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Detector specifications

All Medusa spectrometers are built around our proprietary embedded processing system, implementing fast FPGA-based (*) digital signal processing. The Medusa Detector Operating System (mDOS) performs high-speed full-waveform sampling of the scintillator crystal output, connecting to either classic Photomultiplier tubes or modern Silicon Photomultiplier (SiPM) readout systems. Full-waveform signal processing implies for zero-deadtime operation - an important feature needed in high-countrate applications, with counting speeds up to 250kcps.

The spectra acquired are fully linearised using a built-in "Poisson-preserving" version of the well-known Medusa Full Spectrum Analysis method, allowing for the seamless addition of spectra from any number of records of one or even multiple individual detectors. Spectra are stored internally in 4096 channels. The channel resolution can be increased to 16384 channels upon request.

Our detectors normally are equipped with very robust CsI crystals. Other materials, like NaI, CeBr or BGO are available on request.

1.1. Nomenclature and typical use

Medusa detectors are named as follows: "MS-xxx YYY"; where MS = "Medusa System"; "xxx" denotes the (approximate) detector volume in ml and YYY the crystal type (+application).



Application type


CsI or BGO

  • Sensor for 3rd party borehole tools;

  • Sensor for Medusa RhoC density meter


CsI or CeBr

  • gSMS (Stationary gamma Soil Moisture Meter)

  • (Underwater) pipeline inspection systems

  • Chemical plant inspection systems


CsI or CeBr

Geophysical and agricultural surveying

  • Handheld system for walking surveys

  • Droneborne surveys


CsI or CeBr

Geophysical and agricultural surveying

  • Handheld system for walking surveys

  • Driving surveys

  • Droneborne surveys



Geophysical and agricultural surveying

  • Driving surveys

  • Droneborne surveys



Underwater sediment mapping for geophysical 
and geochemical (pollution) studies



Geophysical and agricultural surveying

  • Driving surveys


CsI / NaI

Geophysical surveying

  • Driving surveys

  • Airborne surveys

1.2. System comparison sheet

Available Crystal types


  • Systems: All

  • Density: 4.5 kg/l

  • Energy resolution: typically better than 8.5% on 137Cs (661 keV)

  • Robust, virtually unbreakable


  • Systems: MS-100; MS-350; MS-700

  • Density 5.1 kg/l

  • Energy resolution: typically better than 3.9% on 137Cs (661 keV)

  • Suited for applications needing peak analysis / high resolution / anthropogenic material detection (nuclear waste).


  • Systems: MS-4000

  • Density 3.7 kg/l

  • Energy resolution: typically better than 7.5% on 137Cs (661 keV)

  • Low-cost but quite shock and temperature sensitive.

  • Not recommended for drone/walking/vehicle-borne use because of its fragility.


  • Systems: MS-50

  • Density: 7.2 kg/l

  • Energy resolution: typically better than 11% on 137Cs (661 keV)

  • Suited for applications where sensor volume is restricted

Crystal electronics


1 inch PMT


4 pcs Silicon PMs

MS-350; MS-700; MS-1000; MS-1200

6 pcs Silicon Photomultiplier (SiPM); CeBr versions contain a 3-inch PMT

MS-2000; MS-4000

3.5-inch or 4-inch PMT

Spectrometer electronics


4k (16k on request).


<0.2% (diff); <0.1 (integral).

Dynamic range

2 Mcps (theoretical),
250 kcps (measured on a CsI crystal, ***).


zero (**).

Baseline restoration, pulse
shaping, pile-up rejection

Digital (full-waveform sampling).

Spectrum sample rate

max 10 Hz to continuous.


The system stabilises on natural peaks (40K, 238U and 232Th).  FSA-based Poisson statistics are preserved.


Internal real-time clock

Embedded CPU (MS-100 up)

Processor system

Toradex Verdin (NXP i.MX 8M Mini Cortex-A53 quad core)

Onboard storage

16GB. Optional 64 GB

Real-time clock


Embedded GPS

  • uBlox ZED-F9P

  • RTK enabled, with a base station

  • Signals: BeiDou, Galileo, GLONASS, GPS / QZSS

  • Update rate: 1 Hz

  • Dynamic positioning precision: 7 mm + 1ppm

  • Static position precision:  4mm +0.5ppm

Embedded internet link

4G e-SIM-based uplink (upon request)

Embedded pressure/temp/hum

  • Bosch BME280

  • Temperature range: -40 ... 85 °C

  • Pressure range: 300 ... 1100 hPa

  • Humidity 0 ... 100%

  • Update rate:1 Hz / 5 Hz (on request)


WIFI, Ethernet, RS232 upon request.

Survey data

Data output

The data stored and downloadable from the sensor consists of

  • Raw (multichannel) gamma-ray spectra;

  • Energy-stabilized gamma-ray spectra (in 10keV/channel format covering 0-3meV);

  • Radionuclide concentrations and their uncertainties (K, U, Th and Cs). Other nuclides can be added on request;

  • Complete GPS records (consisting of lat, long, elevation, DOP, No of satellites, quality of positions

  • Pressure, temperature and humidity.

Data format

Data is stored and streamed in (encrypted) JSON format. JSON definitions are defined on the mDOS JSON descriptionpage.

Data contains:

  1. Energy-stabilised multichannel spectra;

  2. Nuclide concentrations;

  3. GPS locations

  4. Pressure/temp/humidity

Aux Data Format /streaming

Several add-on data formats compatible with 3rd party logging equipment are available on request:


  • RMS

  • Geoduster

  • PicoDAS

Data protection

Survey data can be encrypted or left unencrypted. Encryption and decryption are done via proprietary algorithms embedded in Medusa processing software (GAMMAN).

Unencrypted data storage and/or streaming are available on request.

Survey modes

  1. Autonomous streaming (preset timer)

  2. Triggered streaming (external trigger)

  3. Local (system stores data locally only).

Operating System

Operating system

mDOS (Medusa Detector Operating System). mDOS provides a standardised web interface to our detector system, which allows set-up and check of system parameters and system functioning.



9-36V, 6W max, 3W nominal

Sizes & weights





MS-350 Handheld/drone

Carbon fibre tube

100 ⌀ x 210 mm

2.7 kg

MS-700 Handheld/drone

Carbon fibre tube

100 ⌀ x 290 mm

4.7 kg

MS-1000 Drone

Carbon fibre tube

100 ⌀ x 370 mm

6.7 kg

MS-1200 Underwater

Alu/stainless steel tube

108 ⌀ x 1000 mm

15 kg

MS-2000 Car-borne

Carbon fibre tube

120 ⌀ x 580 mm

11.7 kg

MS-4000 Airborne

Square aluminium box

120 x 198 x 8500 mm

23 kg

NOTE: MS-50 and MS-100 sizes and weights are not listed as they vary depending on the application.

Detailed dimension and drawings of the systems can be found on the system dimension page.

Operating temperature

-10 oC to 50 oC

1.2.1. Notes

(*) FPGA = Field Programmable Gate Array - a high-speed electronic component that can be tailored to a certain data processing job;

(**) Zero dead-time = no dead-time like in classic systems based on peak height determination and pulse conversion times. An "apparent dead time" is included by adjusting the live time clock for loss of system-measured pile-up rejections to ensure the absolute count rate is correct.

(***) The sampling speed of the FPGA and the scintillator output's peak width determines the system's theoretical count rate. The max data rate for real-world NaI or CsI crystals will be around the number mentioned.

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