SrI2(Eu) detectors

[Rob Tayloe]

The folks at CapeScint that made the small SrI2(Eu) detector discussed earlier now have a small USB MCA attached to the 14x14x25 mm detector assembly. I have not seen or used this MCA, however more information may be found in the links below -

https://capescint.com/

The CapeScint contact is -

Ivan V. Khodyuk
CapeSym, Inc.
508-653-7100 x214
www.capescint.com

[Rob Tayloe]

In a previous post I mentioned that CapeSym had come out with a small ScintiClear Strontium Iodide detector (14mm x 14mm x 25mm) that was integrated with a small USB MCA. A link was given for this device.

I obtained one of these integrated MCA ScintiClear detectors. CapeSym has deveoped software that works on a PC to drive the MCA and display and save acquired data. I will share my thoughts and some data from use of this detector and software.

I was also loaned an experimental ScintiClear MCA unit with a smaller detector. The smaller detector was 14mm x 14mm x 6mm and is intended for use in detection of lower energy gammas and x-rays. I believe that this smaller detector has a thin (0.5mm) Be window on the detector end. In an earlier blog post Max Fomitchev-Zamilov (of the Maximus Energy website) posted about an even smaller ScintiClear detector (2mm thick) made for low energy gamma and x-ray detector. He also posted about the 25mm thick ScintiClear detector. Links are given below to his blog postings -

[broken links removed]

Max used his own software with a PicoScope unit to measure various gamma spectra. Earlier in this thread I have discussed my use of the ScintiClear Strontium Iodide detector with a PicoScope 4262 and Max's software. In this and subsequent postings I will show results from the two ScintiClear MCA units and a ScintiClear detector with Max's software.

Following are photos of the two ScintiClear MCA units. The smaller experimental detector has a black shrink tube cover whereas the larger unit has the silver-colored metal cover. The USB end has a single LED to indicated that the detector & MCA is powered -

[Rob Tayloe]

One of the first things that I did after verification that the ScintiClear detector & MCA units were functioning was generate energy calibration curves. Shown below is the tabular data acquired for the three detectors followed by energy calibration curves along with least squares polynomial fitted functions for each curve. These functions are used to map the channel (or bin) spectral data to an energy spectra.

energy-cal-SC-data.jpg (88.46 KiB) Viewed 2129 times

[Rob Tayloe]

The smaller detector is limited in the energy of the gamma ray that is acquired. The 662 keV photopeak from Cs-137 (Ba-137m) is about the upper range that can be obtained.

The two ScintiClear detectors having the 25mm thickness have very similar calibration curves. One might wonder why the 1408 keV photopeak was not recorded for the ScintiClear MCA unit. The reason is because, at present the software displaying the spectrum can only display the data linearly; there is not log display ability for the Y-axis. It is difficult to view the 1408 Eu-152 peak without a log display. Max's software will allow the spectrum to be displayed in either a linear or log manner.

Following are images of the displayed spectrum for Cs-137 for each detector. It should be noted that the FWHM resolution values given have not yet been mapped from channel space to energy space. -

sc-mp-mca-010617-cs137-001.jpg (89.26 KiB) Viewed 2129 times

[Rob Tayloe]

The following image shows the three ScintiClear detectors acquiring data from a small thorium sample. This configuration was used for the subsequent measurements made. This is an unshielded measurement. -

[Rob Tayloe]

I have reconsidered the energy calibration fit shown above for the three ScintiClear detectors. The plot below uses a second order polynomial and gives a very good correlation to the data. Use of more data values (i.e., isotope photo peaks) would no doubt yield an even better energy calibration.
I am also uploading a compressed (7zip) version of my spreadsheet containing the energy calibration data, plot and least squares fit, and data from a number of measurements. Plots from those measurements are also shown below.

[Attachments are broken]

[Rob Tayloe]

Seems as though some stuff was lost in the hack. I am reposting those images and more from the prior post -

7zip version of spreadsheet with calibration data and plots and various spectra data and plots -

SC SrI Energy Cal2105.7z

(1.02 MiB) Downloaded 97 times

Measured spectra with three indicated SrI2(Eu) detectors -

[Mike S]

Rob,

Thank you for all the information you have provided in this thread, I hope you don't mind answering a few more questions. I'm pretty much sold on the CapeScint SrI2(Eu) detector setup, but before I pull the trigger I wanted to see if you (or anyone else with these detectors) had any updated opinions since your last post on the topic a year ago.

