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Dosimetry based on gas detectors operating in the recombination and saturation region provides unique research opportunities but requires high-quality electrometers with a measuring range below 1 pA (10-12 A). The standard approach in electrometry is to strive to increase the accuracy and precision of the measurement, ignoring the importance of its duration. The article presents an algorithm for the measurement of low current values (from 100 fA) that allows both a fast measurement (with a step of 2.3 ms) and high accuracy (measurement error below 0.1%), depending on the measurement conditions and the expected results. A series of tests and validations of the algorithm were carried out in a measurement system with a Keithley 6517B electrometer and a REM-2 recombination chamber under conditions of constant and time-varying radiation fields. The result of the work is a set of parameters that allow for the optimisation of the operation of the algorithm, maximising the quality of the measurements according to needs and the expected results. The algorithm can be used in low current measurement systems, e.g., for dosimetry of mixed radiation fields using recombination methods and chambers. [ABSTRACT FROM AUTHOR]

A model of REM-2-type chamber was modeled with MCNPX code to study the dose-response to monoenergetic neutrons in wide energy range from thermal to 20 MeV for various compositions of gas in the chamber. The energy dependence of the total dose absorbed in the filling gas was compared with the energy dependence of ambient absorbed dose D*(10) and with experimental data. The results of the studies will be useful for designing new, improved generation of recombination chambers.

The REM-2 tissue-equivalent recombination chamber was used for dosimetry measurements performed in monoenergetic neutron reference fields at National Physical Laboratory, UK for the neutron energy range from 144 keV to 5 MeV. Measurement data were used for the determination of the recombination index of radiation quality, ambient dose, and finally ambient dose equivalent, H*(10). Results justify the relevance of the application of this measuring method in mixed radiation fields with dominant neutron component, which are present, for example, at photon and proton radiotherapy facilities. The relative response of the chamber in terms of H*(10) in the investigated neutron energy range, resulted in the correction factor at the maximum level of 1.25. Analysis of the saturation curves and use of the recombination microdosimetric method, RMM resulted in the determination of dose distribution at a nanometric level in terms of restricted linear energy transfer, L Δ. Monte Carlo simulations performed with the FLUKA code allowed to obtain double-differential distributions of L which were compared with those obtained during measurements. Comparison between measured and simulated data showed that RMM is a reliable method for microdosimetric investigations in mixed neutron-gamma fields present around medical radiotherapeutic units. • Dose distributions in restricted L were compared with simulated L spectra. • Correction factor for the REM-2 chamber for monoenergetic neutrons was up to 1.25 • LET distributions for 144 keV to 5 MeV neutrons were measured and calculated. • REM-2 chamber has wide, flat energy dependence in terms of H*(10) for mixed n-γ fields. [ABSTRACT FROM AUTHOR]