What is "delta ray"

n. 1 (context physics English) An electron ejected by recoil when a rapidly moving alpha particle or other charged particle passes through matter. 2 (context physics English) A secondary ionizing particle ejected by recoil when a primary particle passes through matter.

n. an electron ejected from matter by ionizing radiation

A delta ray is sometimes used to describe any recoil particle caused by secondary ionization. The term was coined by J.J. Thomson. A more modern definition is secondary electrons with enough energy to escape a significant distance away from the primary radiation beam and produce further ionization." Delta rays are entirely unrelated to the family of subatomic particles named delta baryon.