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Courtesy of Lawrence Berkeley National Laboratory geoneutrinos For a big view of inner , catch a few ... ingly opaque telescope. The Earth, though, is frustrat- www.sciencenews.org W feature “ . to partner antimatter the are as just counterpart, ter antimat- ’ are which trinos, Park.sity ofMarylandinCollege McDonough, a geochemist at the Univer William saystime,” real in Earth the of possibility of measuring the composition produced withintheplanet itself. by detecting “geoneutrinos” Earth’sthe interior illuminate to down, looking and telescope a taking are scientists earth Now cosmos. the in nos originating in the sun and elsewhere neutrino neutri- study to decades for telescopes used have Astrophysicists neutrinos. as known particles atomic sub- curious the using are they physics, astro from page a Borrowing innards. Earth’sthe probing for tool new a oped rocks, meteorites andthesun. near-surface in found elements the on rely chemistry internal Earth’s about Inferences image. ultrasound of kind a from studying seismic waves, which give planet’scomes the structure of internal Electrons and positrons have opposite have positrons and Electrons Earth,’ the inside from coming ‘antineutrinos than say to natural radioactivity insideEarth. ted todetectantineutrinosproduced by couldbe retrofit- Neutrino Observatory detectoratthe Sudbury the four-story ticles fromspacecalledneutrinos, Originally usedtodetectelusive par-

‘Geoneutrinos’ is just an easier word word easier an just is ‘Geoneutrinos’ Geoneutrinos are actually antineu- actually are Geoneutrinos the have we time, first the for “Now, devel- have geoscientists Recently, down to its outer core with a with core outer its to down kilometers 2,900 gaze might ere the Earth a crystal ball, you | —

geoneutrinos to light. Most knowledge ” McDonough says. McDonough ” — neutrinos neutrinos - - dynamics of geology that we see we that geology of dynamics the of all essentially for responsible from 30billion to 44billionkilowatts. power, the Earth puts out; estimates range troversy over how much heat, in terms of playersisn’tof known. There’s evencon- number a of one is or action heating the dominates decay radioactive whether But Manoa. at Hawaii of University the says John Learned, a particle physicist at spreading,” seafloor and continents ing Powering Earth tion intheEarth’s mantle. convec- driving turn, in and, Earth the up heating in play may elements these decayof the role crucial the about more mantle. Earth scientists are keen to learn and crust Earth’s the in and , of decay radioactive one oftheproposedexperiments. Sudbury,in tember Canada particle physicists at a conference in Sep- with developments new discussed tists ican Geophysical Union, and earth scien- Eos, the weekly newspaper of the Amer in October in experiments the of view over an gave Hawaii of University the ocean detector. deep- submersible mobile, a to Europe, and States United the Canada, in tors istry. These range from deep-mine detec better glimpse of the Earth’s inner chem- even an get to poised are experiments new proposed of array an Now 2005. in Japan in mine a inside deep detector a or may not bethesame particle. nos and antineutrinos, confusingly, may antineutrinos have and no charge. So neutri- neutrinos but charges, electrical Te ovcin n h mnl is mantle the in convection “The enurns rgnt fo the from originate Geoneutrinos McDonoughfrom colleagues two and in observed first were Geoneutrinos — the site of site the — mov - - - - the moltenouter core. stretches 2,900 kilometers from crust to vast,viscous, slowly layerchurning that mantle the in elements these of Earth’s dynamics is knowing the amount understanding to key But rock. of so or kilometers 30 top the crust, the in dant These elements are probably most abun- 40 to 60 percent of Earth’s interior heat. also from potassium, accounts for at least but thorium and uranium from mainly for theradioactive contribution. detectors could pin down better numbers sources. But the new suite of geoneutrino heat might have come from this or other conditions.” sipated it, depending on the atmospheric amount of kinetic energy and rapidly dis- large a with started have could we “or McDonough, saysit,” dissipated slowly large amount of kinetic energy, and we’ve radiated thisheatintospace. thermal energy. Over time, the Earth has became other,energy each kinetic their into slammed meteorites the As Earth. become to mass enough accreted tually even - blocks building planetary These meteorites. colliding by et’sformation plan- the from over left heat is sources sources drivingtheEarth’s engine?’ energy the are ‘What is, today question The sources. other from portion some coal, but some portion from nuclear and from electricity our of all get don’t “We It’s like the energy mix in homes, he says. sources.”energy of subset a or fuel tive radioac- entirely either is that for fuel the “and McDonough, says ride, nents conti the which upon plates geologic siae ae ht radioactivity, that are Estimates much how measure to difficult It’s a with out started have could “We energy possible other the Among the of movement the drives Energy January 17,January 2009

