A new method of alpha ray measurement using a Quadrupole Mass Spectrometer

We 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 241Am 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 1–20 h 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.