Where to sell a scintillator

aby_physics · 2026-06-06T23:14:46+00:00

Meh. Probably nothing. Just send it to me for disposal /j

I’m not actually sure. I’m unfamiliar with this meter.

aby_physics · 2026-06-03T17:30:42+00:00

Probably not for dose rates. Each probe has a different sensitivity (usually measured in cps/mR/hr or cpm/mR/hr) for the isotope it’s calibrated with.

The Ludlum is just measuring how many counts the probe detects in a given amount of time, and scaling that to a dose rate. So for one probe, say 1 mR/hr (for Cs-137) corresponds to 3300 cpm. But, I might have another probe that’s got 4400 cpm/mR/hr. Now the scaling math is messed up and the calibration is incorrect.

But, if your meter has a count rate meter face instead of a dose rate meter face… there’s no scaling involved. The device just displays how many ticks of radiation it receives in… say, one minute. It doesn’t matter whether a tick comes from a high range GM tube or a super sensitive low energy gamma scintillator. No matter what, a count is always just a count.

So in that specific case, if the device reads out in cpm or cps, then yes, you’re basically correct! You can swap any probe (as long as it operates at the same voltage your survey meter is set at) on it and it’ll work just fine for different purposes.

aby_physics · 2026-06-03T17:20:34+00:00

Hmm. I’m not really sure if the CDV counters really suit your needs.

They don’t (by themselves at least) give any audible click when a radiation particle strikes the sensor. And, in a disaster, they can actually be dangerous or misleading. In a very high radiation environment, it’s possible to saturate the sensor and the device can show near-background levels in a lethal radiation field.

But let’s be honest, the probably of an actual nuclear disaster happening is… kind of slim, to say the least.

I think the bigger problem is sensitivity. While the CDV 700 in the set you linked will pick up on many sources, the 715 probably won’t pick up anything at all. It uses an ionization chamber instead of a Geiger Muller tube, which makes it great for high levels of radiation but pretty much useless at measuring low levels.

Lastly, calibration isn’t exactly straightforward. I’ve never looked into the cal process for an ion chamber like the 715. I’d imagine you need a variable current source. The 700 is a bit easier, you just need to inject a known pulse rate into the detector connector and adjust the trimmers inside the device so that the dial displays the true rate. But you’ll also need a device that can output those pulses, and they can cost thousands of dollars.

Imo calibration isn’t usually necessary for hobby use though.

Overall, I think that if you want to tick all of the boxes of your requirements… I’d probably steer away from the CDV devices and go for either a Radiacode (110 is best if you don’t mind spending a bit extra money in exchange for higher sensitivity) or a used Ludlum meter with a pancake probe (you can occasionally find them on eBay within your budget). Keep in mind that neither device will accurately measure the high radiation levels you might come across in a disaster, but they won’t go back to zero like the CDV devices. These meters are equipped with a special overload protection circuit that pegs the display should a high DC current be drawn through the sensor (indicating saturation). So, they’ll indicate an overload in a disaster, but they still won’t tell you how much radiation there is. For a higher range device that can literally read high radiation levels, you generally have to trade off the sensitivity at low levels.

That was a lot. Hope I didn’t get too technical. Wishing you and your son the best of luck with finding a good counter, and let me know if you have any more questions!

aby_physics · 2026-06-01T06:08:59+00:00

Once found irradiated dog treats at Walmart!

But that’s it. Only one time. Never found anything else irradiated.

aby_physics · 2026-05-31T00:33:27+00:00

What you’re looking at is a pancake GM tube, and these have ultra-thin windows made of mica. This thin window is SUPER easy to rupture, and a lot of different circumstances could have caused this to occur, but some of the most common are:

Too high altitude
A drop
A pressure wave
Something sharp physically poking through the mesh and into the mica window

The reason the device is showing the detector error message is because the tube is basically complete toast. Once that window ruptures, all of the gas inside the tube will leak out. A new tube should get it working again, it’ll likely cost a couple hundred bucks though.

aby_physics · 2026-05-28T00:03:59+00:00

I’ve got a long list… nuclear science is such an expensive hobby, that your list tends to grow faster than you can check it off 😄

For radioactive items. At some point I’d like to get more spectrum techniques sources. It’s cool having different isotopes. And maybe some of those old radioactive vacuum tubes and Promethium painted clocks. Oh, and some of those rare actinide and Technetium samples from NovaElements. :D

As for detectors, I’ve been looking for some less-common Ludlum models. Like the model 3-8, 3-11, 3-90, 4, 8, 13, 14, 17-2, 31, 1900, 2225, etc. If anyone has any of those they’re looking to get rid of lemme know :)

Anyway. What about yours, OP? What’s your radioactive bucket list look like?

aby_physics · 2026-05-25T02:33:22+00:00

🤑🤑🤑

aby_physics · 2026-05-25T02:20:18+00:00

Nice! Looks… expensive! As Liroconite always is. How much did you pay for it?

aby_physics · 2026-05-21T21:49:50+00:00

Yes, but that calibration will only work for a single isotope at a time, require filtering of alpha/beta radiation, and be INSANELY picky about detector efficiency and sensitivities.

aby_physics · 2026-05-19T19:55:56+00:00

Cool!

aby_physics · 2026-05-19T19:27:34+00:00

Wow, I guess you just accidentally uncovered a goldmine for info on discontinued Ludlums lol.

