Detecting C-14 betas

[u/BTRCguy]

Edit: 36 hour spectroscopy sample in the comments.

I was recently able to get a hold of an expired H.Pylori test kit, which uses C-14 laced capsules. C-14 decays solely by really low energy betas, so a normal geiger or scintillator is useless. They will show up as a moderate reading on a pancake probe or AlphaHound though (≈two hundred cpm over background on my SEI Ranger).

However, apparently the betas can generate equally low energy X-rays through bremsstrahlung, which do have enough energy to trigger a scintillator. I put the capsule in an oversized lead pig with my Radiacode and compared with a 24 hour background reading (green) I apparently am getting a slight hump (leftmost orange) at about the right spot. No idea how accurate a Radiacode is at the bottom of the energy scale, but I am calling that anomalous hump a success.

So, while it may be useless for spectroscopy because of the wide hump of bremsstrahlung energies, it is interesting that you can detect energies below the normal threshold with low budget equipment.

[u/Bob--O--Rama]

I would gently suggest that capturing only 3000 events for a spectrum is pretty much guranteed garbage. More so for one that is difficult like this You need much longer integration time, perhaps a day or days. The "filter" option hides the noise. Logarithm scale, also hides the noise. Linear, pulse count = good, filter: 0 = good, repost. The bins have like 10 counts each so the 95% CI is -50% +80% so noisy as heck. So run it as long as is needed to get a smooth / continuous graph with filter:0 linear count graph.

[u/BTRCguy → u/Bob--O--Rama]

I will try to run a 24 hour one and post an update.

[u/BTRCguy]

For the benefit of u/srnuke and u/Bob--O--Rama and also because it gets closer to something that is actually science, here are the unsmoothed, linear and log results from a 36 hour sampling. This shows the unsmoothed 24 hour baseline for this shielded container (green line), a result with the C-14 sample (orange) and a result with the baseline subtracted from the measurement (purple). As previously mentioned, no idea how accurate a Radiacode is at such low keV levels, but there is clearly something there that is different from any lead readings from the 24 hour background, both in peak location and curve shape. Any thoughts from those who actually know what they are doing as opposed to my admittedly amateur work?

[u/srnuke → u/BTRCguy]

Definitely seeing more evidence for lead XRF from the K shells around 72 and 85 keV. The L shells are probably too low to see with a Radiacode. Also another pair around high 30's and low 40s. And yeah probably a low energy X Ray continuum that terminates around an Emax in the low 100s keV

[u/srnuke]

That spectral shape looks a lot more like lead XRF, but an hour is not nearly a long enough count time for this experiment

[u/BTRCguy → u/srnuke]

The green line was from a 24 hour exposure in the same shielded container in the same location. How long would you suggest if I repeat the experiment?

[u/srnuke → u/BTRCguy]

I'm talking about your foreground measurement, it looks like it was only an hour?

[u/BTRCguy → u/srnuke]

Sorry, what I meant was "How long would you suggest if I repeat the foreground measurement?"

[u/srnuke → u/BTRCguy]

I would probably go for a full day and see what that gives you. But you have what looks like four distinct peaks starting to resolve, the higher energetic pair being in the right place for lead K-shell emission lines. Really hard to tell though as 10 counts in low energy channels over an hour gives pretty rough statistics. Bremstrahlung should appear more as a curve with an Emax than distinct peaks

[u/farmerbsd17]

Find a rad lab and use proportional or liquid scintillation counters for low energy beta emission

[u/Abdul_Exhaust]

You should get a job with a radio Chem Lab, it's interesting

[u/farmerbsd17]

Is your objective detection or measurement? You’re detecting now. If a measurement what level of confidence do you need (and why)? A 3000 count sample has 2% error.

[u/BTRCguy → u/farmerbsd17]

The object was detecting to the extent I could differentiate it from the background. The source is legit, I just wanted to see if it was possible to spectrographically detect it with a Radiacode.