Low Level Gamma Radiation (2023 Update)

As I understand it, you're seeing is largely Compton radiation and X-ray fluorescence. When naturally occurring gammas (from K40 decay, transuranincs, and cosmic rays) smack into atmosphere or into solid matter, the energy of the gamma is scattered... it's dissipated a bit at a time as the gamma photon interacts with electrons or the nucleus of the impacted materials.

If a gamma scatters off of an electron, some of the energy is transferred to the electron. If the electron is bumped up to a higher-energy orbital and then decays back to its ground state, the decay can cause the emission of an X-ray photon - fluorescence. This necessarily has a lower energy than the gamma, and its energy will depend on just what element was involved in the scattering. The original scattered gamma will have less energy than it did before, of course.

So, the rise you see in the spectrum is probably the sum of a whole bunch of Compton scattering events which involved gammas that were originally of higher energy.

From what I've read, skyglow (gammas and X-rays originating from cosmic-ray impacts on the atmosphere) is a big part of this. NORM is another big part.

A few years ago I collected a box of monazite sand from a local beach. It definitely shows a thorium signature, but the peaks are nowhere near as sharp as the ones in the "quantum pendant" data. I believe this is because the thorium is diffused throughout a much larger amount of base material (I have to use a couple of pounds of it to get a good reading) and most of the decay gammas end up Compton-scattering at least once as they work their way through the sand to the sensor crystal. As a result, the sharp peaks from the original decay events are weakened, and blurred by the Compton scattering effect.

How big are the crystals?

The analog-days solution was a delay line amplifier; the long recovery tail is exponential, so a difference amplification of V(t) - (1+epsilon)V(t-s) flattens the recovery when (1+epsilon) equals the diminution of the signal during 's' seconds. The infinite-impulse response or FIR filter is relatively easy work to do that.

Some good info here:

Thanks to Phil and John, I will soon have a PMT gamma detector to compare with the Radiacode. Hopefully, it will be more sensitive so I can be more certain of measuring Radon in the basement as well as other radiation sources.

Assembling the electronics turned out to be much easier than some DIY pages describe on the web. There is a company in Israel that supplies complete Gamma Spectroscopy electronics. The company is RH-Electronics at

I got the PIC18 MCA Module for $95.00 plus shipping at $17.95:

Generating the high voltage for the PMT turned out to be easy. Amazon sells CCFL inverter boards very cheap. I got one for $13.46 at

The last item is a fast high voltage diode to supply the PMT. This turned out to be the hardest problem until I found Dean Technology in Dallas, Texas, 75370

They sell a 5KV 100ns diode for a couple of bucks:

The total price is CDN $95.00 + $17.95 + $13.46 + $2.50 = $128.91, not including the PMT that the seller refuses to sell to Canada.

The US price is about $120 USD including the PMT, so nobody has any excuse for not being able to detect radon in their basement.

A very lucid explanation. Thanks.

I was able to find out what NORM is without having to ask you: "Naturally ocurring radioactive materials." I'm so proud of myself:)

How big are your scintillator crystals?

False, of course.

Not at all; for human health, what matters is the generation of ion pairs and gamma radiation includes energies that go right through a human body without much likelihood of interaction.

That's just nonsense; word salad, plus some capitalizations.

Ignore him. I PLONKED him long ago as soon as he appeared.

A a really doesn't know what he is talking about.

The Gy - or Gray - is defined in terms of the energy absorbed - in Joules per kilogram - by the object being irradiated. Gamma rays - higher energy X-rays - go straight through human flesh, so the amount of energy deposited is a bit uncertain.

What is certain is that it is the energy deposited that matters. and a a doesn't seem to know enough to understand this.

A simple way of checking whether it is even worth worrying about radon is to look it up!

There are similar maps for lots of other countries.

John

If a a knew what he was talking about, he'd know that the main function of the IEEE is to publish a large collection of high-impact peer-reviewed scientific journals that deal with the science that underlies electronics. That is what science is about, even if a a doesn't have a clue about it.

