Vol.28,

To increase spatial resolution and signal-to-noise ratio in PET imaging, we present in this paper the design and performance evaluation of a PET detector module combining both depth of interaction (DOI) and time-of-flight (TOF) capabilities. The detector module consists of a staggered dual-layer LYSO block with 2 mm×2 mm×7 mm crystals. MR-compatible SiPM sensors (MicroFJ-30035-TSV, SensL) are assembled into an 8×8 array. SiPM signals from both fast and slow outputs are read out by a 128-channel ASIC chip. To test its performance, a flood histogram is acquired with a ²²Na point source on top of the detector, the energy resolution and the coincidence resolving time (CRT) value for each individual crystal are measured. The flood histogram shows excellent crystal separation in both layers. The average energy resolution at 511 keV is 14.0% and 12.7% at the bottom and top layers, respectively. The average CRT of a single crystal is 635 ps and 565 ps at the bottom and top layers, respectively. In conclusion, the compact DOI-TOF PET detector module is of excellent crystal identification capability, good energy resolution and reasonable time resolution, and has promising application prospective in clinical TOF PET, PET/MRI and brain PET systems.

516

The method of energy dispersion in magnetic field is used to analyze the energy-spread of the triple-pulse electron beam generated by the Dragon-II linear induction accelerator. A sector magnet is applied for energy analysis of the electron beam, with a bending radius of 300 mm and a deflection angle of 90°. For each pulse, the time-resolved and integral images of the electron position at the output port of beam-bending line are recorded by a streak camera and a CCD camera, respectively. Experimental results demonstrate an energy-spread of less than ±2.0% for the electron pulses. The cavity voltage waveforms obtained by different detectors are also analyzed for comparison.

603

It is well-known that inter-crystal scattering and penetration (ICS-P) are major spatial resolution limiting parameters in dedicated SPECT scanner with pixelated crystals. In this study, the effect of ICS-P on crystal identification in different crystal configurations was evaluated using GATE Monte Carlo simulation. A ^99mTc pencil-beam towards central crystal element was utilized. Beam incident-angle was assumed to vary from 0° to 45° in 5° steps. The effects of various crystal configurations such as pixel-size, pixel-gap, and crystal material were studied. The influence of photon energy on CI was investigated. Position-detection-accuracy (PDA) was defined as a factor indicating performance of the crystal. Furthermore, a set of ^99mTc point-source simulations was performed in order to calculate peak-to-valley (PVR) ratio for each configuration. The results show that the CsI(Na) manifests higher PDA than NaI(Tl) and YAP(Ce). In addition, as the incident-angle increases, the crystal becomes less accurate in positioning of the events. Beyond a crystal-dependent critical-angle, the PDA is monotonically reduced. The PDA reaches 0.44 for the CsI(Na) at 45° beam-angle. PDAs obtained by the point-source evaluation also behave the same as for pencil-beam irradiations. In addition, PVRs derived from flood images linearly correlates their corresponding PDAs. In conclusion, quantitative assessment of ICS-P is mandatory for scanner design and modeling the system-matrix during iterative reconstruction algorithms for the purpose of resolution modeling in ultra-high-resolution SPECT.

602

Due to variable time for charge collection, energy resolution of nuclear detectors declines, especially compound semiconductordetectors like cadmium zinc telluride (CdZnTe) detector,. To solve this problem, an analog rise-time discriminator based on charge comparison principle is designed. The reference charge signal after attenuation is compared with the deconvoluted and delayed current signal. It is found that the amplitude of delayed current signal is higher than that of the reference charge signal when rise time of the input signal is shorter than the discrimination time, thus generating gating signal and triggering DMCA (digital multi-channel analyzer) to receive the total integral charge signal. When rise time of the input signal is longer than discrimination time, DMCA remains inactivated and the corresponding total integral charge signal is abandoned. Test results show that combination of the designed rise-time discriminator and DMCA can reduce hole tailing of CdZnTe detector significantly. Energy resolution of the system is 0.98%@662keV and it is still excellent under high counting rates.

