What is the cause of the reduction in peak microscopic cross section with increasing temperature, shown here for a nuclear resonance?
The nuclear properties of the target material do not actually change with motion, so why does the peak reduction of the target's microscopic cross section ("effective area") suggest that they do? I understand the need to broaden with respect to relative energy of neutron-target, but not to simultaneously reduce the absolute values of the curve itself.
Taking it to an extreme like T-->infinity, I can see that if Doppler broadening were forced to be anchored to the peak, and the curve were merely expanded outward in energy, then the neutron would be considered always to be within the resonance - and, in fact, at the peak energy - which is the opposite of what is intended. Still, when considering just one neutron at a time - say, in a Monte Carlo simulation - if the target's motion is sampled independently from a temperature dependent distribution (e.g. Maxwellian) it would seem appropriate to use zero Kelvin cross sections. Is this true?