Li-ion batteries used as ubiquitous neutron sensors for nuclear forensics

With an increasingly complex worldwide nuclear environment, nuclear forensics provides a deterrent through proper attribution. Identifying the type of event is important in the attribution process, and the lithium battery has the potential to provide significant information for this purpose. The incident neutron spectral fluence is related to the type of nuclear event. The lithium battery is built using materials that can be used to assess the number of incident neutrons, as well as provide threshold detection dependant on the neutron energy. This study looks at correlating the production of various long-lived radioactive isotopes to the incident neutron spectrum. The analysis uses known nuclear cross sections and battery properties to calculate the number of long-lived radioactive elements that can be produced in the solid winding of the active battery elements, which include the cathode, separator, and anode. Some isotopes are only produced above a threshold energy, such as ⁵⁵Co which requires 10.6 MeV neutrons. Other isotopes such as are produced through various reaction channels, mostly ⁶, which is an exothermic reaction, and is not associated with a threshold energy. For a common battery made using a cathode, the results indicate that the isotope production within the battery volume can be used to delineate between neutrons with energies above or below 10 MeV, which is a delineation where high-energy neutrons are used in the nuclear reaction, particularly from DT reactions. An estimate of the incident neutron spectrum can be recovered by using additional threshold reactions to unfold the incident neutron spectrum. Though the radioactive isotope concentration retains limited spectral information, the results demonstrate the capability of reconstructing the incident neutron spectrum through a simplified model of a lithium battery when multiple isotope concentrations are used.