A New Low-Activity Nuclear Density Gauge for Soil Density Measurements

Abstract

For decades, nuclear density gauges have been used to measure the density and moisture content of soil during compaction testing in road and embankment construction. Worldwide regulatory agencies consider nuclear density gauges as controlled devices because of their inclusion of radioisotope sources. Regulatory requirements, such as the need for licensing, special storage, special transportation procedures, gauge operator training, and personal dosimetry, have become burdens for gauge users. Recently, a new nuclear density gauge for measuring soil wet density was declared exempt from licensing and other nuclear regulatory requirements in the United States. The new gauge uses an extremely low-activity radioisotope source. It further incorporates a separate probe operating on electromagnetic principles for soil moisture measurement or any other moisture measurement method the user desires. This paper presents the design features and measurement properties of this low-activity nuclear density gauge and its associated moisture probe. The measurement properties were determined from laboratory and field studies that were conducted in North Carolina, United States. These studies showed that the sensitivity and precision of wet density measurements made by the low-activity nuclear density gauge were similar to those made by a conventional nuclear density gauge. The wet density measurements made by the low-activity gauge and conventional gauge showed a strong correlation and agreement. For the two field sites studied, a silty sand subbase and a cement-treated aggregate base course, the dry density agreement between the low-activity nuclear density gauge/moisture probe and the conventional nuclear density gauge was within 3 lb/ft3 (48 kg/m3).

Use of Low-Activity Nuclear Density Gauge in Iron Oxide-Rich Soils

“…A literature review on the use of LANDG has shown quite promising results. Troxler Electronic Laboratories evaluated the precision and repeatability of the LANDG at road construction projects in Roxboro, Wayne County, and eight other road construction projects in North Carolina in a variety of soil types (2). Their results indicated that the LANDG showed a high correlation to the NDG.…”

“…Recently, Troxler Electronic Laboratories incorporated a low-activity gamma ray source (strength less than 3.7 MBq, 0.1 mCi) in a device known as the EGauge (ASTM D8167). Generically called a low-activity NDG or LANDG, it utilizes a gamma ray source to measure soil density that is exempt from NRC licensing in the U.S.A. and its territories (2). Moisture content is obtained using a separate device that accompanies the LANDG by measuring the dielectric constant of the soil between the top and bottom of a soil probe.…”

“…This study aims to compare the NDG and LANDG results for two common soil types in Hawaii: basalt-derived soils and coralline soils. 2 3 to 5 Silicon dioxide 1 4.5 Calcium carbonate 1 6.1 to 9.1 Alumina 1 9.3 to 11.5 Iron oxide 1 14.2 Water 1 G80…”

“…The first water layer adjacent to the clay particle is tightly bound by surface forces and has a structure similar to that of ice with a dielectric constant of about 3.2. As the distance of the water molecule from the clay particle increases, the water molecule becomes less affected by surface forces and eventually behaves like free water 2. Porosity, n = 1 À g Gsg w+ uGs where g = soil unit weight, G s = specific gravity of the soil solids, g w = unit weight of water, and u = volumetric water content = G s w(1-n) where w = gravimetric water content.…”

Use of nuclear techniques in soil science: A literature review of the Brazilian contribution

“…It permitted the development of nuclear density gauges that use extremely low-activity radioisotope sources. As a result, in this configuration, these devices were recently declared exempt from licensing and other nuclear regulatory requirements, for instance, in the United States (Dep et al, 2021).…”