【作者】 管永精；

【导师】 姜山； 何明；

【作者基本信息】 中国原子能科学研究院 ， 粒子物理与原子核物理， 2006， 博士

【摘要】 从上世纪70年代末到现在近30年的时间里加速器质谱（Accelerator MassSpectrometry，AMS）技术得到了极快的发展，AMS测量的核素在不断增加。小型化乃至“桌面”AMS是当今AMS装置发展的重要趋势。低能AMS专用加速器的广泛使用以及重裂变产物核素测量的需求，对粒子鉴别方法提出了更高的要求。如何提高同量异位素的鉴别能力一直是AMS方法学研究的热点问题之一。有鉴于此，本工作建立了充气飞行时间探测方法，并用于AMS分析实际样品。本论文首次从理论和实验两方面对充气飞行时间探测方法进行了系统的研究。此方法鉴别同量异位素的能力不仅与离子的入射能量有关，还与离子的剩余能量和飞行距离有关，它结合了ΔE-E法和TOF法的特点，有利于提高低能量下同量异位素的测量灵敏度。本文对GF-TOF法进行了详细的论述，建立了基于原子能科学研究院HI-13串列AMS系统的GF-TOF系统。着重研究了³⁶Cl和³⁶S的鉴别条件，包括系统的时间分辨、离子剩余能量的选择、飞行距离的选择以及得到³⁶Cl和³⁶S鉴别的最佳条件。利用GF-TOF法实现了不同入射能量下³⁶Cl和³⁶S的鉴别。在64、48和33 MeV 3个不同的入射能量下（加速器的工作电压分别对应为8.0、6.0和4.1 MV），不充气时系统的时间分辨分别为352±30、580±30和920±45 ps。利用GF-TOF探测系统对一系列的AgCl标准样品进行了测量，并比较了ΔE-E和GF-TOF这两种方法对同量异位素的鉴别能力。实验结果表明，在离子入射能量较高时（＞40 MeV）ΔE-E法有较好的分辨能力，当³⁶Cl离子的能量在30 MeV左右时，GF-TOF法有较好的分辨能力。利用GF-TOF法在入射离子能量为40 MeV的条件下对两个分别取自地下3158.9和2950 m的水样品中³⁶Cl的含量进行了测定，其³⁶Cl／Cl的比值分别为（1.35±0.41）×10^-12和（3.17±1.10）×10^-13。实验结果表明，在64 MeV和40 MeV这两个能量下此方法对于³⁶Cl的测量灵敏度分别为3.0×10^-15和4.0×10¹⁴。本文最后还在GF-TOF法的基础上，提出了一种新的基于充气磁谱仪的用于同量异位素鉴别的探测方法：充气磁谱仪飞行时间法（Gas-filled magnet and time-of flight，GFM-TOF）。在传统的充气磁谱仪法的基础上初步建立了此方法的运动学计算，并进行了重核素的理论分析计算，如⁷⁹Se和⁹⁹Tc，并与充气磁谱仪法的结果进行了对比，最后从理论上给出了此方法的应用范围。作者的在本文中的贡献：（1）首次对GF-TOF法进行了系统的研究；（2）建立了一套时间分辨好的探测系统；（3）实现了同量异位素的鉴别并进行了相关的应用，测量了一系列的³⁶Cl样品；（4）首次对充气磁谱仪—飞行时间这种新方法进行了理论分析。更多还原

【Abstract】 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 both△E-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 and△E-E method is given. The experiment results indicate that the separation power of△E-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 than△E-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更多还原