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0 pointsarthurcolle5mo ago0 comments

Thank you for the followup (familiar with the XKCD)

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.

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godelski5mo ago

  > Why report the ambiguous "300 CPM" instead of an actual dose estimate in mSv/μSv?

It is a technical document. It is meant to communicate between experts, not to the public.

  > Is there any legitimate reason to report CPM instead of dose after a contamination event?

It's not nefarious, it is the measurement that they had. CPM is an easier measurement to get. And keep in mind that these notices are just a small part of the communication going on. They're meant to be brief.

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.

grey4135mo ago

Looking at these bulletins, they appear to be quick summaries of pretty much any nuclear related incident that happens in the US, no matter how minor. I would assume that these are mostly intended for public transparency, and as for a quick reference point for regulatory action. Introductory slide on a PowerPoint sort of material.

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."

godelski5mo ago

I think you're over interpreting. Publicly available doesn't mean "for the general public"

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 this public? Yes

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"

[0] https://aviationweather.gov/data/metar/?ids=KSFO

beeflet5mo ago

>Is there any legitimate reason to report CPM instead of dose after a contamination event?

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.

LeoPanthera5mo ago

I would imagine the on-site team would know, yes. I don't know why the report only gives a measurement in CPM, but just because the person was sent off-site doesn't mean the levels were dangerous. Thresholds at nuclear facilities tend to be very low for safety.

The USNRC is currently not operating normally due to the government shutdown. Perhaps that has something to do with it.

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godelski5mo ago

  > Why report the ambiguous "300 CPM" instead of an actual dose estimate in mSv/μSv?

It is a technical document. It is meant to communicate between experts, not to the public.

  > Is there any legitimate reason to report CPM instead of dose after a contamination event?

[0] https://www.nrc.gov/reading-rm/doc-collections/cfr/part050/p...

grey4135mo ago

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."

godelski5mo ago

I think you're over interpreting. Publicly available doesn't mean "for the general public"

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 this public? Yes

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"

[0] https://aviationweather.gov/data/metar/?ids=KSFO

beeflet5mo ago

>Is there any legitimate reason to report CPM instead of dose after a contamination event?

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.

LeoPanthera5mo ago

The USNRC is currently not operating normally due to the government shutdown. Perhaps that has something to do with it.

j / k navigate · click thread line to collapse