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Theremino Gamma Spectrometer MSL-GS1 + Gamma Probe with NaI(Tl) or LYSO


Theremino Gamma Spectrometer MSL-GS1

I would like to introduce my new device for Gamma Spectrometry. This equipment is based on Open Source Theremino Multi-Channel Analyser This device is basic version of gamma spectrometer for detecting gamma particles and can be also so used for X-Ray/Gamma Fluorescence Spectrometry.

For correct function of gamma spectrometer must be used gamma probe with scintillator. This probe consist from scintillation crystal (usually NaI(Tl) or LYSO crystals). The very importat is also photomultiplier tube, in this case with Bialkali photocathode with Effective area 15 mm. For correct multiplication must be used also high voltage divider, which consist from 11 MegaOhms resistors.

A gamma ray interacting with a scintillator produces a pulse of light that is converted to an electric pulse by a photomultiplier tube (PMT). The PMT consists of a photocathode, a focusing electrode, and 10 or more dynodes that multiply the number of electrons striking at each dynode. A chain of resistors typically located in a plug-in tube base assembly biases the anode and dynodes.

The electric pulses from probe is very short and must be modified for sound card A/D converter. The power supply for photomultiplier probe dynodes must very low noise and stable. Signal from A/D sound card is processed by multi-channel analyser software which ranks these pulses by frequency and amplitude for display of specific gamma rays energy.

By energy of gamma ray (or x-ray) particles is possible to recognize specific radioisotope by specific gamma energy spectrum. For XRF analysis is possible to recognise kind of non-radioactive material based on the emission of characteristic secondary (or fluorescent) X-rays from a material that has been excited by bombarding with high-energy X-rays or gamma rays for this type of analysis its needed x-ray or gamma ray supply.

NaI(Tl) crystal scintillator has good advantage compared to LYSO scintillator, because eliminates background radiation of LYSO crystal itself. With this type of scintillator NaI(Tl) can be measured samples with low level of radiation. LYSO scintillator is commonly used for samples with higher activity, the advantage is very good measuring resolution at high energy spectrum (due to higher crystal density).

There are some photos from manufacturing :

Probe Photomultiplier :

Lutetium + Americium Gamma Spectrum example :

Americium 241

Caesium 137

Resources :