The mechanical stability is, in addition to thermal and chemical stability, a primary requirement of polymer electrolyte membranes in fuel cells. In this study, the impact of grafting parameters and preparation steps on stress–strain properties of ETFE‐based proton conducting membranes, prepared by radiation‐induced grafting and subsequent sulphonation, was studied. No significant change in the mechanical properties of the ETFE base film was observed below an irradiation dose of 50 kGy. It was shown that the elongation at break decreases with increasing both the crosslinker concentration and graft level (GL). However, the tensile strength was positively affected by the crosslinker concentration. Yield strength and modulus of elasticity are almost unaffected by the introduction of crosslinker. Interestingly, yield strength and modulus of elasticity increase gradually with GL without noticeable change of the inherent crystallinity of grafted films. The most brittle membranes are obtained via the combination of high GL and crosslinker concentration. The optimised ETFE‐based membrane (GL of ∼25%, 5% DVB v/v), shows mechanical properties superior to those of Nafion® 112 membrane. The obtained results were correlated qualitatively to the other ex situ properties, including crystallinity, thermal properties and water uptake of the grafted membranes.

Volcanic gases are very rich in long‐lived radon daughters, especially in 210Po. Thus more than 50×103 Ci per year of 210Po are injected into the troposphere by a normal volcanic activity, and more than 1×103 Ci per year into the stratosphere by volcanic explosions. These fluxes should account for one half of the 210Po content in both of these reservoirs. On the contrary the volcanic sources of 222Rn and 210Pb are generally negligible with regard to the soil production. This new result could explain most of the discrepancies observed by comparing the activity ratios of the different radon daughters, including the existence of 210Po/210Pb figures superior to one (overequilibriums). Stratospheric aerosol residence times calculated on this basis are found to be shorter than the previous figures.

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