Delta ray

A delta ray is a secondary electron with enough energy to escape a significant distance away from the primary radiation beam and produce further ionization.

Collectively, these electrons are defined as delta radiation when they have sufficient energy to ionize further atoms through subsequent interactions on their own.

Delta rays appear as branches in the main track of a cloud chamber (See Figs.

These branches will appear nearer the start of the track of a heavy charged particle, where more energy is imparted to the ionized electrons.

In a bubble chamber, electrons will lose their energy more quickly than other particles through Bremsstrahlung and will create a spiral track due to their small mass and the magnetic field.

Fig. 1: Image taken in the Pic du Midi at 2877 m in a Phywe PJ45 cloud chamber (size of surface is 45 x 45 cm). This picture shows the four particles that are detectable in a cloud chamber : proton, electron, muon (probably) and alpha. Delta rays are seen associated with the proton track.
Fig. 2: A 3D representation of a delta electron knocked out by a 180 GeV muon, measured with a GridPix detector at the SPS at CERN. The colour indicates the height