Neutrinos from the Sun

Neutrinos of all types, Vg, v, and Vr, can scatter elastically from an electron. This process is a result of the weak-interaction coupling between the neutrino and the charged lepton, a coupling that may have a charged and a neutral current component. The cross section for scattering from electrons depends on the neutrino type, Vg, and whether it is a neutrino or an antineutrino. Only the electron neutrino is coupled to the electron by both the charged and the neutral currents, whereas other neutrino types are coupled by neutral currents. These reactions may be represented schematically as follows  

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Which of the following reactions might be used to detect such neutrinos from the Sun ... 

This rare reaction is a source of energetic neutrinos from the sun. 

As we discussed, numerous neutrinos are produced by the proton-proton chain in the Sun. However, neutrinos interact only very weakly with matter. Every second over 100 billion neutrinos from the Sun pass through every square inch of our bodies and virtually none of them interact with us. Because neutrinos interact so weakly with matter, detecting them is very difficult. For example, in the first solar neutrino detection experiment, scientist Ray Davis used 100,000 gallons of cleaning fluid (for the chlorine the fluid contained) in a detector located in a South Dakota gold mine. Davis expected to detect on average of 1.8 solar neutrinos per day. Instead, Davis s observed rate has consistently been much lower than this. Also, the long-term rate, plotted as a function of time, shows an anticorrelation between neutrino rate and sunspot activity. 

Stellar nucleosynthesis The reaction, 4He + JHe - 7Be + photon, happens at the center of the Sun and other stars. The 7Be decay thatfollows is an important factor in the so-called solar neutrino puzzle. Although 7Be is rather rare at the solar center, decaying to 7Li with its 8-week halflife, there is rather a huge mass of 7Be at any given time at the solar center because 7Be is stable against breakup into smaller nuclear particles. That mass of7Be can be reliably calculated. But evidence of neutrinos from the Sun shows that the neutrino flux expected from that mass of 7Be does not entirely arrive at the Earth. 

An area that was pioneered by nuclear chemists is the search for solar neutrinos. Although main-sequence stars, of which the Sun is a typical representative, have for decades been believed to derive their energy from the series of fusion reactions mentioned above, there was no direct observational evidence for this until Raymond Davis in the 1960s undertook to measure the flux of neutrinos from the Sun which accompany these reactions (Davis et al. 1968 Cleveland et al. 1998). The experiment involved measuring the number of Ar atoms (35.0 d) formed by neutrino capture in Cl in a tank of perchloroethylene. With only a few atoms of Ar per month extracted from over 600 t of liquid, this was indeed the ultimate low-level radiochemical separation. Nevertheless, the experiment was successful in detecting the neutrinos, but ever since the first data appeared in 1968, the measured neutrino flux persisted in being only one third of what was expected from model calculations, and this so-called solar neutrino puzzle literally gave rise to a whole new field — neutrino astronomy. 

Abazov AI, Anosov OL, Faizov EL et a] (1991) Search for neutrinos from the sun using the reaction Ga (Ve, e ) Ge. Phys Rev Lett 67 3332 Alvarez LW (1937) Nuclear K electron capture. Phys Rev 52 134... 

In the early 1960s, it was clear that the neutrinos from the sun could be observed. This conclusion was reached after it was realized that the PP-II and PP-III branches were an important part of the energy generation of the sun and sufficiently energetic to drive the neutrino capture reaction... 

The observations of extraterrestrial neutrinos from the sun by different experimental methods have confirmed the details of the nuclear processes in the core of the sun and have verified its internal structure and method of energy generation. Moreover, the neutrinos from the earth s atmosphere and from the sun appear to exhibit the phenomenon of neutrino oscillations which, if fully verified, will conclusively demonstrate that at least one of the neutrinos in the current model of elementary leptons has nonzero mass and that at least two of them can spontaneously exchange flavor. 

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