Stepped-up development of accelerator mass spectrometry method for the detection of 60Fe with the HI-13 tandem accelerator

Abstract

The Moon provides a unique environment for investigating nearby astrophysical events such as supernovae. Lunar samples retain valuable information from these events, via detectable long-lived “fingerprint” radionuclides such as \({}^{60} \hbox{Fe}\). In this work, we stepped up the development of an accelerator mass spectrometry (AMS) method for detecting \({}^{60} \hbox{Fe}\) using the HI-13 tandem accelerator at the China Institute of Atomic Energy (CIAE). Since interferences could not be sufficiently removed solely with the existing magnetic systems of the tandem accelerator and the following Q3D magnetic spectrograph, a Wien filter with a maximum voltage of \(\pm\,60\,\text {kV}\) and a maximum magnetic field of 0.3 T was installed after the accelerator magnetic systems to lower the detection background for the low abundance nuclide \({}^{60} \hbox{Fe}\). A \(1\,\upmu \text {m}\) thick Si\(_{3}\)N\(_{4}\) foil was installed in front of the Q3D as an energy degrader. For particle detection, a multi-anode gas ionization chamber was mounted at the center of the focal plane of the spectrograph. Finally, an \({}^{60} \hbox{Fe}\) sample with an abundance of \(1.125 \times 10^{-10}\) was used to test the new AMS system. These results indicate that \({}^{60} \hbox{Fe}\) can be clearly distinguished from the isobar \({}^{60} \hbox{Ni}\). The sensitivity was assessed to be better than \(4.3 \times 10^{-14}\) based on blank sample measurements lasting \(5.8\) h, and the sensitivity could, in principle, be expected to be approximately \(2.5 \times 10^{-15}\) when the data were accumulated for 100 h, which is feasible for future lunar sample measurements because the main contaminants were sufficiently separated.