Lecture on Neutrinos www assignmentpoint com Neutrinos Nearly

Lecture on Neutrinos www. assignmentpoint. com

Neutrinos Nearly massless particles with no charge. Rarely interact with ordinary matter. Neutrinos travel extremely fast Almost at the speed of light if small mass. Neutrinos pass from the core of the Sun to the surface in only two seconds. They take less than 8. 5 minutes to travel the distance from the Sun to the Earth. www. assignmentpoint. com

Neutrino Counting In principle: Use neutrino count at Earth as indicator of the Sun’s energy output The problem: Neutrinos have a very low probability of interacting with matter. Could pass through a light year of lead and not be stopped by any of the lead atoms! www. assignmentpoint. com

Neutrino Abundance The Sun produces A LOT of neutrinos. In one second several million billion neutrinos pass through your body. Do you feel them? Not to worry! • The neutrinos do not damage anything. • The great majority of neutrinos pass right through the entire Earth as if it wasn’t there. www. assignmentpoint. com

Detecting Neutrinos Increase the odds of detecting neutrinos by using a LARGE amount of a material that reacts with neutrinos in a measurable way. A chlorine isotope changes to a radioactive isotope of argon when hit by a neutrino. A gallium isotope changes to a radioactive isotope of germanium. Neutrinos can interact with protons and neutrons and produce an electron. The electron can be detected. www. assignmentpoint. com

Neutrino Detectors Ray Davis Neutrino detectors use hundreds of thousands of liters of these materials in a container buried under many tens of meters of rock to shield the detectors from other energetic particles from space called cosmic rays. Even the largest detectors detect only a few neutrinos per day. Kamiokande www. assignmentpoint. com Nobel Prize in 2003

Solar Neutrino Production Number of neutrinos produced in the Sun is directly proportional to the number of nuclear reactions taking place in the Sun's core. Same principle with neutrinos produced via the Carbon-Nitrogen-Oxygen chain. The more reactions there are, the more neutrinos are produced and the more that should be detected here on the Earth. www. assignmentpoint. com

Solar Neutrino Production (cont’d) Physicists find that the number of neutrinos coming from the Sun is smaller than expected. Early experiments detected only 1/3 of the expected number of neutrinos. These experiments used hundreds of thousands of liters of cleaning fluid (composed of chlorine compounds) or very pure water. www. assignmentpoint. com

Solar Neutrino Production (cont’d) Later experiments using many tons of gallium were able to detect the more abundant lowenergy neutrinos. However, those experiments also found the same problem: too few neutrinos (the gallium experiments found about 2/3 the expected number). The puzzling lack of neutrinos from the Sun is called the solar neutrino problem. www. assignmentpoint. com

Possible Explanations: Nuclear fusion is not the Sun's power source. Not supported by observations, not likely to be the correct reason. The experiments were not calibrated correctly. Unlikely that all carefully-tuned experiments were tuned in the same wrong way. Experiments independently verified by many other scientists; astronomers think that the results are correct. The nuclear reaction rate in the Sun is lower than what our calculations say. Possible but many people have checked and re-checked the physics of the reaction rates. Strong constraints in how much one can lower the temperature in the core of the Sun to slow down the reactions. www. assignmentpoint. com

Solar Neutrino Solution Three types of neutrinos exist. The Sun produces only one type, called electron neutrinos The experiments detect only electron-type. On their way from the Sun, neutrinos can transform from one type to another we only detect 1/3 of the mix at Earth. This also implies that neutrinos have mass, very small, but not zero. www. assignmentpoint. com