  We consider the survival probability of a particle in the presence of a
finite number of diffusing traps in one dimension. Since the general solution
for this quantity is not known when the number of traps is greater than two, we
devise a perturbation series expansion in the diffusion constant of the
particle. We calculate the persistence exponent associated with the particle's
survival probability to second order and find that it is characterised by the
asymmetry in the number of traps initially positioned on each side of the
particle.
