Determination of first townsend coefficient in pure isobutane - Lima, Iara B; Vivaldini, Túlio C; Gonçalves, Josemary A C; Botelho, Suzana; Tobias, Carmen C B; Ridenti, Marco A; Pascholati, Paulo Reginaldo; Fonte, Paulo; Mangiarotti, Alessio (SBF, 2010)