Dosimetry with alanine/electron spin resonance. Positioning of dosemeter probe and reference substance

The measurement quantity relevant for the radiation therapy is the water energy dose DW. A measure for the dose is the concentration of radiation-induced free radicals of the amino acid alanine, which can be detected by means of the electron spin resonance (ESR). On the base of this procedure in the PTB a secondary normal measurement facility for the water energy dose DW was constructed. Thereby beyond the dosemeter probe of alanine a reference substance was positioned in the ESR spectrometer. By means of this reference substance external influences like fluctuations of temperature anf relative air humidity or a drift of the sensitivity of the ESR spectrometer can be farly compensated. Deciding for the measurement uncertainty, which can be reached by this procedure, is the precise positioning of dosemter probe and reference substance. The present report describes therefore the positioning facility applied in the PTB. Section 2 describes thew principle of the dosimetry with alanine/ESR and explains the referene procedure applied in the PTB. Section 3 deals wqith the positioning of the dosemeter probe as well as different procedures for the positioning of the reference substance. It contains the description for the fabtication of the necessary components and hints to possible error sources. Section 4 explains the mechanical construction and the driving of the positioning facility. In it the construction and the adjustment of the positioning facility, the vacuum suction of the dosemeter probe, as well as the single components of the driving