FIRE (Fission In R-process Elements) is a topical collaboration in nuclear theory jointly funded by the Office of Science of the U.S. Department of Energy and the National Nuclear Security Administration. It involves researchers from three DOE national laboratories, Lawrence Livermore National Laboratory (LLNL), Los Alamos National Laboratory (LANL) and Brookhaven National Laboratory (BNL), as well as from two universities, the University of Notre Dame (ND) and North Carolina State University (NCSU).

The goal of the FIRE collaboration is to determine how the heaviest elements are formed in the cosmos. Most of the heavy elements are formed during the rapid neutron capture process, or r-process. What is the astrophysical environment where such a process takes place remains somewhat of a mystery. Over the past decades, researchers have investigated the possibility that this process occurs in core-collapse supernovae, the merger of two neutron stars, or of a neutron star and a black hole.

Simulations of the r-process involve nuclear reaction network calculations, where the rates of nuclear reactions such as neutron capture and emission, gamma capture and emission, beta decay, and fission are computed for all nuclei involved in the process. This requires both advanced model of nuclear reactions, complex computer codes and high-performance computing facilities, but also a very detailed knowledge of nuclear data. In particular, simulations depend very sensitively on the properties of extremely short-lived neutron-rich atomic nuclei, for which no experimental information is known. Theoretical models of the structure of these nuclei capable of predicting their mass, their excited states, their decay modes, etc., are therefore essential to achieve a reliable prediction of the r-process.

Nuclear fission is an important component of r-process simulations. Since it is one of the main decay mechanisms of heavy and superheavy elements, it will terminate the r-process. In addition, the fission fragments produced when a heavy element splits will also be available to enter the network of nuclear reactions of the r-process, a phenomenon known as fission cycling. Unfortunately, fission is also a very complex quantum phenomenon which is extremely difficult to model. As a result, fission modes (spontaneous fission, neutron-induced fission, beta-delayed fission) have rarely been included in network calculations. The few examples of r-process simulations with fission included make use of over-simplified models of fission. The goal of the FIRE collaboration is to take advantage of the expertise in fission theory of LLNL and LANL to produce the most advanced simulation of the r-process to date.