Solar neutrino problem

Many of the nuclear reactions that provide the energy of the stars also result in the emission of neutrinos. Because of the small absorption cross sections for neutrinos interacting with matter (o lhs 10-44 cm2), these neutrinos are not generally absorbed in the sun and other stars. (This loss of neutrinos corresponds to a loss of 2% of the energy of our sun.) Because of this, the neutrinos are a window into the stellar interior. The small absorption cross sections also make neutrinos difficult to detect, with almost all neutrinos passing through planet Earth without interacting. 

Recently, a good deal of attention has been given to the solar neutrino problem and its solution. The 2002 Nobel Prize in physics was awarded to Ray Davis and Masatoshi Koshita for their pioneering work on this problem. Of special interest is the important role of nuclear and radiochemistry in this work as Davis is a nuclear chemist. The definition and solution of this problem is thought to be one of the major scientific advances of recent years. 

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First results from SNO heavy-water experiment announced, giving definitive solution of solar neutrino problem. 

The remainder of the Fowler article is of great interest, but in detail that is beyond the scope of this encyclopedia. Topics covered by Fowler include early research on element synthesis stellar reaction rates from laboratory cross sections hydrogen burning in main-sequence stars and the solar neutrino problem synthesis of l3C and, 60 and... 

The Davis or Cl detector was the detector used to define the solar neutrino problem, and another type of radiochemical detector, the SAGE/GALLEX detectors, was used to further define the problem. These detectors, GALLEX in Italy and SAGE in Russia, are based on the reaction... 

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. 

The solution to the solar neutrino problem is that something is wrong with our ideas of the fundamental structure of matter, the so-called standard model. This difficulty takes the form of neutrino oscillations as the solution to the solar neutrino... 

Bahcall J. N. (http //www.sns.ias.edu/ jnb) a comprehensive account of the solar neutrino problem and its solution is found at the website. 

Whatever the outcome, great repercussions on science resultfrom the solar neutrino problem. The implications may be for our Sun, or for the nature of neutrinos, or both. Recent evidence is convincing that the problem is in the nature of the neutrino itself namely, that during transit it spontaneously transforms (oscillates) to a neutrino of different flavor, and to which the detector is insensitive. This is possible because of the small rest mass of neutrinos. 

Weak Interaction Processes During pp-Chain and Solar Neutrino Problem... 

Part II deals with explosive nucleosynthesis that plays a critical role in cosmochemistry. The lectures by Kamales Kar provide essential background material on weak-interaction rates for stellar evolution, supernovae and r-process nucleosynthesis. He also discusses in detail the solar neutrino problem. Massive stars, their evolution and nuclear reaction rates from the point of view of astronomers and nuclear physicists are discussed by Alak Ray. His lectures also describe the various stages of hydrostatic nuclear fuel burning with illustrative examples of how the reactions are computed. He also discussed core-collapse (thermonuclear vs. core-collapse) and supernovae in brief. The lectures by Marcel Arnould address the phenomena of evolution of massive stars and the concomitant non-explosive and explosive nucleosynthesis. He highlights a number of important problems that are yet unresolved but crucial for our understanding of Galactic chemical evolution. The p-process nucleosynthesis attributed to the production of proton-rich elements, a topic of great importance but yet less explored is also discussed in his lectures. 

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