[BeO-OSL detectors for dose measurements in cell cultures]. / Anwendung von BeO-OSL-Detektoren zur Dosismessung in Zellkulturen.

AIM: The absorbed dose is an important parameter in experiments involving irradiation of cells in vitro with unsealed radionuclides. Typically, this is estimated with a model calculation, although the results thus obtained cannot be verified. Generally used real-time measurement methods are not applicable in this setting. A new detector material with in vitro suitability is the subject of this work. METHODS: Optically-stimulated luminescence (OSL) dosimeters based on beryllium oxide (BeO) were used for dose measurement in cell cultures exposed to unsealed radionuclides. Their qualitative properties (e. g. energy-dependent count rate sensitivity, fading, contamination by radioactive liquids) were determined and compared to the results of a Monte Carlo simulation (using AMOS software). OSL dosimeters were tested in common cell culture setups with a known geometry. RESULTS: Dose reproducibility of the OSL dosimeters was +/-1.5%. Fading at room temperature was 0.07% per day. Dose loss (optically-stimulated deletion) under ambient lighting conditions was 0.5% per minute. The Monte Carlo simulation for the relative sensitivity at different beta energies provided corresponding results to those obtained with the OSL dosimeters. Dose profile measurements using a 6 well plate and 14 ml PP tube showed that the geometry of the cell culture vessel has a marked influence on dose distribution with 188Re. CONCLUSION: A new dosimeter system was calibrated with beta-emitters of different energy. It turned out as suitable for measuring dose in liquids. The dose profile measurements obtained are suitably precise to be used as a check against theoretical dose calculations.

Investigation of a BeO-based optically stimulated luminescence dosemeter.

The optical sensitivity of BeO-based luminophors has been well-known for many years. The optical stimulation of BeO with blue light is most effective. Then the dosemeters emit luminescent light in the ultraviolet-range around 325 nm. Matched on these facts a simple optically stimulated luminescence (OSL) treatment has been developed. Intense blue light-emitting diodes are used for cw-stimulation. A Hamamatsu solar blind photomultiplier detects the OSL-light. Good separation of both spectral ranges by optical filters is very important. The dosemeter has a linear dose response between approximately 20 muGy and >10 Gy. It was suggested, that a modification of stimulation conditions would allow measurements down to 1 muGy. Fading, photon energy dependence and reproducibility of OSL-signal correspond well with requirements to clinical and personal dosemeters. In addition, basic questions of the OSL-process in BeO have been investigated. A relevant point of interest was the dependency of the OSL-signal on stimulation power.

Application of advanced Monte Carlo Methods in numerical dosimetry.

Many tasks in different sectors of dosimetry are very complex and highly sensitive to changes in the radiation field. Often, only the simulation of radiation transport is capable of describing the radiation field completely. Down to sub-cellular dimensions the energy deposition by cascades of secondary electrons is the main pathway for damage induction in matter. A large number of interactions take place until such electrons are slowed down to thermal energies. Also for some problems of photon transport a large number of photon histories need to be processed. Thus the efficient non-analogue Monte Carlo program, AMOS, has been developed for photon and electron transport. Various applications and benchmarks are presented showing its ability. For radiotherapy purposes the radiation field of a brachytherapy source is calculated according to the American Association of Physicists in Medicine Task Group Report 43 (AAPM/TG43). As additional examples, results for the detector efficiency of a high-purity germanium (HPGe) detector and a dose estimation for an X-ray shielding for radiation protection are shown.

DOSIMETRIC PROPERTIES OF THE NEW TLD ALBEDO NEUTRON DOSEMETER AWST-TL-GD 04.

A new official albedo dosemeter based on thermoluminescent detectors has been introduced in 2015 by the individual monitoring service of the Helmholtz Zentrum München for monitoring persons who are exposed occupationally against photon and neutron radiation. To enhance the sensitivity for fast neutrons, a new badge with an enlarged albedo window has been developed at TU Dresden. The properties of the new albedo dosemeter are discussed, and the results of official intercomparisons and field calibrations are shown.

ENVIRONMENTAL DOSIMETRY WITH THE BeOSL PERSONAL DOSEMETER.

In the course of this work, a dosemeter for measurement of ambient dose equivalent H*(10) based on the BeOSL dosimetry system was designed. Calculations of the energy response of the two-element BeOSL personal dosemeter in terms of H*(10) showed that the response does not fulfil the requirements of IEC 62387 Especially, the response for photon energies of 60-100 keV is too low. It is possible to correct this under-response using a BeOSL two-element dosemeter, a linear algorithm and an additional cover for the dosemeter. The Hp(0.07) element is shielded with lead, and with the help of a linear algorithm, corrections of the energy response are possible. So, the national requirements for an H*(10) area dosemeter in Germany can be fulfilled. The requirements of IEC 62387 are fulfilled for angles of radiation incidence from 0° to 60° for a rotation around the vertical and horizontal axis through the dosemeter, whereas for angles of incidence from 75° to 90°, the requirements are only fulfilled for rotation around the vertical axis through both elements.

PROPERTIES OF THE BEOSL DOSIMETRY SYSTEM IN THE FRAMEWORK OF A LARGE-SCALE PERSONAL MONITORING SERVICE.

The Individual Monitoring Service of the Helmholtz Zentrum München is currently using the BeOSL dosimetry system for monitoring ∼15 000 persons per month. This dosimetry system has a modular structure and represents a complete new concept on handling dosemeters in a large-scale dosimetry service. It is based on optically stimulated luminescence dosemeters made of beryllium oxide. The dosimetric and operational properties of the system are shown and discussed.

Analysis of the main dosimetric peak of Al2O3:C compounds with a model of interacting traps.

The glow curve of Al2O3:C compounds has been analyzed by employing a model consisting of two active traps, thermally disconnected traps and one recombination centre. The analysis takes into account interaction among traps and the thermal quenching of the thermoluminescent emission.

Radioluminescence of red-emitting Eu-doped phosphors for fiberoptic dosimetry.

Fiberoptic dosimetry (FOD) technique has become an attractive method for real-time dosimetry. Al(2)O(3):Cis one of the most used radioluminescence materials for FOD due to its high efficiency but it presents the drawback of emitting in the spectral region, where spurious luminescence is also important. Optical filtering is the simplest technique to remove spurious luminescence, but is useful when red-emitting scintillators are employed. In this work, the feasibility of using red-emitting Eu-doped phosphors as FOD scintillators has been investigated.

Module-assisted preparation of 64Cu with high specific activity.

In this work the production of (64)Cu via the (64)Ni(p,n)(64)Cu reaction with optimized conditions for low current irradiation is presented. Different target setups and cleaning steps for lowering metal contaminations in the product were applied. (64)Cu with high specific activities up to 1685 GBq/µmol was produced despite low overall activity (≈ 4.2 GBq per run). The module processing leads to a highly reproducible, reliable product quality (<1 µg Cu and <7 µg Ni). Besides its diagnostic value (64)Cu may be of interest even for therapeutic purposes due to its decay characteristics.