Are you still happy with your SrI(Eu) detector(s) from CapeScint?

Do you find the 14x14x25mm size is adequate for most samples, or do you find yourself wishing you had a larger crystal?

What is your overall opinion of their built-in MCA when compared to using the MaxE software and a PicoScope?

With the MaxE software, do you think the 8-bit PicoScope with resolution enhancement is adequate, or do you find the 12-bit PicoScope gives notably better results?

Have you tried using the CapeScint detector with the GS-USB-Pro as the capture device?

Thanks again.

Mike S.

[Rob Tayloe]

With gamma spectroscopy results will depend on one's expertise (and/or willingness to learn) and budget. When I was teaching lab classes at The Ohio State University's Nuclear Reactor Lab I had access to very nice (albeit somewhat difficult to use for occasional users) HPGe systems. And I could take small samples of materials and place in the reactor to produce other radioisotopes via neutron activation.

Now that I am retired and have moved several hundred miles further south from OSU I stimulate my interest with less expensive devices. [Although less expensive still doesn't mean cheap]. The SrI(Eu) detectors offered by CapeSym are a less expensive way to get better resolution than one could get with NaI. I will say that excellent NaI detectors and MCA systems can be obtained (e.g. GammaSpectacular, PRA software, and ebay {iradinc and maximusenergy}).

The smaller size detectors give very good results, but are less sensitive; meaning one needs to count for a longer time. From a cost/benefit standpoint I find the 14x14x25 SrI(Eu) detector to be ideal for my hobbyist purposes. If I were the US Government wanting something to identify contraband isotopes of interest to national security, then bigger would be preferable [cost would be not be much of an impediment - one can only hope to someday find these surplus devices for sale at inexpensive prices!]

With the SrI(Eu) and other similar scintillator devices from CapeSym, I have used the MaxEnergy software with PicoScope devices. The MaxEnergy software takes some fooling with to get more ideal results. If you go this route, I can send you screen grabs of my settings. I have used the 8-bit (2204) and 16-bit (4262) PicoScope devices. Not surprisingly better results are obtained with the more costly 16-bit devices. As mentioned several posts back, the 8-bit devices have an effective bit rate of up to 12 bits; thus being able to acquire 2k "channels" of data.

The CapeSym integrated MCA detectors are nice but much more expensive. The software needed to work with these devices is evolving. The software is easy to use and one can save the data for subsequent display / processing. As shown in some of the earlier images in this thread, similar results can be had with the PicoScope (using a 16-bit device) and MaxE software - The cost for the 16-bit device (~$1400) plus the 14x14x25 SrI(Eu) detector with SiPM (~$1300) is about the same as the CapeSym 14x14x25 SrI(Eu) with MCA (~$2600). From an ease-of-use standpoint, the CapeSym integrated MCA is easier. The 16-bit PicoScop with MaxE software takes more effort, but has greater flexibility (i.e., use with other detectors).

As of yet, I have not had success using the GammaSpectacular MCA with the CapeSym SiPM mounted detectors. I have only experimented with my least expensive detector (a 14x14x25 NaI). I have not completely replicated the circuit shown by Steven in a separate thread on this topic. More work to do. I did briefly use the Red Pitaya device with Gamma Spec software with the SrI(Eu). I have not yet tried to use the Red Pitaya with other detectors (e.g., NaI, and CsI).

[Rob Tayloe]

There is one other factor that I failed to mention about the CapeSym integrated MCA detector. Their integrated MCA makes use of the temperature sensor in the SiPM to provide some compensation for thermal drift. I have not made use of the temperature sensor output on the stand-alone detector - SiPM devices. Perhaps this can account for some differences in the peaks shown in above posts. I check temperatures in my basement during my measurements. In general, the temperatures do not vary by more than a few degrees F. As I turn on more computers and electronic devices the room will warm up by a few degrees.