Observation of Tracks of Fast Charged Particles in a Liquid Chamber**)

After preliminary reports,*) in August 1953 a more complete description appeared of a liquid chamber intended for observing the tracks of charged particles.***)

The chamber is a thick-walled cylindrical Pyrex vessel 3 cm long and with an internal diameter of 1 cm, filled with liquid ether. It is connected to a pressure regulator by means of a Pyrex capillary tube 45 cm long. The pressure regulator is a brass cylinder 2 cm long and with an internal diameter of 3 cm. One end of it is closed by an elastic diaphragm of neoprene 3 mm thick, covered with Teflon. On the opposite side the diaphragm is pressed against the liquid by compressed gas.

*) Resolving time of the coincidence circuit \(\sim 10^{-7}\) sec.
**) The English name of the chamber is “Bubble Chamber.”
***) A. Glaser, Phys. Rev. 87, 665 (1952); Bull. Am. Phys. Soc. 28, No. 3, 72 (1953); Phys. Rev. 91, 762 (1953).

To prepare the chamber for operation, ether heated to \(\sim 140^\circ\mathrm{C}\) is subjected to compression by feeding nitrogen into the pressure regulator (at a pressure of about 20 atm.) so that there is no vapor in the system. When the excess pressure is released (by letting nitrogen out of the regulator), the ether proves to be in a superheated state and remains in this unstable state for several seconds, after which it boils vigorously. If, during the period of the unstable state (before boiling), a charged particle passes through the liquid, then along the track of the particle there forms a chain of visible small bubbles, which can be photographed.

Fig. 1.

The author placed the chamber in a telescope consisting of two rows of counters; above the telescope was located a block of lead 10 cm thick. Coincidence of pulses in both rows indicated that a charged cosmic particle had passed through the chamber. The photographing of the particle track was carried out with a short flash of a xenon discharge lamp, which was triggered by the coincidence pulse in the telescope.

In Fig. 1 a photograph of a track is shown for an illumination duration equal to 20 μsec. Fig. 2 was obtained with an illumination duration of 5 μsec. This photograph shows that the particle is scattered through an angle of \(\sim 2^\circ\).

Repeated compression of the ether and preparation of the chamber for operation take about 5 seconds.

It is indicated that an approximate theory was developed describing the state of charged bubbles in a superheated liquid and making it possible to choose liquids, as well as the working temperature and pressure.

The main result obtained under certain simplifying initial assumptions reduces to the following: a bubble in which

Fig. 2.

\(n\) ions have been created by an ionizing particle can grow to visible dimensions if the liquid is superheated to such an extent that the saturated-vapor pressure \(p_\infty\) exceeds the applied pressure by the amount

\[ p_n(T)=\frac{3}{2}\left(\frac{4\pi}{n^2 e^2}\right)^{1/3}[\sigma(T)]^{4/3}[\varepsilon(T)]^{1/3}. \]

In this, the dependence of the surface tension \(\sigma\) and of the dielectric constant \(\varepsilon\) on the curvature of the surface and on the pressure is neglected.

For given values of \(n\), one may plot on the same graph the dependences \(P_{\infty}(T)\) and \(P_n(T)\) on \(T\). The point of their intersection approximately determines the temperature and pressure of the liquid.

For a chamber filled with diethyl ether, the temperatures estimated in this way (for \(n\) between 2 and 10) agree with the temperature measured in the experiment to within \(10^\circ\).

Some preliminary conclusions may be drawn regarding the possibilities of the new chamber as a detector of high-energy charged particles. The chamber is sensitive to particles with minimum ionization, since in the work described here fast \(\mu\)-mesons were mainly recorded. Owing to the relatively high density of the substance (about \(0.5\ \mathrm{g/cm^3}\) under the conditions considered), the probability of recording particle stops is significantly increased; moreover, it becomes possible to observe in detail all secondary phenomena.

The growth of bubbles in the chamber occurs very rapidly; for example, in § 2 it was indicated that the bubbles grow to a size of \(2\ \mathrm{mm}\) in \(200\) microseconds; therefore convection currents in the liquid do not distort the particle track. The rapid growth of bubbles makes it possible, generally speaking, to estimate the relative age of tracks from the sizes of the bubbles (in the time interval \(0\)—\(100\ \mu\mathrm{sec}\)).

In the author’s opinion, it appears possible to construct chambers of larger size, and also to use liquids of various compositions and densities.

No data have yet been presented on the possibility of distinguishing, in the chamber, particles with different ionizing power.

M. D.