Neutrons, in particular thermal neutrons, have a very high scattering cross-section with hydrogen, so irradiating a sample with thermal neutrons and observing a large degree of backscatter probably means the sample has a high hydrogen (usually water) content. Measuring the backscatter of thermal neutrons from a sample of KNOWN composition, may convey if the sample is contaminated with hydrogen (i.e., water). An example that comes to mind is measuring the contamination of crude oil by ground-water. In the old days when I was working in this area, miniature sources of Cf-252 surrounded by a moderating shell were used to create beams pdf thermal neutrons for various applications, ranging from back-scatter analysis to neutron activation analysis. Applications were potentially in the oil drilling industries and medical body composition studies. Fast neutrons (from the Cf-252) fell out of favor in the medical field in the 198's after the very high quality factor/RBE they possessed was discovered specially at very low dose.

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