How doesn't an ionization chamber leak?

Question

I'm sure my understanding of an ionization chamber is incorrect, so please point out the error.

Suppose we are using an sealed ionization chamber to detect the energies (trajectories) of a particular particle. Based on what I've read online, how this is done is the particle comes wizzing through the ionization chamber and ionizes some of the gas particles (which in this case let's say is isobutane or some other non-air gas). The ionized gas particle and its newly freed electron will both travel to the cathode and anode respectively (unless the electron starts a Townsend Avalanche), and then that newly created signal can be read and interpreted.

My question is, how does the particle enter the ionization chamber if it is sealed? If it isn't sealed, then why doesn't that non-air gas within the chamber leak out?

Answer 1

Generally the particles that enter these ionization chambers have such high kinetic energy that they can pass through walls.

The gas inside the ionization chamber is not travelling nearly so fast. Kinetic energies of the gas would be at least a million times lower and often much lower than that. The gas cannot escape through he walls.

High energy particles can generally penetrate a lot of solid material, which is why at nuclear power stations and particle accelerators the shielding is quite a big issue - thick layers of lead and/or concrete may be used to try to protect people from high energy particles.