Accelerator Mass Spectrometry

In 2003, a new AMS program dedicated to nuclear astrophysics was added as an additional dimension to the available detection techniques at the NSL. It provides the capability of measuring radioactive probes and developing innovative AMS detection techniques that only two other facilities worldwide (TU Munich and ANU Canberra) can currently provide.

The current main scientific focus of ND’s AMS group is to provide an additional technique, unique in North America in this configuration, to the nuclear astrophysics research efforts at the NSL. It combines the high sensitivity provided by the gas-filled magnet AMS analysis technique, with the energies and beams made available by the FN accelerator, as well as the accessibility to beam time. This supports a wide ranging experimental portfolio essential to the successful study of stellar reaction processes that drive and characterize the different phases of stellar evolution (e.g. 44Ti, 60Fe). In addition to this, it provides the necessary tools  for the study of radioactivities in the early solar system (e.g. 36Cl, 53Mn, 60Fe, and 93Zr), as well as giving us the ability to detect probes linked to planetary formation and differentiation (e.g. 53Mn, 146Sm). By providing a highly sensitive detection method for radioactive probes associated with environmental and early paleoclimate research (e.g.14C), AMS adds a dimension essential to the development of a comprehensive program geared towards understanding the universe surrounding us.

The high sensitivity that makes AMS such a powerful tool in the measurement of extremely low isotopic compositions of sub-milligram samples, relies on the combination of high isotopic selectivity (provided by a combination of low energy injection and high energy analysis), followed by high isobaric separation and suppression of the interfering isotope. However, instead of distinguishing the ions by their mass only, the AMS method generally measures both the mass and the nuclear charge for individually counted ions. To achieve this, the ions must be accelerated to several MeV per nucleon. After acceleration and pre-selection, the high energy particles enter a detection system. An important aspect is that these detectors, commonly used in nuclear physics experiments, can identify ions otherwise indistinguishable by measuring properties that depend on nuclear charge rather than ionic charge. In particular the range, energy, time-of-flight and stopping power in matter are utilized.