DIFFUSION CLOUD CHAMBER OPERATION AND THE BACKGROUND GAS EFFECT

Key design and operational aspects for thermal diffusion cloud chamber (TDCC) applications an discussed in the context of a two-dimensional solution to the mass and energy balances describing diffusion through a stagnant background gas. The important issue of buoyancy-driven conv ective disturbances and their impact upon nucleation measurements made using a diffusion cloud chamber an discussed. A new derivation of the relation that predicts the upper limit of total pressure allowed for stable (the absence of buoyancy-driven convective disturbances) operat ion of the diffusion cloud chamber is presented. For the first time, t his limit of stable operation can be predicted prior to making experim ental measurements. Nucleation data obtained in our laboratory are exa mined in the context of this predicted limit of stable operation. New nucleation data are presented for 1-pentanol using helium as a backgro und gas. Only data corresponding to stable operation in the cloud cham ber is used in the analysis. The effect of background gas on nucleatio n we have reported previously is confirmed for 1-pentanol, as well as for all the other alcohols that have been investigated in our laborato ry. (C) 1998 Elsevier Science B.V.