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DENSITY DETERMINATION ON NEAR‐SURFACE LAYERS BY GAMMA ABSORPTION *)
Author(s) -
HOMILIUS J.,
LORCH S.
Publication year - 1957
Publication title -
geophysical prospecting
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.735
H-Index - 79
eISSN - 1365-2478
pISSN - 0016-8025
DOI - 10.1111/j.1365-2478.1957.tb01444.x
Subject(s) - absorption (acoustics) , radiation , bending , optics , computational physics , surface (topology) , geometry , expression (computer science) , physics , geology , materials science , mathematics , thermodynamics , computer science , programming language
From gamma ray absorption the density of soil to a depth of i m. can be determined in situ, without taking samples, by a method which has been described in a previous paper (Wendt 1954) and which has been checked with satisfactory results (mean error about 1%). A nearly vertical steel rod with a gamma ray source at its lower end is pushed into the ground, and the gamma radiation is measured at the surface with two counters placed symmetrically with respect to the rod. As a first step in interpreting the observed effects, the assumption had been made that counters are infinitesimally small. This paper shows how a theory can be developed without this assumption, the finite dimensions of the counters being taken into account by an integral expression. For this purpose a determination of the dependence of the counting rate on the angle of incidence of the gamma rays is required. A comparison of the experimental results with the theoretical ones demonstrates that the integral expression is correct. The influence of deviations from the normal geometry of the arrangement (e.g. caused by bending of the probe) on the results is investigated, as well as the influence of variations of the density with depth. The treatment of the basic problems has been carried through in such a manner that the results obtained can be applied to other absorption methods as well.