drip line

noun3

1. •
   The area defined by the outermost circumference of a tree canopy from where water drips onto the ground.

   • Be particularly careful applying within the drip line of trees and other ornamental species. — 2010
2. •
   A pipe that has small holes at intervals, used to irrigate crops.
3. •
   On the table of nuclides, the limit beyond which an atomic nucleus will immediately decay by emitting a proton or neutron.

   • Hydrogen-7 has so many excess neutrons that it lies beyond the neutron drip line, and will spit out neutrons until it becomes a particle-bound isotope.