Recoil distribution

Briihlmarm, U., Dubs, M., and Huber, J.R. (1987). Photodissociation of methylnitrite State distributions, recoil velocity distribution, and alignment effects of the NO(X2n) photofragment, J. Chem. Phys. 86, 1249-1257. 

Similar to QSS, direct recoil (DR) of surface atoms produces energetic atoms that have a relatively narrow velocity distribution. DR particles are those species which are recoiled from the surface layers as a result of a direct collision of the primary ion. They escape from the surface with little energy loss through collisions with... 

Figure Bl.23.2. (a) Shadow cone of a stationary Pt atom in a 4 keV Ne ion beam, appearing with the overlapping of ion trajectories as a fiinction of the impact parameter. The initial position of the target atom that recoils in the collision is indicated by a solid circle, (b) Plot of the nonnalized ion flux distribution density across the shadow cone in (a). The flux density changes from 0 inside the shadow cone, to much greater than l in the focusing region, converging to 1 away from the shadow cone edge, (c) Blocking cones...

In TOF-SARS [9], a low-keV, monoenergetic, mass-selected, pulsed noble gas ion beam is focused onto a sample surface. The velocity distributions of scattered and recoiled particles are measured by standard TOF methods. A chaimel electron multiplier is used to detect fast (>800 eV) neutrals and ions. This type of detector has a small acceptance solid angle. A fixed angle is used between the pulsed ion beam and detector directions with respect to the sample as shown in figure Bl.23.4. The sample has to be rotated to measure ion scattering... 

Oil Contamination of Helium Gas. For more than 20 years, helium gas has been used in a variety of nuclear experiments to collect, carry, and concentrate fission-recoil fragments and other nuclear reaction products. Reaction products, often isotropically distributed, come to rest in helium at atmospheric concentration by coUisional energy exchange. The helium is then allowed to flow through a capillary and then through a pinhole into a much higher vacuum. The helium thus collects, carries, and concentrates products that are much heavier than itself, electrically charged or neutral, onto a detector... 

Attempts have been made to calculate the recoil energy spectrum using an assumed statistical distribution of y-energies and direction. Notably, Hsiung et al. (39) have done this calculation for C1 produced by CCI4 (n,y). While the results of the calculation were in reasonble agreement with experimental data, the complexity of the necessary assumptions makes the agreement seem perhaps fortuitous. 

The temperature dependence of sod is related to that of the recoil-free fraction /(T) = Qxp[— x )Ey / Hc) ], where (x ) is the mean square displacement (2.14). Both quantities, (x ) and can be derived from the Debye model for the energy distribution of phonons in a solid (see Sect. 2.4). The second-order Doppler shift is thereby given as [20]... 

Different locations of parent elements. and Th are generally located in minor phases within host rocks. Due to different U/Th ratios in these phases, recoil from the two chains may be affected by different surrounding matrix characteristics or mineral sizes. Not only might the primary distribution of U and Th be different, but earlier weathering or alteration may also have redistributed U and Th. This is discussed further below. 

From the diversity of potential sites for U and Th, it is clear that the weathering release of and Th, as well as of the recoil and leaching release of daughter nuclides, must be determined for each site. Nonetheless, most studies assume that and Th have similar distributions, so that the values for si (the fraction released by recoil) and wi (the weathering release constant) is assumed to be approximately equal for all nuclides I. 

The distribution of Th is not controlled by decay processes that can be used to constrain its supply rate, but the Th- Ra pair can be used to provide some constraints on Th adsorption. In an area where Ra concentrations are constant, mobile Ra is supplied by only recoil and decay of mobile Th. The amount of Th that is absorbed on surfaces can be obtained if the amount of mobile Ra is constrained (i.e., the Ra partition coefficient and the groundwater concentration are known) and can be compared to an estimate of the recoil rate of Ra (using the measured Rn activity in the groundwater) from the host rock. In this way, Luo et al. (2000) calculated that recoil from the host rock was insufficient to explain the amount of mobile Ra, and argued that adsorbed Th provided much of the mobile Ra then Th partition coefficients can... 

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