Sunday, April 22, 2018

Building DIY Portable Handheld Multi-Channel Analyzer for Gamma Spectroscopy "GammaViewer-1.00"

The project has two parts: first is the NaI(Tl) detector with photomultiplier tube and internally installed driver, second part is the MCA that can count pulses and analyze energy range of the incoming signal. Here I'll show the photos of my build process for the project and if you'll have questions or will need components for yours projects then you are welcome to contact me.

Read the full article under the cut:

1. Spectroscopy detector with NaI(Tl) crystal and photomultiplier tube.  
I used 30x40 NaI(Tl) crystal with R9420 Hamamatsu tube. The tube is optically coupled with the crystal and isolated from any external light with several layers of the black electrical tape. Small amount of an optical compound applied on the crystal window to improve light passage to the PMT.

Photomultiplier tube need to be driven by high voltage. I wire electronic driver for the tube as close as it possible to the tube and it consist of: high voltage module, voltage divider for dynodes and pulse amplifier. The amplifier works as a current to voltage converter, it takes anode current pulses and convert it to voltage pulses with different amplitudes. The amplitudes of the pulses on PMT anode usually are proportional to the photon energy. That allow to identify types of gamma emitting isotopes.

I manually manufacture the enclosure for the detector from an industrial aluminum. The connector on the cap has ready signal output and charging port for the internally installed lipo battery. That's way I get portable spectroscopy detector that can work with computer, iPad or any other hardware.

The typical pulse shape of the PMT amplifier output is:

2. MCA multi-channel analyzer.
After the detector was ready I selected handheld enclosure for the MCA: MHH-95A and then designed PCB version of my MCA module for that case.

The MCA has small display of 128x64 pixels for representation of partial spectra information. The ADC is 10bit 1024 channels. Every collected spectra saved into CSV file on SD cart. After that every spectrum can be opened on computer for detailed view of all 1024 bins. 

After fine calibration of the detector electronics and synchronization with the MCA I was able to detect gamma energies in range of 26keV-3000keV with ~7.30% FWHM on Cs-137 662keV and very good linearity. 

Here is several CSV spectra saved by my MCA and the detector. The files opened in BecquerelMonitor2011 software after 3-points energy calibration. 

Cs-137 one hour:

Radium watch Ra-226 30 minutes:

Lantern Mantle with Th-232 30 minutes:

I have limited stock of PMT drivers, charge amplifiers and MCA boards that can be used for amateur gamma spectroscopy or for scintillation counting. If you interested to purchase any electronics for this project, or even a finished NaI(Tl) detector, you can contact me by email:

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