The Alanine ESR Dosimeter

L-a-alanine, H2NCH(CH3)COOH, is the most commonly used material for ESR dosimetry. Alanine has excellent characteristics for dosimetric purposes in several respects [4] (1) high free radical yield (G-value), (2) short relaxation times so that high microwave power can be applied, (3) linear ESR response with radiation dose up to 5-10 Gy, (4) high stability of the radiation induced free radicals so that the dosimeter can be kept as a document of the radiation dose, (5) tissue equivalence for medical and biological applications, (6) non-destructive read-out of dosimeter so that the dose accumulation at repeated exposures can be monitored. 

X-irradiated polycrystalline L-a-alanine yields the ESR spectrum at room temperature shown in Fig. 9.5. 

L-a-alanine has been employed as an ESR dosimeter since 1962 [26], Regulla et al. [7, 27] have reported detailed studies on its dosimetric properties. It is the most commonly used material in the field of ESR dosimetry being accepted by the International Atomic Energy Agency (IAEA) [28] and other agencies as a secondary reference and transfer dosimeter for high (industrial) dose irradiation. 

Alanine dosimeters are commercially produced in the form of pellets, rods, films and cables. For calibration a set of standards irradiated in advance with known doses and prepared from the same alanine dosimeter batches as those under study are employed. The radiation dose of the unknown sample is obtained by comparison of the heights of the central line of the sample and the standards. Usually a reference ESR standard is recorded simultaneously with the alanine spectra to correct for variations in spectrometer sensitivity. 

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 

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Sophisticated measurement protocols have made it possible to measure low doses with an impressive precision using the alanine ESR dosimeter. Nagy et al. [34] have reported measurements within 1.5 % for doses between 1 and 5 Gy, and Hayes et al. [35] have demonstrated measurement of doses in the range 0.01-1,000 Gy with an uncertainty of 1% for high doses and 10 mGy for low doses. An uncertainty of less than 0.5% was achieved for doses between 5 and 25 Gy [36]. 

The alanine ESR dosimeter is less convenient for low dose dosimetry due to the long measurement times. New materials for the dose determinations in the interval 0.2-10 Gy may therefore be needed if the ESR method shall become a realistic alternative to existing dosimetry systems, e.g. ionisation chambers. Si-diodes, ther-moluminiscence or chemical dosimetry like Ericke solution. Strategies for finding... 

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