What is an mrem?

Smiling stick figure: I try my best to confuse you! Confused stick figure: ????

Image by Tall Chris

The above question was inspired by this excellent article by Dr. James Conca in Forbes magazine, which includes the memorable and much-retweeted line: “I would take 50,000 mrem just to save my cat.” There are many helpful comparative examples in this piece, but after reading it I still had only a vague understanding of what ‘mrem’ meant.

My first thought was to check out the xkcd radiation chart, see how it fits in there, but that chart ranges from μSv (which I still read in my head as ‘USV’ rather than ‘microsieverts’) to Sv. No mrems (which I just discovered should be read ‘millirems’ and not ’em-rems’) in sight.

I’ve heard of sieverts. Mrems are new but I’ve heard of becquerels, though neither is featured in the chart I’ve been using as a demonstration of radiation-made-comprehensible for more than a year. A quick search brought grays, rads and curies into the mix too, none of which I even knew existed!

Revelation of the morning: I’ve been working in the nuclear industry for over 18 months and have no idea how radiation is even measured. Searching “rem sievert becquerel” led me to this article in Slate, which explains that the answer is both simpler and more complicated than I had realised.

Basically, rem are to sieverts what inches are to metres; the two words describe exactly the same thing, in this case “a measure of the potential harm caused by radiation in a sample of living tissue”, but one is an internationally standardised measurement and the other is not. The US uses rem, but the rest of the world, following the International System of Units (abbreviated to ‘SI’ via French), uses sieverts. No doubt everyone in the industry understands both though, the way Brits switch comfortably between litres and pints. (“A litre of your finest ale, please!” – not heard in UK pubs as much as you might expect.)

However, the amount of damage it will do to living things is just one way to measure radiation, and not always the most useful. On top of that, what that measurement actually means depends on multiple factors, from what type of radiation is involved to how long you were exposed to it. I don’t understand how all these factors come together yet, so a deeper look at this topic is for another post.

I will say that this demonstrates three communications challenges of nuclear energy. The first challenge is that radiation is hard to understand and even harder to explain. To effectively explain anything to do with nuclear you must maintain a delicate balance between over-simplifying and over-complicating a topic that feels very high-stakes to a lot of people.

There’s a scene in Godzilla where a character is at the location of an old nuclear accident. He holds some kind of radiation measurement device. It reads “0.0” and he declares the area safe. If I had watched this film before working in the industry I would have thought that made sense. Now I know that we are all exposed to a certain amount of radiation every day, and most of that radiation comes from natural sources:

Pie chart on sources of radiation

Image by WNA

The man-made uses of nuclear energy are almost exclusively to save and sustain life. The most moving responses to the Forbes article that inspired this post came from cancer survivors who owe their lives to radiotherapy. Those who call for an end to nuclear are often unaware of what a large part it plays in medicine or that the sunshine itself is radiation, but it can be hard to explain these connections effectively.

Second, not only is radiation itself a complicated subject, the scientific terms used to explain it are numerous and standardisation is not used by everyone. This doubles the amount of jargon a nuclear layperson has to untangle to reach even the lowest level of clarity. It is a communications difficulty with serious consequences related to such matters as forced evacuation and food safety, most recently illustrated in another of Conca’s articles on Fukushima.

Finally, by the time people have learned enough to be familiar with nuclear they have often forgotten what is common knowledge and what isn’t. Conca does a great job in this article, and I have already shown it to non-industry friends and family, but it would be even better with a line near the start to explain what ‘mrem’ is short for and what it measures before going on to put it in context. Those of us trying to get our heads around the technical side of this industry need all the help we can get, and the biggest advantage this industry has is the enthusiasm and knowledge of its people.

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One response to “What is an mrem?

  1. Pingback: The Nuclear Spectrum | Nuclear Layperson·

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