1.1This guide is focused on the general procedures necessary to conduct neutron or neutron porosity (hereafter referred to as neutron) logging of boreholes, wells, access tubes, caissons, or shafts (hereafter referred to as boreholes) as commonly applied to geologic, engineering, groundwater and environmental (hereafter referred to as geotechnical) explorations. Neutron soil moisture measurements made using neutron moisture gauges, are excluded. Neutron logging for minerals or petroleum applications is excluded, along with neutron activation logs where gamma spectral detectors are used to characterize the induced gamma activity of minerals exposed to neutron radiation.

1.2This guide defines a neutron log as a record of the rate at which thermal and epithermal neutrons are scattered back to one or more detectors located on a probe adjacent to a neutron source.

1.2.1Induction logs are treated quantitatively and should be interpreted with other logs and data whenever possible.

1.2.2Neutron logs are commonly used to: (1) delineate lithology, and (2) indicate the water-filled porosity of formations (see Fig. 1).

N_c = corrected neutron log, N₀ = original neutron log, C_sh = computed shale fraction based upon the gamma log position between the endpoints of 10 and 120 cps, and Φ_sh = estimate of shale non-effective porosity of about 40 % picked from intervals on the log where Φ_sh = 1.0.