749

A conventional multi-channel pulse amplitude analyzer (MCA) acquires single energy spectrum, but provides no information on its tendency with time. To address the limitation, we propose a scheme of time-sharing multi-channel pulse amplitude analyzer (TSMCA). A dual port random access memory (DPRAM) is divided into two storage spaces, one for current energy spectrum data acquisition and another for previous energy spectrum data storage. The two tasks can be performed simultaneously, and the time-related variation tendency of energy spectrum can be obtained. A prototype system of TSMCA is designed. It performs nicely, with maximum channel number of 4096 in capacity of 2³²/Ch, minimal time-sharing slice of 25 ms, the differential non-linearity (DNL) of <1.5%, and the integral non-linearity (INL) of <0.3%.

624

An amidoxime-based polymeric adsorbent was prepared by pre-irradiation grafting of acrylonitrile (AN) and acrylic acid (AA) onto high density polyethylene fibers (HDPE) using electron beams, followed by amidoximation. Quantitative recovery of uranium was investigated by flow-through experiment using simulated seawater and marine test in natural seawater. The maximum amount of uranium uptake was 2.51 mg/g-ads after 42 days of contact with simulated seawater and 0.13 mg/g-ads for 15 days of contact with natural seawater. A lower uranium uptake in marine test can be attributed to the short adsorption time and the contamination of marine microorganisms and iron. However, the high selectivity towards uranium against vanadium may be beneficial to harvest uranyl ion onto adsorbents and the economic feasibility for recovery of uranium from seawater.

638

An accelerator storage ring needs clean ultra-high vacuum. A TiZrV non-evaporable getter (NEG) film deposited on interior walls of the chamber can realize distributed pumping, effective vacuum improvement and reduced longitudinal pressure gradient. But accumulation of pollutants such as N₂ and O₂, will decrease the adsorption ability of the NEG, leading to a reduction of NEG lifetime. Therefore, an NEG thin film coated with a layer of Pd, which has high diffusion rate and absorption ability for H₂, can extend the service life of NEG and improve the pumping rate of H₂ as well. In this paper, with argon as discharge gas, a magnetron sputtering method is adopted to prepare TiZrV-Pd films in a long straight pipe. By SEM measurement, deposition rates of TiZrV-Pd films are analyzed under different deposition parameters, such as magnetic field strength, gas flow rate, discharge current, discharge voltage and working pressure. By comparing the experimental results with the simulation results based on Sigmund’s theory, the Pd deposition rate C can be estimated by the sputtered depth.

458

Alpha radiolysis of nitric acid aqueous solution by a ²³⁸Pu source is investigated experimentally and theoretically. The time dependence of the nitrous acid yield on dose rate, nitric acid concentration, and nitrate ion concentration is studied. A novel kinetic model for the α-radiolysis of nitric acid aqueous solution is established, by considering the direct and indirect effects,. The simulation results agree well with the experimental data, indicating the validity of our model to treat the reaction paths for generation and consumption of nitrous acid. It is shown that the redox reactions involving Pu cannot be neglected in the α-radiolysis of the solution. The results provide a better understanding of the α-ray radiolysis of aqueous nitric acid.

621

To the transverse beam collimation system in a rapid cycling synchrotron (RCS), an important component is the primary collimator, which improves emittance of the beam halo particles such that the particles outside the predefined trajectory can be absorbed by the secondary collimators. Given the material properties and power deposition distribution, the beam scraper of the primary collimator is a 0.17 mm tungsten foil on a double face-wedged copper block of 121.5 mm×20 mm. The heat is transferred to the outside by a ϕ34 mm copper rod. In this paper, for minimizing brazing thermal stress, we report our theoretical analysis and tests on brazing the tungsten and copper materials which differ greatly in size. We show that the thermal stress effect can be controlled effectively by creating stress relief grooves on the copper block and inserting a tungsten transition layer into the copper block. This innovation contributes to the successful R&D of the primary collimator. And this study may be of help for working out a brazing plan of similar structures.

618

A method for analyzing the dynamic energy spectrum of intense pulsed ion beam (IPIB) was proposed. Its influence on beam energy deposition in metal target was studied with IPIB produced by two types of magnetically insulated diodes (MID). The emission of IPIB was described with space charge limitation model and the dynamic energy spectrum was further analyzed with time-of-flight (TOF) method. IPIBs generated by pulsed accelerators of BIPPAB-450 (active MID) and TEMP-4M (passive MID) were studied. The dynamic energy spectrum was used to deduce the power density distribution of IPIB in the target with Monte Carlo simulation and infrared imaging diagnostics. The effect on the distribution and evolution of thermal field induced by the characteristics of IPIB dynamic energy spectrum was discussed.

