Gamma Spectrometry Forum

Hello from the southern boundary of Rocky Flats, Colorado (yes, *that* Rocky Flats).

Check sources appear quite expensive (I think I've seen them as low as USD 82 each, for disks), so money IS an object. What is a minimal set that would be generally useful for gamma spectrometry? Can I get by with just two (with a 241Am source--see below)

I was thinking about a 137Cs source (because I could in principle use it to calibrate a couple Geiger-Muller counters too) and a second with precise but widely spaced lines covering a broad energy range with a half-life of at least several years. 207Bi looks promising for medium to higher energies, 569.7, 1064, 1770 keV, with a nice 32 year half life.

I already have a 241Am [smoke detector] source which would provide a decent low-energy 59.5 keV calibration. In the experience of the group, are these sources good to, say, plus-or-minus 20% of their nominal values?

Many thanks!

I use 22Na, 226Ra, and 241Am for calibration. I have other disk sources, but for calibration I find that my homemade 226Ra and 241Am cover a wide enough range that I don't need much else. I use the 22Na 1274keV peak for my maximum.

I'm not sure about the tolerance of the disk sources, I use a pulser for calibration.

You are very lucky to live in the US where disk sources are readily available, things are much more complicated in the EU :)

If it is about energy calibration only, there are quite a lot of cheap options still. A thorium source provides lots of peaks to calibrate against, I personally use thoriated tungsten welding rods as they are really cheap and readily available. Potassium chloride is a good 1461 kev source. Americium from smoke detector for its low energy peak.

If you need sources of known activity, it gets more complicated though. Potassium chloride an option, lutetium 1g samples you can order, americium in smoke detectors has known and labeled activity (but it's illegal to dismantle in the US, I don't think it's illegal here though). Then of course if you want that to be of a certain geometry it gets way more complicated, perhaps even impossible without those damn disk sources.

I use a thorium gas mantle or even better a hand full of polished Apatite mineral samples I bought from a shop near my house - they give a very good Thorium decay chain spectrum. I also have a bag of low salt which gives K-40. I do have some disk sources as well but I prefer the leave them in the lead pig. The natural Apatite + salt gives me these obvious peaks
238.6
338.3
583.2
911.2
1460.0
2103.0
2614.5

Thank you all for the remarks and suggestions! I too have a gas lantern mantle (I bought it new in the 80s as a spare for a Coleman lantern!). I'll bear in mind that it's a cleaner source than I would have guessed. Lost my Apatite :)

For simple energy calibration, a minimal set of disk sources would be none.
There's loads of options for natural, historic, or otherwise readily available radioactive material that have plenty of peaks to pin down an energy cal without splashing out on manufactured sources. Am-241 smoke detectors; K-40 in your background or enhanced with low sodium salt (KCl); Th-232 and daughters (lantern mantles, thoriated welding rods); Ra-226 and daughters (watch hands and aircraft dials) or more generally the full U-238/Ra-226 decay chain (fiestaware, uranium glass etc). Between a couple of these you have lines spanning 59keV at the low end, 186, plenty of intermediate peaks, and at the higher end 1460, 2614 and more.

If you're looking to have an efficiency calibration, you will want something with better known activity. From there, it depends how accurate you want to go. The nominal activity of the Spectrum Techniques disk sources is probably good enough for hobbyist purposes, but professionally it's usually worth paying the extra for a proper calibration traceable to national standards.

My recommendation for a minimal source would be a single Eu-152 disk - with lines from 122 to 1408 and plenty in between, you can pin down the majority of your efficiency curve with just the one source; and the 13 year half-life means it should last you a while.

Going further from there, it depends what you want to measure.

My work generally involves activation products, and having Co-60 and some of the other activation product peaks well calibrated is critical, so we usually get sources with Co-60 and activation nuclides to calibrate those exactly rather than interpolating from something else. There's a bunch of standard off-the-shelf mixed nuclide sources that provide most of what we need in one source.
For some things, though, it can be helpful to have a single line source. Cs-137 is usually a good readily available option for that, although I have had uses for others.
A beta+ source can be good for coincidence experiments with the opposite-direction annihilation photons, so something like Na-22 is a good choice.

gwgw wrote: ↑

22 Oct 2019, 08:02

You are very lucky to live in the US where disk sources are readily available, things are much more complicated in the EU :)

It's still possible to get Spectrum Techniques sources imported, although probably a few more paperwork hoops to jump through, especially for a hobbyist. There are other suppliers in Europe too, Orano/CERCA LEA in France and E&Z Nuclitec in Germany - although nothing quite as accessible to hobbyists as Spectrum Techniques tend to be.