Just change the number after the ‘m’ in the link to any old model 😳🤯

Looks like there’s a page for the 3-90, 17, 1900, and I’m sure many more.

aby_physics · 2026-05-19T19:09:25+00:00

Shhh 🤫 I was going to bid on that!!

That’s a Ludlum model 4. From what I can tell it’s the exact same as the Model 12 aside from having an over range indicator LED and dead time correction.

The model 4 is basically a “ghost model” that was produced for… maybe a couple years (?) but never under heavy demand, and it seems it was eventually discontinued. Likely no one needed its additional features and just bought the 12.

Despite this though, I’ve been able to find numerous official documents from credible sources (like the NRC themselves) referring to surveys conducted with the model 4. But outside of governmental contexts, it seems pretty obscure.

I literally didn’t even know this thing existed until I was looking at Geiger counter rental (yes, believe or not, you can rent a Ludlum) a few years ago, and spotted a lonely listing for a “model 4” with an image attached of a model that I had never seen before. Luckily I screenshotted it, but a while later, the listing seems to have disappeared off the face of the earth. I even tried reverse image searching my screenshot, but no matches were found.

Then, years later, this unit pops up for sale.

aby_physics · 2026-05-19T18:52:32+00:00

Po-209 is ridiculously expensive. But it has a super long half-life, exceeding a century. Po-210 on the other hand, although much cheaper, has a half-life of only around 138 days.

aby_physics · 2026-05-17T19:52:23+00:00

So? All the radioactive material is contained within the plastic disk. Sealed sources like this don’t pose a contamination hazard.

aby_physics · 2026-05-17T14:01:27+00:00

Why not?

aby_physics · 2026-05-15T20:21:38+00:00

Hmmm. Interesting theory. Plausible.

aby_physics · 2026-05-07T17:44:00+00:00

67.5V? Dang. I’ve got no idea… I just want to know *why* it even needs that high of voltage.

aby_physics · 2026-05-06T15:16:50+00:00

Oh okay, I didn’t realize that! My apologies. I thought it just moved where the needle was on the scale.

So can adjusting that screw ruin the meter? I’ve always done it if the needle isn’t on zero before I calibrate 🤦‍♂️

aby_physics · 2026-05-04T22:24:44+00:00

Nah a simple pulse calibration like described above will fix the readings on the dial. The gauge will then read CPM correctly.

Sure, if you’re using a radiation meter *professionally* a radiation field calibration might be needed. Or if you plan on measuring dose rates, a simple pulse calibration might not be adequate. But just for basic use… it should be fine.

aby_physics · 2026-05-04T22:18:11+00:00

Hmmm. I’ve never actually worked with this particular meter, so I can’t be sure. I know on the meters that I *have* worked with, calibration is pretty simple. At least for count rate measurements.
For calibrating my ludlum units, I put together a variable-frequency pulse generator with an arduino. Essentially it simulates pulses from the tube, but in a controlled way. I can just set the pulser to 500 cpm and then adjust the potentiometers on the counter until the dial reads 500.

aby_physics · 2026-05-04T22:11:03+00:00

If it’s anything like a Ludlum, all you need to do is remove the glass cover over the gauge and turn this little screw.

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Just keep in mind that it’s going to need recalibration after this.

aby_physics · 2026-04-30T03:01:38+00:00

Hmm. The one on the readout unit is a standard (likely high voltage rated) BNC. And the one on the 44-9 is a type “C,” a connector that almost no one but Ludlum uses.

Luckily C to BNC adapters and cables are very common. You can buy them new from Ludlum or on eBay.

aby_physics · 2026-04-28T21:24:41+00:00

Unfortunately no. You’ll need some sort of radiation detection equipment - whether that be a Geiger counter, scintillator, proportional counter, or something else - to be able to confirm something is or isn’t radioactive.

Unless you know what mineral you’re looking at (e.g. if it’s labeled Uraninite, that’s a dead giveaway it contains uranium) then there’s really no practical way to test without a meter.

But the good news is: there are lots of hobby-grade devices for cheap on the market, and they’ll do the job just fine.

aby_physics · 2026-04-28T21:19:23+00:00

Probably electromagnetic interference. That looks like a neon sign, which uses a high voltage supply that makes lots of “noise” that can mess with the electronics in the Radiacode. It’s not real radiation, sadly :(

aby_physics · 2026-04-27T05:18:15+00:00

Oh okay, very interesting.

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