Experimental Study of the Method of Bubble Formation in Bubble Chambers

To help put a lower limit on the sensitive time of organic liquids commonly used in bubble chambers a static electric field of 15 kv/cm was applied across a small propane bubble chamber which was then expanded in the conventional manner when a beam of 450 Mev protons was passed through it. The bubble density along the tracks was measured with both field on and field off. Within statistics (±4%) no difference in bubble density was observed for the two cases. To interpret this result it is assumed that δ rays produce bubbles if they deposit a certain minimum amount of energy within a critical volume of the liquid. It is then concluded from this experiment that either recombination effects are not important in bubble formation or that the recombination time of ions in a critical volume of propane is ≲ 10−11 sec. This figure appears to represent a reasonable theoretical estimate of the sensitive time of propane, liquid hydrogen, and liquid helium.