Velocity Dependence of the Bubble Density for Charged Particle Tracks in Liquid Hydrogen

Bubble densities of tracks of 635-Mev/c protons and pions in a liquid hydrogen bubble chamber operated at 26.5°K, 62 psig have been determined from measurements of the distribution in spacing of the individual bubbles. The velocity dependence of the bubble density has been obtained by fitting the bubble densities observed to the expression $m=\frac{A}{{\beta }^b}$ by the least-squares method, yielding the values $A=8.64\mathrm{}$ bubbles/cm, and exponent $b=1.935\mathrm{}\pm 0.077$. The constant $A$ is a function of the temperature of the liquid hydrogen, varying ∼30% per 0.1°K. If the number of bubbles per unit track length observed is correlated with the rate of delta-ray formation, it would appear that an energy of the order of 400 ev is necessary for bubble nucleation in liquid hydrogen.