Proton decay

Proton decay, delayed, 27 303-304 Proton-exchange membranes, 23 720 electrolyzer, 73 843 Proton exchange membrane process, 73 783... 

Proton decay should be a simple extension of a decay with the same ideas of barrier penetration being involved. A simplification with proton decay relative to a decay is that there should be no preformation factor for the proton. The situation is shown in Figure 7.12 for the case of the known proton emitter 151Lu. One notes certain important features/complications from this case. The proton energies, even for the heavier nuclei, are low (Ep 1 —2 MeV). As a consequence, the barriers to be penetrated are quite thick (Rom = 80 fm), and one is more sensitive to the proton energy, angular momentum changes, and so forth. 

All nuclei with A > 210 are a emitters, yet very few emit protons spontaneously. Yet both decays lower the Coulomb energy of the nucleus. Why is proton decay not more common ... 

Use one-body theory to calculate the expected half-life for the proton decay of 185Bi. 

It is clear from these basic facts and our picture of fission that spontaneous fission is a barrier penetration phenomenon similar to a or proton decay. The nucleus tunnels from its ground state through the fission barrier to the scission point. Therefore, we would expect the spontaneous fission (SF) half-life to have the form... 

How it is that this GUT theory can be tested is a matter of some difficulty. It is still possible that low energy effects of a GUT may be detected. This was the hope for proton decay with the minimal 517(5) model. As there may be issues with chirality, or residual chirality in QCD it may be possible that GUTs can be experimentally tested. 

The issue of proton decay rests upon the mass of the X,Y,V bosons, and the flavor mixing Cabibbo angles. The Cabibbo angle is defined as... 

Table 2.1 Isotopes of arsenic (Audi et al., 2003 Holden, 2007 Lindstrom, Blaauw and Fleming, 2003).15As is the only stable arsenic isotope. The possible decay modes include electron capture (EC), electron emission (P ), positron emission (P+), proton decay (p), internal transition (IT), and neutron emission (ne). Superscripts on some of the arsenic isotope mass numbers designate excited-state isomers. The first (lowest energy) excited state is designated with an m and a second excited state is designated with an n. ...

Proton decay A hypothetical form of radioactive decay, where a proton decays into lighter subatomic particles. 

The 8-delayed two-proton decay of Ca yields a value for the mass 35... 

The fractions of protons decaying according to relaxation functions Rx and R2 are given by fj and f2. In molten polymers this relationship has long been exploited to provide a measure of the crosslink density in many polymer systems [64-83]. The form of the decay functions has been the subject of much discussion, however, it is often observed that Rj and R2 can be approximated by simple exponential decay functions. It is generally accepted that the protons with short relaxation times are those directly attached to or adjacent to crosslink points. As an example Figure 13.4 shows the decays of transverse... 

The notion of proton decay is still controversial, but many physicists believe that these extraordinarily long-lived particles eventually die as a result of baryon nonconservation decay paths. 

Proton Decay and Other Rare Decay Modes... 

Thus, besides a decay, fi decay and y transition, a fourth type of decay is known since 1982. In the meantime, further examples of proton decay have been discovered, all on the extreme proton-rich side of the chart of nuclides. In this region, proton emis-siori (p decay) competes with emission of positrons decay), and because in most cases decay is favoured, p decay is observed relatively seldom. 

More frequently, p emission occurs after decay in a two-stage process P decay leads to an excited state of the daughter nuclide, and from this excited state the proton can easily surmount the energy barrier. This two-stage process is called jff -delayed proton emission. It is observed for several P emitters from to " Ti with N = Z - 3, with half-lives in the range of 1 ms to 0.5 s. Simultaneous emission of two protons has been observed for a few proton-rich nuclides, e.g. Ne ti/2 10 ° s). Proton decay from the isomeric state is observed in case of Co (probability 1.5%, q/2 0.25 s). 

The search for rare processes, such as proton decay, neutrino oscillations, neutrinoless beta decay, precise measurements of parameters of known particles, experimental searches for dark matter represent the widely known forms of such means. 

Despite all these impressive progress, we are still too far from the ultimate theory of everything. I listed some obvious avenues for future research in particle physics and cosmology. If I am allowed to say my personal prejudice, I would say that the flavor problem is beyond our reach for years to come, but our understanding of the law of force may further be advanced by a new discovery of violation of empirical conservation laws. The Majorana nature of neutrino masses and proton decay are just manifestation of violation of lepton and baryon numbers, and in my view there is no fundamental obstacle against these being discovered in future, however remote it might be. 

Let us elaborate some of these conditions. First, the baryon nonconservation. Needless to say, grand unified theories (GUT) predicts proton decay, along with more general baryon number violating processes. This is... 

The simplest GUT model [10], namely the SU(5) unification and its super-symmetric extension, is almost certainly ruled out from many reasons lack of proton decay at the predicted lifetime level, inability to produce neutrino masses, and so on. On the other hand, the next target, SO(IO) models, and their SUSY extensions in particular, are very promising. It has just the needed component of the right handed Majorana lepton for realization of the seesaw mechanism. The models also accommodates B - L violation which is needed for baryogenesis, as is explained later. 

Related effects have been noted in proton decay [Lane 1983] more recently for radiative decay in cavities [Kofman 1996], in Rabi oscillations betwen coupled quantum dots [Gurvitz 1997], in photodetachment [Lewenstein 2000]. See also [Facchi 2000 (a)]. 

From the above discussion, it is clear that measurement of the change of the complex water proton decays can be related directly to structural changes within samples, provided the conditions of Equation 6 are met. Unfortunately, these conditions are rather strict and will rarely be completely fulfilled. 

In the darkest Communist times, a colleague of mine came to my office. Conspiratorially, very excitedly, he whispered The proton decays He just read in a government newspaper that the lifetime of protons turned out to be finite. When asked about the lifetime, he gave an astronomical number, something like 10 years or so. I said Why do you look so excited then and why all this conspiracy He answered The Soviet Union is built of protons, and therefore is bound to decay as well ... 

One prediction of GUTs is the occurrence of proton decay. Some also predict that the neutrino has nonzero mass. There is no evidence for proton decay at present, although there is some evidence that neutrinos have very small nonzero masses. See also super-string THEORY. 

Proton decay is possible also from ground states or from long-lived isomeric states. These decay modes are common among the strongly proton-rich nuclei. In the Z> 50 region already >41 proton emitters are known, e.g., "Sb, "l, " Cs, " La, Re, Au, =Bi. 

Q-values (decay energies for different decay modes) for beta minus (QP—), electron capture (Qe), alpha (Qa), and proton decay (Qp) are from Audi and Wapstra (1995). Systematic values are shown in square brackets. 

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