This is why the Sievert exists as a unit.
As a general rule, falling into a reactor pool is probably fine, as long as you don't reach the bottom. (But please don't try it.)
There's even an XKCD "What if" about it. https://what-if.xkcd.com/29/
> On August 31st, 2010, a diver was servicing the spent fuel pool at the Leibstadt nuclear reactor in Switzerland. He spotted an unidentified length of tubing on the bottom of the pool and radioed his supervisor to ask what to do. He was told to put it in his tool basket, which he did. Due to bubble noise in the pool, he didn’t hear his radiation alarm.
When the tool basket was lifted from the water, the room’s radiation alarms went off. The basket was dropped back in the water and the diver left the pool. The diver’s dosimeter badges showed that he’d received a higher-than-normal whole-body dose, and the dose in his right hand was extremely high.
The object turned out to be protective tubing from a radiation monitor in the reactor core, made highly radioactive by neutron flux. It had been accidentally sheared off while a capsule was being closed in 2006. It sank to a remote corner of the pool floor, where it sat unnoticed for four years.
The tubing was so radioactive that if he’d tucked it into a tool belt or shoulder bag, where it sat close to his body, he could’ve been killed. As it was, the water protected him, and only his hand—a body part more resistant to radiation than the delicate internal organs—received a heavy dose
I love this book. Randall is such a gifted artist
But just to be sure, I got in touch with a friend of mine who works at a research reactor, and asked him what he thought would happen to you if you tried to swim in their radiation containment pool.
“In our reactor?” He thought about it for a moment. “You’d die pretty quickly, before reaching the water, from gunshot wounds.”
> A CPM value means nothing without additional context
For CPM, what matters is "CPM of <WHAT>"
CPM just tells you the number of particle detection. It does not tell you the particle type (e.g. alpha, beta, gamma) nor the energy level (i.e. eV). Without context, it is meaningless.
As an example, I can confidently say you are getting over 100bn CPM right now. The reason it doesn't matter is that this is neutrinos and they're not interacting with you[0]. 1CPM or 1e20CPM, who cares. Conversely, 1 CPM can be deadly. You definitely don't want to be hit by a single ReV (10^27) proton (good luck producing that though). Context matters.
> This is why the Sievert exists as a unit.
Sievert is joule per kilogram. So energy divided per mass, much like pressure is force over area. But determining biological impact still takes interpretation. You have weight factors by particle types (e.g. alpha = 2x beta) and there is also weighting factor for internal/external dose and locations like soft tissue (e.g. higher weighting for dose at throat vs dose at hands).
This is why it is incredibly important to use caution when interpreting radiation values. If you don't have training in this it is incredibly easy to unknowingly make major errors. The little details can dramatically change the outcome. Context is critical.
I'm not here to tell you how to actually do the calculation (you'll need a lot more info), I'm here to tell you that it's not easy and you're likely doing it wrong. The experts are not dumb. You're just missing context and a first order approximation is nowhere near enough for an accurate conclusion. It's nuclear physics lol
It shouldn't need be said, but nuclear physics is, in fact, complicated.
I mean, if you actually had a neutrino detector that produced 10e10 CPM over your cross-section, then it would matter for you, because particle physicists would kidnap you to learn the secret :)
Sufficient to say that you'd be very popular, but in probably the least fun way possible.
Dumb question from a true non-expert:
So CPM varies with all those factors you mention, but wouldn't the site HP team know exactly what detector they used, the geometry, distance, etc.? They could convert to dose if they wanted, right?
Why report the ambiguous "300 CPM" instead of an actual dose estimate in mSv/μSv? Seems like that would be more useful for any medical team, any set of potential regulators or regulatory bodies as well as just general public understanding (drawing on my father's work here as he always emphasized the tension between "public fears radiation unnecessarily" and "industry safety protocols are inconsistent")
Follow-up: Is there any legitimate reason to report CPM instead of dose after a contamination event? Or does staying with CPM keep things conveniently vague? Because from my limited understanding, if they did a proper survey, they have everything needed to calculate dose.
The USNRC is currently not operating normally due to the government shutdown. Perhaps that has something to do with it.
Basically, the procedures for certain environments differ. If you want to gather dosage data, you use a dosimeter. If you want a binary Yes/No method of detecting contamination, you use a geiger counter and determine if the count rate is above a certain range (depending on background radiation and other factors).
The 300CPM metric just indicates whether they're clean or not after they've been scrubbed down. It doesn't measure the dose they took.
> Why report the ambiguous "300 CPM" instead of an actual dose estimate in mSv/μSv?
> Is there any legitimate reason to report CPM instead of dose after a contamination event?
To get the actual effective dosage you'll need a lot more information and calculations. The CPM can give you a decent estimate, if you already know context, but it is meaningless if you don't. So to an expert in that space it's a good quick estimate, but to an average person it isn't (even to above average people).
In context is also being used as a stepping stone for quick evaluation. They sent the guy to the hospital and he'll get a better estimate of dosage there. I'm sure they also were doing those calculations prior to sending him out. It may just be customary to use CPM units. That part I don't know. Here's the page they reference though[0] (there's only a single (xii) so easy to find).
[0] https://www.nrc.gov/reading-rm/doc-collections/cfr/part050/p...
[disclosure] I have training in nuclear physics, including in radiation dosages (I worked on developing shielding materials), but I have not worked on a reactor (though I've seen reactors and Cherenkov Radiation :) so the customs of the bureaucracy are beyond my wheelhouse. But from my experience I'm not surprised by this. I would expect a lot more documentation and accurate measurements are being passed through other channels.
In that context, I'd guess that the 300 CPM figure is just a signpost that says "we measured the worker to make sure that he was safe to release to a hospital."
Here, take METAR as an example. This is broadcast on open airwaves and every pilot can read this. Here's the latest one from KSFO[0]
METAR KSFO 260756Z 29004KT 10SM SCT012 BKN042 16/14 A3007 RMK AO2 SLP183 T01610139 401890133
Is the information intended to be given out to the public in a manner in which the general public can interpret? No. It's encoded lol. But you can hear that on the radio and if you're trained (could go to a public library to train yourself) and yeah it makes sense. It is specifically intended to be concise and communicate only the absolute minimum amount of necessary information.
For another example, look at arXiv. Is it public? Yes. Are the papers published there written for the general public? No. They are written for peers.
So yes, it is "public transparency", but not for transparency to people who aren't train in nuclear physics. (Which is what I previously said)
Don't confuse "public" with "for you"