Yaohong Liu

A portable gas sensor based on cataluminescence

We describe a portable gas sensor based on cataluminescence. Miniaturization of the gas sensor was achieved by using a miniature photomultiplier tube, a miniature gas pump and a simple light seal. The signal to noise ratio (SNR) was considered as the evaluation criteria for the design and testing of the sensor. The main source of noise was from thermal background. Optimal working temperature and flow rate were determined experimentally from the viewpoint of improvement in SNR. A series of parameters related to analytical performance was estimated. The limitation of detection of the sensor was 7 ppm (SNR = 3) for ethanol and 10 ppm (SNR = 3) for hydrogen sulphide. Zirconia and barium carbonate were respectively selected as nano-sized catalysts for ethanol and hydrogen sulphide.

Development of a C-Band 4/8 Mev Dual-Energy Accelerator for Cargo Inspection System

Modern cargo inspection system applies dual-energy Xray for material discrimination. Based on the compact Cband 6 MeV standing-wave accelerating structures developed at Tsinghua University, a compact C-band 4/8 MeV dual-energy accelerator has been proposed, fabricated and tested. Compared with that of the conventional S-band 3/6 MeV dual-energy accelerator at Tsinghua University, the volume and the weight of the C-band one has been reduced by ~40% and ~30%, respectively. Detailed review of this C-band dual-energy accelerator is present in the paper. INTRODUCTION Nowadays, cargo inspection system is essential for homeland security and customs control. Dual-energy Xray is necessary for effectively discrimination of materials with similar atomic numbers [1]. Over the last decade, dual-energy accelerators within the energy range of 1-10 MeV have been developed by various research groups [16]. Most of these accelerators are operated at S-band (2856 or 2998 MHz). Accelerators operated at higher frequency such as C-band (5712 MHz) and X-band (9300 MHz) are preferable when space is limited and accurate positioning is required [7]. Compared with X-band ones, C-band accelerators require less production precision and are less likely to detune after brazing [7]. Recently, the research of C-band accelerators for medical and industrial applications is of high interest and many prototypes have been developed [7-12]. Two prototypes of C-band 6 MeV standing-wave biperiodic on-axis coupled linear accelerating structure have been developed at Tsinghua University [7]. A compact 4/8 MeV dual-energy accelerator has been developed based on the prototypes by adjusting the input power as well as the beam loading. ACCELERATING STRUCTURE The prototypes of C-band 6 MeV standing-wave linear accelerating structure have a compact size with a narrow spectrum and a small spot size that can be used for medical and industrial applications. The two prototypes share nearly the same design for the bunching cells and normal cell. Compared with the prototype I, the prototype II has one more normal cell to lower the required input power to achieve the same acceleration. The main parameters of the accelerating structure prototype II are listed in Table 1. In Table 1, the length of the accelerating structure excludes the thermal-cathode gun and the flange at the exit for test. Pm is the required input pulsed power to accelerate 130 mA beam to the nominal 6 MeV. Ea is the corresponding accelerating gradient of the normal cell. Table 1: Parameters of the C-band 6 MeV Accelerating Structure Prototype II Parameter Value Frequency (MHz) 5712 Number of bunching cells 3 Number of normal cells 10 Length (cm) ~31 Quality factor 10000 External coupling factor 1.6 Pm (MW) 1.95 Ea (MV/m) 24 The accelerating structure is cooled by a water jacket. The prototype II after fabrication is shown in Fig. 1. Figure 1: The C-band 6 MeV accelerating structure prototype II. DUAL-ENERGY ACCELERATOR The compact C-band 4/8 MeV dual-energy standingwave accelerator has been developed based on the accelerating structure prototype II, as shown in Fig. 2. The power source of the accelerator is the VMC3109 magnetron from CPI and it’s fed by a domestic solid state modulator. The maximum pulsed and average power are 2.5 MW and 2.5 kW, respectively. Taking the attenuation of the waveguide system between the magnetron and accelerator to be 0.5 dB, the maximum pulsed input power available for the accelerator is ~2.23 MW. The energy variation has been achieved by adjusting the input power as well as the beam loading. Proceedings of IPAC2016, Busan, Korea TUPOW016 08 Applications of Accelerators U04 Security ISBN 978-3-95450-147-2 1775 C op yr ig ht