Account for Dead Time

Use the RPS > Account for Dead Time option (geogxnet.dll(Geosoft.GX.Radiometrics.AccountForDeadTime;Run)*) to apply instrument dead time (or live time) corrections to airborne radiometric data (potassium (K), uranium (U), thorium (Th), total count (TC), and cosmic channels). For additional information, refer to the Application Notes below.

To rerun the process with previous settings, select the header cell of any channel created by the process, then right-click to open the context menu. The last item in the menu represents the most recently executed process (GX). Select it to reopen the associated dialog. From there, you can rerun the process with the existing settings, adjust parameters before execution, or simply close the dialog. Learn more about Dynamic Process Links (Makers).

Account for Dead Time dialog options

Use this dialog to specify the correction method and configure relevant parameters.

Input channel suffix

If Generate Radioelement Counts has been run on the current database, the suffix for the generated channels (K, U, Th, TC, cosmic) is automatically detected and preselected. If multiple sets exist, all suffixes are listed, with the most recent one selected by default.

Once a suffix is chosen, the associated channels are listed below the field.

Script Parameter: SPECTRO.ACCOUNT_FOR_DEAD_TIME_INPUT_SUFFIX

Correction method

Choose how to apply the correction:

  • Live time: Select this option if a live time channel is available for correction.

  • Dead time: Select this option if a single dead time value applies to the entire survey.

Script Parameter: SPECTRO.LTMETHOD [0 - live time; 1 - dead time]

Live time channel (ms)

Enabled when the Live time option is selected. Choose the instrument's live time channel.

Ensure the units for your live time channel are in milliseconds.

Script Parameter: SPECTRO.LIVETIME

Dead time factor (µs/pulse)

Enabled when the Dead time option is selected. To compensate raw data for instrument dead time, enter the instrument's dead time factor in microseconds per pulse.

  • Default: 0–no correction is applied.

  • To assess the impact of dead time correction, enter a non-zero value.

Script Parameter: SPECTRO.DEADTIME

Output channel suffix

Specify a suffix to append to corrected output channels.

Default: _live.

The information string below the field updates dynamically to show resulting channel names.

Script Parameter: SPECTRO.ACCOUNT_FOR_DEAD_TIME_OUTPUT_SUFFIX

Application Notes

Dead Time and Live Time Corrections

Spectrometer data are typically recorded in counts per second. However, instruments may briefly pause to process incoming signals—this pause is known as dead time, during which no counts are registered. Some systems also report the live time, which is the actual duration the detector is actively measuring and receptive to incoming pulses. Live time is calculated as the difference between the total sample accumulation time and the dead time.

Sampling time represents a balance between measurement precision and field efficiency. For a 350 cm3, NaI(Tl) detector, a sampling time of 2 seconds is suitable for highly radioactive rocks, while 6 seconds is appropriate for rocks with lower radioactivity—offering a practical compromise.

Most modern spectrometers automatically record dead time (or live time) and include it in the data for later processing. Typical dead time is about 5–15 µs per pulse. Refer to your equipment manual for specific guidance [1].

This tool enables you to apply corrections for both dead time and live time effects.

Dead Time Correction

Dead time corrections are applied to each window using the following expression [2]:

Where:

N = Corrected count rate (counts per second)

n = Raw counts recorded over a one-second interval

dt = Dead time duration–the time required to process all pulses reaching the detector in one second.

Where:

total_count = Total count rate across all channels

dead_time = Equipment dead time factor (µs/pulse)

Dead time corrections should be applied to each window in the downward-looking detectors. For some spectrometers, dead−time corrections should not be applied to the cosmic−ray channel or the upward−looking data as these may be processed by different circuits. Refer to the equipment manual for details [2].

Live Time Correction

Alternatively, if the live time is recorded (i.e., a live time channel is provided), the corrected window counts per second are calculated using the following equation [2]:

Where:

N = Corrected counts per second

n = Raw counts recorded in one second

lt = Live time duration for that interval (in milliseconds)

*GX.NET tools are embedded in the geogxnet.dll file located in the \Geosoft\Desktop Applications\bin folder. To run this GX interactively (outside the menu), first navigate to the bin directory and provide the GX.NET tool in the required format. See the Run GX topic for more guidance.

References

  • [1] G. Erdi-Krausz et al. (2003), Guidelines for Radioelement Mapping Using Gamma Ray Spectrometry Data, IAEA-TECDOC-1363, International Atomic Energy Agency.
    https://www-pub.iaea.org/MTCD/Publications/PDF/te_1363_web.pdf
  • [2] R.L. Grasty and B.R.S. Minty, A Guide to the Technical Specifications for Airborne Gamma-Ray Surveys, Australian Geological Survey Organisation, 1995/60, p. 32.
    https://www.ga.gov.au/bigobj/GA7667.pdf

See Also