CZT Am 241 Spectrum

[Jim Kovalchick]

I toyed around a little with one of the small eV products CZT detector that made the rounds through eBay several years ago. I applied a HV of 1000 V and 12 V to its preamp. I sent the signal through a Canberra 2025 amplifier, through an ADC, and into my homemade MCA. Here is a spectrum I made last night of a smoke detector button. The x axis is channel number, not energy. To start, the signal is quite noisy, but I was able to get rid of most of that, but it causes my electronics to be quite busy in comparison to the relatively slow count rate that comes with an inefficient small crystal. I see the two major peaks I expect, and I think there are some x-rays in there as well. The shape is quite odd though, and I feel like there are some things going on here unrelated to Am 241. Let me know what you think.

Jim Kovalchick

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[Rob Tayloe]

Attached is a spectrum of Am-241 acquired using a RadAngel CZT detector from eV Products (now Kromek). This CZT device uses a 5 mm x 5 mm x 5 mm crystal and is in a package that uses a USB connection. It also has a sound output and there was software to used the detector with an iPad. In the attached example I use the eV Products software KSpect. Kromek does not appear to offer the RadAngel any longer. Too bad, as this is a very nice, compact, easy to use device. In the free version of KSpect the first few hundred channels are suppressed. I had a temporary "full" version of KSpect and it had all channels of data displayed, but I did not pay for the full version license. The resolution of this CZT is pretty good, but the sensitivity of such a small crystal is such that longer counting times are needed for higher energies and lower activity spectra.

https://www.kromek.com/news/radangel-cz ... -in-stock/

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[Sesselmann]

I applied a HV of 1000 V

Jim, 1000V sounds awfully high for the eV-CZT, I recall playing with these many years ago at around 70V, think it was 700V with a 1:10 divider.

Steven

[Jim Kovalchick]

Rob,
Thanks for posting the info on your CZT and the Kspect software. I think I have a version of that somewhere myself. It doesn't show in the spectrum you posted, but I am curious if your crystal will see the 26 keV gamma and some of the xrays that cluster just below it.

Steve,
The recommended voltage range for the detector is 1000 V to 500 V. Others have run in this range and managed to get decent spectra. Running too low as you suggest significantly diminishes sensitivity. Yesterday I ran tests from 500 V to 75 V, and with each step down, count rate reduced. Further, at 75 V, the 26 keV peak was all but gone.

I did manage to improve the symmetry of my peaks though. I was using 5/8 inch steel plates to shield my detector and source. When I removed the shielding, the main peak became much more symmetrical.