Vol.23,

In order to improve accuracy of electron beam transverse sizes measurement, the vertical and horizontal synchrotron radiation light interferometers have been designed to measure beam transverse sizes for the upgrade project of Hefei Light Source (HLS II). In this paper, the light intensity distributions of the interferogram are descussed, and parameters of the interferometers are optimized. The interferograms are simulated under MATLAB. Taking integrations of two-dimensional interferogram intensity, normalized one-dimensional interference intensities distribution of the vertical and horizontal interferogram are obtained. The two curves are fitted to compare the beam transverse sizes with the designed sizes, and this verifies the feasibility of this method. Finally, several factors that affect the beam sizes measurement are discussed.

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The performance of a single gas electron multiplier (GEM) in pure Xe at an atmospheric pressure is investigated by Particle in Cell-Monte Carlo Collision (PIC-MCC) model. The micro development processes with electrons and ions distributions in space have been revealed. Based on the micro development processes, the macroscopic parameters such as GEM gain and the effective efficiency have also been obtained. The simulation results indicate that after tens of nanoseconds, electrons are collected by the readout electrode while the ions still exist in the gas space for several microseconds. The main signal current is formed by the electrons arriving at the readout electrode, but electrons and ions are also collected by the copper electrodes near the GEM hole and the thin Kapton film boundary. The simulated gain of GEM exponentially increases with the applied GEM voltage. With the PIC-MCC simulations, both the physical amplification and charging mechanisms in the GEM device can be well understood, which is beneficial to the device design.

422

The far-infrared optical properties of melamine and its deuterated isotope, melamine-d₆ were experimentally and theoretically investigated in the frequency range from 0.2 to 3.0 THz. Under the room temperature and dry air nitrogen conditions, three absorption bands were observed at 2.0, 2.3 and 2.6 THz in the melamine sample by use of terahertz time-domain spectroscopy. Whereas, in the melamine-d₆ sample, the observed absorption bands shift towards lower frequencies and the relative intensity of the absorption bands reduces. Numerical simulation results based on the Parameterized Model number 3 (PM3) were compared with the experimental data and the observed vibration spectra were assigned according to the PM3 calculations. The absorption bands of the measured melamine samples at terahertz frequencies are highly correlated with the intermolecular hydrogen bond stretching and π-π stacking vibration. Also, the red shift of the absorption bands is due to hydrogen/deuterium substitution.

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Tomography reconstruction algorithm is one of the key components of positron emission tomography (PET) scanners, most PET scanners use statistical iterative reconstruction algorithms from data in sinograms currently. However tomography reconstruction using list-mode data has many unique advantages, in recent years great attention has been paid to it, being in the process of rapid development and improvement. In this paper, using experimental data of small animal PET scanner Eplus-166, exploiting ordinary subsetized list-mode EM (S-LMEM) algorithm and orthogonal distance-based ray-tracer (OD-RT), we eventually achieve list-mode tomography reconstruction. System response matrix (SRM), which establishes mapping relationship between the image and the projection space, is one key problem in iterative reconstruction algorithm. OD-RT is based on an optimization Siddon's algorithm to calculate the SRM, generating line-of-response (LOR) which is approximately Gaussian-shaped, achieving better modeling of detector response function (DRF). The results demonstrate that image resolution recovery achieves the inherent properties of the scanner and that on-the-ﬂy ray-tracer for real-time calculation of system response matrix is feasible for dynamic reconstruction. Meanwhile, the optimal parameters for calculating SRM are found by experiments.

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In this paper, the spatial resolution and geometry sensitivity of parallel- and pin-hole collimators in compact gamma camera are presented, and quantitatively compared by GEANT4 code in Monte-Carlo library. The results show that the geometry sensitivity for pinhole collimator rapidly drops with increasing the gamma source-to- collimator distance (SCD); and for parallel-hole collimator, mildly. Meanwhile, the spatial resolution for pin-hole collimator mildly deteriorates; and for parallel-hole collimator, severely. The pin-hole collimator for close imaging objects has higher geometry sensitivity than parallel-hole collimator. Our findings are helpful for setting compact gamma camera collimators in nuclear medicine imaging.

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Due to the large scale of Water Cherenkov Detector Array in Large High Altitude Air Shower Observatory, the frontend digitization is imperative. Thus a clock distribution system is desired, which broadcasts the synchronous clock signals with low jitter to the frontend electronics distributed in the field of 90 000 m². The White Rabbit protocol provides an option, which has been approved to achieve sub-ns accuracy and ps jitter in the synchronization of around 1 000 nodes in the order of 10 km. But the hierarchy of the original is too complex for Large High Altitude Air Shower Observatory application. Thus we proposed a reduced scheme based on the White Rabbit protocol. The validation circuit shows that the clock skew due to the fiber length difference can be adjusted to less than 25 ps and the clock jitter is less than 62 ps.

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A 16-channel gated integrator (GI) module following semi-Gaussian shaping amplifiers was developed for high-resolution energy spectroscopy systems at Institute of Modern Physics, Chinese Academy of Sciences. This GI solved the ballistic deficit problem by integrating the signal until all the charge was collected from the detector at counting rates up to 100 K. In this paper, a fast shaper was used to optimize the gate logic to ensure nonlinearity of the GI less than 0.17%; and a novel compensation approach, to reduce the charge injection from the switches in the GI; and a T-switch configuration, to eliminate leakage current in the reset switch.

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To validate neutronics calculation for the blanket design of fusion-fission hybrid reactor, experiments for measuring reaction rates inside two simulating assemblies are performed. Two benchmark assemblies were developed for the neutronics experiments. A D-T fusion neutron source is placed at the center of the setup. One of them consists of three layers of depleted uranium shells and two layers of polyethylene shells, and these shells are arranged alternatively. The ²³⁸U capture reaction rates are measured using depleted uranium foils and an HPGe gamma spectrometer. The fission reaction rates are measured using a fission chamber coated with depleted uranium. The other assembly consists of depleted uranium and LiH shells. The tritium production rates are measured using the lithium glass scintillation detector which is placed in the LiH region of the assembly. The measured reaction rates are compared with the calculated ones predicted using MCNP code, and C/E values are obtained.

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Fluorescence enhancement in a DNA-dye system is favorable for sensitive and accurate DNA detection/ sensing technologies. In this paper, we report that the fluorescence of the double-stranded DNA (dsDNA) and SYBR Green I (SG) system (dsDNA-SG) can be effectively enhanced by negatively charged magnetic iron oxide (Fe₂O₃@DMSA) and gold nanoparticles in suitable concentrations, but positively charged nanoparticles quench the fluorescence. Effects of the Fe₂O₃@DMSA on the fluorescence intensities are investigated with dsDNA-SG of different lengths or complexities. The results show that nanoparticles perform similarly in enhancing fluorescence intensity for several kinds of dsDNA. However, the dsDNA concentration determines the fluorescence amplitude. It shows that fluorescence intensity of lower concentration dsDNA is enhanced remarkably in DNA-SG. The finding may be useful in sensitive biomolecular detection.

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To study the influence of ethanol molecules on the melittin tetramer folding, we investigated the dewetting transition of the melittin tetramer immersed in pure water and 8% aqueous ethanol solution (mass fraction) by the molecular dynamics simulations. We found that the marked dewetting transitions occurred inside a nanoscale channel of the melittin tetramer both in pure water and in aqueous ethanol solution. Also, ethanol molecules promoted this dewetting transition. We attributed this promoting effect to ethanol molecules which prefer to locate at the liquid- vapor interface and decrease the liquid-vapor surface energy. The results provide insight into the effect of ethanol on the water dewetting phenomena.

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