We raced into the Panofsky Auditorium. I won by going through the grass. I wanted to eat some cookies but I couldn't find any. There were only SLAC T-shirts. We ran into the auditorium and found seats really close to the stage. Finally, Dr. Peter Rowson started his lecture.
He first talked about the history of the neutrino. In 1933, Wolfgang Pauli wrote a funny letter to a conference ("Dear Radioactive Ladies and Gentlemen..."). In this letter, he theorized that there was a small particle which had small mass that was taking some energy away during chemical reactions. In 1934, Enrico Fermi from the University of Rome, coined the term neutrino ("little neutral one" in Italian) for the particle.
The problem of detecting neutrinos forced physicsts to the poles or underground. The problem was that they needed only the neutrinos coming into their detectors and not cosmic rays and muons. When you go underground, the soil above filters cosmic rays, but you have to go down a certain depth or below to get rid of muons. All current neutrino experiments are conducted below depths of 1000 ft. Since neutrinos can pass through one light year of lead, they will not be filtered by the soil.
The closest source of neutrinos to the earth is the sun. Every day, millions of neutrios pass through you and you don't even notice them. There are three types of neutrinos: electron-type neutrinos, muon-type neutrinos and tau-type neutrinos. In a star's fusion, there are many reactions which give off electron-type neutrinos. Neutrinos can change form from one type to another. When a neutrino escapes out of the sun, it will be an electron-type neutrino. But, when we detect it, it can be any of three types. The elctron-type neutrino's charged partner is the electron, the muon-type neutrino's charged partner is the muon and the tau-type's charged partner is the tau lepton.
Dr. Rowson is doing his experiment in a mine in Carlsbad, New Mexico which is also used by the U.S. Department of Energy to store nuclear waste. His experiment consists of a tub of Xenon-136. When a neutrino hits water, it emits a particle called a muon. To the human eye, the muon is a tiny spark of blue light. This is how a neutrino is usually detected. This experiement is called EXO200. Sometimes, radioactive materials give off beta particles or just high speed electrons. People now want to detect if a radioactive atom gives off two of these beta particles and two neutrinos.
Questions:
1) What is Dr. Rowson's experiment? Is he trying to determine the mass of a neutrino?
2) What is the purpose of using Xenon-136 in this experiment?
3) How is the double beta decay being used in this experiment?
4) What happens in this experiement after the neutrino hits the xenon?
2)Xenon is one of the few substances that may detect neutrinos.
ReplyDelete4) Screens detect the light.
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