Solar neutrino detection

The capability of neutralizing daughter ions emitted by a parent atom in nuclear decay would result in practical realization of ULLC for solar neutrino detection, weak interaction physics, cosmochronology, geophysics, environmental research, and other important applications. 

Five experiments have so far detected solar neutrinos. These are Homestake (USA), GALLEX, SAGE, KAMIOKANDE and SUPERKAMIOKANDE, all set up down mines or tunnels. Detected fluxes agree qualitatively with theoretical predictions, both in numbers and energies. We may say that we have basically understood how the Sun shines. The same set of nuclear reactions invoked to explain the solar luminosity does give rise to neutrinos. 

The solar neutrino problem was identified by the first results of Davis et al. using the Cl detector at the Homestake Mine. Davis et al. observed only about one-third of the expected solar neutrino flux as predicted by standard models of the sun, which assume 98.5% of the energy is from the pp chain and 1.5% of the energy is from the CNO cycle. The final result of the Cl detector experiment is that the observed solar neutrino flux is 2.1 + 0.3 SNU compared to the predicted 7.9 + 2.4 SNU, where the solar neutrino unit (SNU) is defined as 10-36 neutrino captures/second/target atom. The GALLEX and SAGE detectors subsequently reported solar neutrino fluxes of 77+10 SNU and 69+13 SNU, which are to be compared to the standard solar model prediction of 127 SNU for the neutrinos detected by these reactions. 

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. 

A large international collaboration ("Gallex ) is setting up a neutrino detection station in a rock facility in the Mont Blanc. Some Ga atoms in 30 tons of gallium metal is expected to react with solar neutrinos to form Ge (t, 11.4 d) which is to be converted to the gaseous hydride, GeH, and counted in a proportional detector. About 1 atom of Ge formed per day is expected. 

The hydrogen burning in the Sun (4p He -h 2e + 2Ve + Qeff) produces low energy (<20 MeV) electron neutrinos, but the flux ( (Vg) of neutrinos detected fell insistently short of the flux expected. Some of the electron neutrinos produced in the solar core changed flavor. The result, interpreted in this way, is... 

Neutrino deficit Subatomic particles predicted to be released by the nuclear reactions on the Sun and should be detected on Earth. The number of neutrinos observed on Earth is much less than predicted by the models of solar nuclear fusion. 

Table 5.3. Outline of stellar structure and evolution Solar neutrino fluxes expected and detected in different experiments ... 

Neutrinos inform us almost instantaneously of what is happening in the Sun s core. However, the main interest of this solar cardiograph is hardly to detect some failure in the Sun s cycle. In capturing solar neutrinos, the aim of contemporary physics is rather to catch the Sun in the act of nuclear transmutation. By measuring the neutrino flux, we may check our understanding of the Sun as a whole and at the same time analyse the relationship between this strange particle and more commonplace forms of matter. 

Fig. 5.3. Solar neutrino spectrum and detection ranges of the various underground neutrino observatories. The main part of the emission comes from the proton-proton reaction. About 3000 bilhon neutrinos pass through this figure every second. These neutrinos left the Sun eight minutes and two seconds earlier.

Table 5.1. Solar neutrinos confronting prediction with detection. The unit of flux is the SNU, or solar neutrino...

One of the areas in which the skills of radiochemists are used is the area of low-level chemistry and low-level counting. Areas as diverse as the detection of solar neutrinos or the study of environmental radioactivity involve low-level techniques. For example, despite concentration of the radiotracers of interest during sampling procedures in environmental studies, quite often one is left with a sample containing... 

Solar neutrinos, which interact very weakly with matter, should also be produced by the nuclear fusion reactions in the Sun. However, scientist s detect much fewer neutrinos than expected, which may suggest that our knowledge of the solar processes that cause the Sun to shine or of neutrinos themselves is incomplete. 

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