Positron-electron

Corpuscular emission (neutrons, protons, electrons, positrons) + + ... 

Similar to beta decay is positron emission, where tlie parent emits a positively cliargcd electron. Positron emission is commonly called betapositive decay. Tliis decay scheme occurs when tlie neutron to proton ratio is too low and alpha emission is not energetically possible. Tlie positively charged electron, or positron, will travel at higli speeds until it interacts with an electron. Upon contact, each of tlie particles will disappear and two gamma rays will... 

Rays of the highest energy can interact in a third way with matter, namely by pair production. In this process, which begins at about 106 ev and becomes dominant as the energy increases, the 7-ray disappears in the field of a nucleus or of an electron, and there is produced an electron-positron pair. Owing to the energy requirement, pair production is impossible with x-rays commonly used for analytical purposes. 

Electron penetration, of aluminum, 176 of x-ray target, 8, 9 Electron-positron pair production, 290 Element determinations,. bibliography, 328-331... 

The above rules are readily applied to the case of the electron-positron field interacting with an external field for which... 

Outer-sphere electron transfer reactions involving the [Co(NH3)6]3+/2+ couple have been thoroughly studied. A corrected [Co(NH3)6]3+/2+ self-exchange electron transfer rate (8 x 10-6M-1s-1 for the triflate salt) has also been reported,588 which is considerably faster than an earlier report. A variety of [Co(NH3)g]3+/2+ electron transfer cross reactions with simple coordination compounds,589 organic radicals,590,591 metalloproteins,592 and positronium particles (electron/ positron pairs)593 as redox partners have been reported. 

Pair production, in which the photon is annihilated in a nuclear interaction giving rise to an electron-positron pair, which carries the energy of the photon less twice the rest energy of the electron. 

Positron A positively charged particle of mass equal to an electron. Positrons are created either by the radioactive decay of unstable nuclei or by collision with photons. 

During most of the first 0.1 second after the Big Bang (ABB), the relativistic particles are photons, electrons, positrons and Nv species of neutrinos and antineutrinos Nv is expected to be 3, from ve, vfl and vr. There is a sprinkling of non-relativistic protons and neutrons which make a completely negligible contribution to the energy density. The temperature is then given by... 

Materials and substances are composed of particles such as molecules, atoms and ions, which in turn consist of much smaller particles of electrons, positrons and neutrons. In electrochemistry, we deal primarily with charged particles of ions and electrons in addition to neutral particles. The sizes and masses of ions are the same as those of atoms for relatively light lithiiun ions the radius is 6 x 10 m and the mass is 1.1 x 10" kg. In contrast, electrons are much smaller and much lighter them ions, being 1/1,000 to 1/10,000 times smaller (classical electron radius=2.8 x 10 m, electron mass = 9.1 x 10" kg). Due to the extremely small size and mass of electrons, the quantization of electrons is more pronoimced than that of ions. Note that the electric charge carried by an electron (e = -1.602 X 10 C) is conventionally used to define the elemental unit of electric charge. 

Expectation Values of the Li-H Internuclear Distance, Its Square, and Electron-Positron Contact Densities Evaluated at 3200-Function Basis Size [122] ... 

An important characteristic of positronic systems relevant to the experiment is their lifetimes. The expectation value of the electron-positron contact density allows us to evaluate the two-photon annihilation rate for a positronic system using the expression... 

The definition of the pair part or, equivalently the no-pair part of Hmat is not unique. The precise meaning of no-pair implicitly depends on the choice of external potential, so that the operator Hm t depends implicitly on the external potential, whereas the sum Hmat Hm t + Hm t is independent of the choice of external potential. Since the no-pair part conserves the number of particles (electrons, positrons and photons) we can look for eigenstates of Hm j in the sector of Fock space with N fermions and no photons or positrons. Following Sucher [18,26,28], the resulting no-pair Hamiltonian in configuration space can be written as... 

The radioisotope nitrogen-13 has a relatively short half-life of about 10 minutes that produces a positron as it decays. This makes N-13 useful in PET (Positron Emission Tomography) scan technology, in which it is injected into the patient. The positive electrons (positrons) interact with the patient s negative electrons to produce an image similar to an X-ray. 

It is interesting to compare the properties of positive electrons, positrons, with the properties of electrons in nonpolar liquids. Values of the mobility of positrons, )x +, are now available for a few liquids. Early measurements for in -hexane ranged from 8.5 to 100 cm /Vs [181,182]. In a recent study, the Doppler shift in energy of the 511-keV annihilation gamma ray in an electric field was utilized to measure the drift velocity. This method led to fi+ = 53 cm /Vs in -hexane and 69 cm /Vs in 2,2,4-trimethylpentane [183]. Interestingly, these values are comparable to the mobilities of quasi-free electrons in nonpolar liquids. 

Another important characteristic is that ion beams can produce a variety of the secondary particles/photons such as secondary ions/atoms, electrons, positrons. X-rays, gamma rays, and so on, which enable us to use ion beams as analytical probes. Ion beam analyses are characterized by the respectively detected secondary species, such as secondary ion mass spectrometry (SIMS), sputtered neutral mass spectrometry (SNMS), electron spectroscopy, particle-induced X-ray emission (PIXE), nuclear reaction analyses (NRA), positron emission tomography (PET), and so on. 

---