Peaks beta decay

This quantity depends on the ratios of neutron-capture to beta-decay rates. For some scenarios [BLA81, C0W82, CAM83] it is possible to reproduce the observed r-process abundances without reaching (n,y) equilibrium. Then the abundance peaks will largely be determined by the neutron capture cross sections away from stability as demonstrated in [CAM83]. 

The fluctuations in neutron peak intensities arise from the Porter-Thomas distributed beta decay widths to levels in the NE nuclide. In the simplest case only a single state in the GC nuclide can be fed and only one neutron partial wave is significant. The observed levels will be a subset of levels in the NE nuclide and will be distributed in energy following a Wigner distribution. In a typical GC nuclide, however, there will be a number of accessible final states and the delayed neutron spectrum will be a superposition of transitions from several parts of the NE nuclide level structure. 

Where possible, the r-process flow follows the magic neutron numbers. At these points, the nuclei present lie closer to beta stability than elsewhere in the flow. This means that the beta-decay rates decrease, which causes a traffic jam in the upward flow in nuclear mass thus, there is an abundance build up for these nuclei. When the flux of neufrons ceases, the r-process nuclei decay back to stability. Because the r-process flow encounters the magic neutron numbers at nuclear masses less than die s-process flow, the resulting r-process abundance peaks lie lower in nuclear mass than the corresponding s-process peaks. 

Water detectors measure the Cerenkov light produced as the positron from the inverse beta decay process (equation 2) slows in the medium. The most probable positron energy is about two MeV, corresponding to the peak antineutrino energy of about 3.8 MeV. A two MeV positron travels about 1 cm through H2O, producing about 270 Cerenkov photons in the 350 to 550 nm range which may be detected by phototubes. For... 

In principle, it is possible to correct for TCS errors mathematically. Take the simplest possible decay scheme in which we could expect TCS in Figure 8.12. The beta decay to one of two excited states is followed by the emission of the three gamma-rays shown. To simplify matters for the purposes of illustration, assume that the internal conversion coefficients for the gamma-rays are all zero. If the source activity were A Becquerels, in the absence of TCS, the count rate in the full-energy peak 1 would be ... 

The La isotope is present in the natural lanthanum with an abundance of 0.09% and its lifetime is of the order of 1011 years. The contribution of La dec in the energy spectra of Figure 8 consists in i) the multi peak structure located at approximately at 1460 keV (from EC La -> Ba), the structure between 750-1000 keV generated by the sum of the 789 keV gamma with the coincident electron of the beta decay La -> Ce) and iii) the low energy continuum structure. The contamination due to the produces the P continuum up to approximately 1400 keV due to the beta decay of "Pb and ° T1 in the decay chain of this nucleus. There are also events due to a emission from Th, Ra, Rn, Po, and "Bi populated by the Ac alpha-decay chain. 

The fission process produces radioactive as well as stable nuclides with masses ranging from 72 to 167 and with two broad peaks in the regions of 95 and 138. The masses are identified rather than the specific nuclides because in fission many short-lived nuclides are produced that quickly decay by beta... 

Readers may notice the absence of certain terms in common use. The exclusion of some such terms is a deliberate choice. For example, instead of photopeak we prefer full-energy peak we have avoided the statisticians use of error to mean uncertainty and reserve that word to indicate bias or error in the sense of mistake . Branching ratio we avoid altogether. This is often used ambiguously and without definition. In other texts, it may mean the relative proportions of different decay modes, or the proportions of different beta-particle transitions, or the ratio of de-excitation routes from a nuclear-energy level. Furthermore, it sometimes appears as a synonym for gamma-ray emission probabihty , where it is not always clear whether or not internal conversion has been taken into account. 

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