THE INFLUENCE OF NON-RADIATION INDUCED ESR BACKGROUND SIGNAL FROM PARAFFIN-ALANINE PROBES FOR DOSIMETRY IN THE RADIOTHERAPY DOSE RANGE

The yield of radicals induced by ionizing radiation in the amino acid alanine and its quantification by ESR spectroscopy has proven excellent reproducibility. Those radicals trapped in the crystal lattice are prevented from recombination providing a thermally very stable system. This allows alanine to be applied as a transfer dosemeter. With paraffin-alanine probes ESR dosimetry can be performed with a standard deviation of +/-0.5% in the dose range from 20 Gy up to 100 kGy. At 1 Gy dose level the error increases to +/-6%. This dose level is three orders of magnitude higher than the calculated detection threshold for alanine with modem X-band ESR spectrometers. It was found that the poor standard deviation at the 1 Gy dose level, is not mainly produced by a bad signal-to-noise ratio but by a variable non-radiation induced ESR background signal from the alanine probes within a batch. In the present study the main sources of error for ESR dosimetry in the dose range below 20 Gy were analyzed. The influences of the production process, UV light and humidity upon the ESR background signal from paraffin-alanine probes were investigated. Measurements are shown indicating a second stable structure of the alanine radical at room temperature.