A blind test of the alanine dosimetry secondary standard of the PTB conducted by the BIPM

In order to verify the reliability of the PTB's secondary standard measurement system for the absorbed dose to water, D-W, based on alanine with read-out by electron spin resonance (ESR), a blind test was conducted. Nine detectors consisting of four alanine pellets each were irradiated in the Co-60 reference field of the BIPM. The doses were restricted to the range between 10 Gy and 20 Gy in order to minimize the influence of noise. The values of the delivered doses were not communicated until after the measurement results were reported back to the BIPM. The absorbed dose to water D-W was measured using a slightly simplified procedure, compared to previous publications, i.e. without construction of a calibration curve. On average, the measurement results are 0.12% higher than expected from the known difference between the primary standards for D-W of the BIPM and the PTB. Compared to the combined measurement uncertainty of the ratio of determined and delivered dose of approximately 0.45%, the agreement is good.