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Instrumentation Effects on Errors in Nuclear Methods for Soil Water and Density Determination¹

ABSTRACT

The commonly used ratio calibration of neutron scattering soil moisture meters tends to obscure errors due to random event counting, dead time, and drift phenomena not fully compensated for by the ratio. These effects are analyzed in the light of the demands of the very high count rates in many scintillation systems being currently reported. Dead time is always reduced by using high pulse-rate resolution equipment. Such is not always available for experimental work and the errors entailed are discussed. Equations describing the errors in ratio counting are discussed. The size of the standard material is a factor in some of the error terms. Some of the errors reduce to zero at the point where the count obtained in the soil is equal to the reading in the standard. Thus, it is desirable to construct the standard such that the ratio = 1 appears on the calibration curve (preferably above the center).

¹ Journal Manuscript no. 2113, of the Oklahoma Agr. Exp. Sta., Stillwater 74074. Work supported under Station Project H-1466.

² Professor of Agronomy, Oklahoma State University, Stillwater.

Received for publication November 17, 1970. Accepted for publication November 8, 1971.