Herb Chen’s experiment Neutrino observatory pioneer – in 1984 Herb Chen of UC Irvine first pointed out the advantages of using heavy water as a detector for solar neutrinos. The 33 m deep, 22 m diameter chamber that houses the detector is lined with several layers of plastic material that help to keep the radiation level from uranium and thorium a full nine orders of magnitude lower than in the surrounding rock. Systems for purifying the SNO detector’s light and heavy water fill most of the available space. The emphasis on purity does not end with the air. Even more impressive is that these clean conditions were maintained throughout the construction of the experiment. A typical room would give a count of around 100 000 particles and the SNO drift considerably more. That means that everywhere within the laboratory there are fewer than 3000 particles of 1 µm or larger per 1 m 3 of air. Incredibly, the laboratory maintains class-100 clean-room conditions in the most sensitive areas and all areas are class-3000 or better. Scrupulous attention to cleanliness is one of the keys to SNO’s success. Arriving at the lab, boots are rinsed down, clothes are removed and everyone takes a shower before changing into a clean set of overalls and entering the lab. Everything to be taken into the lab must be carefully wrapped in plastic to protect it from the omnipresent mine dust. Overalls, miners’ lamps and safety harnesses are the order of the day. Scientists and miners are indistinguishable in all but their conversation as they descend in the lift. Here the rock is constantly at a temperature of 40☌, making for a sticky 1.5 km walk along the “SNO drift” – the tunnel connecting the mine shaft to SNO’s underground laboratory. “All you have to add is light,” said Art McDonald, director of the Sudbury Neutrino Observatory (SNO) as we stepped off the lift 2000 m underground. NASA even sent moonshot astronauts there for training. Today the trees are coming back, thanks in part to the mines themselves, where underground nurseries provide warm stable conditions for trees to grow. The Sudbury landscape still has an unearthly quality about it. Early mining efforts stripped away trees to provide fuel for smelting the ore, with the result that in the 1960s the Sudbury basin resembled a moonscape. ![]() Today the Sudbury basin is circled with the world’s largest concentration of nickel mines and in one of them, scientists accompany the miners on their morning descent to the 6800 ft (2000 m) level. The impact allowed a rich seam of nickel-copper ore to rise through the Earth’s crust around the rim of the crater. It all began 1.8 billion years ago when geologists believe that a meteorite struck the Earth, creating what is now the Sudbury basin in Canada. Operational since 1999, the Sudbury Neutrino Observatory has ambitious plans for the future. Some 2000 metres underground in a working nickel mine, physicists have installed one of the world’s most sensitive instruments for observing the universe.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |