A free neutron decays is about 15 minutes, right ? Besides, neutrons almost don't interact electromagnetically (their total electric charge being zero). If you want to call a material "neutron absorber", most probably you are refering to the ability of this material to stop and store free neutrons, and most probably this happens because of nuclei absorbing the neutrons, thus becoming new isotopes of the element they correspond to. Cadmium-113 for instance does just that in nuclear plants. This does involve nuclear reaction.