By ConwL

2019-04-15 13:55:31 8 Comments

I am curious about how much radiation do experimental nuclear physics researchers/students suffer in nowadays research environment. I know this may be a dumb question, but I have can found answer nowhere.


@J. Manuel 2019-04-15 15:02:13

In 1990 de International Commission on Radiological Protection (ICRP) recommended the following radiation dose limits to workers and to the general public:

  • 100 mSv in 5 years of effective dose for workers (maximum 50 mSv in any single year, average 20 mSv per year) of any branch, including medicine, industry, research, etc.
  • 1 mSv per year to the general members of the public;

These recommendations have been implemented with minor changes into regulations in most countries, including the US and the European countries.

Radiations workers are obliged to use a personal dosimeter to record the amount of radiation they are exposed to. In my particular experience, most of workers don’t get more that 5 mSv in a single year, unless a radiation incident has occur, that’s why values higher than that used to be investigated. In fact I would investigate any reading in a particular workers dosimeter above the natural background.

The 1990 recommendations of ICRP have been recently updated, with almost no change to these values.

@Loong 2019-04-15 16:28:23

According to the German Federal Office for Radiation Protection (BfS), the average occupational radiation exposure (in mSv per year) in the group “research” (19489 persons in 2016) in the last years was as follows.

0.37 (2007)
0.41 (2008)
0.36 (2009)
0.35 (2010)
0.33 (2011)
0.35 (2012)
0.30 (2013)
0.28 (2014)
0.26 (2015)
0.27 (2016)

These values are generally lower than in other groups (medicine, industry, nuclear, flight personnel, or radon workplace).

Note that the dose limit for workers of category A is an effective dose of 20 mSv per year, averaged over defined 5 year periods (100 mSv in 5 years), with the further provision that the effective dose must not exceed 50 mSv in any single year. Nevertheless, the radiation exposure should be as low as reasonably achievable.

@craq 2019-04-16 00:07:51

Do they have figures for the maximum (or a high percentile)? That might be more relevant for safety purposes than the average. Also, a link would be nice.

@jwenting 2019-04-16 08:21:49

@craq the maximum (even the high percentile) can be seriously affected by a single high accidental exposure due to the limited number of individuals and small number of events.

@craq 2019-04-17 04:59:07

@jwenting aren't most safety analyses based around the statistics of rare events? As an analogy, the average deceleration force of passengers in a landing aeroplane will be dominated by those who land safely. It doesn't really tell us anything about how often planes crash. (I should add that both planes and scientific labs have very good safety records.)

@jwenting 2019-04-17 05:04:41

@craq Depends on what you're looking to measure. What you in cases like this really want is to ensure that no more than a (tbd) very low percentage of exposures will cause permanent damage to human beings. The actual magnitude of the exposures beyond that cutoff point are then largely irrelevant.

@Ben Crowell 2019-04-15 14:18:59

In the US, the NRC limits whole-body occupational exposure to 5 rem/year. Specific labs or employers may impose much lower limits on their workers. For comparison, a CT scan is about 1 rem, and natural background is about 0.2-0.7 rem. There is not really any typical dose for people working on experiments. Depending on what their work is and how the experiment is set up, someone could have a dose that is not measurably higher than background. Or their measured dose could mount to the level where they're warned that they're nearing their limit for the year, in which case they might have to find someone else to whom to hand off the task that's causing all the exposure.

@Jon Custer 2019-04-15 14:35:36

For me to be authorized to receive 5 rem/year would require the signature of the Secretary of Energy. My current authorization is not to exceed 100 mrem/yr. Over the 30 odd years I've worked on ion accelerators and pulsed power I think I exceeded background once (and it wasn't quite clear how - likely a TLD read error), so something like 20 mrem above background total over those 30 years.

@Ben Crowell 2019-04-15 14:58:11

@JonCuster: Thanks for the comment. I've edited to say that specific labs have lower limits than the NRC's regulatory limit. I'm curious about your lab's rules, though. Can they even measure background well enough to know if your exposure is above background by an amount as tiny as 20 mrem? At some point with these very small doses, it gets silly, e.g., you could go over your limit by mistakenly taking your badge home to your house that has radon in it.

@Nuclear Wang 2019-04-15 16:25:39

As another anecdote, I used to work at a DoE lab where basically any detectable amount above background was too much. At some point, it does get silly - I remember hearing stories about painstakingly remediating an area for an outdoor patio to eat lunch, despite the fact that someone could get a higher radiation dose by eating a banana on the finished patio.

@Jon Custer 2019-04-15 18:00:46

The typical 'errors' are by mistakenly taking a TLD through airport security (our folks have tables of expected exposures at different airports), or folks having nuclear medicine tests and wearing their badges too soon afterwards. As for 'background', they apply a bit of a fudge factor to account for some variation in background and a bit of margin. Actually reading the TLDs has a lot of data analysis behind it. A consistent 20 mrem above background would be considered significant. Biggest wild card in my departments has been getting the right neutron energy spectrum.

@Jon Custer 2019-04-15 18:24:46

As a further data point for those wondering what 5 rem is, my wife received 3000 rem (localized) during cancer treatment. Full body exposure, that would be a quick death. And that was in a dose reduction trial - the normal dose would be 6000 rem (localized).

@wizzwizz4 2019-04-15 20:33:02

@JonCuster That is, according to Randal Munroe, probably enough to kill a horse. (They didn't let him test this.)

@Jon Custer 2019-04-15 20:51:48

@wizzwizz4 - indeed. Just shows you the gulf between allowed occupational exposure and necessary medical treatments. And why going through radiation treatments is a really hard thing to do.

@allo 2019-04-16 13:37:35

Shouldn't the unit for the background radiation be rem/year?

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