In-elastic collision

The subexcitation electrons lose their energy in small portions, which are spent on excitation of rovibrational states and in elastic collisions. In polar media there is an additional channel of energy losses, namely, the dipole relaxation of the medium. The rate with which the energy is lost in all these processes is several orders of magnitude smaller than the rate of ionizaton losses (see the estimates presented in Section II), so the thermalization of subexcitation electrons is a relatively slow process and lasts up to 10 13 s or more. By that time the fast chemical reactions, which may involve the slow electrons themselves (for example, the reactions with acceptors), are already in progress in the medium. For this reason, together with ions and excited molecules, the subexcitation electrons are active particles of the primary stage of radiolysis. 

Studies of the depolarization process in elastic collisions for excited states of a number of diatomic molecules, such as H2(S1E+) [311], Li2(A1E+) [147, 332], NaR II) [24, 291], CdH(A2II1/2) [130], Na2(S1nu) [237], BaO(A1E+) [350], Se2 [205] and Te2 [154] have shown that, unlike the case of atoms, the efficiency of purely disorienting collisions is mostly very low in comparison with quenching collisions. The results of the works in which the differences 02 — < i — o have been... 

Because neutrons are electrically neutral, their interaction with electrons is very small and primary ionization by neutrons is negligible. The interaction of neutrons with matter is practically confined to the nuclei and comprises elastic and inelastic scattering and nuclear reactions. In elastic collisions the total kinetic energy remains constant, whereas in inelastic collisions part of the kinetic energy is given off as excitation energy. 

In a binary in-elastic collision, on the other hand, the two bodies collide and stick together. The overall momentum is normally conserved in these collisions too, but the overall kinetic energy of the center of mass of the two bodies is not conserved ([96], p. 13). 

It is noticed that in-elastic collisions are characterized by the degree to which the relative speed is no longer conserved. For this reason the coefficient of restitution e in a collision is defined (i.e., with basis in (2.120)) as the ratio of the relative velocity after collision, divided by the relative velocity of approach [45] [69] ... 

Elastic Collisions Transfer of Energy. In elastic collisions of electrons with heavy gas molecules, two effects are of importance. First there is a redistribution of directions of travel of the electrons and second there is a very slight loss of energy (and therefore speed) as a very small amount of momentum and energy are transferred to the molecule by the electron. 

Again if this power gain is equated to the loss of energy of electrons in elastic collisions with the gas molecules, as would occur in the steady state, then... 

In either experimental method the principal mechanism for maintaining a high electron temperature is removed. Under most circumstances the electrons will cool in elastic collisions with the neutral gas with temperature decay times of the order of 10 /xsec. Excited states will decay according to their various lifetimes and at times of the order of a msec, one is left only with those species whose decay constants are slow. 

Winterbon, K.B., Sigmund, P., Sanders, J.B. Spacial distribution of energy deposited by atomic particles in elastic collisions. Mat. Fys. Medd. Dan. Vidensk. Selsk. 37(14) (1970)... 

Irradiation stability. Any solidified HLW will be exposed to energetic radiation from radioactive decay of fission products and actinides. Part of the radiation energy is dissipated in elastic collisions with atoms from the solid material, thereby displacing them and causing radiation damage. This may affect macroscopic properties such as mechanical or chemical ones, and it may cause storage of energy. 

The energy dissipated in elastic collision is at least two orders of magnitude lower for gamma and beta radiation than for the others. The total fast-neutron and fission recoil doses... 

Using the explicit form of which follows from (7.21), and number conservation in elastic collisions, it follows that... 

The second term in the brackets in (9.5) may also be reduced further. Using number conservation in elastic collisions, one may show that... 

These investigations are largely performed on the basis of the two-term approximation, allowing for anisotropic scattering in elastic collisions, but assuming mainly isotropic scattering in the conservative inelastic collision processes. 

Using two different scales for the cross-section values, the important inelastic collision cross sections of Ne and N2 are shown in Fig. 1 together with the respective cross section Qf U) for momentum transfer in elastic collisions, denoted by d. With respect to Ne, the individual collision cross sections have been taken from Hayashi (1996). The relevant total cross sections Q U),... 

This is confirmed to a large extent by the representation of the mean power losses in the various collision processes, also given in Fig. 3 (right). It can be easily observed from the course of the loss in elastic collisions jn and of the total loss in collisions / / that in the steady-state neon plasma, the dominant contributor to the power loss changes around the field strength E = 0.5 V/cm from elastic to inelastic collisions. With respect to the latter. Fig. 3 additionally shows that the excitation of the s levels represents the dominant power-loss channel among the three inelastic power losses P" jn, jn, and P jn in the range... 

The impact of a finite gas temperature has been considered (Shkarofsky et al., 1966 Winkler et al, 1990), to allow an energy transfer from the atoms or molecules back to the electrons in elastic collisions at very low electric fields. 

This interpretation of the electron response to the field disturbances is largely confirmed by the temporal course of the power gain from the field jn and power losses P" /n, and P /n in elastic, inelastic, and all collisions given in Fig. 18. For example, if the field pulse starts and ends with the low field (left), at the beginning of the pulse and in the later relaxation phase the power gain is almost compensated for by the power loss in elastic collisions, and this leads to the large relaxation time at these periods. However, around the pulse maximum, the power... 

The behavior of the individual terms in the momentum balance (right) is similar to that in the power balance. Now the normalized momentum loss in elastic collisions r (z)/I oo) oscillates around the oscillating momentum gain /(z)// (oo), and the somewhat lesser deviations between these quantities are compensated for to a large extent by the normalized source term d/dz) [(2/3m )u z)]/P oQ) of the momentum balance (dotted-dashed curve) containing the spatial derivative of the mean energy density , (z). 

The neutron interacts primarily with the nucleus of the absorbing atom, by elastic and inelastic scattering. In elastic collisions, the target nucleus is not itself ionized. However, it may produce ionization in other atoms. In inelastic scattering, including nuclear transformation, the newly formed nuclide and the emitted photon or charged particle may produce ions. 

The motion of the particles is governed by the potential energy U. If U is independent of the position of the center of mass, as is the case in field-free space or in the presence of homogeneous fields, the equations of motion (classical or quantum) factorize into separate equations for the center of mass and for the relative motion. The total linear momentump is conserved in a collision, so the center of mass moves uniformly (constant velocity V) and is unaffected by the collision. The kinetic energy T is conserved in elastic collisions, and L is conserved if the angular momenta of the particles themselves do not change in magnitude or direction. 

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