That's why I joined the organisation back around 1980. It's not all that obvious the current activities of the NSW Branch, but that's where the serious effort goes , and where the serious money gets spent.

I've got just one short comment in that literature

Sloman, A.W. "Comment on 'Computer aided simulation study of photomultiplier tubes'", IEEE Transactions on Electron Devices, ED-38 679-680 (1991).

Because I mostly worked in the UK I published more the UK Institute of Physics journals, but there aren't as many of them, and Americans do tend to ignore them.

Oh God. Is this "a a" a new troll or a renamed version of the old ones. Perhaps new, some of the old ones at least knew to not be too loud on topics other than politics. Perhaps posting utterly illiterate claims is a technique to engage us, who knows. Like I do at the moment, what am I thinking....

The tricky bit would be finding something that you would comprehend as having anything to do with science or research.

The comment that I published in the IEEE Transactions on Electron Devices and listed above - which you have snipped - had a quite a lot to do with research - it cited a bunch of references on photomultiplier non-linearity which are relevant to anybody doing serious research that exploits photomultipliers. So you've already had what you asked for, but failed to recognise it, which is exactly how you have always performed ever since you started posting your inanities here.

Oh dear. if you are to be a troll at least learn how to post. Finding me/my photos is about the easiest thing to find on the net, at least learn how to do it. Better, instead of trolling invest your time into learning how to do something useful.

====================================================== Dimiter Popoff, TGI

Quite welcome!

:-)

The next step in the obsession is to find NORM sources for yourself. Government and business buildings with granite facades are one source.

Ugh... it's been years since I built the probes so I don't recall the exact size. I think they're both about 1" in diameter and an inch or two long.

I also experimented with using one or more small LYSO crystals, as are used in PET scanners. They do work, but the lutetium is itself slightly radioactive and there's a constant flux of pulses from gammas generated within the crystal itself. Commercial PET scanners deal with this by ignoring (filtering out) pulses of the specific height corresponding to this gamma energy. That approach doesn't seem to work as well (for me at least) for doing gamma spectroscopy of low- level sources since the lutetium gammas still generate a broad Comptom continuum which tends to obscure the features I'm looking for.

Wow! That's big. That's why your detectors are so sensitive.

I found some sources for crystals. The smaller ones are not too expensive:

1. formatting link
2. Saint-Gobain has a lot of papers as well as crystals:

1. Hiler has more info on crystals. Quotes on request:

1. More info:

1. Berkeley has a wide variety of detectors:

Wow! You could get really deep into this topic. And spend 11,780 bazillion dollars.

Thanks,

Mike

Phil, can you elaborate on this point? If the crystal and PMT are well- insulated from their surroundings, which they are, what mechanism would cause noticeable amounts of ion migration?

It's definitely more convenient to run these with negative HV than it would be with positive HV, where you not only have to worry about DC blocking but also ripple. The latter seems to be a big deal, going by the Theremino docs and other sources.

-- john, KE5FX

A high voltage across a photomultiplier faceplate will do it.

At Cambridge Instruments, the photomultipliers we bought were selected to deliver the gain we needed with less than 1kV across the tube - which is to say across the glass faceplate.

A quartz - silicon-dioxide - face-plate might have been expected to be immune, but they needed an expensive graded seal to couple them onto the glass body of the photopmultiplier tube

Quite how 1kV got to be selected as the cut-off point was never revealed to me, but it was embedded in our purchasing specification.

The tubes themselves were mounted hard up against a glass window in the (grounded metal) specimen chamber, so that they could detect the flashes of light coming of the scintillator in the Everhart-Thornley secondary electron detection system.

Regular glass seems to contain enough metal ions for ionic migration to be a problem under kilo-volt potential differences.

I see, so the issue is the potential difference between the photocathode and the exterior metalwork. They seem to have thought of that, as the tube's metal frame is tied to the cathode pin.

-- john, KE5FX

Some of it is. The anode isn't and none of the dynodes are, and every last one of them it is tied to a metal pin coming out of the base.