I am working at a National Lab in the US and this is the main focus of my research. Please have a look at our website if you are interested in learning more about this type of things [1].
[1]: https://anp.lbl.gov/
Nice, so, just speculating with what is in the public domain here;
* what kind of counts would you expect from a 19-becquerel caesium 137 ceramic source in a 50 litre NaI spectrometer ~ 40 metres away in a 1 second window ?
I mean the spectrum is going to look like [1], of course, but I'm imagining a crop duster [2] draping at 70 metres / second for along the centre line of the 1,400km stretch of road, maintaining a 40 m clearance and coming preloaded with the 256 NASVD Hovgaard kernel of the West Australian Outback looking for a Cs137 peak and compton.
Would you be expecting any radon interference here?
Of course the fun starts if our nugget of interest isn't on the road but was picked up in a 4x4 | truck tire and carried along for a few hundred km.
Would you expect a contact trace to show up along the road here, good enough that if it dies off one can investigate whether it fell out, or got carried elsewhere by the vehicle turning away?
[1] https://www.gammaspectacular.com/blue/gamma_spectra/cs137-sp...
For simplicity lets assume 50 Liter is a 1 meter x 1 meter x 5 centimeter thick panel. 5 centimeter is usually sufficient to give you a good change to measure gamma rays at most energies and you want to have a large surface area exposed to the source, so this seems a quite optimal configuration for 50 Liter of NaI.
A source emits gamma rays in all directions uniformly, so to calculate the fraction of gamma rays that end up in our detector we calculate in "solid angle space".
The surface area of such the detector is 1 meter^2. The solid angle coverage can be approximated by surface area / distance^2 [1], so at 40 meter that would be about 0.000625. The full solid sphere is 4PI ~ 12.5, which is the surface area of a ball with 1 meter radius.
The fraction of the full solid angle that is covered by the detector is 0.000625 / 12.5 = 0.00005.
You have 19 Becequerel = 19 Gamma rays per seconds leaving the source so 0.00005 * 19 Bequerel * 60 seconds = 0.057 gamma rays per minute reaching the detector. You won't see this over the background.
Putting 37 Million Becquerel into this equation, we will get roughly 111,000 counts / minute in the detector. Remembering correctly (and this is only a rough guess) you would expect about 700,000 gamma rays per minute from background (what we call naturally occurring radioactive materials or NORM) in that much detector volume. So that is about a 1:7 signal to background ratio. You should have a very good chance of seeing that.
I neglected here that not all gamma rays that reach the detector actually will leave a signal in the detector. But at 662 keV, the energy most of the gamma rays in Cs137 are emitted at, about half of them do so in a 3 cm thick detector. At 5 cm I would estimate about 75% or more doing so.
Hope that gives you an idea how you can estimate these types of questions.
[1] https://en.wikipedia.org/wiki/Solid_angle
Edit: Forgot to mention the radon. Usually you do not measure much radon unless it rains. It is mostly a dessert there so I don't think that should be an issue
Edit: ok found it: https://en.m.wikipedia.org/wiki/Lia_radiological_accident
> DFES Country North chief superintendent David Gill said there would be "challenges" in locating such a small object.
Wouldn't the radioactivity make finding such a small object far, far easier? It looks like the road is two lanes with a dirt shoulder. Couldn't they get a truck, mount several geiger counters on a pole long enough to sweep the road and shoulder, and drive the road looking for a spike in radiation?
I assume that's the reason for the announcement.
If it stayed on or very near the road, I would expect it could be detected this way.
Now, if it washed off the road in a storm, well good luck.
And then you also must consider the natural background rate of radioactivity across that enormous area. Crank your sensitivity up too high to gain range and you might just detect radon or potassium, or whatever else is out there decaying.
Yeah. I would think they'd look for localized "spikes", then follow that up with an on-the-ground search. They don't need to eliminate all false positives.
My idea is to have multiple Geiger counters spread across a 10+ meter pole. Since what they're looking for is small and localized, they could control for varying natural radiation by looking for a spikes that don't affect all the sensors equally.
Like how household smoke dectors have a small radioactive source, only scaled up for a hundred tonnes an hour of throughput.
(The X8 capsule from [1] is a dead ringer for the one described.)
[1] https://www.qsa-global.com/industrial-cs-137-gamma-sources
I'd love to see the post-mortem on this one. That at first glance reads like several failures.
Perhaps this would be a place to use that equipment?
It's smaller than a coin and could be sewn into someone's favorite shirt. I'd call that a weapon!
The city was closed almost a day because a truck driver lost the capsule while driving his truck.
The mayor concern was someone trowing that to the river.
That was 25 years ago I think.
Edit: I'm reading that 6 years ago the same happened..
