ABSTRACT
Historical Background .......................................................................................................545
Description of Accelerator Mass Spectrometry..................................................................547
Accelerator Mass Spectrometry Method............................................................................548
Considerations for Human Subjects...................................................................................548
Mathematical Modeling .....................................................................................................549
Human Folate Metabolism ................................................................................................549
Human Vitamin A and b-Carotene Metabolism................................................................ 551 Calcium ..............................................................................................................................553
Summary ............................................................................................................................553
Acknowledgments .............................................................................................................. 554
References .......................................................................................................................... 554
Accelerator mass spectrometry (AMS) harnesses the power of advanced nuclear instruments
to solve important and heretofore unsolvable problems in human nutrition and metabolism.
AMS methods are based on standard nuclear physics concepts. Isotopes of a given element
differ from one another by the number of neutrons in their nucleus. Generally, the isotope
with the lowest number of neutrons in its nucleus is the natural isotope (e.g., 1H,12C). Adding
one neutron typically creates a stable isotope (e.g., 2H,13C), which is similar in most properties
to the natural isotope, but differs in mass and can thus be separated and detected by mass
spectrometry. Isotopes with even greater numbers of neutrons (e.g., 3H,14C) become unstable.
An unstable nucleus such as 14C has excess energy, which is released in the form of particles of
radiation. These radioisotopes can also be detected by mass spectrometry, while more
common and familiar instruments such as liquid scintillation and Geiger counters can detect
their radioactive decay products.
