The status of TOF-E detection system at MALT and its proceedings
Mr Li Zheng1, Mr Takeyasu Yamagata1, Mr Hiroyuki Matsuzaki1
1The University Of Tokyo, , Japan
Accelerator Mass Spectrometry (AMS) is the most sensitive technique for the measurement of ²³⁶U. A Time of Flight-Energy (TOF-E) detection system is the most appropriate technique to discriminate ²³⁶U from ²³⁸U, ²³⁵U and other interferences. Micro Analysis Laboratory, Tandem Accelerator (MALT) aims to improve the sensitivity of ²³⁶U/²³⁸U from 3×10-¹⁰ to 10-¹³ with the installation of TOF-E detection system.
Due to only 0.4% of energy difference of ²³⁶U and ²³⁵U and 0.8% of energy difference of ²³⁶U and ²³⁸U, it is difficult to clearly identify them by gas ionization chamber (GIC). However, with their distinct velocity difference among ²³⁵U, ²³⁶U and ²³⁸U, it is sufficient to separate ²³⁶U from ²³⁵U and ²³⁸U even in naturally occurring ²³⁶U sample using flight time technique. Currently, MALT has acquired starting timing signal and stopping timing signal using two identical Microchannel Plates (MCPs). Additionally, a silicon surface barrier detector (SBD) is also scheduled to the determination of stopping timing and energy with its fast time response and higher energy resolution. In order to achieve higher sensitivity of uranium AMS, several TOF-E detection configurations will be set and optimized.
Prior to the construction of realistic TOF-E detection system, a (Geometry and Tracking version 4) Geant4 Monte Carlo simulation of TOF-E detection system has been completed. several detection configurations with three thicknesses of carbon foil as secondary electron device have been simulated. From simulation results, it shows that the thickness of carbon foil is one key factor to efficiency and time resolution. The thinner the carbon foil, the better efficiency and time resolution. Adopting the setting of a MCP as starting timing detector and SBD as stopping timing detector and energy detector with 2.4 meters of flight path and 3 ug/cm² of carbon foil, flight time difference of ²³⁶U and ²³⁵U, and ²³⁶U and ²³⁸U are 3 ns and -6 ns, respectively, and the full width at half maximum (FWHM) of ²³⁵U, ²³⁶U and ²³⁸U are nearly identical, 1 ns. The simulation results have demonstrated that the above setting is adequate to identify ²³⁶U from ²³⁵U, ²³⁸U.
SBD can be set as energy detector with its higher energy resolution and at same time as stop timing detector with its fast time response. The time response and energy reconstruction of SBD has been simulated by using Garfield simulation. The uranium energy reconstruction with Pulse height spectrum is needed to compare with the following realistic experiment.
Simulation can offer useful information to experiment.The related experiments are under proceeding and uranium AMS will be measured by using this TOF-E detection system.
Mr Li Zheng, a PhD candidate, focus on the study of uranium AMS. He is working on the development of time of flight detection system in order to improve the sensitivity of uranium AMS.