Generate Radioelement Ratios

Use the RPS > Generate Radioelement Ratios option (geogxnet.dll(Geosoft.GX.Radiometrics.GenerateRadioelementRatios;Run)*) to calculate standard ratios such as U/Th, U/K, and Th/K. These ratios are commonly used for final map presentation and for identifying subtle, geologically significant features in the data.

You can apply thresholding to exclude very low denominator values. Additionally, low-pass filters can be applied to smooth noisy data.

Generate Radioelement Ratios dialog options

Input channel suffix	If Generate Radioelement Concentrations 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_RATIOS_INPUT_SUFFIX
Minimum Concentrations Specify the minimum concentration thresholds for each radioelement. These values help prevent division by very low denominators during ratio calculations. See the Application Notes for more details.
Threshold method	Choose a method for handling values below the specified minimum concentration: Clip (default): Values below the specified minimum concentration are set to the minimum value. Dummy: Values below the minimum concentration are replaced with placeholder (dummy) values. Script Parameter: SPECTRO.RMETHOD [0: Clip; 1: Dummy]
Potassium (K) in %	Enter the minimum concentration value for potassium (K), expressed as a percentage (%). Default: 1 Script Parameter: SPECTRO.KMIN
Uranium (eU) in ppm	Enter the minimum concentration value for the equivalent uranium (eU)*, expressed in parts per million. Default: 1 Script Parameter: SPECTRO.UMIN
Thorium (eTh) in ppm	Enter the minimum concentration value for the equivalent thorium (eTh)*, expressed in parts per million. Default: 1 Script Parameter: SPECTRO.THMIN
Low-Pass Filter Cutoffs Specify the cutoff values for low-pass filtering to smooth noisy data. These filters reduce statistical noise, particularly in areas with low count rates. To disable filtering for a specific channel, set its cutoff value to 0. See the Application Notes for more details.
Potassium (K)	Enter the cutoff value for low-pass filtering for K. Default: 25 Script Parameter: SPECTRO.KRATIOSW
Uranium (eU)	Enter the low-pass filtering cutoff for eU*. Default: 25 Script Parameter: SPECTRO.URATIOSW
Thorium (eTh)	Enter the low-pass filtering cutoff for eTh*. Default: 25 Script Parameter: SPECTRO.THRATIOSW
* Refer to the Radioactive Decay and Gamma Ray Emission section under Application Notes for more details.
Output Channel Names The calculated ratios will be stored in the corresponding output channels in your database.
Uranium / Thorium	Specify the output channel for the uranium-to-thorium ratio. Default: UTh Script Parameter: SPECTRO.UTHRAT
Uranium / Potassium	Specify the output channel for the uranium-to-potassium ratio. Default: UK Script Parameter: SPECTRO.UKRAT
Thorium / Potassium	Specify the output channel for the thorium-to-potassium ratio. Default: ThK Script Parameter: SPECTRO.THKRAT

Application Notes

This tool operates on preprocessed channels generated by Generate Radioelement Concentrations, which are labeled *_conc when the default suffix has been retained. Using these concentration channels, it computes radioelement ratios and produces output ratio channels with user‑defined names (for example, UTh, UK, and ThK).

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).

Calculating U/Th, U/K, and Th/K Ratios

When calculating radiometric ratios, two key challenges must be addressed:

• Avoiding zero values in the denominator

• Extracting meaningful ratios from areas with low count rates

Handling Zero Denominators

The tool offers two methods to manage zero denominator issues:

1. Dummy Values: Inserts placeholder values to indicate that certain data should not be processed. This method is advantageous because the system interpolates smoothly across dummy values using adjacent data.

2. Minimum Thresholding: Sets values below a defined threshold to a specified minimum concentration, ensuring that the denominator remains valid.

Managing Low Count Rate Data

Low count rate regions tend to have higher statistical errors. To address this, the tool applies a low-pass filter to smooth the data. This technique is based on the principle that smoother input yields smoother output.

Choosing Minimum Concentration Cutoff Levels

To determine appropriate minimum cutoff values:

• Examine the concentration data (in the channels generated through Generate Radioelement Concentrations) on lines flown over water where no ground-based radiation is expected.

• Ideally, these readings should be zero, allowing you to set the cutoff at zero.

• If the data is not zero, select cutoff values based on the lowest reliable concentration levels observed for each channel.

Choosing Filter Cutoff Levels

To determine appropriate filter cutoff values:

• Review the concentration data for each channel.

• Look at the profile view to identify visible noise and choose a cutoff value that effectively reduces this noise without distorting the underlying signal.

• If you want to keep a channel unfiltered, set its cutoff value to 0.