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Comments on “Moisture Content and Bulk Density Measurements Using a Dual‐Energy Beam of Gamma Radiation”
Author(s) -
Loch J. P. G.,
Kay B. D.,
Groenevelt P. H.
Publication year - 1980
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1980.03615995004400030053x
Subject(s) - agricultural experiment station , resource (disambiguation) , agriculture , agricultural land , library science , geography , agricultural science , agricultural economics , environmental science , archaeology , computer science , economics , computer network
The work performed by Wood and Collis-George as reported in the above letter is a welcome contribution to the further development and refinement of the dual-coinciding-beam scanner. An important aspect of this work is the matching of the pairs of amplifiers and pulse height analyzers. Improved electronic equipment will ultimately remove several sources of inaccuracies. The main concern with this technique is the contribution by the Cs source to the Am intensity. It should be pointed out that the origin of this contribution lies in the Nal crystal and not in the column. This is the reason why the relation between this contribution and the intensity in the Cs-window is independent of the attenuating material. Our measurements with lead, brass, aluminum, wood, water, and plexiglass also showed this independence. The statement by Wood and Collis-George, "The attenuated gamma radiation, in the energy range of the Am window, contains photons emanating from the Cs source, but reduced in energy by Compton scattering which occurs during their passage through the soil sample", is true, but this type of additional "Am-counts" is negligibly small. This can be verified with a crossed-beam arrangement. It is the direct "bombardment" of the crystal by 660 keV gamma's which produces the high "background" of the Am intensity. In a crossed-beam arrangement this direct bombardment does not occur and the high background is absent. The mathematical form of the relation between the Cs intensity and the Cs-contribution to the Am intensity, whether linear or curvilinear, is not of crucial importance as the method of correction by subtraction is very simple in either case. The smaller the range over which the relation is determined, the easier it is to formulate the relation by a linear function.