For a high resolution version of this picture click here (pdf file).
This picture, taken in the Fermilab 15-foot bubble chamber filled with a mixture of neon and hydrogen, shows curved lines of bubbles produced by charged particles as they force their way through the liquid.
Let us focus on the spray of particles produced when a track entering from the bottom of the picture interacts with a neon nucleus.
Slightly downstream of this interaction there is a V-shaped secondary interaction consisting of two (dark) proton tracks knocked out of a neon nucleus by a neutral particle. Since neutrons are by far the most numerous of neutral particle candidates (the others being the strange particles , and ) the vee-shaped secondary interaction was almost certainly produced by a neutron produced at the primary collision.
For more details of this attractive event, cradled between two cosmic ray tracks, click here.
For a demonstration of a rather complicated event which demonstrates the
existence of a neutron from
the decay of a sigma plus ,