Electron-Ion Pair

In a strong electric field, a free electron acquires enough kinetic energy to cause an impact ionization i.e., an electron impacting on a neutral molecule causes an emission of a new electron, leading to the formation of new electron-ion pair. The new free electron is, in turn, accelerated to a velocity sufficient to cause further ionization. This leads to an avalanche-type generation of free electrons and ions. The electric field provides the necessary energy in such a way that the process can continue without the external radiation which was necessary for the onset of the process. 

Ionization is the process of removing one or more electrons from a neutral atom. This results in the loss of units of negative charge by the affected atom. The atom becomes electrically positive (a positive ion). The products of a single ionizing event are called an electron-ion pair. 

An electron-ion pair is the product of a single ionizing event. 

For reasons which will become apparent in section 1.8.2, it is assumed that each electron-ion pair eventually produces one molecule of hydrogen. In an earlier section (p. 160) it was seen that in HC1 an additional 0.20+0.2 hydrogen atoms per ion pair should come from dissociative ionisation and charge transfer processes. In the absence of hydrogen atom scavengers they will undergo the reaction... 

In the second step, the thermalized electrons will either recombine with the ions in the track or spur or escape. The yield of free electrons is the integral of the product D r) x P(r) times the number of electron-ion pairs formed initially in the spur or track, Gtot, where P(r) is the probability of escape. For a single ion pair, P(r) is given by [5] ... 

Furthermore, the equivalent conductivity is known to decrease with concentration as c1/2 for dilute solutions (Kohlrausch law). At higher concentrations the conductivity usually increases above the Kohlrausch law value [107]. Furthermore, in weakly polar solvents, there is extensive evidence that strong electrolytes do not dissociate completely, but neutral ion pairs remain in solution [107]. Indeed, solutions of alkali metals in ethers have received considerable attention and two forms of alkali-metal-cation—solvated electron ion pair have been characterised by Seddon et al. [108]. Reactions of an ion as an ion or when ion-paired should be considered as two totally different processes. 

Zaitsev, V.D., Protasova, E.L., Khaikin, G.I. 1993. Kinetics of primary electron-ion pair recombination in liquid trialkyl phsophate radiolysis. High Energy Chem. 27(1) 28-34. (Translated from Khimiya Vysokikh Energii 27(1) 30-36.)... 

A small dose of a soluble fast-decay positron-emitting artificial radioisotope (produced as needed not too far from the PET instrument 6C11, 8015, 9F18 or 37Rb82) is put into human tissue (e.g., blood) the positron typically travels about 1 mm, meets an electron from within the human body, and the pair decays into two y photons of energy 0.51 MeV each, within microseconds to nanoseconds. Two spin states are possible for the positron— electron ion pair before their annihilation singlet and triplet. The annihilation rate for the triplet state depends sensitively on the electron density of the body tissue. Two y counters are set in coincidence mode, and several hundred thousand coincidence events are used to provide valuable tissue information (in addition to a CT scan). 

The chain of reactions, which played the key role in these arguments, was, firstly, a vibrational excitation of molecules by electron impact (through resonant H2 levels), then, secondly, an ion conversion p + Ho(v) —> II If), followed by, thirdly, an immediate dissociative recombination e + H. — H + H. The excited atom decays by spontaneous emission. At the end of this chain, one electron-ion pair has recombined into an H-atom, and the H2 molecule has dissociated into H + H. 

H + H [25]. The excited atom decays by spontaneous emission or electron collisions into the ground state. Other possibilities are re-ionization of the excited atom or both atoms are ionized, these processes are the Molecular Assisted Dissociation (MAD) and Molecular Assisted Ionization (MAI), respectively. At the end of the MAR chain, one electron-ion pair is recombined... 

Eqs 4 and 5 shown below describe the currents for electrons and ions respectively. The total energy transport Qg is described by Eq. 6. Production of electron-ion pairs is described by Eq. 7. Production of heat within the plasma is described by Eq. 8. Definition of symbols for all of these equations is given in the nomenclature section at the end of the paper. 

Salmon GA, Seddon WA. (1974) Production of solvated electrons, ion-pairs and alkali metals anions in tetrahydrofura studied by pulse radiolysis. Chem Phys LettlA 366-368. 

In the stationary-ion approximation the relative coordinate and momentum of each electron—ion pair are fj and kj (i = 1,2). The relative coordinate and momentum of the electron—electron pair are, in atomic units,... 

The constant value of e for different types of radiation and for different energies contributes to the versatility and flexibility of semiconductor detectors for use in nuclear spectroscopy. The low value of compared with the average energy necessary to create an electron-ion pair in a gas (typically 15 to 30 eV) results in the superior spectroscopic performance of semiconductor detectors. 

The data of Table 3.2 show that, primarily, the beams of a standard intensity produce each second 1016 to 1017 electron-ion pairs per cm3. It goes to about one percent of the 2.6 x 1019 cm-3 molecules present at STP. However, recombination of the electrons with the molecular ions is fast - typical values of rate constants... 

A mole of a chemical species is 6.022 X 10 atoms, molecules, ions, electrons, ion pairs, or subatomic particles. 

For most gases, the average energy required to produce an electron-ion pair is about 30 eV. This number takes into account all collisions, including those that lead to excitation. If a 3-MeV alpha and beta particle deposits all its energy in the counter, it will produce, on the average,... 

The discussion up to this point has been limited to the effects of the ionization produced directly by the incident particle. This is called primary ionization. There are types of gas counters in which the electric field is so strong that the electrons of the primary ionization acquire enough kinetic energy between collisions to produce new electron-ion pairs. These new charges constitute the secondary ionization. Primary and secondary ionization are generated within such a short period of time that they contribute to one and the same pulse. 

Assume that one electron-ion pair has been formed at a distance Xq from the collecting plate (collector). The electron and the ion start moving in the electric field, and they acquire kinetic energy at the expense of the electrostatic energy stored in the capacitance of the chamber. If the charge moves a distance dx, conservation of energy requires that... 

If N electron-ion pairs are produced, the final voltage will be... 

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