Urgent public health warning issued over lost radioactive capsule
abc.net.au
abc.net.au
> 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.
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
As such it radiates equally in all directions.
Of course a manufacted Source(TM) for industry might actually be a slug of doped Cs-137 surrounded by a lead casing with a window to direct emissions.
This still leaves us talking about the actual source of the radiation which emits equally in all directions .. but being blocked in some directions by either a casing or perhaps the earth below, a pool of water, etc.
Isn't it just?
I'm glad you picked that up as 1.9 MBq through up to 750 MBq is more of the range I would have expected for a mining instrumentation source [1].
I'm guessing both the The Guardian [2] and AAP [3] relied on the same reporter who missed fact checking and an M (and possibly a decimal place) when interviewing the W.Australian Health minister (who, of course, may have bumbled that himself).
The W.Australian official press release avoided details [4].
Take note when going forward in your career as there'll likely be some moment of unexpected public relations in the future.
Any thoughts on the "full quote" ?
Chief Health Officer Andrew Robertson said the small silver cylinder was a 19-becquerel caesium 137 ceramic source commonly used in radiation gauges.
“That may not mean a lot to people but probably more concerning is that it does emit a reasonable amount of radiation,” he said.
Dr Robertson said the unit emits about two millisieverts of radiation per hour, which is the equivalent of having 10 x-rays in an hour.
“Two millisieverts is also the amount of natural radiation we would receive in a year just by walking around,” he said.
“This is a source we have to be very careful of … It is quite a large radiation dose.”
I confess to a distaste for Sieverts as a per kilo absorbed dose (or is that Grays) as its kind of subjective to target rather than source properties (as the source may be partially shielded by lead, water, etc.)
Moving on, 700 k counts / minute background (or 12 k counts/sec for those of us working in one second over lapped accumulation windows) sounds ballpark.
The interesting twist on the source, though, is it might be shaped in the sense of having a wrapper of lead (say) with an aperture of preference to direct the radiation preferentially.
> I neglected here that not all gamma rays that reach the detector actually will leave a signal in the detector.
For at least two reasons, 'eh?
* Not all gammas passing through the crystal will cause a flash (you covered by implication), AND
* Not all flashes will be counted (oft neglected) as the scintillation counters get saturated by single events and need to recover, they also fluff damn near simultaneous multiple events as singles (all this dependant on scintillation detection equipment).
> Hope that gives you an idea how you can estimate these types of questions.
I was very interested to hear your reasoning, I appreciate it and I hope your comment gets a few eyeballs, although HN moving on apace as it does, who knows?
> 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
Hmm. You might want to look into this further I suspect.
My poor understanding is that rainstorm fronts drop the barometric pressure which draws radon gas from the cracks and crevasses in which the gas has already been expressed from the rock sources.
So, yes, there is an increase in radon gas where radon gas is normally expressed due to pressure drops.
However, in a hypothetical environment with no pressure changes .. radon continues to be expressed if it is being created.
I've found, in my humble experience, that even on clear days rain free days in Western Australia radon is thick on valley floors in those areas that have it in the still of the mornings, and gone later in the afternoon as the winds increase and clear the heavy ground hugging gases.
I would suggest that radon is a function more of geology and topography .. modified in variance by air pressure and wind conditions.
In any case, thank you for your response, I look forward to any further thoughts you may have, and, in closing, you may enjoy this entertaining A0 wall map [5] .. or perhaps the larger raw datasets (also available) [6]
[1] https://inis.iaea.org/collection/NCLCollectionStore/_Public/...
[2] https://www.theguardian.com/australia-news/2023/jan/28/missi...
[3] https://www.aap.com.au/news/search-for-radioactive-capsule-i...
[4] https://ww2.health.wa.gov.au/Media-releases/2023/January/Sea...
[5] https://ecat.ga.gov.au/geonetwork/srv/api/records/a05f7892-f...
[6] https://www.ga.gov.au/scientific-topics/disciplines/geophysi...
