Boltzmann-equation analysis of electron kinetics in a positive column of low-pressure Hg–rare-gas discharges

International audienc

Design of a 10 nm electron collector for a track-nanodosimetric counter

Recently we have developed a track-nanodosimetric counter, which is a gas detector that measures the distributions of electrons induced by a charged particle in nanometric volumes of tissue equivalent matter, positioned at different distances from the track. Sites equivalent to 20 and 24 nm were defined by means of an electron collector, which is a system of electrodes enclosing an almost wall-less cylindrical volume. In this paper, we present the design of a new electron collector that is able to simulate a volume as small as 10 nm in diameter

A detector for track-nanodosimetry

In this paper, we describe a gas counter able to measure electron cluster distributions in nanometric sized sites. We designed a system of electrodes that is able to collect electrons from a nanometric wall-less sensitive volume and to transfer them to a counter that detects single electrons. Measurements of electron collection efficiency in propane gas confirm that we successfully collected electrons from a wall-less sensitive volume, of about 20 mm width, with an average efficiency of more than 20%

Study of non-equilibrium electron avalanches, application to proportional counters

The process of gas multiplication in uniform and non-uniform electric fields is analyzed on the basis of a numerical solution of the Boltzmann equation, Monte Carlo simulations and experimental gas gain measurements. We give a brief Boltzman equation description of gas multiplication that points out the different behaviour of the ionization coefficient in uniform and non-uniform electric fields. We introduce the concept of quasi equilibrium as an extension of the equilibrium formulation to non-uniform electric fields. Monte Carlo results for the reduced ionization coefficient and reduced gas gain for methane and propane in cylindrical geometry are presented illustrating their simultaneous dependence on the reduced voltage K and the reduced electric field S. Gas gain measurements for a propane-tissue-equivalent gas mixture are presented, which demonstrate this dependence

Nanodosimetric Measurements with an Avalanche Confinement TEPC

This paper illustrate, a tissue-equivalent proportional counter designed to have high gas gain and good energy resolution at nanometric simulated site sizes. Microdosimetric neutron and gamma spectra were measured in dimethyl ether and in propane-based tissue-equivalent gas mixture down to 35 nm, The comparison of experimental data with the results of Monte Carlo calculations shows a satisfactory agreement

Track-nanodosimetry of an Alpha Particle

Experimental measurements and calculations are described of ionisation distributions in propane wall-less gas cavities of about 20 nm simulated size, performed at different distances from a 244Cm alpha particle track. Ionisation events are detected one by one by collecting electrons from the sensitive volume and by separating them with a drift column. Experimental results and Monte Carlo calculations indicate that, in the delta ray cloud, conditional probability curves, average cluster size and the ratio of second moment above first moment of the cluster distribution are invariant with track distance