Generate Radioelement Concentrations

Use the RPS > Generate Radioelement Concentrations option (geogxnet.dll(Geosoft.GX.Radiometrics.GenerateRadioelementConcentrations;Run)*) to convert corrected count rates for potassium (K), thorium (Th), uranium (U), and total count (TC) into apparent radioelement concentrations.

Generate Radioelement Concentrations dialog options

Input channel suffix	If Height Correction has been applied to the current database, the suffix used for the generated channels is automatically detected and preselected. If multiple channel sets exist, all detected suffixes are listed, with the most recent one selected by default. Once you select a suffix, the associated channels are listed below this field. Script Parameter: SPECTRO.GENERATE_RADIOELEMENT_CONCENTRATIONS_INPUT_SUFFIX
Broad Source Sensitivities Specify the sensitivity coefficients for your instrument configuration or survey characteristics. These values are retained after you run the tool and will be available the next time the dialog is opened. See the Application Notes for more details.
Potassium (cps/%K)	Enter the sensitivity value for the potassium (K) channel. Script Parameter: SPECTRO.KSENS
Uranium (cps/ppm eU)	Enter the sensitivity value for the equivalent uranium (eU*). Script Parameter: SPECTRO.USENS
Thorium (cps/ppm eTh)	Enter the sensitivity value for the equivalent thorium (eTh*). Script Parameter: SPECTRO.THSENS
Total count (µR/hr)	Enter the sensitivity value for the total count (TC). Script Parameter: SPECTRO.TCSENS
* Refer to the Radioactive Decay and Gamma Ray Emission section under Application Notes for more details.
Output channel suffix	Specify the suffix to append to output channels. Default: conc As you type, the information string below the field updates to show the resulting channel names. Each name is formed by combining the radiometric element name with the suffix (letters and numbers only). Output channels follow the pattern element_suffix. Script Parameter: SPECTRO.GENERATE_RADIOELEMENT_CONCENTRATIONS_OUTPUT_SUFFIX

Application Notes

This tool operates on preprocessed channels generated by Height Correction, which are labeled *_ht when the default suffix has been retained. Using the specified broad‑source sensitivities, it converts corrected count rates into radioelement concentrations and generates output channels labeled *_conc by default.

Radioactive Decay and Gamma Ray Emission

Potassium concentrations in rocks and soils are commonly estimated using gamma‑ray spectrometry, which detects the 1461 keV gamma rays emitted by the radioactive isotope potassium-40 (⁴⁰K). Unlike ⁴⁰K, which decays directly to a stable daughter isotope, uranium‑238 (²³⁸U) and thorium-232 (²³²Th) decay through long chains of intermediate, unstable daughter products.

For gamma-ray spectrometry, the energies associated with these decay series are identified through their most prominent daughter isotopes:

• ²³⁸U → ²¹⁴Bi (bismuth)

• ²³²Th → ²⁰⁸Tl (thallium)

Characteristic gamma‑ray energy peaks — most notably the 1765 keV line from ²¹⁴Bi and the 2615 keV line from ²⁰⁸Tl — serve as markers for the uranium and thorium decay chains. The intensities of these emissions are then scaled to estimate concentrations of uranium and thorium, reported as equivalent uranium (eU) and equivalent thorium (eTh).

Converting Count Rates to Apparent Radioelement Concentrations

Measured count rates depend not only on the actual concentrations of radioelements in the ground but also on the survey equipment and nominal flight height. Count rates should therefore be converted to ground-level radioelement concentrations.

Calculation Formula

Apparent concentrations of potassium, uranium, thorium, and total count  are calculated by dividing the corrected window count rates by their respective "sensitivity" coefficients ^[1]:

where:

• C — Apparent average ground concentration of the element (%K for potassium, ppm eU for uranium, ppm eTh for thorium, µR/hr for total count)

• Ns — Average background-corrected and stripped window count rate at the nominal survey height (after applying height attenuation)

• S — Sensitivity coefficient for the window

Sensitivity coefficients for each window are determined from airborne survey data collected over a calibration range. Ground concentrations of radioelements along the calibration range are measured using a well-calibrated portable spectrometer at the same time as the airborne data is acquired. This approach accounts for variations in ground radiation output caused by factors such as soil moisture and other environmental conditions.

Alternatively, sensitivity coefficients are estimated by dividing the average background-corrected and stripped window count rates (at nominal survey height) by the corresponding average ground concentrations measured along the calibration range. These coefficients are typically determined during calibration and are often provided by the instrument manufacturer.

Reviewing Results

At each stage of radiometric processing, compare the raw, filtered, and corrected channels in the profile window to evaluate the impact of each correction step.

Complete Expressions for Apparent Radioelement Concentrations

To understand the calculation of the final concentrations, the complete expressions for the Potassium and Total Count channels are provided below.

References