These combine ion-counting detection with an ion optic design to maximize sensitivity, capable of measuring a few thousand atoms.
Noble gases are the natural places to study nuclear effects in nature.
Their low natural abundance means that their isotope ratios are easily changed by even low yield nuclear reactions. Combining nearly perfect ion optics with the ultimate sensitivity afforded by ion-counting detection and the unique chemical properties of noble gases resulted in an instrument that can measure samples containing as few as several thousand noble gas atoms. Focused laser heating allows the noble gases contained in individual micron-sized mineral grains to be routinely studied. Iodine-129 is made only in supernovae where freshly processed material is ejected molecular clouds. These clouds coalesced to form the solar nebula and eventually solid material while live Iodine-129 did exist in the early solar system.