Electron beam irradiation dosimetry

Calorimetry is an absolute method of dosimetry, since almost all absorbed radiation energy is converted into heat that can be readily measured as a temperature rise of the calorimetric body. Calorimeters that are used as primary dosimeters do not require calibration and, ideally, their response is independent of dose rate, radiation characteristics, and environmental factors (Domen 1987). The calorimeters that are used in radiation processing for the measurement of absorbed dose are relatively simple and need calibration (ISO/ASTM 2003b). The use of calorimeters as primary standard dosimeters for electron beam irradiation is described by McEwen and Dusatuoy (2009) and for gamma irradiation by Seuntjens and Duane (2009). 

The most commonly used sources of radiation are the 60 Co gamma source for continuous irradiation and pulsed high-energy (>1 MeV) electron beams for fast kinetic studies. Detailed descriptions of several such sources and accelerators are given in numerous books, as are the various methods used by radiation chemists for dosimetry, sample preparation and irradiation, and common product analysis. Several new developments in the analytical procedures, both in the determination of final products and in the direct observation of transient species, will be discussed below. 

Radiation processing by electron beam or y-irradiation is a commonly employed method for the sterilization of medical devices. The method has on one hand the advantage that sterilization can be carried out with the items in their original packages. On the other hand, dosimetry is required to ensure that the radiation treatment is at a tolerable level to avoid toxicological hazard as emphasized in the standards on radiation sterilization drafted by international standards organizations. Dosimetry... 

Other groups of these dosimeters contain certain dyes mixed into the basic material (in most cases a polymer), and the optical absorption of these dyes changes upon irradiation. These systems are simple to measure and apply, but their response is affected by environmental factors such as humidity, light, and temperature. Some of these systems are preferred in gamma processing, while the main application field of others is electron-beam dosimetry. 

Type of Radiation and Dosimetry The overall radiation effect does not depend on the type of radiation (such as X rays, gamma rays, electron beams, nuclear reactor irradiation, or other accelerated particle radiation), but only on the absorbed dose. There are some uncertainties about the given dose, especially to different types of radiation. In the following tables, the accuracy of the dose is estimated to be 10% for gamma-rays and 20% for electron beams or accelerated particles. 

Figure 1. X-irradiation set-up for simultaneous Fricke or LiF and hydrated electron dosimetry. Left to right Linac, tungsten target, an 11.3 cm. water container with dosimeter bulb on the beam axis and a multiple reflexion cell for transient absorption spectrophotometry. From the multiple reflexion cell the light beam passes into a monochromator-photomultiplier assembly...

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