u/Bob--O--Rama

LOL! But seriously, when you get it, please post a spectrum. Very curious what's actually in it.

Safety Notice: Do not attempt, the radon source and the way radon is dispensed in the video includes passive safety aspects not easily discernible from the video. I will post a reply with more details. Do not attempt.

The video depicts the construction of a ZnS(Ag) coated vial - essentially a toy model of a Lucas Cell - which is then inoculated with 3 uCi of radon in air ( based on gamma dose rate assay ). This is about 5x the radon concentration of my prior attempt - and the entire interior of the vial is phosphor coated utilizing all of the alpha particles produced to full effect. This activates the radioluminescent phosphor such that it is faintly visible without darkness adapted vision, and rather amazing when captured with low light photography.

At the end of the video, the radon assay is also performed via dilution and a radon monitor for which a callibration curve is available from testing in an AARST approved STAR chamber. This again produced the frustrating and puzzling 3.3x discrepancy between gamma dose rate and radon concentration measurements. So is it 3 uCi or 10 uCi depending of if you believe physics or if you believe AARST? If it is some gross experimental error on my part, I have yet to discover it.

The Lucas Cell is a radon detection probe constructed of a radioluminescent phosphor lined canister mated to a photomultiplier tube. The tube can either run in current mode for high activity samples or in pulsed mode for decay event counting. In the vial above there is likely > 600,000 scintillations / second. For a typical radon monitor it may be dozens / second or minute at residential levels of radon. This works similarly to the ZnS(Ag) alpha probes used for contamination detection, except the sample is the enclosed air.

If the tube were placed in a light proof box with a photomultiplier, one could attach it to a common geiger counter to measure the radon. As it decays over the next 3 months, the residual will be ²¹⁰Pb in nanocurie quantities. This is easily detected by a well shielded consumer gamma spectrometer. The ²¹⁰Po will continue produce alpha particles for decades, replenished by its parent ²¹⁰Pb. This scintillation may be visible to well adapted eyes.

I deal with radon a lot, but due to some unforeseen medical shenanigans I "obtained" a sample of ⁹⁹Tc*. Since taping a probe to my forehead for a day was not a [ socially acceptable ] option, I collected an, ahem,*renal* sample.

5 cc of an aqueous solution of Tc-99m / Tc-99g bound to soluble proteins was "placed" in a thin wall glass vial. The vial was placed in contact with an RC-110. This produced a laughably high contact reading, even after 2 half lives had elapsed. On monitoring the sample as it decayed, you obtain the count and dose rates over time. This can be used to assess the dead time compensation of a meter as the actual activity is known to diminish in a predictable way. This does not help assess the absolute rate reported, but the relative rate can be evaluated, and hence the linearity of the response over a range of activity.

Since the position of the sample and the probe is constant, this avoids geometric factors inherent in using different distances from a constant source to provide different activity levels as well as things like air kerma and changes in buildup.

The calculated 6.032 hour figure is from the RC-110 provided dose rate, the 6.431 hour figure is from count rate. The expected half life value is 6.006 hours. As with radon decay, the RC-110 was spot on for the calculated half life of Tc-99m when based on dose rate - this suggests very good dead time compensation baked into the dose rate calculation. The count rates appear to be uncooked. So for higher rates, the RC under-reports counts, this has the effect of making half lives appear longer.

A little while ago I noticed a little "blip" when recharging while making long term measurements of a fairly active sample. I caught it in the act this time. It seems to be an instant, abrupt shift when charging completes. The logs shows the count rate and dose rate drop by 5% over the course of a second - so not related to thermal issues. Unfortunately when when starting a charging cycle this time I had to disturb the source / RC so I don't know if charging increased the things by 5% and this is just returning to normal.

Its unclear to me what the "charging ... interrupted" means but basically this is what I always see when charging finishes. And after it finishes, the RC seems to ignore the USB power and the battery will run flat after a week of normal usage - unless I physically unplug and replug in the USB cable. In other words it seems to charge once, and does not seem to run of the external supply. This makes continuous long term measurements more difficult. I'm not sure if this is expected behavior or some argument between the RC and the chargers I use.

It's also unclear if the sensitivity changes with charge level when running off the battery - my sources decay rapidly, so I might not notice. I would need to use a ¹³⁷Cs button and a fixture to see how that plays out.

While this is definitely in the "minor annoyance" category, it might be worth trying to reproduce and address.

I finally got around to cleaning the grime of these. "Someone liked their menthols!" 😬 The Rumrill Radioactive Holstein pattern jug has a cork under the cap, so perhaps it was intended to be a decanter. The twins flanking it are Stangl. I need to do some spectroscopy on the Stangl ones as one is definitely darker and the mold stamp indicates "usa" on the lighter glazed one. So perhaps natural vs depleted uranium.

I got a couple Ludlum 243 well type probes, these include a beefy lead shield - which is why I got then. These are the probes mounted in the shield. Predictably the crystals in them are bad... one sorta works for counting, the other maybe more suitable as a Muon sponge. I'd like to re-use the PMT or perhaps make a plastic scintillator slug to replace the old crustal. Does anyone know how these are assembled? Is it just a naked NaI(Tl) slug or is it a windowed unit? The black bands look like the way, but I don't want to just bust it open.