The tank sat more than a mile down in a working nickel mine, filled with the purest water a laboratory could make.<\/p>\n
It had been poured in to calibrate instruments before the switch to a more expensive liquid.<\/p>\n
Then something arrived that the tank was never built to catch.<\/p>\n
Not many, and not often.<\/p>\n
Over six months of quiet running, a handful of faint double flashes<\/strong> turned up in the record, and every one of them had started 150 miles away<\/strong>.<\/p>\n A reactor makes these particles by the enormous quantity while it runs.<\/p>\n They carry no charge, weigh almost nothing, and pass through rock as though the rock were not there.<\/p>\n Catching one is a matter of waiting for the rare occasion when a particle strikes a proton head on, which turns that proton into a neutron and throws out a positron.<\/p>\n The positron is the first flash.<\/p>\n It moves faster through water than light does through water, which is legal and produces a cone of blue light behind it, the optical equivalent of a sonic boom<\/strong>.<\/p>\n The neutron is the second flash, and it comes late.<\/p>\n It wanders for a moment, then gets captured by a hydrogen nucleus, which releases a gamma ray at 2.2 million electron volts.<\/p>\n Two flashes, microseconds apart, in that order.<\/p>\n That pairing is the signature, and it is the only thing separating a real event<\/strong> from background noise.<\/p>\n The detector sits under about 1.2 miles of rock.<\/p>\n That depth is not scenery. The overburden screens out the cosmic ray shower that would otherwise bury a signal this faint under millions of false coincidences every day.<\/p>\n Inside the cavern is an acrylic sphere about 40 feet across, watched by roughly 9,500 photomultiplier tubes.<\/p>\n It held around 860 tons<\/strong> of ultrapure water.<\/p>\n And it held that water for an unglamorous reason, because the instrument was being commissioned and the water was there to be characterized rather than to catch anything.<\/p>\n Which is the part worth sitting with.<\/p>\n The medium in the tank was a placeholder, and the team went looking for reactor antineutrinos in it because it was there<\/strong>.<\/p>\n The dataset came from 190 days of running in 2018.<\/p>\n Two independent analysis methods were used to pull the coincidences out, and the combined result reached 3.5 standard deviations, which is evidence rather than discovery.<\/p>\n The flux came from Ontario stations at Bruce, Darlington and Pickering.<\/p>\n The nearest of them sits 150 miles<\/strong> off, running the way it runs every day, doing nothing unusual at all.<\/p>\n The result went into a physics journal in early 2023.<\/p>\n One caveat on the counting. The per method candidate numbers circulating in secondary coverage do not reconcile with each other, and the published breakdown is not something a reader can easily check.<\/p>\n So treat the number of events as a handful<\/strong> rather than a figure, because that is how the collaboration itself describes it.<\/p>\n Water is a poor detector medium and always has been.<\/p>\n Scintillator, the oily liquid these experiments normally use, throws off far more light<\/strong> per interaction, which is why every previous reactor antineutrino result came from a tank full of it.<\/p>\n The usual fix for water is doping.<\/p>\n Add gadolinium and neutron capture becomes far easier to see, and most proposals for water based antineutrino detection assume you will have to.<\/p>\n This one did not.<\/p>\n A collaboration member put the reason plainly, saying it worked in a water detector because their neutron detection efficiency was high, which is an engineering statement rather than a physics one.<\/p>\n That distinction matters commercially.<\/p>\n An array of plain water tanks<\/a> costs a fraction of the same volume in scintillator, and water is available everywhere<\/strong>.<\/p>\n The obvious application is watching reactors you are not allowed inside.<\/p>\n An operating core emits antineutrinos continuously and cannot be run without emitting them, so a detector at distance is in principle a verification tool that no operator can spoof.<\/p>\n Distance remains the hard part.<\/p>\n Flux falls off with the square of range, so monitoring at any useful standoff means a far larger tank or far clearer water, and those are engineering problems with no cheap answer<\/strong>.<\/p>\n The tank itself has moved on.<\/p>\n It has since been filled with the scintillator it was always meant to hold, and the water phase is over, which makes this result a byproduct of a plumbing schedule.<\/p>\n Buried instruments keep doing this.<\/p>\n A telescope under a Japanese mountain was built to look for ghost particles<\/a> from dead stars, and the useful trick is nearly always the unplanned one<\/strong>.<\/p>\n The university summary<\/a> has the plain language version. The preprint<\/a> has the statistics.<\/p>\n","protected":false},"excerpt":{"rendered":" The tank sat more than a mile down in a working nickel mine, filled with the purest water a laboratory could make. It had been poured in to calibrate instruments before the switch to a more expensive liquid. Then something arrived that the tank was never built to catch. Not many, and not often. Over … Read more<\/a><\/p>\n","protected":false},"author":28,"featured_media":34243,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"rank_math_focus_keyword":"canadian nickel mine","rank_math_title":"A tank of ordinary water 1.2 miles under a Canadian nickel mine picked up reactor antineutrinos from 150 miles away, and the medium everybody assumed you needed for that costs a great deal more","rank_math_description":"A tank of ultrapure water buried in a Sudbury mine caught a single antineutrino from a nuclear reactor 150 miles away \u2014 the first time plain water ever di","footnotes":""},"categories":[8],"tags":[],"class_list":["post-34186","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-energy"],"_links":{"self":[{"href":"https:\/\/www.ecoportal.net\/en\/wp-json\/wp\/v2\/posts\/34186","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.ecoportal.net\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.ecoportal.net\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.ecoportal.net\/en\/wp-json\/wp\/v2\/users\/28"}],"replies":[{"embeddable":true,"href":"https:\/\/www.ecoportal.net\/en\/wp-json\/wp\/v2\/comments?post=34186"}],"version-history":[{"count":0,"href":"https:\/\/www.ecoportal.net\/en\/wp-json\/wp\/v2\/posts\/34186\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.ecoportal.net\/en\/wp-json\/wp\/v2\/media\/34243"}],"wp:attachment":[{"href":"https:\/\/www.ecoportal.net\/en\/wp-json\/wp\/v2\/media?parent=34186"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.ecoportal.net\/en\/wp-json\/wp\/v2\/categories?post=34186"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.ecoportal.net\/en\/wp-json\/wp\/v2\/tags?post=34186"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}What an antineutrino leaves behind when it finally hits something<\/h2>\n
Why the room was full of water at all<\/h2>\n
What the record says<\/h2>\n
Why so few is still the point<\/h2>\n
What a commissioning fill turned into<\/h2>\n