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Illustration of the IceCube neutrino observatory. Source: LBNL
Earlier today, the Energy Blog featured Los Alamos National Lab’s system to track Santa. However, while there is a lot of attention focused on the North Pole right now, the Geek-Up[date] team is taking a look at the opposite end of the Earth. This past weekend, a collaborative group of 40 institutions from around the world, including DOE’s Lawrence Berkeley National Lab, celebrated the completion of the IceCube Neutrino Observatory at the South Pole. This immense telescope encloses a cubic kilometer of clear ice, beginning one and a half kilometers beneath the surface and extending downward another kilometer. The telescope has to be this big because neutrino-matter collisions are extremely rare. In fact, out of the trillions of neutrinos constantly passing through the ice, IceCube will observe just a few hundred a day.
How does this all work?
Well, when neutrinos collide with the nuclei of oxygen atoms in the ice, they turn into energetic charged particles called muons, and because these muons are moving faster than light can travel through ice, they radiate a shock wave of blue Cherenkov radiation visible to IceCube’s photodectectors.
IceCube will study neutrinos created high in the atmosphere and search for neutrinos created by gamma-ray bursts, active galactic nuclei, the interaction of cosmic rays with the universe’s background radiation and the annihilation of dark matter particles.
Every year, this season is illuminated with thousands and thousands of lights, and as the Energy Information Administration says, “the type of lights you choose is very important!” In fact, while the largest holiday incandescent bulbs use between 4 and 10 watts per bulb and incandescent mini light bulbs use about one-tenth as much, LED (light emitting diode) lights use only 0.04 to 0.1 watts per bulb. LED lights can also last 50 times longer than incandescents and if a bulb on a string of LED lights does go out, the rest of the lights in the string will still work.
All this talk of LEDs has got Geek-Up[date] thinking about how these lights work:
According to DOE’s Solid-State Lighting program, an LED light is a semiconductor diode which is engineered to create a structure called a p-n (positive-negative) junction. Current flows from the p-side to the n-side and charge-carriers flow into the junction from electrodes. When an electron meets an electron hole, it releases energy as a photon.
You might ask how different color LEDs are made. The color (or wavelength) emitted by an LED depends on the diode’s materials. Reds are based on aluminum gallium arsenide, blues on indium gallium nitride and green on aluminum gallium phosphide. White lights are created by combining the light from red, green and blue LEDS.
In 1962, Nick Holonyak developed the first practical LED by inventing a method to synthesize gallium arsenide phosphide to emit a red light when other researchers were focusing on infrared light.
Niketa Kumar is a Public Affairs Specialist with the Department of Energy