Natural gamma ray spectroscopy applied to borehole measurements

Radial distributions of /sup 60/Co contaminants surrounding wellbores at the Hanford Site

“…This is because these tools have steel housings and Figure 3 shows that the inside versus outside spectral differences are subtle above 150-keV. Nevertheless, the characteristics of borehole versus formation gamma ray signatures have been known for a number of years [ 101. The conclusion that the is inside the casing is based on extensive investigations related to HES's oil field work [3,4,5]. The question of how the radioisotope, 6oCo, came to be in its present location may be explained by adsorption to a rust layer inside the casing.…”

“…For each gamma-ray-emitting radionuclide that is observed in the measured spectra, there must Figure 1 be a unit shape ("fingerprint") for that nuclide incorporated into the WLS analysis procedure [3]. This shape describes the complete energy response (0-3,000 keV) of the CSNG instrument to a unit quantity of a specific nuclide in the specific geometry for which the measured data are collected.…”

“…The Compensated Spectral Natural Gamma (CSNG) instrument was designed to determine the concentrations of the naturally-occurring radioactive elements potassium (K), uranium (U) and thorium (Th) in boreholes [3]. The CSNG logging system is shown in Figure 1.…”

“…Experimental calibration procedures for borehole environments have been described previously [ 3,4] and numerical simulation calculations were performed to support this work [5]. For this CRADA the gamma ray spectroscopy adaptation requires that a unit spectrum be determinedl for several common gamma-ray-emitting radionuclides found on the Hanford Site.…”

“…The Caliper curve is a mechanical measurement of the inside diameter of the casing [2]. The Gamma Ray curve is the spectral count rate summed above 140-keV and normalized to API (American Petroleum Institute) gamma ray units [3]. The Gamma Ray Curve is quite variable with maximum readings of 800 API.…”