EXPERIMENTAL-OBSERVATION OF EXPLODING ELECTRON BUBBLES

Since free electrons form small voids in liquid helium they are expect ed to be preferred sites for nucleating macroscopic bubbles when the l iquid is exposed to sufficiently large negative pressures. We have per formed a series of cavitation experiments using focussed ultrasound wh ere free electrons were introduced into the liquid by a radioactive so urce. The electron bubbles are found to explode at negative pressures significantly lower than those required for homogeneous nucleation. We present measurements of the thresholds for cavitation at electrons in the temperature range 1-4.5 K. Reasonable agreement with a simple mod el for the stability limit of the electron bubble is obtained.