Neutron radiographic measurement of porosity of crystalline rock samples: a feasibility study

Neutron radiography (NR) provides a sensitive and quantitative technique for the determination of hydrogen. NR can therefore be used to determine the porosity of rocks impregnated with a hydrogen-containing material: in this feasibility study, the water content of granodiorite and mylonite samples was determined by quantitative NR combined with densitometric scanning. For a sample of 1-cm thickness, this technique allows porosity detection down to 0.015 with a resolution of 1 mm2, down to 0.005 with a resolution of 1 cm2, and is applicable for porosities higher than 0.05 with a precision of ±0.5% at a resolution of 1 cm2. 3-D information may be gained by combination of 2-D radiographs. The accuracy of the technique was estimated by comparing the NR results with those obtained by gravimetry. Extension to resin-impregnated porosity and to other types of rock is discussed.