2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/179780We propose a new method of alpha($α$)-ray measurement that detects helium atoms with a Quadrupole Mass Spectrometer(QMS). A demonstration is undertaken with a plastic-covered $^{241}$Am $α$-emitting source to detect $α$-rays stopped in the capsule. We successfully detect helium atoms that diffuse out of the capsule by accumulating them for one to 20 hours in a closed chamber. The detected amount is found to be proportional to the accumulation time. Our method is applicable to probe $α$-emitting radioactivity in bulk material.8 pages, 6 figuresNuclear Experimenttext