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Discussion (17 Comments)Read Original on HackerNews

toomuchtodo•4 days ago
Original title "Bayesian Parameter Estimation for the Localization of a Radioactive Source in a Heterogeneous Urban Environment" compressed to fit within title limits.

Author was inspired to write their PhD dissertation on radiation source search due to the Goiânia incident. Thank you to them for sharing this with us.

Goiânia Accident - https://news.ycombinator.com/item?id=49202635 - August 2026

gh02t•about 2 hours ago
Ha, that's me. Thanks for posting this. It's late where I am but I can answer questions. I took a brief break on this topic after I graduated and worked on other stuff, but the company I'm at now has done a lot of subsequent work on this, including making it practical in the field. Though as I mentioned in the prior thread, bridging the valley of death and selling it as a product is still a challenge.
defrost•about 1 hour ago

  There's been a lot of development since this dissertation to let it run in real time, and to integrate with tactical radiation detectors that the military/police/civil defense teams tend to use. Unfortunately that's mostly unpublished work at present.
~ https://news.ycombinator.com/item?id=49214068

Australia had some fun with a lost mining source - rather than run a geophysics plane 80m above ground from mine to city they held off to test a gadget with some whirly stuff about a crystal pack ... as I understand it.

Any comment, or all still a bit unpublished?

gh02t•about 1 hour ago
Not us, but probably an imaging radiation detector with LIDAR. Its another technology for search, with its own tradeoffs and advantages. We are friends with a couple companies that make that tech, but it's a different thread of R&D. Arguably a bit more mature; doing localization like we do with "normal" detectors on the ground is pretty challenging. We've done pretty realistic joint exercises with the military with our tech (called QkRad) but nobody has actually fielded it in a real emergency yet. We are around TRL 7 if you know that terminology.

These sort of loss events happen much more often than is reported widely. Not like something that happens every day, but there are a non negligible number of events every year. The Nuclear Threat Initiative catalogs publicly known events if you want to browse.

3dedb728-3f77•about 1 hour ago
Related to this, is it normal that radioactivity detector are not everywhere?
gh02t•about 1 hour ago
They are more prevalent than you think, especially in places like ports and airports. But part of the problem is they are typically expensive for anything more sophisticated than a basic Geiger counter, like most commercial offerings start at $5k and can very quickly go into the hundreds of thousands or millions of dollars per unit. And they require a lot of training to use effectively.

At least in the US there is also a pretty substantial network of teams and equipment for providing radiological technical support in an emergency. Examples of this are DoE RAP and the USNG CST. Now part of the motivation for this work was that a lot of the techniques for actually doing a search are fairly primitive, but there is a major support network with most of the tools and skills ready to go 24/7. It tends to all be very low key and fly under the radar, mostly because even a hint of one of these teams being deployed tends to cause a panic.

copperx•about 1 hour ago
I was born in the city where this happened, right on the US border: https://en.wikipedia.org/wiki/Ciudad_Ju%C3%A1rez_cobalt-60_c...

In fact, the house down the street to my parents' was torn down and rebuilt in the 80s because it had contaminated rebar.

When I was a kid, a neighbor, who is a civil engineer had a Geiger counter and went through the neighborhood and said he found nothing abnormal.

However, there is a cluster of cancer cases of people in the neighborhood of all kinds (breast, testicular, melanoma, liver, and kidney, of which my mother died of), including two friends who still lived there, and were diagnosed in their early 30s. Could be just bad luck, but I still wonder. My father still lives there.

I guess I should at least skim your dissertation, but is there a device that could be employed to sweep the neighborhood?

gh02t•about 1 hour ago
The cheapest worthwhile detectors out there are the Radiacode ones. They are excellent for what they are, but they run around $300. Cheaper Geiger counters are unfortunately kinda useless, at least for this. It's also not particularly easy to know what you're looking at and how to interpret it even with a good detector, unfortunately I'm not sure how much luck you'd have so don't waste $300.
wildzzz•26 minutes ago
When doing heavy ion testing for space flight hardware, there's a potential for the hardware to be a little hot after a full day of testing. Not really dangerous but hot enough that you need to let it sit for a day. At one facility I went to, the physicists there said in the past a group didn't let their hardware cool off and it alerted radiation detectors in the Lincoln Tunnel, NYC.
_trampeltier•about 1 hour ago
At least in Europe, there are a lot.

There is even a public realtime map.[1]

Also at least in Switzerland, all old metal scrap companys, waste incineration plant, and so on, have radiactive detectors on the entrance.

[1] https://remap.jrc.ec.europa.eu/Advanced.aspx

[Edit] It seems since April 2026, Switzerland has also a lot radioactive checks in border/customs control and bigger post/packet centres.

snovv_crash•about 1 hour ago
I've seen work using smartphone camera sensors to detect radiation, so with the right software maybe they're everywhere.
gh02t•about 1 hour ago
Unfortunately smart phone cameras kinda suck performance wise. Radiation detectors fundamentally need some mass to actually absorb and detect radiation, so while cameras are basically similar to semiconductor radiation detectors the performance is so bad as to be useless. I haven't really ever seen the camera detectors be used for anything useful.

Radiacode detectors are about the only affordable detector with actually useful performance out there, and they are around $300. Which is also drastically cheaper than anything else out there, the next cheapest actually useful detector out there that I know of is 10x that price.

defrost•about 1 hour ago
It's normal that radiation detectors are not everywhere.

It's also normal that radiation can be detected everywhere (subject to terms and conditions with respect to sensitivity and sensing time).

The least radioactive places are just above the middle of large bodies of freshwater.

Still detectable there, just from very stray land sources, drifting airborne sources, and plucky cosmic sources that made it through the atmosphere.