Neutrino losses

The first major set of nuclear reactions in stellar evolution involves hydrogenburning through the pp chains and the CN cycle or CNO bi-cycle, which liberate 6.68 MeV of energy per proton minus neutrino losses (2 neutrinos are emitted for each 4He nucleus synthesized). The first two reactions of the pp chains are... 

Electron Capture and /5" "-Decay. These processes are essentially the inverse of the j3 -decay in that the parent atom of Z andM transmutes into one of Z — 1 andM. This mode of decay can occur by the capture of an atomic electron by the nucleus, thereby converting a proton into a neutron. The loss of one lepton (the electron) requires the creation of another lepton (a neutrino) that carries off the excess energy, namely Q — — Z(e ), where the last term is the energy by which the electron was bound to the atom before it was captured. So the process is equivalent to... 

Neutrinos are also generated by purely nuclear processes involving weak interactions, e.g. in the Sun. Such neutrinos can be an important cause of energy losses in compact stars through the Urea process, in which an inverse / -decay is followed by a normal fS-decay resulting in a neutrino-antineutrino pair. 

Insofar as these reactions occur relatively rapidly at the high temperatures now prevailing, the star s evolution accelerates enormously. This is exacerbated by the fact that it suffers a significant energy loss due to thermal neutrino production via the reaction... 

The conceptually simplest way of forming a black hole at the heart of a massive star, thereby setting up the conditions of the hypernova model, is to begin by repudiating the traditional explosion model detonated by neutrinos. The iron core then collapses without remission in the space of one second. A black hole prospers, pulling down the rest of the stellar edifice. This may be a common occurrence for stars of 35 to 40 Mq. However, uncertainties remain concerning convection, mass loss and mixing due to rotation, not to mention the explosion mechanism itself. 

Allowing neutrino leakage would allow some small reduction in Kq. but would lead to neutrino energy losses, larger in the GR case than in the Newtonian, because of the smaller inner core and the larger hot overlaying mantle. 

The rate of mass loss is proportional to T (Duncan et al. 1986). Thus, an analogue of HR diagram with neutrino luminosity versus neutrino effective temperature is desirable to represent numerical results. If we assume the structure of polytrope with N=3 and take account of the definition of the neutrino sphere, we can calculate a neutrino Hayashi-line analogously to that for red giant stars. We have shown that numerical results could be understandable if analyzed with appropriate concepts. 

FIG. 1. - Pair, photo, and plasma neutrino energy loss rates. ( ergs s-1 cm-3) for T=109K. 

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. 

Calculate the rate of fusion reactions in the sun. Be sure to correct for the energy loss due to neutrino emission. 

Electron scattering by photons may alternatively result in pair neutrino production, with a nett energy loss as shown ... 

Fig. 4. The p-p chain starts with the formation of deuterium and 3 He. Thereafter, 3He is consumed in the sun 85% of the time through ppl chain, whereas pp II and pp III chains together account for 15% of the time in the Bahcall Pinsonneault 2000 solar model. The pp III chain occurs only 0.02% of the time, but the 8B f3+-decay provides the higher energy neutrinos (average Ev = 7.3 MeV). The net result of the chains is the conversion of four protons to a helium, with the effective Q-values (reduced from 26.73 MeV) as shown, due to loss of energy in escaping neutrinos. See [38,37] for updated branching ratios and neutrino fluxes for BPS2008(AGS) model...

During the carbon-burning and subsequent stages, the dominant energy loss from the star is due to neutrinos streaming out directly from the stellar thermonuclear furnace, rather than by photons from the surface. The neutrino luminosity is a sensitive function of core temperature and quickly outshines the... 

In such an unsatisfactory state of affairs, the best one can do is to try to understand better the physics of neutrino-driven winds through the development of (semi-)analytical models some aspects of which may be inspired by (failed) explosion simulations, and to try to delineate on such grounds favourable conditions for the development of the r-process. These analytical models confirm that the wind nucleosynthesis depends on Ye, entropy s, and Tdyn, as in the o-process discussed in Sect. 7.2. The wind mass-loss rate M is influential as well. Ultimately, the quantities acting upon the synthesis in the neutrino-driven DCCSN model depend crucially on the details of the interaction of neutrinos with the innermost supernova layers, as well as on the mechanisms that might aid to get a successful DCCSN, and whose relative importance remains to be quantified in detail. 

Indium occurs in widespread association with both zinc and tin ores. It seems improbable that this can be due to chemical segregation, for isomorphism of indium and tin compounds, for example, appears to be ruled out by their difference both in valency and atomic radius. It has been suggested that the tin isotope 115 has gradually been transmuted into iftdium 115 by loss of an electron and a neutrino. The process is presumed to take place extremely slowly so that in finite time it escapes observation. Tin has eleven natural isotopes of these Sn 115 constitutes 0-44 per cent. Indium comprises In 115, 95 5, and In 113, 4-5 per cent. The high percentage of isotope 115 in natural indium is in harmony with the above suggestion. 

In 1928 Pauli became professor of theoretical physics at the Federal Institute of Technology, Zurich largely through his efforts it became a leading center for research in theoretical physics. In 1931 he observed that when an electron was emitted from a nucleus, a loss of energy occmred that could not be explained by then-current theories. He proposed that it was due to the existence of another particle which carried no charge and had very low mass. The American physicist Enrico Fermi named this particle the neutrino it was eventually discovered some twenty-five years later. 

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