Primary result of ²³⁶ U measurement with accelerator mass spectrometry at CIAE

Abstract

The rare isotope 236U has a half-life of 2.342(3) × 107 years, and is produced principally by thermal neutron capture on 235U. The isotopic atom ratio of 236U/238U depends on the integral thermal neutron flux received by the material of interest. 236U is potentially useful as a “fingerprint" for indicating the presence of neutron-irradiated uranium usually originating from nuclear activity. By extracting negative molecular ion UO− from the uranium oxide target, simulating the 236U16O− beam transport with 238U16O− and 208Pb216O− pilot molecular ion beam, transporting the 236U-containing ion beam with a high resolution injection magnet analyzer and electrostatic analyzer system, and finally identifying and detecting 236U with a time-of-flight detector (TOF), a method for AMS (Accelerator Mass Spectrometry) measurement of 236U was established on the HI-13 Accelerator AMS system at China Institute of Atomic Energy.

A comparison between Geant4 simulation and experiment for time-of-flight measurement

“…accelerator mass spectrometry (AMS) has been the most ultrasensitive tool to measure 236 U. [1][2][3][4][5][6][7][8][9] With the small energy difference among 235 U, 236 U and 238 U, it is difficult to precisely separate 236 U from the interference of 235 U and 238 U. A time-of-flight and energy (TOF-E) detection system has been developed at Micro Analysis Laboratory, Tandem Accelerator (MALT), The University of Tokyo, for the measurement of 236 U AMS.…”