ASTM/ISO 51956-05

4.1 During the irradiation of certain crystalline materials, for example, LiF, CaF2, CaSO4, Li2B4O7, and Al2O3, the filling of electron and hole traps between the ground state and the conduction band results in stored energy that can be released as fluorescence during heating. Thermoluminescence dosimetry systems provide a means of determining absorbed dose to materials by measuring this fluorescence by the controlled heating of the irradiated crystalline material.

4.2 Thermoluminescence dosimeters (TLDs) are available from different commericial suppliers in different forms such as loose powder, chips or crystals encapsulated in glass or plastic.

4.3 TLDs can be reused by subjecting the irradiated TLDs to an annealing process at a higher temperature to release all the electron and hole traps.

4.4 In radiation processing, TLDs are mainly used in the irradiation of blood products (see ISO/ASTM Practice 51939), food (see ISO/ASTM Practices 51204 and 51431), and insects for sterile insect release programs (see ISO/ASTM Guide 51940). TLDs may also be used in other radiation processing applications such as the sterilization of medical products, modification of polymers, irradiation of electronic devices, and curing of inks, coatings and adhesives. (See Refs (1, 2)4 and ISO/ASTM Practices 51608, 51649, and 51702).

4.5 For radiation processing, the absorbed-dose range of interest is from 1 Gy to 100 kGy. Some TLDs can be used in applications requiring much lower absorbed doses (for example, for personnel dosimetry), but such applications are outside the scope of this practice. Examples of TLDs and applicable dose ranges are given in Table 1. Further information on various types of TLDs and their applications can be found in Refs (3-8).

4.6 Regulations for sterilization of medical products, irradiation of blood products, and radiation processing of food exist in many countries. These regulations may require that the dosimetry system be calibrated with traceability to national standards (9, 10, 11, 12). Adequate dosimetry, with proper statistical controls and documentation, is necessary to ensure that the products are properly processed.

4.7 Proper dosimetric measurements shall be employed to ensure that the product receives the desired absorbed dose. The dosimeters shall be calibrated as outlined in Section 8. All possible factors that may affect the response of dosimeters, including environmental conditions and variations of such conditions within a processing facility, should be known and taken into account. The associated measurement instrumentation shall also be calibrated.

1.1 This practice covers procedures for the use of thermoluminescence dosimeters (TLDs) to determine the absorbed dose in materials irradiated by photons or electrons in terms of absorbed dose to water.

1.2 This practice covers systems that permit absorbed dose measurements under the following conditions:

1.2.1 The absorbed-dose range is from 1 Gy to 100 kGy.

1.2.2 The absorbed-dose rate is between 1 10 ² and 1 10¹⁰ Gy s¹.

1.2.3 The radiation-energy range for photons and electrons is from 0.1 to 50 MeV.

1.3 Absorbed dose and absorbed-dose rate measurements in materials subjected to neutron irradiation are not covered in this practice.

1.4 Procedures for the use of TLDs for determining absorbed dose in radiation-hardness testing of electronic devices are given in ASTM Practice E 668.

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.