Borexino experiment detects geo-neutrinos

Mar 16, 2010 by Lin Edwards report
View of the Borexino "Stainless Steel Sphere" (SSS) from from the "Water Tank", before cables and PMTs installation.

(PhysOrg.com) -- The Borexino collaboration of about 80 scientists from six countries, who have been working with a detector buried 1.5 km beneath the Gran Sasso mountain near l'Aquila in Italy have detected geo-neutrinos, which are electron antineutrinos created by radioactive decays inside the Earth's mantle and crust.

Neutrinos are extremely inert, chargeless, fundamental particles of almost zero mass that are emitted by the Sun and created by cosmic rays arriving on Earth. They have been the subject of research for many years, and studies of them have increased our knowledge of the physics of the Sun.

Geo-neutrinos are electron antineutrinos that are created inside the Earth when of elements such as thorium and uranium decay. Measurements of the flux of geo-neutrinos may help scientists understand how much of the Earth’s internal heat is caused by decays, and this could increase our understanding of processes arising from convection currents within the mantle that affect movements of the and .

Detecting any kind of neutrino is difficult since huge volumes of detector material must be used, and the detector must be deep underground to avoid interference from . Solar and atmospheric neutrinos can be studied by their interactions with heavy water nuclei, but signals from geo-neutrinos would be swamped by the radioactivity in the heavy water, and so the researchers used materials instead. A geo-neutrino passing through the hydrocarbon can collide with a proton to create a neutron and positron, and this collision generates a dual gamma-ray emission and small burst of detectable light.

Geo-neutrinos were first detected by Japanese researchers in 2005 during a project known as the KamLAND experiment. Their detector was in a mine one kilometer underground, and was located close to several nuclear reactors, since the team was studying reactor antineutrinos. They had to separate the geo-neutrino signals from the stronger antineutrino emissions from the reactors.

In the current two-year study, named the Borexino experiment, there were no strong background signals because the nearest nuclear reactor is hundreds of kilometers away. The detector, photomultiplier tubes and liquids used were also specifically chosen because of their low levels of intrinsic radioactivity.

The aim of the Borexino experiment was to detect low-energy solar in a detector comprising 300 tonnes of pseudocumene, a doped hydrocarbon fluid, encased inside a nylon sphere. The sphere was encased inside a stainless steel sphere containing 1,000 tonnes of pseudocumene and lined with 2,200 photo-sensors capable of detecting single photons of light. The steel sphere was suspended in an 18 meter diameter steel tank containing 2,400 tonnes of highly purified water.

During the experiment, 9.9 geo-neutrino events were detected, with uncertainties of +4.1 and -3.4. One of the researchers, Professor Gianpaolo Bellini from the University of Milan, said the results rule out the hypothesis that most of the planet’s internal heat is generated by a uranium-fuelled nuclear geo-reactor in the Earth’s core.

Several larger experiments are being planned, including one in which a 10,000 tonne detector would be built on the bottom of the Pacific Ocean, where the Earth’s crust is very thin. Professor Bellini said the experiment marks the start of a new era in the study of Earth’s interior.

This video is not supported by your browser at this time.
Borexino vessel installation (View from the Borexino CCD cameras)


Explore further: The unifying framework of symmetry reveals properties of a broad range of physical systems

More information:
-- The group's paper will be published in the Europhysics Letters B and is available on Arxiv website.
-- Borexino Experiment: borex.lngs.infn.it/

Related Stories

New results confirm standard neutrino theory

Feb 16, 2010

(PhysOrg.com) -- In its search for a better understanding of the mysterious neutrinos, a group of experimenters at DOE’s Fermi National Accelerator Laboratory has announced results that confirm the theory ...

CERN neutrino project on target

Aug 16, 2005

Scientists at CERN announced the completion of the target assembly for the CERN neutrinos to Gran Sasso project, CNGS. On schedule for start-up in May 2006, CNGS will send a beam of neutrinos through the Earth to the Gran ...

Green light for the neutrino beam from Cern to Gran Sasso

Sep 12, 2006

The delivery of the neutrino beam (Cngs) from Cern and the beginning of a new generation of experiments were officially celebrated today at Infn (Italian National Institute for Nuclear Physics) National Laboratories of Gran ...

Probing Question: What is a neutrino?

Oct 16, 2007

Neutrinos are tiny -- really, really tiny -- particles of matter. They are so small, in fact, that they pass between, and even through, atoms without interacting at all. Neutrinos are everywhere: If you start ...

Recommended for you

What time is it in the universe?

Aug 29, 2014

Flavor Flav knows what time it is. At least he does for Flavor Flav. Even with all his moving and accelerating, with the planet, the solar system, getting on planes, taking elevators, and perhaps even some ...

Watching the structure of glass under pressure

Aug 28, 2014

Glass has many applications that call for different properties, such as resistance to thermal shock or to chemically harsh environments. Glassmakers commonly use additives such as boron oxide to tweak these ...

Inter-dependent networks stress test

Aug 28, 2014

Energy production systems are good examples of complex systems. Their infrastructure equipment requires ancillary sub-systems structured like a network—including water for cooling, transport to supply fuel, and ICT systems ...

Explainer: How does our sun shine?

Aug 28, 2014

What makes our sun shine has been a mystery for most of human history. Given our sun is a star and stars are suns, explaining the source of the sun's energy would help us understand why stars shine. ...

User comments : 3

Adjust slider to filter visible comments by rank

Display comments: newest first

El_Nose
not rated yet Mar 16, 2010
they are going to build a detector on the bottom of the pacific -- or are they going to build a reactor and let it sink to the bottom of the pacific -- and where in th epacific are they going to drop it.
dirk_bruere
1 / 5 (1) Mar 16, 2010
9.9 events, +4.1, -3.4
And these guys sneer at the stats thrown up in Psi expts!
frajo
5 / 5 (1) Mar 17, 2010
9.9 events, +4.1, -3.4
And these guys sneer at the stats thrown up in Psi expts!
It's not the same.
While the Psi people claim to have positively proven something unphysical with numbers like that the outcome of this experiment is the falsification of a certain hypothesis.