Helium: When you must be sure it’s ultra-pure

A new method detects residual contaminants in ultra-pure helium gas, critical to nuclear physics experiments

The gas that makes balloons float is also vital to scientific experiments. In these experiments, natural helium (He) is purified, but it contains a tiny bit of a slightly different form of helium, known as the isotope ³He. A sample can contain just one ³He in every million helium atoms. That’s too much for many experiments. Many experiments require ultra-pure helium, with a ³He component at least another million times smaller, or one in a trillion of the He atoms. Although techniques are believed to produce ultra-pure helium, until recently no experimental methods have confirmed that the amount of ³He present in a sample is indeed that small. Now, scientists at the ATLAS facility at Argonne National Laboratory have used accelerator mass spectrometry (AMS) to precisely measure the very small concentrations of ³He present. Read more.