Objective
Equilibrium calculations of the ionisation coefficient (and of all the swarm parameters) have been carried out and the importance of the nonequilibrium behaviours of electrons in this type of geometry has been studied. The modelling of the kinetics of ions and electrons in a cylindrical proportional counter allowed (the accurate following of) the space and time evolutions of ionic and electronic densities when a space charge field was present, and also the determination of the onset of the appearance of this charge space field and the calculation of the various parameters playing an important role in the variation of the gas gain (nonequilibrium of electrons, space charge fields, etc). It was shown that, at low pressure, large gain may be obtained as a consequence of the nonequilibrium electrons rotating around the central wire. Clearly, this result is of paramount importance in microdosimetry.
PROPORTIONAL COUNTERS ARE THE SUBJECT OF A GREAT NUMBER OF EXPERIMENTAL OR THEORETICAL STUDIES. THIS GROWING INTEREST IS MOTIVATED BY NEW APPLICATIONS, IN RADIATION PROTECTION STUDIES OR FOR HIGH ENERGY PARTICLE PHYSICS. THE OPTIMIZATION OF THE OPERATING MODE OF THESE COUNTERS NEEDS THE PERFECT UNDERSTANDING OF THE BEHAVIOUR OF THE VARIOUS CHARGED SPECIES IN THE ACTIVE VOLUME. ALTHOUGH INFORMATION CAN BE OBTAINED FROM EXPERIMENTAL STUDIES, IT IS GENERALLY INSUFFICIENT TO ALLOW A COMPLETE EXPLANATION OF THE BASIC PROPERTIES OF THESE COUNTERS.
THE COUNTERS NEEDED FOR MICRODOSIMETRIC PURPOSES (ROSSI-TYPE COUNTERS FOR EXAMPLE), REQUIRE THE CONTRUCTION OF COUNTERS WITH HIGH GAS AMPLIFICATION. THE SEARCH FOR THE GAS GIVING THE HIGHEST AMPLIFICATION CAN BE EASILY ACHIEVED IF ON KNOWS THE IONIZATION COEFFICIENTS OF THE CONSIDERED GAS. TAKING INTO ACCOUNT THE NUMBER OF COMPONENTS OF THE MIXTURE, IT IS CLEAR THAT SUCH AN OPTIMISATION IS LESS TIME CONSUMING, IF A RELIABLE METHOD TO CALCULATE THE IONIZATION COEFFICIENT IS AVAILABLE. OPTIMIZATION OF THE GEOMETRY IS ALSO DONE MORE EASILY BY CALCULATION.
ADVANCES IN PARTICLE COUNTER DISCHARGE MODELLING HAVE BEEN SO RAPID OVER THE PAST FEW YEARS, THAT A COMPLETE MODELLING OF PROPORTIONAL COUNTER MAY BE CONSIDERED AS A SHORT TERM PROJECT. THIS MODELLING COULD BE ACHIEVED IN THREE STEPS.
IN A FIRST STEP, TRANSPORT PARAMETERS WHICH CHARACTERIZE THE ELECTRON MOTION IN THE DISCHARGE (DRIFT VELOCITY, DIFFUSION COEFFICIENTS, IONIZATION AND ATTACHMENT COEFFICIENTS, ETC...) HAVE TO BE CALCULATED IN ORDER TO DETERMINE THE GAS MIXTURES WHICH HAVE THE HIGHEST GAIN. NOTE THAT THE CALCULATION OF THESE TRANSPORT PARAMETERS WILL BE DONE WITH THE HELP OF THE VERY POWERFUL AND ACCURATE METHOD OF SOLVING THE BOLTZMANN EQUATION DEVELOPED IN THE CENTRE DE PHYSIQUE ATOMIQUE DE TOULOUSE. THE CONSIDERED MIXTURES WILL CORRESPOND TO THE USUAL FILLINGS OF PROPORTIONAL COUNTERS INCLUDING ONE OR MORE ORGANIC VAPOURS. THIS STUDY COULD BE REALISED IN ABOUT A YEAR.
THE SECOND PART OF THIS PROGRAMME WILL BE DEVOTED TO THE MACROSCOPIC MODELLING (BASED UPON THE SIMULTANEOUS RESOLUTION OF THE CONTINUITY EQUATIONS OF ELECTRONS AND IONS AND OF THE POISSON EQUATION) OF THE MOTION OF ELECTRONS AND IONS IN A SINGLE WIRE COUNTER WITH A CYLINDRICAL GEOMETRY. THIS STUDY WILL LEAD TO A DETERMINATION OF THE TIME VARIATION OF THE VOLTAGE PULSE GENERATED BY THE CHARGED PARTICLE MOTION IN THE COUNTER. THIS RESULT WILL FIRSTLY ALLOW THE "REAL" GAIN OF THE COUNTER TO BE CALCULATED. IT WILL THEN BE POSSIBLE TO DETERMINE THE END OF THE PROPORTIONALITY REGIME (DUE TO THE GENERATION OF THE POSITIVE ION SPACE CHARGE) AND TO DEFINE THE EXTREME CONDITIONS OF THE WORKING PROPERTIES OF THE COUNTER. THIS MODELLING WILL BE DONE FIRSTLY BY CONSIDERING ONLY ONE SPATIAL DIMENSION. THE ESTIMATED DURATION OF THIS WORK WILL BE ABOUT ONE YEAR.
IN A THIRD STEP, THE ABOVE MODELLING WILL BE EXTENDED TO TWO DIMENSIONS. THE INFLUENCE OF THE BOUNDARY EFFECTS ON THE SHAPE AND THE SIZE OF THE VOLTAGE PULSES WILL BE STUDIED.
THE DURATION OF THE ENTIRE PROGRAMME WILL BE THREE YEARS.
Fields of science (EuroSciVoc)
CORDIS classifies projects with EuroSciVoc, a multilingual taxonomy of fields of science, through a semi-automatic process based on NLP techniques. See: The European Science Vocabulary.
CORDIS classifies projects with EuroSciVoc, a multilingual taxonomy of fields of science, through a semi-automatic process based on NLP techniques. See: The European Science Vocabulary.
- natural sciences physical sciences theoretical physics particle physics
- natural sciences mathematics pure mathematics geometry
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Coordinator
TOULOUSE
France
The total costs incurred by this organisation to participate in the project, including direct and indirect costs. This amount is a subset of the overall project budget.