The previous chapters concerning neutron emission measurements highlight phono-fission reactions during mechanical tests on iron-rich natural materials. Based on this experimental evidence, iron can be considered as a chemical element subject to fission into aluminum or into magnesium and silicon. In the present chapter, the Instrumental Neutron Activation Analysis (INAA) is applied in order to provide an additional experimental evidence to elemental content variations in mortar specimens subjected to compression tests up to crushing failure. To emphasize the occurrence of such a phenomenon also in artificial materials, the specimens are highly enriched of iron oxide. Twenty-four chemical elements, including iron, aluminum, magnesium, and silicon, are quantified before and after the mechanical tests by means of both chemical and INAA analyses. Our intention is mainly that of confirming the presence of low-energy nuclear reactions involving fission of iron into aluminum. To this purpose, the volumetric concentrations of iron and aluminum before and after the compression tests of the mortar specimens are presented and discussed.