Gamma Spectrometry Forum

During Christmas, I bought a Measall KC761 gamma spectrometer—one of those small handheld devices that are just on the edge of being affordable.
I’ve been doing some testing with it (searching for fallout Cs¹³⁷, for example), and soon came the wish to get better spectra by shielding the device from background radiation. I also wanted to engage my 12-year-old son in the topic. Since he’s been quite into 3D printing lately and I had no clue about it, I asked him if we could build a lead castle together—he could handle the printing, and I would take care of the design and other tasks (like handling the lead).

So I had to teach myself how to work with Fusion 360, the software we used to create objects from scratch. After about 20 design attempts, we had a prototype ready to bring to life: first in PLA, to test the threads and make sure all the measurements fit. But PLA isn’t great for more demanding applications, so we switched to PETG.

After roughly 96 hours of printing (3kg of filament)—total overkill—we finally had the enclosure ready to be filled with lead and copper sheets. Altogether, 17 kg of lead (3 mm lead balls) were poured into the chambers. The lead walls are 17 mm thick, and the copper shield, which lines the inner perimeter, is 2 mm thick.

This is by no means a professional shielding setup. The goal was simply to reduce the counts per second (CPS) a bit and to lower the lead X-ray fluorescence. We also wanted the device to remain portable, so the final weight came in at 22 kg.

We also designed a Marinelli beaker that fits snugly into the lead castle—one version for solids and one for liquids. One final thing still needed to be done: securing the lead balls! We filled the chambers with epoxy resin to turn everything into a solid block.

The normal background radiation in my basement is about 120 nSv/h at 12–14 CPS. Inside the shielded device we could lower the background by 88.3% (10 hour measurement).
So, while it’s not perfect, it definitely does its job (for such a small spectrometer). And most importantly, I managed to get my son away from computer games—doing something more creative with a scientific background.

To illustrate what we have done, here a link to a video which shows the device and the obtained background spectra: https://youtu.be/-r-SNqNHFNU

The future plan is to build an adapter for the gamma spectacular GSB-1515-CsI kit detector. I already have a draft in Fusion. So I want to see how a much more sophisticated detector works in that tiny lead castle...

Nico,

Excellent project and video with special effects (hopefully not real radiation speckle 😂 ). 3D Printing looks nice, I have often made similar shields from relatively cheap PVC plumbing pipes, these come in all sizes and you can usually find caps and adaptors to fit, sometimes a 3D printed plug to fit.

PS: Consider adding a signature to the bottom of your posts - do this in the UCP (User Control Panel)

Steven

If one is wishing to learn about radiation and radioactivity I would suggest adding some other types of detectors. What I am going to suggest is fairly inexpensive and intended for educational purposes.

Firstly, I'd suggest building a simple ion chamber. A very simple, inexpensive device can be made with a few electronic parts and an old tin can. I made such a device and have used it to measure radioactive decay of the radon daughter from thorium. (I used a thorium laden lantern mantle in a plastic baggie with a syringe to collect the radon sample and inject this into the ion chamber). Instructions for this simple device can be found in the link below -
https://techlib.com/science/ion.html

Another type of radiation detector comes as a kit that will require some basic soldering. All components are through-hole type and the instructions are quite clear. This device is a geiger-muller type of detector. It is available from Adafruit -
https://www.adafruit.com/product/483

Some interesting items (e.g., uranium rock samples, and sometimes small quantities of radioactive chemical compounds [UO2, ADU, etc.]) can be purchased along with other educational items (e.g. Spinthariscope) from United Nuclear -
https://unitednuclear.com/

I obtain sources for calibration of gamma spectroscopy instruments from Spectrum Techniques. This company primarily makes radiation detectors (and sources) for educational purposes. There are manuals available describing simple experiments that one can perform. -
https://www.spectrumtechniques.com/

Hi Rob,

great ideas, thank you for sharing that. I will consider that in the next projects to come up.With Uranium ore I am still quite hesitating, as I fear contamination.
We bought uranium glass, as that is easy to handle and no fear of contamination.

What we have been trying to achieve is the detection of Cs137 in soil samples. South of Germany (where we live) has been hit quite hard by the Chernobyl fallout in the 80s. You can still find quite some Cs137 here in soil samples, even after 1.X half-lives.

I know the debate about Cs137 being present almost anywhere on the planet due to the nuclear weapons tests back in the 50s and 60s. So of course there is an overlay, but it is much less intense. And also the vertical migration in the soil is different: weapons fallout you find here in about 40-50cm deep. The Chernobyl fallout is at about 10-15cm and much more intense.

What makes this so interesting:

- the distribution in the area around here is quite heterogeneous. This comes from where the dust clouds have rained the materials to the ground, in some areas there is more, in others there is much less. Especially the Alps are a natural barrier for such clouds, thats why you find Cs137 predominantly there.

- as a local you are somehow tied to this story around Chernobyl. I remember the days when I was a kiddo. My parents were quite afraid back then. I still remember that we could not go to school because there is a silent/invisible threat outside. You cant see it, you cant smell it….taste it. Sun was shining outside, but we could not go to the playground. So it was a mysterious experience I can tell my kids about. And there are lots of documentaries you can watch together with them.

So hunting for Cs137 here makes „fun“, even small devices like the Radiacode110 show quickly when there is something spicy in the soil, esp in 10cm deep.

The challenge is the identification of Cs137 as it is in many cases in a quite low concentration. Of course the peak is easy to identify at 661keV, but my detectors are still too small.

Thats why I need a lead castle and soon a bigger detector to get better readings.

I wish I could quantify the presence of Cs137, but there is no way to have a efficiency calibration I guess.

@Steven: thank you for the feedback. No the flashes are artficial, a plugin in my video editing software ;-)
I considered those PVC pipes as well, but I wanted to engage my son with his 3D printing hobby. Next time I do it also with PVC parts, I guess much easier.

Regards, Nico

For small uranium and thorium ore samples - I double bag these small samples to prevent flakes of radioactive material from spreading contamination. The plastic bags do little to attenuate the gamma radiation measured for spectroscopy. If one wanted to measure or observe the alpha and beta particles (e.g., in a cloud chamber) then more care should be taken (i.e., use tweezers to place the small samples in measurement position).

If one is handling lead, cadmium, or non-sealed radioactive materials, then it is strongly advised to wear gloves and to thoroughly wash ones' hands afterwards.

So finally I built an adapter for the soon arriving GS1515-CsI detector. The lid has an inner compartment I need to fill with copper flakes and lead BBs + epoxy.
The lid has also a ring with a holder for the GS-MAX-8000, I hope the specified dimensions are right :-)

What I still miss is a way to also shield the top where the detector tube is extruding upwards - I guess there is no way to fill that "gap"....

so, my son and me have finished that project:

adapter is ready for the new detector, filled with lead (2.5kg) and copper (1kg). Also did some "fingers" and marinelli beakers for it.

But of course there is a downside: previously I had 89% background reduction in that lead castle. Now with the much larger detector and shortcomings with the lid, the reduction has shrinked to 83%.
But maybe for an amateur setup, still "acceptable" ?

Hope to do some soil sample testings soon :-D

Question:
With my GS-MAX-8000 I had no temperature probe, but I found one from my astrophotography setup. When I connect that one it reads temperature, but funny it reads it 10 times higher, so for 19°C it shows 190°C.
Or is that a normal bug in the ImpulseQT device screen?

Nice looking project..., and 80 % background reduction is not too shabby.

The proper temperature sensor reads the correct value in ImpulseQT - you should have the proper sensor shortly.

Steven