimetric titration analysis as a standard readout procedure for the ECB dosimeter when used as a reference standard dosimetry system. Other readout methods (spectrophotometric, oscillometric) that are applicable when the ECB system is used as a routine dosimetry system are described in Annex A1 and Annex A2.1.4 This practice applies only to gamma radiation, X-radiation/bremsstrahlung, and high energy electrons.1.5 This practice applies provided the following conditions are satisfied:1.5.1 The absorbed dose range is between 10 Gy and 2 MGy for gamma radiation and between 10 Gy and 200 kGy for high current electron accelerators (1, 2).2 (Warning—the boiling point of ethanol chlorobenzene solutions is approximately 80 °C. Ampoules may explode if the temperature during irradiation exceeds the boiling point. This boiling point may be exceeded if an absorbed dose greater than 200 kGy is given in a short period of time.)1.5.2 The absorbed-dose rate is less than 106 Gy s−1(2).1.5.3 For radionuclide gamma-ray sources, the initial photon energy is greater than 0.6 MeV. For bremsstrahlung photons, the energy of the electrons used to produce the bremsstrahlung photons is equal to or greater than 2 MeV. For electron beams, the initial electron energy is greater than 8 MeV (3).NOTE 1: The same response relative to 60Co gamma radiation was obtained in high-power bremsstrahlung irradiation produced by a 5 MeV electron accelerator (4).NOTE 2: The lower energy limits are appropriate for a cylindrical dosimeter ampoule of 12-mm diameter. Corrections for dose gradients across the ampoule may be required for electron beams. The ECB system may be used at lower energies by employing thinner (in the beam direction) dosimeters (see ICRU Report 35). The ECB system may also be used at X-ray energies as low as 120 kVp (5). However, in this range of photon energies the effect caused by the ampoule wall is considerable.NOTE 3: The effects of size and shape of the dosimeter on the response of the dosimeter can adequately be taken into account by performing the appropriate calculations using cavity theory (6).1.5.4 The irradiation temperature of the dosimeter is within the range from −30 °C to 80 °C.NOTE 4: The temperature dependence of dosimeter response is known only in this range (see 5.2). For use outside this range, the dosimetry system should be calibrated for the required range of irradiation temperatures.1.6 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. Specific warnings are given in 1.5.1, 9.2 and 10.2.1.7 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.