Trap lifetimes

At low fields, the transit time may become comparable to the trapping lifetime. Under these conditions, some of the carriers will be trapped before they transit the thickness and their contribution to the photoinduced discharge will be proportionally less. For these conditions... 

Seki (1974) measured electron mobilities in TNF and PVK mixtures. The mobilities were in the range of 10-9 to 10-6 cm2/Vs and strongly field dependent. A key feature of Seki s results is the superimposition of current transients, when normalized to the transit time, for transit times varying by over two orders of magnitude. This is described as universality and a fundamental prediction of the Scher-Montroll (1975) formalism. The room temperature results are illustrated in Fig. 20. Seki argued that the free and trapping lifetimes... 

A spectrum is built up from at least a million lifetime measurements from individual positrons. Standard computer codes are available for the decomposition of the spectra including POSITRONFIT in which a least squares fit is used to fit a model spectrum with a given number of decay components to the observed spectrum. Maximum entropy techniques have also been used to determine the most probable underlying distribution of trap lifetimes. As the number of different traps increases, interpretation becomes increasingly difficult. Several research groups have published positron annihilation lifetime data on irradiated RPV steels (see Section 9.11.1). 

Starting with the field-free diffusion lifetime, the trap lifetime can be obtained by solving the diffusion equation with the boundary condition that the molecule density be zero at the walls of the cylindrical cell. The lifetime of the lowest-order field-free diffusion mode is given by... 

This spin-spin driven helium induced Zeeman relaxation is likely to be the dominant relaxation mechanism for molecules for which the spin-spin coefficient (kss) is larger than the spin-rotation coefficient (ysr). It is not clear from this qualitative model whether the additional 1 (jlb of magnetic moment gained in moving from E molecules to E states is worth the trouble. If the spin-spin driven Zeeman relaxation of E molecules is too strong, the trap lifetime will be substantially limited by inelastic collisions and not the trap depth. In 2003, a quantitative calculation was performed by Krems and colleagues that predicted a favorable Zeeman relaxation rate coefficient for imidogen (NH) with helium [35,36]. Furthermore, experiments... 

Spin Trap Synthesis and purification -Octanoljwater partition coefficient Examples of radicals trapped Lifetime of superoxide radical adduct relative to DMPO Comments... 

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