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Results of the periodic comparison measurements of beta extremity dosimeters from 2002 to 2007


In Germany, for persons who are occupationally exposed to radiation, monitoring with personal dose equivalent meters is legally prescribed. Besides the whole-body dosimeters which are to be worn on the trunk, also passive extremity dosimeters are used which are often worn around the fingers. Extremity dosimeters are used for beta radiation measurements, especially in medicine. All dosimeters of this type are released and assessed by dosimetry services. PTB is thereby responsible for quality control. Quality control takes place in two stages:

In the first stage, the designs are submitted to a thorough check with regard to their properties before the dosimeter is released for use. In the case of beta dosimeters, this control is carried out according to a directive.

In the second stage, the routine operation is checked yearly at the dosimetry services via so-called "periodic comparison measurements". The dosimeters are thereby exposed by PTB to a well known dose - which we we will call HPTB in the following. Then, the dosimetry services analyse the dosimeters and determine their measured value, HDST, of course without knowing the value of HPTB. As a measure of quality, the quotient HDST/HPTB is used which is 1.0 for an ideal dosimeter. The figure shows the values of these quotients in relation with the dose for all comparison measurements which have been carried out with beta radiation up to now. The lines plotted indicate the admissible limits for this quotient. Due to the requirements of radiation protection, these limits narrow towards high doses.

The condition for passing the yearly comparison measurements is that 90% of all quotients for each design of a service lie within these limits. If this requirement is not met by one dosimeter design for the comparison measurement, a repetition is carried out for this dosimeter. This has never been the case up to now. In summary, one can say that this type of two-stage quality control is particularly efficient.

Figure : Results of the beta comparison measurements that have been carried out up to now. The lower and upper red-dotted limits and the red data points are valid for the very low-energetic radiation of promethium 147.