| By DianaSteele science news science —

| ” the

17 - feature | geoneutrinos

Like the better-known solar neutrinos, Converting SNO into SNO+ — which Ontario’s nuclear power plants are They came from Earth there’s a major source of radioactivity geoneutrinos can pass through thou- would detect the lower-energy geoneutri- far enough away to not overwhelm the Like its cousin the neutrino, a geoneutrino in a layer just above the core” — an idea (an antineutrino produced in Earth) can pass sands of miles of solid rock without being nos — means changing out the fluid that geoneutrino signal. “Certain problem- through Earth unimpeded and, researchers proposed early last year by Dutch and stopped or even deflected. That makes filled the detector. SNO operated from atic backgrounds from cosmic rays are hope, into detectors built to catch it. South African scientists writing in the them ideal for studying deep Earth — but 1999 to 2006 using heavy water — water even further reduced because we just South African Journal of Science. At the proposed SNO+ detector in Canada, also makes them very difficult to catch. with atoms of , heavy hydro- happen to be deeper underground than passing geoneutrinos would collide with Another scenario, which Stevenson gen — to snag solar neutrinos. Pending other, similar detectors,” Chen says. in fluid inside the detector (bottom ProtoP onn thinks is extremely unlikely but Learned Catching geoneutrinos final approval of funding, the detector With SNO+, he says, it will be possible right). Such a collision gives off a — acknowledges “would be quite cool,” is producing a flash of light — and changes the Neutronn One surefire way to catch some is to will be filled with a hydrocarbon-based to do some interesting things “with less into a (right). When the neutron that enough uranium exists in the core build a detector near a concentrated scintillation fluid, which, when a geoneu- background and improved precision.” approaches another proton, the two bond to that there is essentially a nuclear reactor source of antineutrinos. Conveniently, trino is caught, will luminesce and trig- SNO+ has an ambitious scientific create deuterium (a heavy version of hydro- Positront humming away down there. gen), producing a second flash of light. “You’ve the uranium and other radioactive ele- ger the detector. agenda that includes better understand- got a flash associated with the positron pro- San Diego–based independent scien- ments used in a nuclear reactor provide The fluid is a common, mass-produced ing the fundamental nature of neutrinos. duction, and 200 microseconds later you have tist J. Marvin Herndon first proposed Geoneutrino a flood of these ghostly particles. petrochemical called linear alkylben- One goal is to pin down the mass of the another flash,” says University of Maryland, such a core reactor in 1993. Although College Park geochemist William McDonough. Proton That’s why the first geoneutrino detec- zene, or LAB, used to make clear deter- neutrino — a quantity even more elu- “And you say, ‘Eureka! I’ve got an antineutrino not widely believed, his hypothesis tor was built near a cluster of reactors in gents, like liquid hand soap. It’s less toxic sive than the neutrino itself. Another that’s come in.’ ” would explain some puzzling observa- Japan, with an aim to further character- than most chemical liquid . is to determine whether neutrinos and tions, such as an excess of an isotope of ize antineutrinos. Consequently, parti- “It produces a lot of light, and it’s very antineutrinos are the same particle — the INNER EARTH SNO+ helium emitted from volcanoes, Learned cles from the reactors swamped those transparent, but it’s a safer ,” lack of charge makes it difficult to tell. points out. produced by naturally occurring ura- says SNO+ director Mark Chen. “It’s That question “connects to our under- Hanohano would be able to tell fairly Inner Core nium in the crust and mantle. much easier to use it, especially in a set- standing of the early universe and might Outer Core quickly whether such a reactor exists at Nonetheless, in 2005, this experiment, ting where we are taking a thousand tons inform us about why … we see matter in Mantle all, Learned reported last May at a neu- called KamLAND (short for Kamioka Liq- of it into an active mine.” the universe but much less antimatter,” Crust trino symposium in New Zealand. uid Scintillator Anti-), The detector is a four-story acrylic Chen says. For all their promise, these geoneu- provided the first glimpse of geoneutrinos sphere surrounded by electronic eyes trino detectors won’t be able to unearth and a first approximation of uranium and that scan the fluid for flashes of light char- Mantle signature the whole picture of Earth’s interior. thorium’s contribution to the Earth’s heat. acteristic of geoneutrinos’ presence. SNO+ is the furthest along of the wouldn’t begin for at least several years. das in astrophysics and particle physics Stevenson points out that all the Unfortunately, because the number of Chen, a particle astrophysicist at up-and-coming geoneutrino experi- These detectors would be, for the most as well as earth science. geoneutrino detectors proposed share geoneutrinos was so small, the estimated Queens University in Kingston, Canada, ments. Other detectors under discus- part, counting geoneutrinos that origi- With funding, Hanohano could be built a shortcoming: They can’t detect the heat contribution, in terms of power, had hopes SNO+ will start up in late 2010. sion include one in the Homestake mine nate in the Earth’s crust, where thorium within about two years, McDonough geoneutrinos coming from radioactive a range of 19 billion to 60 billion kilowatts; It should catch about 50 geoneutrinos in South Dakota and a large detector to and uranium are concentrated. Looking estimates. Preliminary design stud- potassium-40. These geoneutrinos have consistent with but not more precise than a year, considerably more than either be built in Europe, possibly in Finland. close to the crust is like having your eye ies for Hanohano are underway, and too little energy to trigger the detector. previous estimates. KamLAND or Borexino. The longer Startup and operating costs are esti- close to a bright flashlight. McDonough is hoping for another $5 mil- “So there is one part of the expected Since then, the geoneutrino detector SNO+ runs, the better the picture it will mated to be on the order of hundreds To get a better idea of what’s going lion of seed money to continue design. heat production that we cannot measure, Borexino, located in an Italian mine, has get of the inner Earth. of millions of dollars, and construction on in the mantle — a dim and more dis- But to construct and deploy Hanohano and haven’t figured out how to measure,” come online. And new experiments are tant flashlight — requires a geoneutrino and to keep it running for 10 years could he says. And although only a tiny fraction on the horizon, though it may be at least detector situated in a place where the cost around $200 million, he estimates. of potassium-40 is actually radioactive, two years before the first of the next gen- crust is only a few kilometers thick, like That’s expensive, but it’s about a fac- and most of it has already decayed over eration of detectors starts up. at the bottom of the ocean. tor of 10 less expensive than sending a Earth’s 4.6-billion-year history, potas- The SNO+, or Sudbury Neutrino Obser- McDonough and his colleagues are spacecraft to another planet, points out sium still contribute up to 20 percent of

