Actinides measurement with He stripping at the Centro Nacional de Aceleradores

Trabajo presentado en la 14th International conference on Accelerator Mass Spectrometry, celebrada en Ottawa (Canadá), del 14 al 18 de agosto de 2017
The 1 MV AMS system at the Centro Nacional de Aceleradores (CNA, Seville, Spain) was the first multielemental compact device designed and manufactured by High Voltage Engineering Europa (HVEE, Amersfoort, Netherlands). In February 2015, the stripper gas was changed from Ar to He. Since then, our group has worked extensively on the optimization of the new parameters of the measurement for actinides (236U, 237Np, 239,240Pu and 241,243Am). Besides, additional information on the stripping process with He gas at terminal voltages between 500 and 1000 kV has been gained. Maximum stripping yields for U3+ are achieved at about 650 kV, with a transmission through the accelerator of 38% (47% stripping yield). This is in contrast with Ar gas, with 11% maximum transmission for U3+ (16% stripping yield) [1]. Scattering processes with residual stripping gas along the highenergy acceleration tube, limit drastically the abundance sensitivity that can be actually achieved, on a system where only a sector magnet is available on the high-energy side. A thorough adjustment of the slits and of the stripper gas pressure becomes necessary to achieve competitive figures of merit for: a) 236U, being 9x1011 the lowest 236U /238U atom ratios that can be measured; and b) 237Np, where the 238U scattering tail imposes serious restrictions on the limit of detection. The experienced gained during these years on our system will be shared. On the other hand, the state of the art of the CNA actinides measurement program will be briefly presented.