Using exotic atoms to keep borders safe

Abstract

Muons, created by a particle accelerator, can be used to scan cargo for special nuclear materials (SNM). These muons have a sufficiently long lifetime and are penetrating enough that they can be used to actively scan cargo to ensure the non-proliferation of SNM. A set of "proof-of-concept" experiments have been performed to show that active muon analysis can be used. Experiments were performed at high intensity, medium energy particle accelerators (TRIUMF and PSI). Negative muons form exotic atoms with one electron replaced by the muon. Since the muon is captured in an excited state, it will give off x-rays which can be detected by high purity germanium detectors. The characteristic x-ray spectrum can be potentially used to identify nuclides. The muonic x-rays corresponding to the SNM of interest have been measured, even with the use of various shielding configurations composed of lead, iron, polyethylene, or fibreglass. These preliminary results show that muon scanning systems can be successfully used to find shielded SNM, helping to ensure the safety of all citizens.