vatory Plus, would sit two kilometers lat; detector photo proposing a 10,000-ton submersible David Stevenson, a planetary physicist at the radioactive heat, Stevenson says. b underground in the Creighton nickel detector they have named “Hanohano” the California Institute of Technology in “But if you go back in time, potas-

mine near Sudbury, Ontario. SNO+ would . koren (Hawaiian for “magnificent”), for the Pasadena, who is not directly involved in sium-40 becomes increasingly impor- j y piggyback on and use the same detector as b Hawaii Anti-Neutrino Observatory. the geoneutrino experiments. And “it’s tant,” he adds. “And that’s why, if you a highly successful solar neutrino proj- Hanohano would be about 10 times inconceivable to me that we could get the want to reconstruct the history of the ect called the Sudbury Neutrino Obser- the size of the SNO+ detector and filled same information with the accuracy we Earth, you would like to know how much vatory, which played an important role with the same scintillator fluid. It would desire by any other method,” he says. potassium you had.” s in solving a long-standing conundrum. be towed out to sea on a barge and sunk, He also hopes for the unexpected. oration; top: graphic

Researchers had detected fewer neutri- b anchored about 4,000 meters deep and “I’ve learned as a planetary scientist, Diana Steele is a freelance science writer nos coming from the sun than expected. about 90 m from the bottom. After catch- that when you go to a planet, you actu- based in Ohio.

SNO showed that neutrinos have a tiny + colla ing neutrinos for a year or two, it could ally discover things, you are surprised,” bit of mass and are shape-shifters, turn- SNO be serviced and redeployed elsewhere. he says. “And in the case of the neutri- Explore more age: P ing from a detectable form into another, A physicist boats in water surrounding Canada’s SNO detector, which is filled with Like SNO+, Hanohano will be a multi- nos, you may be surprised. You may be ss Visit the SNO+ website at

undetectable one. heavy water to detect neutrinos. A new fluid will be used to detect geoneutrinos. LEFT m ISTOCKPHOTO / A lesVeluscek fro courtesy of b erkeley la ; E arth i m age faceted experiment, with research agen- surprised, for example, to discover that snoplus.phy.queensu.ca/

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