I have been reading papers related to the theoretical computation of a neutron monitor count rate, which is defined as the integral of the "yield function" of the specific neutron monitor times the energy spectrum of CR in the insterstellar medium. I know that the "yield function" is related to the response of the the neutron monitor, but I still don´t understand what information do you get when you plot or analyse this function, does it have any physical meaning itself?
It's just how much signal the monitor "yields" for a given energy. You'd like that function to be 100% everywhere, but typically there is some efficiency which drops that maximum efficiency to, well, whatever, 17.3%, and then in addition, there will be a energy dependence for example due to neutron cross sections being energy dependent and due to a trigger roll-off, etc.
Hence, yes, there is a physical meaning: This yield function by itself is the response of a monitor to a hypothetical neutron spectrum that is flat in energy.