(Left) Principle of the crystal blocking technique. Heavy ions bombard a single-crystal target at an angle relative to the crystal planes, causing a projectile nucleus and crystal nucleus to fuse. Fission fragments from very short lived nuclei () are emitted in the plane of the target atoms (that is, the angle of emission relative to the crystal axis ) and are thus blocked from reaching the detector. Fragments emitted from nuclei that survive long enough to move into a channel between the crystal planes (e.g., at a distance d from a plane) are detected with little energy loss. Thermal vibrations in the crystal determine the lower time limit for blocking. (Right) The blocking dip observed for for reactions (at 6.09 MeV per nucleon collision energy) and fragments in the range of . The width of the dip depends on atomic number and kinetic energy of the fragment.