Significance and Use
4.1 Self-contained dry-storage gamma-ray irradiators contain radioactive sources, namely 137Cs or 60Co, that emit ionizing electromagnetic radiation (gamma rays), under properly shielded conditions. These irradiators have an enclosed, accessible irradiator sample chamber connected with a sample positioning system, for example, irradiator drawer, rotor, or irradiator turntable, as part of the irradiation device.
4.2 Self-contained dry-storage gamma-ray irradiators can be used for many radiation processing applications, including the following: calibration of dosimeters; dosimeter studies for research; irradiations of relatively small samples for inducing desired radiation effects or for radiation process validation purposes; irradiation of materials or biological samples for process compatibility studies; batch irradiations of microbiological, botanical, or in-vitro samples; irradiation of small animals; radiation "hardness" testing of electronics components and other materials; and batch radiation processing of relatively small containers of samples, such as blood products, insect canisters, prosthetic devices, and pharmaceuticals.
NOTE 1 - In the case of irradiated health care products, pharmaceuticals, foodstuffs, animals and plants, the assurance that they are properly irradiated is of crucial importance. The irradiator operator must demonstrate by means of accurate absorbed dose measurements in sample, or in simulated product, that the specified absorbed dose is achieved (see ISO/ASTM Guide 51261, ISO/ASTM Practices 51204, 51400, 51702, and ISO 11137). For most applications, the absorbed dose is expressed as absorbed dose in water (see ISO/ASTM Guide 51261). For conversion of absorbed dose in water to that in other materials, for example, silicon, solid-state devices, polymers, see Annex A1 of ISO/ASTM Guide 51261.
4.3 Self-contained dry-storage gamma-ray irradiators contain a sealed source, or an array of sealed sources completely held in a dry container constructed of solid materials. The sealed sources are shielded at all times, and human access to the chamber undergoing irradiation is not physically possible due to design configuration (see ANSI N433.1).
4.4 For each irradiator, an absorbed--dose rate at a reference position within the sample or sample holder is measured. That measurement is used to calculate the timer setting required to deliver the specified absorbed dose. The irradiator manufacturer may perform reference-standard measurements and dosemapping measurements within the irradiation chamber.
NOTE 2 - For reference-standard dosimetry, the absorbed dose and absorbed-dose rate can be expressed in water or other material which has similar radiation absorption properties to that of the samples or dosimeters being irradiated. In some cases, the reference-standard dosimetry may be performed using ionization chambers, and may be calibrated in terms of exposure (C kg–1), or absorbed dose in air, water or tissue (gray). Measurements performed in terms of exposure apply to ionization in air, and care should be taken to apply that measurement to the sample being irradiated.
4.5 Dosimetry carried out with such sources may be part of a measurement quality assurance program that is applied to ensure that the radiation process, test or calibration meets predetermined specifications (1).9
4.6 Absorbed-dose mapping for establishing the locations of minimum (Dmin) and maximum (Dmax) doses usually is performed using the sample or simulated product (see 9.3).
1.1 This practice outlines dosimetric procedures to be followed with self-contained dry-storage gamma-ray irradiators. If followed, these procedures will help to ensure that calibration and testing will be carried out with acceptable precision and accuracy and that the samples processed with ionizing radiation from gamma rays in a self-contained dry-storage irradiator receive absorbed doses within a predetermined range.
1.2 This practice covers dosimetry in the use of dry-storage gamma-ray irradiators, namely self-contained dry-storage 137Cs or 60Co irradiators (shielded freestanding irradiators). It does not cover underwater pool sources, panoramic gamma-ray sources such as those raised mechanically or pneumatically to irradiate isotropically into a room or through a collimator, nor does it cover self-contained bremsstrahlung x-ray units.
1.3 The absorbed dose range for the use of the dry-storage self-contained gamma-ray irradiators covered by this practice is typically 1 to 105 Gy, depending on the application. The absorbed-dose rate range typically is from 10-2 to 103 Gy/min.
1.4 This practice describes general procedures applicable to all self-contained dry-storage gamma-ray irradiators. For procedures specific to dosimetry in blood irradiation, see ISO/ASTM Practice 51939. For procedures specific to dosimetry in radiation research on food and agricultural products, see ISO/ASTM Practice 51900. For procedures specific to radiation hardness testing, see ASTM Practice E 1249. For procedures specific to the dosimetry in the irradiation of insects for sterile release programs, see ISO/ASTM Guide 51940. In those cases covered by ISO/ASTM Practices 51939, 51900, 51940, or ASTM E 1249, those standards take precedence. In addition, this practice does not cover absorbed-dose rate calibrations of radiation protection instrumentation.
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.