How does helium help detect leaks in aerospace and vacuum systems?

Helium is highly effective for leak detection in aerospace and vacuum systems primarily due to its small atomic size and its nonreactive, inert nature.1

To locate leaks, a small mass spectrometer equipped with an electron-bombardment ion source is connected to the system being tested. The mass spectrometer is specifically calibrated to detect helium. When the gas is applied to suspected areas using a capillary, it enters through any existing leaks. Once the helium enters the system, it triggers a signal in the mass spectrometer, allowing technicians to pinpoint the exact location of the leak through careful manipulation of the capillary.2