Americium-241 has been used as a source of low energy gamma photons, it has been used in some applications such as portable X-ray fluorescence equipment (XRF) and common household ionizing smoke detectors. Americium-241 is produced from Pu in nuclear reactors through multiple neutron captures and subsequent beta decays with the plutonium-239 itself being produced mostly from neutron capture and subsequent beta decays by U (99% of natural uranium and usually roughly 97% of low enriched uranium or MOX fuel).