Gas-Filled Time-of-Flight Method And Its Application In Accelerator Mass Spectrometry Measurements

Accelerator mass spectrometry (AMS) technique has been developing rapidly since 1970's. More and more nuclides were measured by AMS. Strengthening the ability of isobaric identification has been one of the most important goals in the development of AMS techniques. The development of small size (or even "on desk") AMS facilities has become one of the trends in nowadays AMS community. On the other hand, heavy fission nuclides, such as ⁷⁹Se, ⁹³Zr and ⁹⁹Tc AMS measurements required better resolution. That makes the isobaric identification even more acute topic. In an effort to improve the resolution of isobaric identification, a new kind of gas-filled time-of-flight (GF-TOF) detection method developed in this work is to be described.GF-TOF method was first studied from both theoretical and experimental aspects. The separation power of the method is dependent on the ion energy and flight length. It combines the advantages of bothâ–³E-E and TOF methods, so it was expected to improve the sensitivity of isotope measurements.A GF-TOF detection system has been set up based on the CIAE HI-13 tandem AMS system. The ³⁶C1 and ³⁶S ions were selected to test the GF-TOF detection system. The time resolution of GF-TOF system in relation to the residual energy and flight length was carefully studied. Finally, the optimum conditions to identify ³⁶C1 and ³⁶S ions have been obtained. ³⁶C1 and ³⁶S ions have been successfully identified at different incident energies. The time resolutions of the system without gas filled are 352±30, 580±30 and 920±45 ps with the ³⁶C1 incident ion energy of 64, 48 and 33 MeV, namely, the terminal voltages of accelerator are 8.0, 6.0 and 4.1 MV, respectively. A Series of AgC1 samples have been measured by the GF-TOF detector. The comparison of the separation power between the GF-TOF method andâ–³E-E method is given. The experiment results indicate that the separation power ofâ–³E-E method is better than GF-TOF method at the energy larger than 40 MeV, while the separation power of GF-TOF method is better thanâ–³E-E method at the energy about 30 MeV. Two water samples taken from 3158.9 m and 2950 m underground have been measured with the energy of 40 MeV by the GF-TOF method. The values of ³⁶C1/C1 are (1.35±0.41)×10^-12 and (3.17±1.10)×10^-13, respectively. Our results also show the sensitivity of the GF-TOF detection method for ³⁶C1 AMS measurements is about 3.0x10^-15 and 4.0x10^-14 with the energy of 64 and 40 MeV, respectively。A new detection method for isobaric identification, named gas-filled magnet and time-of-flight (GFM-TOF) is proposed based on the GF-TOF method and gas-filled magnet. A kinematical calculation of GFM-TOF method has been carried out through some modification of gas-filled magnet method and GF-TOF method. Some heavy nuclides, such as ⁷⁹Se and ⁹⁹Tc are theoretically analyzed by GFM-TOF method. The comparison of the separation power between the GFM-TOF method and GFM method is given. Finally, the possible application of the method is discussed.The author's main contributions of the work include the following aspects:(1) Development of GF-TOF detector system with good time resolution(2) Identification of ³⁶C1 and ³⁶S ions by this system(3)Measurement of a series of samples for ³⁶C1 using this system(4)Proposition and theoretical analysis of a new kind of GFM-TOF detection system for AMS...