Ams Measurement In The Gf-tof Detection Method

Isobaric identification is very important in accelerator mass spectrometry measurement. Be, 14C, 26A1, 36C1 and 41Ca have been measured using AMS. Measurement of these nuclei are often limited by interferences of isotopes and isobars. The energy loss method is depended on the resolution of the detector and the ion energy. Usually, energy loss method is effective to measure 10Be,14C and 26A1 with the low energy tandem accelerator (Terminate Voltage<5MV), but in measurement of heavy nuclei(e.g. 79Se and 99Tc), most of the accelerator mass spectrometry system is difficult to achieve the requirement, so the energy loss method is limited. In order to improve the power of isobaric identification in accelerator mass spectrometry measurement with low energy, a gas-filled time-of-flight (GF-TOF) detector has been designed and set up in Chinese Institute of Atomic Energy. GF-TOF method is a new method to identify particles. It is significant for miniaturization and popularity of AMS. The principle, construction of this system and the test results off-line and on-line are described respectively.Isobaric identification with GF-TOF method is based on the different time of flight caused by the different energy loss. The resolution of GF-TOF is mainly affected by two factors. First, the rises time of current pulse from start and stop detector. Second, time straggling caused by the energy loss straggling. In order to improve the resolution power, the energy method need increase ion total energy, while, the choice of the right gas pressure, the right flight length and increase total energy are effective to improvement of resolution for GF-TOF method.The structure of the GF-TOF detector system is mainly consisted of microchannel plate (MCP), a surface barrier detector (SBD) and a gas filled chamber. MCP detector determining the start time, SBD determining the stop time and the gas filled chamber is utilizing to design a E-E detector.The article is composed of five sections. First, the application and development of AMS. Second, the isobaric identification methods in AMS measurement. Third, the principle, design and test of the GF-TOF detector system. Fourth, AMS measurement with GF-TOF detector system. Fifth, conclusions and discussions.GF-TOF method is described in detail at chapter 3. Alpha particles of 241Am were used to test the GF-TOF detector system, and the best resolution (FWHM) is about 300ps in vacuum.Measurement of 36CI is very important, 36S interference is unavoidable in AMS measurement. At the same time, CIAE AMS group has a certain experience in measurement of 36C1, so 36C1 was used to test the GF-TOF detector system. The test for the GF-TOF detector system was carried out by the measurement of a 36C1 sample with the HI-13 AMS system. The experimental results for the GF-TOF method and energy loss method are shown in chapter 4.Conclusions and discussions are shown in Chapter 5. The experimental results, problems and shortcomings existed in the experiment are analyzed, and the improve method in the later experiment are discussed.The author designed and improved the GF-TOF detector system based on the original system with the guide of tutors. As the major participant of experiment, the author took apart in the experiment from tip to toe.