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).

System	Variants	Application type
MS-50	CsI or BGO	Sensor for 3rd party borehole tools; Sensor for Medusa RhoC density meter
MS-100	CsI or CeBr	gSMS (Stationary gamma Soil Moisture Meter) (Underwater) pipeline inspection systems Chemical plant inspection systems
MS-350	CsI or CeBr	Geophysical and agricultural surveying Handheld system for walking surveys Droneborne surveys
MS-700	CsI or CeBr	Geophysical and agricultural surveying Handheld system for walking surveys Driving surveys Droneborne surveys
MS-1000	CsI	Geophysical and agricultural surveying Driving surveys Droneborne surveys
MS-1200	CsI	Underwater sediment mapping for geophysical and geochemical (pollution) studies
MS-2000	CsI	Geophysical and agricultural surveying Driving surveys
MS-4000	CsI / NaI	Geophysical surveying Driving surveys Airborne surveys

1.2. System comparison sheet

Available Crystal types
CsI	Systems: All Density: 4.5 kg/l Energy resolution: typically better than 8.5% on ¹³⁷Cs (661 keV) Robust, virtually unbreakable
CeBr	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).
NaI	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.
BGO	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
MS-50	1 inch PMT
MS-100	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
Channels	4k (16k on request).
Nonlinearity	<0.2% (diff); <0.1 (integral).
Dynamic range	2 Mcps (theoretical), 250 kcps (measured on a CsI crystal, ***).
Dead-time	zero (**).
Baseline restoration, pulse shaping, pile-up rejection	Digital (full-waveform sampling).
Spectrum sample rate	max 10 Hz to continuous.
Stabilisation	The system stabilises on natural peaks (40K, 238U and 232Th). FSA-based Poisson statistics are preserved.
Timing	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	PCF8523
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)
I/O	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: Energy-stabilised multichannel spectra; Nuclide concentrations; GPS locations Pressure/temp/humidity
Aux Data Format /streaming	Several add-on data formats compatible with 3rd party logging equipment are available on request: MAVLINK 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	Autonomous streaming (preset timer) Triggered streaming (external trigger) 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.

Physical
Power	9-36V, 6W max, 3W nominal
Sizes & weights	Type	Housing	Size	Weight
	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.