2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/124655By placing a ${}^{133}Cs$ $γ$-ray source embedded in a solid at the center of a platinum (gold) cylinder, we try to change the width of the 81-keV level. Our results show a narrowed energy level and, equivalently, a prolonged lifetime. With a 0.5-mm-thick, 5-cm-long, 2-mm-diameter platinum cylinder, we obtain a width narrower by $6.1 % $ at $4.2 \: K$.Nuclear TheoryNuclear Experimenttext