Electron beam dosimetry

Burns, D.T. and Morris, W.T., Recent developments in graphite and water calorimeters for electron beam dosimetry at NPL, Proc. Int. workshop on Water Calorimetry, Report NRC-29637, National Research Council of Canada, Ottawa, Canada (1988) 25-30. 

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. 

Radiation Dosimetry Electron Beams with Energies between 1 and 50 MeV International Commission on Radiological Units and Measurements Bethesda, 1980 Report No. 35. 

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. 

Resist films of approximately 0.5ym thickness were spun on silicon wafers and cross inked by baking either in an oven or on a hotplate. Incremental exposures were made by a JEOL JBX6A2 electron beam machine at 20 keV. The UV flood exposures were carried out under nitrogen using a 185nm UV lamp. UV dosimetry was carried out on the basis of exposure time which had previously been correlated with the equivalent electron beam exposure by measuring dissolution rates. 

Dosimetry with high-energy particles is a sensitive point because there are not enough experimental data for each type and energy of ion beams and the calculated yields depend strongly on the dose. The evaluation of the dose cannot be as accurate as for y or high energy electron beams for which a few secondary dosimeters have been determined such as Fricke dosimeter, thiocyanate and ceric systems, for example. 

Dosimetry. The G value for the production of ferric ion in a standard Fricke solution was taken as 15.6 for 60Co y-rays and x-rays produced by primary electron beams with energies of 3 and 14 Mev. Ferric ion was estimated spectrophotometrically in a Beckman DU spectrophotometer using an extinction coefficient of 2197 M"1 cm."1 at 304 m/x at 25°C. 

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... 

The response of the aqueous and aqueous-alcoholic solutions of tetrazolium violet (2,5-diphenyl-3-(l-naphthyl)-2H-tetrazolium chloride, TV) was found usefiil for dosimetry purposes in the 0.25-60 kGy dose range. The polyvinylalcohol-based TV-containing dosimeter films showed also suitable response in the 1-60 kGy dose range making it usefiil for radiation process control both in gamma and electron beam radiation processing (Emy-Reynolds et al. 2007a, b). 

Film dosimeters. The radiation-induced change of optical absorption in various film systems has been utilized for dosimetry purposes for many decades. Although correct application of films requires controlled conditions because their response is affected by almost all environmental factors, these systems are widely used in both gamma and electron beam radiation processing. They are well suited for dosimetry of electron radiation because of their good spatial resolution characteristics, e.g., for dose distribution measurements as compared to other systems. 

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). 

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. 

Absolute dosimetry with the electron accelerator is less accurate than with the cobalt-60 source since penetration of the electron is a variable— directly proportional to the energy of the beam and inversely proportional to the density of the material. The absorbed dose varies with depth (18) and is about 60% of maximum at the surface with a steady increase to a maximum at about one-third of the total penetration depth. At about two-thirds of the total penetration, the dose is equivalent to that absorbed at the surface. Therefore, if all parts of the sample are to receive the same minimum dose, the useful penetration is approximately two-thirds of the total, or about 0.33 gram per square centimeter per m.e.v. 

Hydrated Electron and Thermoluminescent Dosimetry of Pulsed X-ray Beams... 

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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