Shallow ground investigation using radiometrics and spectral gamma-ray data

Potassium (K), uranium (U) and thorium (Th) are the three most abundant radioactive elements found in rocks or sediments and are thus considered to be the likely sources of gamma-ray variation detected both at outcrop and in the subsurface from radiometric analyses. With the advent of the spectral gamma-ray (SGR) tool, the variation shown by these three elements in rocks has been considered to reflect different host minerals. This review aims to make an assessment of the usefulness of SGR data in archaeological investigations by reviewing the sorts of buried materials the method can detect. Compared with many investigative methods currently used (e.g. ground-penetrating radar), SGR data gives only indirect information concerning the depth of burial. Conversely, SGR data has the advantage of providing direct information concerning the mineralogical differences in near-surface materials. When used to analyse known geophysical anomalies, the SGR method can give non-destructive information on the location of sand-filled pockets in clay; clay-filled pockets in sand, limestone or basalt and the location of buried stone walls. The location of trenches, moats, walls, industrial waste and burial grounds are all detectable with the method. The SGR data are usually derived passively, or by the natural radioactive emission of minerals. Induced radioactivity may be used in remote sensing by controlling the spectral qualities of ingoing gamma-rays and thus allow a far greater sensitivity in the non-destructive analysis of interlayered, hidden or enclosed materials such as sarcophagi. Copyright © 1998 John Wiley & Sons, Ltd.