Detection of buried explosives

A method of detecting explosives, comprising:

• providing a neutron generator and a gamma ray detector;
• detecting gamma radiation by the detector;
• directing neutrons from the generator toward a material during a first period of time;
• detecting gamma radiation from excitation of the material by the directed neutrons during a second period of time that ends one tenth of a second or less after the first period of time;
• and
• quantifying the amount of detected radiation that varies with the amount of nitrogen in the material and the amount of detected radiation that varies with a substance other than nitrogen in the material.

A method of detecting explosives, comprising:

• providing a neutron generator and a gamma ray detector;
• emitting a pulse of neutrons by the neutron generator toward a region of interest;
• receiving gamma radiation by the gamma ray detector from the region of interest;
• preparing data corresponding to the received gamma radiation;
• and
• applying a gain to the data, the gain varying in relation to neutron die-away during said receiving.