In a working lifetime of fieldwork, the radiation dose that matters almost never comes from standing next to a rock. It comes, in this order:
| 1 | Radon in an unventilated working. Adits, cellars, caves, shafts, old stopes. It accumulates where air does not move, it is invisible to every sensor in your pocket, and it is the one genuine occupational risk in this trade. Ventilation is the whole answer, and a cheap passive test badge is the whole measurement. |
| 2 | Dust, hands and food. Getting it inside you is worse than standing beside it, by a long way. Bag samples, do not pocket them, and wash before you eat. This costs nothing and it is the protection people skip. |
| 3 | Carrying a hot sample home. An hour at an outcrop is nothing. The same specimen on a desk for a year is not nothing. Store the interesting ones somewhere that is not where you sleep. |
| 4 | External gamma from the outcrop itself. Last, and usually a long way last, out in the open air. |
When there is something to manage, three things always work and nothing else does: less time, more distance, something in between. Distance is the cheap one — twice as far is a quarter of the dose rate, so stepping back two paces does more than anything you can buy.
This is the part that actually protects people, and it is the only part that can warn you before you are standing in something. It reads the mapped unit under your feet by itself — nothing to cover, nothing to calibrate, nothing to switch on. Correct it below if the map is wrong, which on old sheets it often is.
This is the least useful thing on the page, and it is here last for that reason. It cannot run in the background — no app can, web or native; both iOS and Android stop the camera the moment it leaves the screen — so it has to be open, on screen, lens fully covered. While it is, the screen stays awake, it clicks once per particle like any survey meter so you hear it quicken as you walk, and it warns in three stages: rising while you are still approaching, then raised, then high.
And it is not a dosimeter. A phone sensor only starts to see anything at rates far above natural background, so silence here is not safety — it means nothing dramatic is happening, not that the ground is clean. For real monitoring, pair a Bluetooth counter below; that one is an instrument, and this page will log and calibrate against it.
Four things make this work despite the browser.
① It takes manual control of the sensor where the phone allows it — longest exposure, highest ISO,
fixed focus and white balance — which is what actually raises sensitivity.
② It builds a separate statistical model for every single pixel, so hot pixels and fixed-pattern
noise are subtracted rather than counted. This is the single biggest gain.
③ It looks for events in time, not brightness in space — a hit appears in one frame only, and
temporal outliers survive the denoising that kills spatial ones.
④ It requires particle-shaped clusters of one to six touching pixels and rejects anything larger,
which throws out light leaks and compression artefacts.
Then it stops guessing and does statistics: counts are Poisson, so it reports how many standard
deviations above your own background you are. Below 3σ it will not claim anything.
The browser is a weak sensor and an excellent logger. Pair a proper counter over Bluetooth or plug one in over USB, and the phone stops guessing — you get calibrated numbers, logged to depth, position and time, exported with everything else. Chrome on Android supports both. Safari on iPhone supports neither, so on an iPhone use the manual entry below.
It reads the common serial-over-Bluetooth profile that most consumer counters use, and pulls any number followed by CPS, CPM, µSv/h or uSv out of the stream. If your device speaks something else, the raw feed is shown above so the mapping can be added — send me a few lines of it.
Do this once, next to anyone who has a calibrated instrument. Count with the camera for two minutes while they read their meter, enter their number, and from then on the camera reports an approximate dose rate with an honest error bar instead of a bare count. Two points — your background and this one — define the scale.
If you carry a scintillometer, a Geiger counter or a personal dosimeter, log its readings here. These are the numbers that count — the ones above are not.
Radon accumulates in adits, caves, cellars and any poorly ventilated working — and it is the exposure that most often matters to a geologist, far more than handling a specimen. It is invisible, odourless, and it concentrates where air does not move.
Held by you, not an employer. Exportable, portable between jobs, and it does not disappear when a contract ends. No geologist has ever had this.
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