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What is NOvA?By Richard C. Ross
I were to simply tell you that physics has changed my life, the
article that included all the reasons would likely be lengthy and
boring… so I am going to ask you to take my word for it. More
importantly, it was the teaching of the subject that had a greater
impact than just the subject itself. And that is because in learning
to teach the topics, I developed an almost insatiable curiosity
about the world around me; it was a curiosity that has never abated,
and has never failed to bring new and exciting revelations into my
One such revelation took place recently when I had traveled to Minnesota for a bit of business, punctuated with some "down" time on a large lake named Kabetogama. Not far from where I was staying - about a 15 minute drive by car - is the Ash River (it empties into Kabetogama), accessed by the Ash River Trail. A turn off that road and onto Bright Star Road will take you deep into the woods... and bring you to a modern-looking but otherwise almost non-descript long and low structure behind a tall and gated chain-link fence.
This is NOvA: the NuMI Off-axis Neutrino Appearance. (NuMI, by the way, stands for "Neutrinos at Main Injector" beamline at Fermilab) From a handout there, "The NOvA experiment is a liquid scintillator detector experiment searching for electron neutrino appearance in the NuMI muon neutrino and antineutrino beam". A mouthful to be sure, and probably one that most could have a difficult time pronouncing, let alone comprehending. The facility is there to study neutrinos in order to help - among other things - answer questions about the universe around us.
Several years ago, I wrote an article that included the topic of high energy particle physics at a facility called Fermilab, in Batavia, IL. Back in the 80s, Fermilab was generating neutrinos and firing them at a 300 ton detector made of iron. Now they are firing them 500 miles north - through solid rock - to Ash River, Minnesota and into a specially-designed detector.
But here is the interesting thing (well, at least one of many): Neutrinos are one of the most abundant subatomic particle types in the universe, and yet they're darn near impossible to detect. The reason? Well, the simple answer is that they have an incredible tendency to not react with much of anything at all. (One trillion neutrinos pass right through you every second and you never know it; they pass through the planet as if it were empty space). So, very large detectors are needed to do the job.
At about 270 feet in length, holding almost three million gallons of special liquid scintillator fluid and buried 70 feet underground after the excavation of thousands of cubic yards of billion-year-old, northern Minnesota granite, the detector at Ash River is huge! It's referred to as the "Far Detector" and is currently the world's largest free-standing PVC structure. Just building the detector that weighs in at 14,000 tons (to collect data from only a few neutrino interactions per month of the billions sent every few seconds), filling it with scintillator and rigging the electronics and photo-sensors to record the particles passing through it, took two years. It was quite an intricate and complex engineering feat, to say the least. (There's a short video below)
By the way, the beam needs no tunnel; travel time for the 500 mile journey from Batavia, Illinois to Ash River, Minnesota takes less than .003 seconds, since neutrinos easily pass through solid rock - and anything else for that matter - without interacting. The particles will pass underneath Wisconsin, the western edge of Lake Superior and up into Minnesota, at a depth of up to six miles, to the Ash River detector, before continuing their happy journey as they cross the border and into Canada, never pausing to offer any passport or identification.
We enjoyed a marvelous and informative tour of the building, given that day by Cole Hraban from the University of Minnesota; I would recommend it highly. Even though the scope of the project and perhaps the concepts themselves may at times approach incomprehensible, the tour is not long and it is indeed fascinating; it is certainly worth a side trip if you are anywhere in the vicinity.
I am guessing that there are those who would question the wisdom of
spending large amounts of money on this kind of research. I'm not
the person to properly address that issue, but having taught science
for twenty-five years and therefore acknowledging the value and need
for research, I am nothing short of fascinated by what is being done
in Ash River and wholeheartedly embrace and support it, as it gives
scientists a clearer understanding of the nature of matter and
energy. But I don't believe those particles are just useful for
physicists hoping to crack the mysteries and origin of the universe.
For the pragmatists out there, there is little doubt that useful and
applied solutions to everyday problems will also eventually arise
out of this important research (see