Accelerator mass spectrometry with ANU’s 14 million volt accelerator

Deep-Sea and Lunar Radioisotopes from Nearby Astrophysical Explosions

“…AMS is a mass spectrometric technique that is able to identify radionuclides at their natural abundances, which can be 10 to 17 orders of magnitudes lower than the stable (terrestrial) isotope (e.g., radionuclide 60 Fe versus stable Fe) (117,121). Different than other mass spectrometric techniques, the use of an accelerator allows complete suppression of any interfering background molecules of the same mass from the beam (115)(116)(117).…”

“…Owing to the high particle energies provided by the accelerator, the radionuclides can be identified via nuclear physics-based particle detection methods. Isobaric background suppression improves with particle energy, thus large accelerators providing high particle energies are often necessary; this is especially the case for 60 Fe detection (121,122). By contrast, 244 Pu has no stable isobar (note, molecules are completely destroyed in AMS), thus it faces background from isotopic interference only.…”

“…A 5-mg sample contains ∼5 × 10 18 56 Fe atoms, which at a ratio of 60 Fe/Fe ∼ 5 × 10 −16 corresponds to ∼25,000 60 Fe atoms. A fraction of 2 × 10 −4 ions in the sample will eventually be transmitted and identified with the particle detector (35,68,121), which is equivalent to yielding about five detector events for this sample. Such a sample would last for several hours of measurement before it is fully consumed, i.e., sputtering rates in the ions source are on the order of milligrams per hour.…”

“…If sent unattenuated to the detector, its intensity would completely overwhelm the detector with ∼1,000,000 particles per second. Thus, the 60 Ni beam intensity needs to be reduced before entering the detector, e.g., by the use of a gas-filled magnet, which spatially separates the 60 Ni from the 60 Fe beam (20,121). of magnitude less abundant than the rare 60 Fe.…”

Recent nucleosynthesis in the solar neighbourhood, detected with live radionuclides

“…Both were able to deliver high enough energy in conjunction with dedicated detection systems, as needed to suppress any possible background events. Details of the Munich and ANU (Canberra) system can be found in reference [5] and references [12,13], respectively. For 244 Pu the labs in Vienna (VERA) [14] and Sydney (ANSTO) [15] with their small accelerators could compete and efficiently determine concentrations, because for 244 Pu the determination of the mass number is sufficient for identification, since 244 Pu is the only long lived iosobar.…”