[en] At HERA PIN-diodes will be used for proton beam loss monitors. These monitors will be placed at superconducting magnets and at points where the beam pipe aperture is limited, in order to indicate critical beam losses, which could lead to a quench of the superconducting magnets. In this thesis, as regards monitor calibration, the sensitivity of charged particle and photon detection was measured. The number of charged particles and photons per lost proton was determined with the monte carlo programm GHEISHA 8.02. With these parameters the signal rate at various beam momenta for critical beam losses was fixed. The calibration function for the narrow parts of the ring was also fixed. These calibration functions define the number of signals corresponding to one lost proton. (orig.)

[en] We have tested the radiation resistance of two 10 cm long CsI(Tl) crystals in the radiation environment of the PETRA e⁺e^- storage ring. The crystals were exposed for 38 d to an average dose of 50 and 20 rad, respectively. The exposure leads to a continuous decrease of pulse height with a final reduction of 13+-1% (crystal 1 with photodiode readout at 50 rad) and 19.5+-2% (crystal 2 with photomultiplier readout at 20 rad). Most of the damage occurred in the first day of exposure. After the end of the exposure we observed a partial recovery of a few percent. (orig.)

[en] We have tested the radiation resistance of two 10 cm long CsI (Tl) crystals in the radiation environment of the PETRA e⁺e^- storage ring. The crystals were exposed for 38 days to an average dose of 50 rad and 20 rad, respectively. The exposure lead to a continuous decrease of pulse height with a final reduction of 13 +- 1% (crystal 1 with photodiode readout at 50 rad) and 19.5 +- 2% (crystal 2 with photomultiplier readout at 20 adout at 20 rad). Most of the damage occurred in the first days of exposure. After the end of the exposure we observed a partial recovery of few percent. (orig.)

[en] For monitoring of potentially incorporated radioactive materials normally whole body counters are used which are optimized for measuring low levels of radioactivity. In radiological emergency situations higher incorporated activities have to be estimated in a short time in many persons. Therefore, the use of the equipment in nuclear medicine facilities (e.g. gamma cameras) could be considered. Gamma cameras and other devices applied in nuclear medicine are optimized for measuring high activities; they are generally designed for diagnostics or pre- and posttherapeutic dosimetry. The aim of this study is to test these devices in radiological emergencies for their general suitability for absorbed dose estimates after incorporations. In addition it should be checked if these devices are useful for identification of radionuclides. For the most relevant radionuclides a manual should be developed for calibration, adjustment and any other necessary conversion of the equipment. For three gamma cameras with crystal thicknesses of 3/8'', 5/8'' and 1'', the count rate over the entire detection range of the cameras (50 keV-600 keV) was recorded for three photon energies (140 keV; Tc-99m, 364 keV; I-131, 511 keV; F -18) and varying activities. Based upon these data the lower limits of detection, the dead time behavior, the linearity and the detector efficiency were determined. Furthermore, for some radionuclides relevant for incorporation in radiological emergencies energy spectra were recorded, and calibration factors calculated. In addition, a thyroid uptake probe and external probes were tested for their potential use as incorporation monitors in a radiation accident scenario. Finally, an estimate of the effort of upgrading the equipment for the purpose of incorporation measurements was made and a manual for this conversion was developed. Gamma cameras are able to detect a wide range of activity linearly (without collimator: 100 Bq to 5 MBq, with collimator: 100 kBq to a maximum of 0.8 GBq) so that nearly 7 orders of magnitude are covered. The sensitivity of gamma cameras without collimation is higher by a factor of about 100 as compared to measurements with a high energy collimator. Photo peaks can be identified in an energy range between 50 keV and 700 keV. The uptake device registers photons linearly in a similar energy range as gamma cameras for an activity range between 0.05 MBq and 50 MBq. The field of view, however, is limited by the collimation. Dose rate meters can only be used in cases of severe incorporation and/or contamination (activity > 10 MBq). An estimate of the photon energies and thus a nuclide specific distinction is not possible as well as a subsequent dose assessment; these devices should primarily be used for a preliminary measurement. The use of dose rate meters for incorporation measurements is limited in radiologic emergencies. Gamma cameras or scintillation based detectors are capable to identify and quantify small and high incorporated activities in the energy range between 50 and 700 keV without major modifications. The limitation of the detectable photon energy is the most critical constraint on the applicability of the diagnostic instrumentation in nuclear medicine facilities in radiological emergency situations. (orig.)

[en] Thyroid volume measurement by ultrasonography (US) is essential in numerous clinical diagnostic and therapeutic fields. While known to be limited, the accuracy and precision of two-dimensional (2D) US thyroid volume measurement have not been thoroughly characterized. Objective: We sought to assess the intra- and interobserver variability, accuracy and precision of thyroid volume determination by conventional 2D US in healthy adults using reference volumes determined by three-dimensional (3D) US. Design, methods: In a prospective blinded trial, thyroid volumes of ten volunteers were determined repeatedly by nine experienced sonographers using conventional 2D US (ellipsoid model). The values obtained were statistically compared to the so-called true volumes determined by 3D US (multiplanar approximation), the so-called gold standard, to estimate systematic errors and relative deviations of individual observers. Results: The standard error of measurement (SEM) for one observer and successive measurements (intraobserver variability), was 14%, and for different observers and repeated measurements (interobserver variability), 17%. The minimum relative thyroid volume change significantly different at the 95% level was 39% for the same observer and 46% for different observers. Regarding accuracy, the mean value of the differences showed a significant thyroid volume overestimation (17%, p <0.01) by 2D relative to 3D US. Conclusion: 2D US is appropriate for routine thyroid volumetry. Nevertheless, the so-called human factor (random error) should be kept in mind and correction is needed for methodical bias (systematic error). Further efforts are required to improve the accuracy and precision of 2D US thyroid volumetry by optimizing the underlying geometrical modeling or by the application of 3D US. (orig.)