526

In this paper, the ⁹⁰Sr/⁹⁰Y coating effects on scattering width (SW) of cylindrical conductor targets are investigated. The electron density distribution of plasma around cylindrical targets of different radiuses is simulated under different radioactivities in normal or oblique incidence. In normal incidence, the SWs are examined as functions of frequency and scattering angle; while in oblique incidence, the SW is inspected as a function of incident angle at the frequency of 1.5 GHz. The results obtained are compared with those from an ideal perfect electric conductor (PEC) cylinder. It is demonstrated that the SW decreases over a wide frequency range in the back scattering region by coating a ⁹⁰Sr/⁹⁰Y layer on the cylindrical target. Moreover, the reduction of bi-static SW amplitude can reach 3–20 dB, when the incident angle is smaller than 30° at 1.5 GHz. It is a significant improvement in the stealth effect.

435

Traditional Fourier transform infrared (FTIR) spectroscopy has been recognized as a valuable method to characterize and classify kinds of microorganisms. In this study, combined with multivariate statistical analysis, synchrotron radiation-based FTIR (SR-FTIR) micro- spectroscopy was applied to identify and discriminate 10 foodborne bacterial strains. Our results show that the whole spectra (3000–900 cm⁻¹) and three subdivided spectral regions (3000–2800, 1800–1500 and 1200–900 cm⁻¹, representing lipids, proteins and polysaccharides, respectively) can be used to type bacteria. Either the whole spectra or the three subdivided spectra is good for discriminating the bacteria at levels of species and subspecies, but the whole spectra should be given preference at the genus level. The findings demonstrate that SR-FTIR microspectroscopy is a powerful tool to identify and classify foodborne pathogenic bacteria at the genus, species and subspecies level.

524

Heavy-ion collisions are powerful tools for studying hypernuclear physics. We develop a dynamical coalescence model coupled with an ART model (version 1.0) to study the production rates of light nuclear clusters and hypernuclei in heavy-ion reactions, for instance, the deuteron (d), triton (t), helium (³He), and hypertriton (Λ3H) in minimum bias (0-80% centrality) ⁶Li + ¹²C reactions at beam energy of 3.5 A GeV. The penalty factor for light clusters is extracted from the yields, and the distributions of θ angle of particles, which provide direct suggesetions about the location of particle detectors in the near future facility–High Intensity Heavy-Ion Accelerator Facility (HIAF) are investigated. Our calculation demonstrates that HIAF is suitable for studying hypernuclear physics.

438

In pursuit of high-precision beam position measurements at micrometers or sub-micrometers for the Shanghai soft X-ray free-electron laser (SXFEL) facility which is under construction in the vicinity of the Shanghai Synchrotron Radiation Facility (SSRF). A high Q cavity beam position monitor (CBPM) with a resonant frequency of 4.7 GHz is developed by the Shanghai Institute of Applied Physics, and the relevant BPM electronics with a dedicated RF front end, and a digital BPM (DBPM), are completed. The cavity design, cold test, system architecture, and first beam test are performed at the Shanghai Deep ultraviolet free-electron laser ^[1] (SDUV-FEL) facility. Results of the beam experiment show that the performance of the CBPM is consistent with basic expectations, and the beam position resolution can fulfill the requirements for the SXFEL project if the beam conditions are optimized.

661

Laser oscillator synchronization with RF reference signal is ultra important for a modern light source based on the accelerator. For Tsinghua Thomson-scattering X-ray source (TTX), we have synchronized the mode locked laser oscillator to RF reference signal with 48.2 fs RMS relative jitter. Both fundamental and harmonic signals derived from photo diode detection are used for laser-RF synchronization in our scheme. The fundamental signal is for coarse laser-RF synchronization and multiple laser oscillators synchronization. The harmonic signal is for high precise phase locking. The digital phase detector is implemented in the synchronization scheme for less noise, replacing the mixing to DC phase detection scheme. The digital processing algorithm for synchronization is commonly used in Low Level RF control (LLRF) field. In order to test the phase locking loop logic without damaging the real laser oscillator, a laser oscillator emulator was developed for phase locking. This paper will report the laser-RF synchronization scheme and its performance. The laser oscillator emulator system will also be introduced here.

629