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The Spectrum page displays the collected spectra in real-time, along with the radionuclide concentrations that result from the onboard spectral processing. The plotted lines and data present in this view are explained in this section. Both the raw and the stabilized spectrum can be shown in the plot. The raw spectrum represents the measured spectrum and is plotted on an x-axis representing channels. The onboard microprocessor stabilizes (converts to an energy scale) and analyzes (extracts radionuclide concentrations) this spectrum resulting in an energy spectrum and radionuclide concentrations.


When the detector is switched on, it first needs to collect 10k counts in the analysis windows before it can calculate the energy-stabilized spectrum. During this time, no radionuclide concentrations will be visible, and only the raw spectrum will be shown.

Gamma Spectrum

The live spectrum is shown to check the spectral shape, energy stabilisation and the derived radionuclide concentrations (40K, 238U, 232Th and optionally 137Cs). When this page is opened, the incoming and accumulated spectra are shown in the figure. The accumulated spectrum (blue dots) is fitted using the calibration curves (the coloured lines extracted from the calibration file), yielding (a) the blue "fitted spectrum" and (b) the concentrations of K, U, Th, and Cs listed in the Spectrum block. The principles of the fitting procedure can be found in the Gamman Software manual. More info on translating the measured spectrum to an energy scale and the procedure of extracting the nuclide concentrations using standard spectra can be found by clicking on the respective links. 



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Grey dots

The spectrum collected by the spectrometer stabilised to an energy scale


Blue dots

This is the accumulated spectrum by summing the grey dots


Red line*

The standard spectrum for 40K multiplied by the concentration shown in the Spectrum block.

Individually for each measured spectrum

Green line*

The standard spectrum for 238U multiplied by the concentration shown in the Spectrum block.

Individually for each measured spectrum

Blue line*

The standard spectrum for 232Th multiplied by the concentration shown in the Spectrum block.

Individually for each measured spectrum

Yellow line*

The standard spectrum for 137Cs multiplied by the concentration shown in the Spectrum block.

Individually for each measured spectrum

Blue surface

The sum of the 40K, 238U, 232Th and 137Cs lines.


* The calibration spectra for these nuclides are extracted from the active Medusa Calibration File (MCF) on the device. Calibration spectra are unique for each detector and cannot be interchanged between sensors.

The spectrum boxes contain an information icon in the top bar. By clicking on the information icon, the sensor infobox is opened. Through this window, inspecting the incoming data displayed in the Medusa-defined JSON sensor format, described on the JSON documentation page, is possible.

Spectrum block




Counts per second

Count rate from the last measured spectrum (grey dots)

counts per second

Plot every

An input value that accumulates spectra before plotting



The time the detector actually measured during the last recording. In brackets is the dead time (in percentage) of the measurement


Accumulated live time:

The live time of the stacked spectrum (blue dots)



A parameter that describes the stabilization shift


Dose rate (µGy/h)

The dose detected by the crystal: the energy per kilogram deposited in the spectrometer.

Note that this is a more rudimentary dose rate calculation. Gamman should be used for determining the biological effects of radiation that is encapsulated in a H*(10) dose rate calculation. See the Gamman manual:15. Determining dose rate


Potassium (K)

The concentration 40K found (red line)

Becquerel/kilogram or %

Uranium (U)

The concentration 238U found (green line)

Becquerel/kilogram or ppm

Thorium (Th)

The concentration 232Th found (blue line)

Becquerel/kilogram or ppm

Cesium (Cs)

The concentration 137Cs found (blue line)


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