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PTRC Signs Agreements on Sensor Research, CCS Cooperation in The...
Standing in an elevator surrounded by tough looking miners wearing even tougher looking gear and equipped with heavy tools, it takes 3 minutes to descend from above ground to level 6.800 located at 2.070 meter underground inside the Creighton mine in Sudbury, Canada. Then a 25-minute walk in the half-dark warm and humid tunnel (30 °C, 100% humidity), avoiding puddles on the gravel floor while in the air the smell of dust and explosives faintly lingers. After a corner a large garage door and a little side door appear into sight. Entering these followed by showering and putting on clean clothing leads to a different place, a “clean mine”, white smooth walls, epoxy coated floors, cool air, people in white coveralls doing delicate work. Here one of world largest sensors, the Sudbury Neutrino Observatory (SNO) is located. SNO is a big water filled cavity (22 meter diameter 34 meter high) with suspended inside an acrylic sphere of 12 meter diameter surrounded by thousands of golden yellow electronic eyes, photomultipliers, ready to register any flash of light. This light is generated if a neutrino hits the heavy water (D2O) inside the acrylic sphere. These neutrinos, the tiniest of particles are formed in stars during the fission processes generating the energy released by stars. The experiments done with SNO have proven that neutrinos oscillate between the place where they were made (the sun) and the place where they are detected. Oscillating means that for example a factory makes only red cars but by the time they arrive at the dealer half of them have spontaneously turned blue.
But why build this all under 2.000 meters of rock? Why not above ground which would logistically be a great deal more convenient? The answer has to do with signal to noise ratio. There are a few neutrinos measured per day but above ground cosmic rays, hadronic particles and muons provide an avalanche of noise; millions of flashes of light in the detector totally drowning the neutrino signal. The rock above SNO acts as a shield only allowing neutrinos through and keeping the noise down. Why the clean room? Everywhere around us are minute traces of radioactive particles, these trace amounts are harmless to people but devastating for the delicate experiments. People and materials going inside the lab have to be washed thoroughly to avoid any contamination coming into the facility (the earlier mentioned side door is for people, behind the garage door something resembling a DIY car wash is situated complete with brushes and high-pressure washer).
Why was INCAS³ there? Large parts of the technology are relevant for the realisation of the antineutrino detectors INCAS³ is developing for the monitoring of nuclear power stations. During a workshop organised by the community of low radioactivity techniques for researcher from all over the world the latest developments in the field are discussed. For example how do you remove 400 lead atoms from 1 m³ of liquid, how radioactive is copper used for tubing in the detectors, how to reduce radiation emitted by PMTs, how is the upgrade from SNO to SNO+ going. The community also recognised that there is a need to share know-how, techniques and experimental data between each other and first steps in this direction have been taken. Fruitful contacts have been made with the intention to enhance our own detector but also to improve the experiments of others.
Peter Dijkstra is a PhD-student at INCAS³ involved in the development of novel scintillation materials (sensors) for the detection of anti neutrino’s.