@defrost Great discussion and addition by the way. I only have one additional comment concerning radon. Radon is produced in a radioactive decay in the ground, and as it is gaseous it usually dissipates into the atmosphere rather quickly, so there is not too much of it near the detector at any given time. As you mention correctly, certain weather condition obviously can trap it near the ground. We usually study urban centers, with lots of asphalt covering the ground, affecting the amount released near the ground and near our detectors. We usually see it during rain, as then the radon in the atmosphere is washed down through the rain and accumulates on top of the ground for a while, which we often see as a strong uptick followed by an exponential decay. I have a coworker that just submitted a paper for review regards modeling this, sorry can't link the work yet. Overall, radon is quite tricky to understand and what you mention seem very reasonable. It would be quite interesting putting a detector for a while in these areas. Nevertheless, the measured amount of radon usually fluctuates on larger scales, maybe hundreds of meters, while the source will create a very localized signal, so it shouldn't cause too much troubles for a search like this.
[1] https://en.wikipedia.org/wiki/Western_Australian_radioactive...
For context, Rio Tinto operations in Mt. Newman are mining iron ore from near surface open pit | mesa deposits; blasting rock with minimal crushing to fit in rail carriages for transport to the ocean ports where ore is crushed smaller, screened and graded (blended) for shipping overseas .. in total some 850 million tonne per annum of iron ore from that region (not just Newman alone).
I'm guessing the guage is for estimating ore density | grade on the fly as rocks tumble through the load out (from the remote operated semi autonomous near robot trucks) into kilometre+ long robot trains.
> Considering they still haven't found it
Yeah, I'm very surprised the search is still on, I'm leaning towards it's well off route in a tire in a truck (or already fallen free) OR some heavily tatted FiFo worker (fly in | fly out) nicked it as a souvenir for the local bikkie clubhouse and hasn't came home from a holiday in Thailand yet .. .
Radon: IIRC there are additions in the Australian AGSO radiometric processing guidelines re: radon removal that derived from work I did levelling out radon smearing back in the 1990s - somewhat out of date these days, but hey, that's the world for you.
There are also potential modifications to the work by Brian Minty | Jens Hovgaard | Bob Grasty using an NASVD to firstly highlight the use of Radon eigenvectors and then to rotate them out of the signal space in the processing pipeline.
I'm guessing (completely w/out context) that perhaps your friend is moving down that path (or perhaps well past and elsewhere, as I said, it's been a while).
If yourself, your friend, or anyone else gets bored searching the sidewalks for traces of terrorism (or whatever the hell it is that you're doing and not talking about) .. have a look into this:
A Radiometric Renaissance
https://www.uwa.edu.au/Projects/A-radiometric-Renaissance
( some geology and big data required )
I'm not Mike, I do know him and it might interest some.
I'd love to see the post-mortem on this one. That at first glance reads like several failures.
Edit: ok found it: https://en.m.wikipedia.org/wiki/Lia_radiological_accident
(The X8 capsule from [1] is a dead ringer for the one described.)
[1] https://www.qsa-global.com/industrial-cs-137-gamma-sources
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..
Like how household smoke dectors have a small radioactive source, only scaled up for a hundred tonnes an hour of throughput.
Not for something that small (as a source) given the atmosphere thickness etc.
If you're interested:
Guidelines for radioelement mapping using gamma ray spectrometry data International Atomic Energy Agency (2003)
https://www-pub.iaea.org/mtcd/publications/pdf/te_1363_web.p...
( Although, frankly, IMHO, AGSO (Australian Geological Survey Org) have a similar better document, but lets not quibble )
179 pages of breezing overview with simplified details, note that airborne radimetric surveys with ~ 50 litre sodium iodine crystal packs (that flash on an energy spectrum when a gamma ray interects with them) are flown at 80 metres ground clearance and NOT at 20 km+ ground clearance because of EXPONENTIAL signal strength decay . . .
The penetration of a pachinko ball through a volume of various gases, densities, pressures and at tempretures hasn't changed either.
The signature of a Cs137 bolt head sized source on the ground [1] peaks at 662 kev and has the entire atmosphere above, water vapor and all.
That's a lot to push through for a small number of low energy gamm's in order to reach a satellite that would then have to pick out that signature from ALL the ground area below (with no obvious means to determine direction).
This is very different, obviously, to a thunderstorm driven electrical field generating MeV events high above the cloud levels from (presumed) relativistic Bremsstrahlung.
Err, I mean, you do read and understand these links you're providing, I guess?
If not, maybe start there with a picture of what's actually going on here.
[1] https://www.gammaspectacular.com/blue/gamma_spectra/cs137-sp...
Gamma…either.
I’m assuming they’re probably not trying to detect directly but interactive signatures, no？
Err,I mean,you do read and understand these links you're providing,I guess?If not, maybe start there with a picture of what'sactually going on here.
Probably work on reading up on detection methods.
( See upstream attached overview on basics )
There's a source object here, the size of a bolt, it emits a certain amount of detectable energy (why? worth checking) in All directions - at any distance the energy that reaches that far is spread across the surface of a sphere .. the surface area of that increases R-squared and so the energy per unit area decreases with the square of the distance.
Worse still, the energy is in packet form - when it hits or interacts it changes or gets knocked out of the game - what energy survives gets smushed out and down to lower energy levels.
By the time energy from our source reaches a satellite it's been spread out to less than nine tenths of sweet fuck all and stretched out and down shifted to have little discernible form ..
AND .. (here's the big one)
it's also coming out to the satellite alongside the competing signals from several hundred square kilometres of adjacent ground, replete with similar (but initially different) spectra from Potassium, Uranium, Thorium, et al .. that have now all weakened, lost their distinct shape, and been smooshed together in a blender.
The high altitude high energy stuff stands out and proud, the rest is an amorphous blob of bachground radiation .. if you could identify a few counts from a Cs137 source, how would you even know where it came from (other than "probably below")?
Probably work on reading up on detection methods.(See upstream attached overview on basics)
So is it really impossible secret projects came up with a way to detect x-ray/gamma via photon emission of collision with atmospheric particles? Sparsity/AI/DSP to work the data... truly impossible?
Does not sound impossible to me. I get if you're unaware of it or sounds impossible to you, yeah? OK? No worries. This may be related: https://iaea.org/newscenter/news/what-is-cherenkov-radiation
I have, more or less off and on semi continuously since the 1980s. FWiW I've read and edited multiple versions of guidelines to terrestrial radiometrics from several countries and the international agencies (such as the one I linked above).
> No need to fake arrogance.
Just a bald statement of rather dull facts I'm afraid.
> Does not sound impossible to me. I get if you're unaware of it or sounds impossible to you, yeah? OK? No worries. This may be related:
Just to be clear .. are you suggesting that a coin sized Cs-137 mining instrumentation source with 667 kev gamma peak might be causing observable cherenkov radiation?
And that no one has noticed or thought to look since 1900 or the post WWII Cold War boom in domain study?
That's an interesting notion.
Anyway, you’ve clearly got skin in the game in this argument, Aussie. I wonder what your role is: an interested observer or an involved party?
It should be clear by now that I've measured and mapped radiation events of several kinds for 40 odd years.
It's clear that you're suggesting there might be some novel as yet unknown way to detect and location pinpoint a coin sized industrial Cs-137 source used in a mining radiation gauge from the distance of a low orbit (?) satellite.
I'm open to hearing how exactly this might be achieved, I'm sure the other person in this parallel discussion would also have an interest, as they stated they're working at a US national lab in precisely this area.
If you turn to that discussion they've addressed the measured and known way in which the gamma radiation falls off with distance .. although they didn't address how that also falls off with air column mass (air pressure, tempreture, water vapor level (humidity)) etc. and determined this is possible to detect in a one second window from 40 metre distance.
It also rather rules out using direct gamma detection of such a weak source from 25km through the full mass of the atmosphere so, again, it'd be nice to have a concrete indication from you of what it might useful to look for.
Concrete, mind, and not more of this handwavy Sir Kenelm Digby Powder of Sympathy [1] remote sensing magic.
So I'm going now. I do not want to do this with you all day. So I hope your day gets better from here, bye! :)