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.