Ab Initio Structure of Carbon-14
Code: MFDn
Allocation: 30 million
Carbon-14 (14C), a radioactive isotope found in the atmosphere in trace quantities, has a half-life of years—meaning half the 14C atoms in a sample will have decayed in that time to nitrogen-14. Because of its long, predictable decay process, 14C in organic material provides an invaluable dating method for ages up to about 60,000 years in archaeological and geological samples. The reason for the slow decay rate of the 14C atom, however, is a puzzle. The nucleus of 14C (where the radioactive decay takes place) contains six protons and eight neutrons, and something about the properties of this nucleus leads to the surprisingly long half-life. David Dean of ORNL and colleagues will use 30 million hours on the petascale Jaguar supercomputer at ORNL to calculate properties of the various low-energy states of 14C, which are thought to be responsible for its scientifically useful half-life.
Researchers now know that detailed structure effects lead to an unusually small coupling between some of these low-lying states. The structural anomalies of the low-lying states provides a challenging problem that has not yet been explained by the interactions of the 14 protons and neutrons inside this nucleus. The collaboration will carry out a comprehensive ab initio study of 14C using realistic interactions among the neutrons and protons, including possibly crucial spin-orbit forces that describe the coupling between the orbital motion of neutrons and protons and their internal angular momentum. To carry out these calculations, the speed of the MFDn (Many-Fermion Dynamics nuclear structure) code has been increased by about a factor of 5 when run on the Jaguar supercomputer.
