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During the French-Soviet space mission 'Aragatz', the experiment CIRCE (Computer Intégrateur de Rayonnement Complexe dans l'Espace) recorded the dose rate and quality factor values inside the MIR station. This paper presents results obtained with a new active dose equivalent meter based on microdosimetric techniques and using a low pressure tissue-equivalent proportional counter. In terms of lineal energy the CIRCE device works in the 0.2 - 1200 keV.µm-1 range in tissue. Preliminary studies were performed in photon, neutron and heavy ion beams, and in the real stratosphere cosmic radiation field. Long-term measurements on board the MIR station from December 1988 to April 1989 gave an average quality factor value equal to 1.9 ± 0.3. Through the South Atlantic Anomaly (SAA), the quality factor was equal to 1.4. The temporal orbital variations of the dose rates and quality factors have been established in space dosimetry for the first time.

W, the average energy loss per ion pair produced, was measured in propane and in propane-based tissue-equivalent (TE) gas (54% C3H8-40.5% CO2-5.5% N2) for H+, He+, C+, N+, O+ incident particles in the energy range 25-375 keV. This was done using charged particles produced by a 400 kV electrostatic accelerator, and stopped in a chamber operating alternately as a proportional counter and as an ionisation chamber. The Bragg additivity rule, which gives the W value of a gas mixture from the W values of its components, was found not to be applicable to this TE gas. Nevertheless, the calculated values could be taken as a reasonable first approximation, the maximum discrepancy being 10%.

The total ionisation produced by ions stopped in nitrogen, methane and carbon dioxide has been measured in the energy range 25-375 keV using a chamber described previously. The chamber was operated alternately as a proportional counter and as an ionisation chamber to measure respectively the particle rate and the total ionisation produced. This procedure was repeated 20 to 40 times and a statistical treatment of the data was carried out. The average energy loss per ion pair (W-value), the associated standard deviation and the systematic error (+/- 2.5%) were determined for H+, He+, C+, N+, O+ and Ar+ ions stopping in the three gases. The W-value was found to be dependent on the velocity of the incident ions. For nitrogen gas, values range from 35 eV for 25 keV H+ to 84 eV for 25 keV O+. For methane, the values are 30.3 and 66.4 eV. For carbon dioxide, W-values range from 33.4 eV for 50 keV H+ to 135.9 eV for 25 keV Ar+. Finally, the Bragg additivity formula was tested for tissue-equivalent gas. The agreement between W-values calculated by this formula and those measured was found to be within 2% except for 25 keV O+ where the discrepancy is 10%.