Wars have been fought around the globe, and land mines were used extensively by the battling parties. There may be up to 100 million abandoned mines just waiting to maim and kill unsuspecting civilians. Techniques similar to airport weapons detectors have been considered for finding and neutralizing these mines without loss of life.
A promising technology involves nuclear quadrupole resonance. Nitrogen, a common component in explosives, has a nucleus with an ellipsoidal shape. Depending on what kind of crystalline structure the nitrogen nuclei find themselves in, their non-sphericity produces a unique set of very narrowly spaced energy levels that is characteristic of the crystalline solid itself. An explosive compound can therefore be identified by the subtle effect of its constituent nitrogen atoms. This technique could also differentiate explosives from scrap metals in the ground. More details may be found in the reference at the end of this chapter.