What Is An Antineutrino Map Good For?

Here’s how I try to figure out news about scientific advances. This example relates both to nuclear science and to nonproliferation, so it’s of interest, and one might think I could interpret it easily. Maybe not so much, if the information isn’t there.

A friend sent me this article. Antineutrinos – oh noes! What I know about them is that they go through matter. Plus beloved of physicists for the way they fit (or not) into elaborate schemes of particles I long ago gave up keeping track of. Heat produced in planet’s interior? Okay. But the map is of antineutrinos (emission? absorption?), and what do they have to do with heat? Hm…nuclear reactors, the sun and radioactive material in the earth…okay, but the article never really tells us what antineutrinos are good for.

I  couldn’t find the journal cited, “Scientific,” and the article had no link to the original article. Ah, here we are, found by searching the authors’ names: Scientific Reports, actually a part of the famous scientific journal Nature, complete with all the maps of antineutrino emissions.

The only things that were obvious to me on the maps were dots that seemed to correlate with nuclear reactor locations, although there were similar dots all over Antarctica, as well. Radioactive sources for experiments? There was a reactor there from 1962 to 1972, apparently not now. Plus a large area under the Tibetan Plateau. The maps show “energy bins,” which means ranges of antineutrino energies, each range giving a different map and showing something about the source of the antineutrinos, but what is not clear.

During the week, another popular account came across my Twitter feed. The map shows reactors and might identify clandestine reactors. Since I’ve been thinking a lot about Iran lately, it had occurred to me that this would be one more way to identify a clandestine program. Couldn’t hide those reactor antineutrinos under a mountain. Then some friends shared this, from 2006. Looks like the idea of detecting reactors with antineutrinos has been around for a while.

But detectors are as big as a small office building, and have to be a mile deep. Mmm-kay! The fact that two exist and have made these maps is progress. One of the authors is a geologist and particularly excited about what the maps tell us about the deep earth, but he doesn’t say much about what that is. Fuel budget? Mmm-kay!

At that point, I’m wondering if the natural radioactive isotopes in the deep earth separate out, and whether we know what phases they separate into. We know some things about deep earth structure, and minerals do separate out or arrive already separated with downward plate motion. Do they separate enough to make sharp pictures of structure. All the maps look pretty blurry.

The original article says that the maps are available to all, so others can use them for their analyses. The geology application still isn’t clear, although the author who is a geologist is enthusiastic about it. My take is that the total amounts of heat-producing radionuclides in the earth is not well known, and the antineutrino measurements help to bound those amounts. That heat is believed to be the driver for plate movements and convective activity within the earth, so knowing more about how it is generated is important. It looks like there is more to be done, and this is only a start. With the maps generally available, we should be hearing more about this.

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