You can build a cheap and heavily shielded ionization or Geiger system, or a more expensive spectrometry system. In this case, Ruthenium is a condensed solid, and would be ideally detected by an air particle sampling system that continuously concentrates air onto a filter, and measures emitted radiation with a detector capable of resolving very narrow peaks in the spectrum. I would pick up Knoll’s book on detector systems if you are really interested in building such a system.

I was at Trinity many years ago, and some peeps had a portable spectrometer that they used to measure the trace amounts of plutonium (or maybe its decay products) left in the sand and glass.

See this article as an example:

http://www.fourmilab.ch/documents/cosmic/

It's easy to record something cheaply, but as other commenters already wrote, it's hard to recognize what causes the "average" counts in any time period. The author of the article measured the variations dependent of the time of day 17 years ago and it seems he wasn't able to explain them since. At the time he used a 486 machine and a Geiger counter connected to the serial port, today something like Raspberry Pi would be more convenient for the computer side and less power hungry.

He published what he recorded, so before doing anything, check his data to see an example of the results that you'd have in such a setup.

Digital camera sensors can actually be used to detect gamma particles. There's a legitimate app you can use on some android phones that can act as a relatively accurate cheap radiation detector. It requires you to tape over your camera lens with a piece of electrical tape and then to calibrate your phone in an area with only normal background radiation.

The app is https://play.google.com/store/apps/details?id=com.rdklein.ra....

You can't reliably do it. This type of thinking has led many to invent conspiracy theories based on the natural background radiation that we and everyone on planet Earth are awash in. Background radiation also varies significantly unless you use very long averaging time frames.

Get a second hand (army surplus is a good source) Geiger counter with an instrumentation output. You may have to do some conversion if your current computer does not do RS232.

The problem is differentiation from background.

A release from NK or Russia, by the time it hits your Geiger counter, will likely be so low that it will be lost in the noise of background radiation. And local sources (such as radon gas) would mask anything but significant nearby events.

The reason why France identified the release is because their detectors can determine different radioisotopes.

It's a little like the difference between a photovoltaic cell and a camera. Your Geiger counter can tell when the "light's on" (presence of radiation) but it takes a different instrument to determine that it's Ruthenium 106.

GGP spoke about general levels, not specific elements, and yes, you are 100% right, a Geiger counter is a pretty blunt instrument.

Even after Chernobyl and Fukushima, outside of the impacted area, there really wasn't any detectable increase in background.

You're much more likely to get an increase in background going into your basement (because of Radon daughters) than from an nuclear release halfway around the planet.

I did some research on this. James Mahaffey who is a nuclear engineer talks about this a bit in his book 'Atomic Adventures.': "Professional-grade Geiger counters, such as the Eberline E-120, are available as surplus, but they are usually sold without the probe assemble, which is what wears out when in constant use in a nuclear power facility. The probe is the expensive part, and installation of a new one will require calibration."

In Japan they sell hand-held radiation detectors in electronics stores like Bic and Yodobashi (think Best Buy on steroids). They're in the little section with the first aid kits and earthquake alarms.

I know Yodobashi ships some items internationally, so it might be worth checking both of their web sites. They're just hanging on the wall in blister packs, so they appear to be cheap commodity items. Maybe $50 is my guess. I never looked at the tags.

There are smartphone add-ons available that you can try.

For example the FTLAB FSG-001. This is a devices that outputs the result to your headphone jack.

The HN comments (https://news.ycombinator.com/item?id=12191456) don't inspire much confidence regarding the error rate.