A 1 MV AMS system for analysis of actinides

HVE has designed a new high-energy side mass spectrometer with two detection beamlines for its 1 MV multi-element AMS system, supporting analysis of rare isotopes ranging from ¹⁰Be to ²⁴⁴Pu. The beam line that is used for actinide measurements features two high-resolution analyzing magnets with a spherical electrostatic analyzer (ESA) in between and is designed for minimizing measurement background from interfering masses. The mass-energy product of the analyzing magnets of nominal 100 (max 108) AMU × MeV supports measurement of ¹²⁹I²⁺ or ²⁴⁴Pu³⁺ from PuO⁻ at 1 MV terminal voltage. The radius of the magnets was chosen to be 1.2 m to keep its nominal field at a relatively low 1.2 T, avoiding degradation of ion optical quality by saturation effects. For the analysis of actinides like Pu, typically up to 5 isotopes are measured in a cyclic fashion. For this, both high-energy side analyzing magnets are equipped with bouncing capability to direct the various isotopes into suitable Faraday cups or into the final gas ionization detector. Average switching times of the high-energy magnets during bouncing are below 10 ms, and 8 isotopes can be measured at a cycle frequency of more than 1 Hz. Because the various isotopes have a small, but noticeable energy difference in the high-energy spectrometer, a deflector with bouncing capability is incorporated in the mid-plane of the ESA. Minor adjustment of the deflector voltage is incorporated in the isotope cycling, thereby optimizing the transmission of every individual isotope.