August 6, 2008 | 6:19 am
Inside the Super-K detector
A new genre of television extols the virtues of those willing to get dirty and sweaty for a living. Dirty Jobs, Ice-Road Truckers and Ax Men highlight workers who face danger, rather than paperwork deadlines, to get a pay check.
These shows tout the working class as tougher than its white-collar counterpart.
Maybe those producers haven’t met experimental physicists yet. Especially Mark Vagins.
As a US lead scientist working on Super-K, or Super Kamiokande, a neutrino observatory in Japan, Vagins works in conditions that at times can rival any reality TV obstacle.
His underground laboratory, sits 3300 feet underground within an old zinc mine housed in a mountain 200 km from Tokyo. Traffic jams give way to rocky terrain and freezing winds for the morning commute. While angry fellow motorists are absent, bears and snow monkeys whose eyes follow their every move confront the scientists on their way into the mountain.
“They just stare,” Vagins says. “It is really creepy.”
Bells tied to clothing to deter predators became the norm after a black bear chased Vagins’ coworker, who was walking from the main above-ground laboratory to the cave entrance. The bear encounters have stopped, for now.
Using the Earth as a filter
The Super-K tank half-filled with water
Vagins, a University of California -Irvine, scientist with a joint appointment at the University of Tokyo, and about 120 other researchers from several countries run the gauntlet to the underground laboratory because it’s one of the few ways to study the mysterious, subatomic particle, the neutrino. These elusive particles are produced in nuclear reactions occurring in the sun, supernovae, and cosmic rays that shower the Earth.
Neutrinos could hold the key to explaining why particles cling together to form matter, including planets and people, rather than remain as they were just after the Big Bang 13.7 billion years ago–clouds of free-floating energy and light.
Neutrinos move at nearly the speed of light, passing through most matter unnoticed. Trillions pass through your body each second. Because they are essentially invisible and rarely interact with matter, scientists must build giant detectors to increase the probability of seeing a signal of a neutrino. Rock and dirt layers covering the detectors ease this task by absorbing the particles that are not neutrinos but that create a static-like signal in the underground detector. By using the earth to filter out these “background” particles, scientists can get a clearer signal of the neutrino’s passage through the detector to study.
To get to the Super-K detector, Vagins rides 16,404 feet in a mine car to a lift reminiscent of a window washer cart that drops him another 128 feet.
And he’s inside.
“I like to think of it as a big cathedral,” Vagins says. “The inside is like a giant silent chamber. When you stand at the bottom and you look up, you have to shout at the absolute top of your voice to be heard at the top of the tank. The space inside the detector tends to swallow up all the sound.”
A 14-story tall tank holding 50,000 tons of ultra-pure water is covered on the inside with 11,146 television-sized photomultiplier tubes that record flashes of light given off when a neutrino passes through the water exciting other particles with its wake. The other particles give off light. These flashes are collected by detectors, which translate the light into computer data to paint a picture of the energy, direction, and type of neutrino incident.
“Every so often we have to go in there and replace the photomultiplier tubes that have failed,” Vagins says.
That’s when the job gets even tougher.
Getting wet for science
Mark Vagins performs maintenance by boat in the Super-K tank
Since the detector started taking data in 1996, scientists have had to drain it three times for maintenance. More maintenance could occur as soon as summer 2009, though likely a couple years later. Typical cleaning takes two months. An infamous malfunction that shattered 7000 tubes and left 250,000 pounds of glass in the water took close to a year to repair.
Jumping in row boats, scientists hand clean each tube as the water rises. They try not to contaminate the water by touching it, but mishaps do occur.
“Once when we bought some cheaper boats in town, it got half way around the detector before it began to sink,” Vagins says. “Also, one of our Japanese colleagues fell into the water after losing his balance while working on and jumping among large floating pieces of foam.”
Dropped equipment such as flashlights require scuba divers to swim the 120 feet to the bottom of the detector where they risk decompression sickness.
Cleaning the photomultiplier tubes in the Super-K tank
While the cleaning can get monotonous, the view makes it worthwhile.
“Just being in the tank is kind of a kick,” Vagins says. “When you are in the center of the detector in the boat or hanging in the air in the gondola lift, all of these hand-blown glass tubes kind of twinkle in the half light in a different way.”
by Jennifer L. Johnson
Photos courtesy of Mark Vargins and the Super-K collaboration.
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