Objectif
The efforts of the groups participating in the contract have been directed towards:
1) further development of the variance-covariance technique,
2) the construction of improved twin- and multiple proportional counters and of twin ionization chambers and,
3) the design of suitable electronics for the detectors in their various operational modes.
A new approach for the evaluation of microdosimetric parameters in time varying fields has been proposed at the University of Munich. The new algorithm obviates the restriction of constant dose-rate ratio at the locations of two simultaneously working detectors. The variance-covariance measurements in the new form can be applied under very general circumstances, including, for example, measurements in moving objects in non-uniform radiation fields, for example on aircrafts and in satellites.
The efforts of the group at the University of Munich have been directed toward design and fabrication of multi-element detectors with high neutron sensitivity. A test and calibration method, applicable for small proportional counters and especially for multi-element detectors that utilises argon-37, has been developed. The activities of the Aarhus group are directed mainly towards the application of the method in measurements in diagnostic and therapeutic beams. Because of the high dose rate in such fields no gas multiplication is applied and the detectors are operated as ionization chambers. Twin ionization chambers have therefore been developed.
Electronic equipment has been developed, with emphasis on different applications, by the Aarhus and Stockholm groups and by the PECO partner Micro Vacuum Ltd.
The Stockholm group developed low noise electrometers which are central components in the electronic systems. Two electrometers based on charge integrating technique and current measurement technique have been designed, investigated and compared at the Radiation Protection Institute in Stockholm.
The next important step in the signal processing is the analog to digital conversion of the electrometer signal. Different ADCs have been tested by the group in Aarhus to find the converters that satisfy best the requirements of high accuracy and high speed of the conversion.
The task of Micro Vacuum Ltd was the development of a portable instrument for variance-covariance measurements. Low noise and low offset electrometers were designed and adjusted to the parameters of tissue equivalent proportional counters of the Munich group. Analog to digital converters with high resolution (20 bit) were implemented, and suitable high voltage supply was developed. The unit can work as a battery powered stand-alone device. To adjust the instrument for different applications the unit can be re-programmed via RS232 interface.
Within this contract the variance-covariance method has been successfully applied in measurements in pulsed neutron fields, therapeutic electron and x-rays beams, in diagnostic x-rays fields, and on board of aircraft.
The recent reductions of dose limits in radiation protection require increased assurancy and practicability measurements and methods. Beyond the determination of absorbed dose and rate there is an added need for determinations of radiation quality.
Microdosimetric measurements are required to determine dose averaged lineal energy, which is the measurable parameter to derive the quality factor in radiation protection.
In previous projects the theoretical basis and the practical implementation of the variance-covariance method have been developed. This method has two major advantages. It is neither restricted to the very low dose rates that are required for measurements of single event spectra nor is it limited to constant dose rates, as they must prevail for the conventional variance method.
Tissue equivalent twin proportional counters and ionization chambers have been developed for application in variance-covariance measurements. These instruments (using electrometers in the integrating or in the current measuring mode) have demonstrated the advantages of the method and they are now ready to be adapted for radiation protection practice.
While the variance covariance method admits high dose rates, there are frequent situations where, in personal dosimetry or in area monitoring, especially in neutron fields detectors are insufficiently sensitive. Rossi multi-element proportional counters will be developed for routine applications with the variance-covariance method to meet this difficulty.
A further improvement of sensitivity can be achieved by the use of modified electrometers. A design with novel characteristics by Ström, which will in miniaturized form be suitable for the purposes of project 1, will be developed within project 2. In further work project 2 will also improve the dosimetry protocol for high energy photons.
Champ scientifique (EuroSciVoc)
CORDIS classe les projets avec EuroSciVoc, une taxonomie multilingue des domaines scientifiques, grâce à un processus semi-automatique basé sur des techniques TLN. Voir: Le vocabulaire scientifique européen.
CORDIS classe les projets avec EuroSciVoc, une taxonomie multilingue des domaines scientifiques, grâce à un processus semi-automatique basé sur des techniques TLN. Voir: Le vocabulaire scientifique européen.
- ingénierie et technologie génie mécanique génie automobile génie aérospatial technologie satellitaire
- ingénierie et technologie génie électrique, génie électronique, génie de l’information ingénierie électronique traitement des signaux
- ingénierie et technologie génie mécanique génie automobile génie aérospatial avion
- sciences naturelles sciences physiques physique théorique physique des particules photons
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Coordinateur
80336 MUENCHEN
Allemagne
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