236U accelerator mass spectrometry with a time-of-flight and energy detection system

Abstract

A time-of-flight and energy (TOF-E) detection system for the measurement of 236U accelerator mass spectrometry (AMS) has been developed to improve the 236U/238U sensitivity at Micro Analysis Laboratory, Tandem accelerator (MALT), The University of Tokyo. With observing TOF distribution of 235U, 236U and 238U, this TOF-E detection system has clearly separated 236U from the interference of 235U and 238U when measuring three kinds of uranium standards. In addition, we have developed a novel method combining kernel-based density estimation method and multi-Gaussian fitting method to estimate the 236U/238U sensitivity of the TOF-E detection system. Using this new estimation method, 3.4 × 10−12 of 236U/238U sensitivity and 1.9 ns of time resolution are obtained. 236U/238U sensitivity of TOF-E detection system has improved two orders of magnitude better than that of previous gas ionization chamber. Moreover, unknown species other than uranium isotopes were also observed in the measurement of a surface soil sample, which has demonstrated that TOF-E detection system has a higher sensitivity in particle identification. With its high sensibility in mass determination, this TOF-E detection system could also be used in other heavy isotope AMS.