delta rays 
plural noun Physics
Rays of low penetrative power consisting of slow electrons or other particles ejected from atoms by the impact of ionizing radiation.These are all negative particles which, like the delta rays turn to the left....
- The fraction due to delta rays and capacitive coupling has been increased to 24% for the first stack and to 19% for the other stacks.
- They suggest that delta ray action rarely produces DSBs at locations away from a primary ion track, and that the average energy per delta ray has little biological importance.