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Giant Neutrino Detector, 2km Underground
yulek writes: "Yesterday's APOD ran an incredible photograph from the recently completed SNO Detector, a giant geodesic neutrino detector buried 2km (!) underground near Kingston Ontario. Neutrinos are some of the most bizarre subatomic particles, having virtually no mass and able to 'pass through matter like smoke.' The SNO Detecter is definitely one of the coolest and most ambitious experiments i've seen in recent years."
While I was there I noticed that the CERN neutrino beam went right down the main street of the nearby town of St. Genis in France and on into the Jura Mountains. I wonder if the townspeople in St. Genis would feel comfortable knowing they were being irradiated, even if they understood the particles wouldn't interact.
You see, while the detector that's the subject of this story detects neutrinos of cosmic origin, you can also make them artificially, and with controlled energies and other desirable characteristics, by shooting a high energy particle beam into one end of a long pile of dirt.
The particles shower but are then absorbed by the dirt - except for the neutrinos produced by the showers. Enough dirt, and whatever comes out the other end is pretty much pure neutrino beam.
If you put in an intermediate amount of shielding, you get a mix of muons and neutrinos.
The way you detect these artificial particle beams is typically with packs filled with photographic film sealed in a dark chamber. Just beam it for a while and every zillionth particle will leave a little speck on some of the film.
Ever heard of neutrino oscillations? They proposed the theory to explain the lack of expected neutrino flux in one of the earlier underground neutrino detectors. It takes 10,000 years for heat from the center of the Sun to convect to the surface before it can shine directly on the earth, but neutrinos radiate from the core to the earth in 8 minutes because they don't interact.
Only problem is, we weren't getting many neutrinos. The first suspicion was that the Sun had begun to die but the cooling part of the interior hadn't reach the surface yet - that is, we hadn't visibly received the bad news but had found out ahead of time with the neutrino detector.
If neutrinos change identities into types that a given sensor is not sensitive to, though, it would explain this. But for this to be the case, the neutrino would have to have a very small, but non-zero mass. It's been the work of decades to try to measure this mass.
In the particle beam at CERN they would measure the neutrino flux at different points along the beam to see if they got more and less intense as they oscillated between electron, muon and tau neutrinos.
Enjoy!
Mike
-- Could you use my software consulting serv
Neutrinos are the least studied elementary particles because of they interact very, very rarely. It's no joke that they can "pass through matter like smoke", as the story said. The typical neutrino can pass through several light-years of lead without interacting once. The only reason they can be detected at all is that a tremendous number of them pass through the Earth every second. I forget the exact number, but it's something like trillions per square meter per second. Even so, a decector the size of SNO will only see a few hundred events per second. On the other hand, this is also why neutrino experiments like SNO or Super-K are so exciting for astrophysicists. The light that we see from the sun has all come from the surface, photons produced in the core can't make it through the sun to get to the earth. Neutrinos produced in the core can easily penetrate the whole of the sun and reach the earth. As a result, a very good neutrino telescope can look directly into the core of the sun. There are a berzerk number of other reasons to be excited about neutrino experiments, see the Particle Adventure for more.
Oh, and if you thought the SNO picture was cool, check out some of the photos on the Super-K, they've pretty much won the best-looking physics experiment ever contest.
That SNO is the Sudbury Neutrino Observatory and that Sudbury Ontario is not even close to Kingston Ontario. The confusion comes about from the fact that much of the research being done at SNO is being done by professors from Queens University, located in Kingston.
It is in Sudbury's Creighton mine. Technically, it is in a suburb of Sudbury. Despite working for the project, I don't recall it's name. Just outside Lively I think... And although Queens is a major participant, Universities all over North America are contributing to one degree of another. IIRC there was quite a bit of U.S. hardware lying around, the University of Pennsylvania provided computer hardware, Oxford did some heavy computer programming during the engineering phase, they may have gone beyond. Laurentian in Sudbury provided labour and communications, that was my 'in'.
It is an active nickel mine. The bulk of the mining was ocurring at the 7200/7400 ft level, it may have gone deeper, or fluctuations in Nickel prices may have moved them to another drift. The observatory is at 6800 ft.
The observatory is a barrel-shaped cavity. They extended a drift into granite. It is 2km underground to achieve passive sheilding from radiation. When I was there they were working on the problem of building a bottle in a cavity.