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The de Broglie?Bohm interpretation of quantum mechanics with and
without spin-dependence is used to determine electron
trajectories, arrival-time distribution of electrons and the mean
arrival time of spin$-1/2$ particles (including electrons) in the
presence of a uniform field and a barrier separately. The
difference for the mean arrival times, which are calculated with
different guidance equations, is examined versus mass of the
arriving particle and versus group velocity of the arriving
electron wave packet and also versus the width of the barrier.
Numerical calculations show that these differences are of the
order of $10^{-18}?10^{-17}$ s. Another feature of the modified
guidance lawis that Bohmian trajectories cross each other, but
this does not contradict the single-valuedness of the
wavefunction.
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