The Medusa Radiometrics MS-4000-CsI "Airborne" gamma-radiation detection system (AGRS) is our "classic" lightweight radiation sensor that was first introduced in 2006 and used for a large regional uranium survey in Madagascar. The size and weight of  “classic” systems (consisting of one or more 16L packs of NaI crystals) often exceeds the available payload of modern small, lightweight platforms or even unmanned drones for radiometric surveys.

To allow for a sizeable reduction of the “payload consumption” imposed by airborne gamma-ray systems, we developed a novel measurement methodology that combines a (much) smaller detector and the use of full-spectrum data in the spectral analysis.


The system comprises a 4x4x16 inch (4L) CsI-based scintillation detectors connected to a tailor-made spectrum processing unit. This unit contains a 4096-channel MCA, an RTK-ready GPS, real-time data processing and embedded storage. The system works as a stand-alone unit, and the data can be viewed by connecting to the interface using WiFi or ethernet on a cabled connection. 

The unit runs the  Medusa Detector Operation System (mDOS) that provides access to the multiple functions of the device:

  • Set-up of the system;

  • Status view to inspect data and functioning of the system;

  • Single and continuous measurement modes;

  • View the data in real-time plotted on a map;

  • Download data for custom post-processing.

The data is stored in records containing energy-stabilized gamma-ray spectra, together with count rate and activities of 40K, 238U, 232Th and 137Cs. Other radionuclides can be added on request. The data is geo-referenced using the built-in GPS.

System Operation

The system is designed for minimum operator interaction. It provides various views on the data streams while being acquired, allowing for online system checks. The system has embedded data storage with a standard capacity of 16GB, yielding space for over 700 hours of continuous data logging. The system can be user-configured to output gamma-ray spectra continuously, connecting the sensor to multiple data acquisition systems.

Data acquisition occurs via the embedded web-based data acquisition system or our MASS data acquisition software. MASS is a Windows app that runs on a standard PC or laptop. In addition, the system can be integrated into any modern DAS system, like the Geoduster DAS. This way, spectrometer data can continuously be logged and combined with other sensors like GPS and elevation meters.


Key Parameters

Radiation Sensor

System Data

  • High sensitivity

  • Lightweight and rugged carbon housing

  • CsI scintillator for enhanced stability

  • Full spectrum recording

  • Automatic gain stabilization

  • Online nuclide-specific count rates

  • On-board data logging

  • Set up, control and viewing of data via built-in web server running mDOS

  • CsI crystal, other crystal types on request

  • Dedicated Spectrum Processing Unit comprising

    • 4096 channel MCA,

    • Spectrum stabilization

    • HV supply

    • Nuclide-specific data

  • Housing: Carbon fibre; end caps: Anodized aluminium

  • Connectors: one 8-pin LEMO Arctic grip M-series

  • Environmental: -40 0C to +85 0C; IP68 protected

  • Power input 5-35V, (3W nominally, 6W max)

  • Data acquisition rate: up to 10Hz

  • Data storage capacity: 16GB internal

  • Wireless connection via WIFI

  • Battery-powered

  • Connectivity: user-configurable output streams over IP or serial link

  • Size: 174x203x856mm

  • Weight: 28kg

  • Technical drawing