as a countermeasure to reduce the vulnerability and "harden" nuclear warheads from the effects of externally generated neutrons. Radiation hardening of the warhead's electronic components as a countermeasure to high altitude neutron warheads somewhat reduces the range that a neutron warhead could successfully cause an unrecoverable glitch by the transient radiation effects on electronics (TREE) effects. At very high altitudes, at the edge of the atmosphere and above it, another effect comes into play. At lower altitudes, the x-rays generated by the bomb are absorbed by the air and have mean free paths on the order of meters. But as the air thins out, the x-rays can travel further, eventually outpacing the area of effect of the neutrons. In exoatmospheric explosions, this can be on the order of in radius. In this sort of attack, it is the x-rays promptly delivering energy on the warhead surface that is the active mechanism; the rapid ablation (or "blow off") of the surface creates shock waves that can break up the warhead. Use as an area denial weapon In November 2012 British Labour peer Lord Gilbert suggested that multiple enhanced radiation reduced blast (ERRB) warheads could be detonated in the mountain region of the Afghanistan-Pakistan border to prevent infiltration. He proposed to warn the inhabitants to evacuate, then irradiate the area, making it unusable and impassable. Used in this manner, the neutron bomb(s), regardless of burst height, would release neutron activated casing materials used in the bomb, and depending on burst height, create radioactive soil activation products. In much the same fashion as the area denial effect resulting from fission product (the substances that make up most fallout) contamination in an area following a conventional surface burst nuclear explosion, as considered in the Korean War by Douglas MacArthur, it would thus be a form of radiological warfare—with the difference that neutron bombs produce half, or less, of the quantity of fission products relative to the same-yield pure fission bomb. Radiological warfare with neutron bombs that rely on fission primaries would thus still produce fission fallout, albeit a comparatively cleaner and shorter lasting version of it in the area than if air bursts were used, as little to no fission products would be deposited on the direct immediate area, instead becoming diluted global fallout. However the most effective use of a neutron bomb with respect to area denial would be to encase it in