Electron epithermal

Electrons of still lower energy have been called subvibrational (Mozumder and Magee, 1967). These electrons are hot (epithermal) and must still lose energy to become thermal with energy (3/2)kBT — 0.0375 eV at T = 300 K. Subvibrational electrons are characterized not by forbiddenness of intramolecular vibrational excitation, but by their low cross section. Three avenues of energy loss of subvibrational electrons have been considered (1) elastic collision, (2) excitation of rotation (free or hindered), and (3) excitation of inter-molecular vibration (including, in crystals, lattice vibrations). 

Liquefied rare gases(LRGs) are very important both from the fundamental point of view and in application to ionization chambers. In these media, epithermal electrons are characterized by a very large mean free path for momentum transfer -10-15 nm, whereas the mean free path for energy loss by elastic collision is only -0.5 nm. This is caused by coherence in momentum transfer scattering exhibited by a small value of the structure factor at low momentum transfers... 

In a later report, Schmidt and Allen (1970) extended their measurement to 38 pure liquids and mixtures at room temperature and to 5 liquids as a function of temperature. The free-ion yields are arranged by the alkanes and their isomeric and cyclic counterparts, which show considerable differences in the results. Thus, the free-ion yield in neopentane (NP) is about seven times that in n-pentane. Some of the results are shown in Table 9.1. In mixtures of NP with CC1, or CS, the observed decrease of Gf with the additive concentration has been interpreted by Mozumder and Tachiya (1975) as due to epithermal electron scavenging (vide infra). 

Implicit in such a dependence is the recognition that scattering lengths of thermal and epithermal electrons are similar. A least-squares fit of the data for compounds containing only hydrogen and carbon leads to the solid line shown in Fig. 1 for which a = 0.25 and X = 0.33, for in cm /Vs. 

The distance to which the ion-pair separates before the ions have vibrationally relaxed (and can then be considered as discrete well-characterised species) has been the subject of much theoretical research [315—317] (see Sect. 4). It has proved a very difficult subject to develop [318], though it does appear that the majority of the distance travelled by ejected electrons is travelled once their energy is little greater than thermal (epithermal). Typical separation distances may be 5—10 nm in... 

It is interesting to note the structure in the total electron attachment cross section o (e) below M eV in Fig. 5, which indicates the existence of tSree NISs in this energy range. Since at thermal and epithermal energies the ions formed are long-lived and the measured attachment rates showed ( 8, ] ) no pressure... 

Nuclear reactors consist of uranium or uranium oxide, enriched in dispersed in a moderator of graphite, water, or deuterium oxide which slows down the fission (or fast) neutrons (energy, or E. > 1 MeV, M = mega. eV = electron volt) to epithermal (1 MeV > E > 0.5 eV) and thermal (E < 0.05 eV) neutrons. 

Here Mu is assumed to be formed as a result of combination of and an excess electron. This view is the same as for the spur model of positronium (Ps) formation. While the spur model has received strong support for positronium yield in condensed phases, the validity of the same model for Mu formation is not clear. Figure 11 presents the original form of the spur model of Mu formation, since it helps to contrast the difference between the epithermal model (Fig. 2) and the spur model of Mu formation. Alternatively, the part of Mu formation, i.e., p and excess electron combination, in Fig. 11 may be replaced with the picture of Mu... 

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