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).