Vol.28,

The Shanghai Advanced Proton Therapy (SAPT) facility employs 3^rd integer slow extraction. In order to achieve accurate treatment, high quality spill is needed. Therefore, parameters that may affect slow extraction should be investigated by simulation. A computer model of the synchrotron operation slow extraction was constructed with Matlab^®. By simulating the motion of the circulating protons, we could quantify the influence of machine and initial beam parameters on properties of the extracted beam, such as ripple, uniformity, stability, on- and off-time of the spill and spill width in the synchrotron. Suitable design parameters including the horizontal tunes, power-supply ripple, longitudinal-RF cavity voltage, RF-KO and the chromaticities were determined.

395

In this paper, we present an energy calibration method based on steep Compton edges of the Laser Compton Scattered (LCS) photon energy spectra. It performs consecutive energy calibration in the neighborhood of certain energy, hence the improved calibration precision in the energy region. It can also achieve direct calibration at high energy region (several MeV) where detectors can only be calibrated by extrapolation in conventional methods. These make it suitable for detectors that need wide range energy calibration with high precision. The effects of systematic uncertainties on accuracy of this calibration method are studied by simulation, using the design parameters of a LCS device –SINAP III. The results show that the SINAP III device is able to perform energy calibration work over the energy region of 25–740 keV. The precision of calibration is better than 1.6% from 25 keV to 300 keV, and is better than 0.5% from 300 keV to 740 keV.

420

Cleaning of carbon contaminated beamline optics was studied by RF plasma discharge process using O₂/Ar. Carbon coated samples were prepared and through their cleaning processes key parameters were determined, such as the optimal RF output power, mixing rates of O₂/Ar and chamber vacuum. Considerations were made against possible adverse effects in cleaning the beamline optics, such as comparing the roughness of samples before and after cleaning, and possible detrimental kinetic effects on cable insulation. Under the cleaning parameters to clean the beamline optics, the thickness of removed carbon film and the change in beamline photon flux were analyzed.

432

A setup based on CMOS sensor and ARM microcontroller is designed to measure the γ-rays. STM32F103 is used as the main platform to control real-time on-line analysis of the image collected by the OV7670 CAMERACHIP^TM, and send the image into the LCD at the desired frame rate. Accuracy of sampling interval can be regulated and controlled. The frame number of image is adjusted by STM32F103 to achieve better monitoring. Two methods are adopted to analyze the image data from the CMOS sensor. Although the CMOS sensor is of low efficiency for γ-ray detection, the results show that it is able to discriminate the ⁶⁰Co γ-rays.

349

The detection efficiency of the Fission Chamber (FC) is very important for studying the Neutron Flux Measurement (NFM) system in ITER. In this article we mainly focus our attention on the influence of the moderator. With the Monte Carlo particle transport simulation tool named Geant4 we make a simulation of FC detection efficiency with different levels of thickness of a beryllium moderator. Two manufactured FCs for ITER NFM systems are then used to test the parameters and performance. The test results agree well with our simulation.

504

To improve the accuracy and usability of the superconducting electron cyclotron resonance ion source with advanced design in Lanzhou (SECRAL), an upgraded version of the control system was designed and tested. This paper details the architecture of the optimized control system, and presents the results of its use in the long-term operation of the accelerator. The control system software, based on Visual C++, was developed following the model-view-controller architecture (MVC) design pattern. The data acquisition system was based on a field-programmable gate array (FPGA) integrated circuit. In addition, control strategies were optimized for higher operational stability. The upgraded control system was tested with a U³³⁺ ion beam at SECRAL, where it provided a data acquisition time of less than 1 ms. The fast reaction time and high-precision data processing during beam tuning verified the stability and maintainability of the control system.

467

Beta-ketoacyl-acyl-carrier-protein synthase II, an important enzyme in biosynthesis of bacterial fatty acid, is an attractive target in antibacterial drug design. Platensimycin (PTM), produced by Streptomyces platensis, has a strong, broad-spectrum Gram-positive antibacterial activity by selectively targeting to FabF but exhibits no inhibition to the FabF from Streptomyces platensis (spFabF). To study the self-resistance mechanism within the PTM-producing strain and provide hint for development of novel antibiotics, it is imperative to solve the structure of spFabF and elucidate the difference between spFabF and other FabFs which are not resistant to PTM. To this end, we constructed four chimeric FabFs based on the sequence of spFabF and its homologous protein after the expression of wide-type spFabF was failed. The crystal structure of one chimera, js₂₀₀FabF, of 91.2% sequence identity to spFabF, was solved. A structure comparison of js₂₀₀FabF with a PTM-bound FabF suggested that three loops nearby the catalytic site might play key roles in preventing the binding of PTM to spFabF. The results provide an encouraging basis for further studies on the self-resistance mechanism and structure-based design of novel antibiotics targeting FabFs.

392

Studying interaction between peptides and lipid membranes is helpful for understanding the working mechanism of amyloidogenic peptides and antimicrobial peptides, which are toxic to cells through disruption of the cell membrane. Although many efforts have been made to find out common mechanisms of the peptides–induced membrane disruption, detailed information on how the peptide’s amino acid sequence affects its interaction with lipid bilayers is still lacking. In this study, three peptides termed as Pep11, P11-2, and QQ11, which share a similar backbone, were employed to explore how modifications on the peptide sequence as well as terminal groups influenced its interaction with the lipid membrane. Atomic force microscopy (AFM) data revealed that the peptides could deposit on the membranes and induce defects with varied morphologies and stiffness. Fluorescence resonance energy transfer (FRET) experiments indicated that the introduction of the three peptides resulted in different FRET effects on either liquid or gel lipid membranes. DPH fluorescence anisotropy and Laurdan’s generalizated polarization analysis showed that P11-2 could insert into the lipid membrane and impact the lipid hydrophobic region while QQ11 influenced the order of the hydrophilic head of the lipid membrane. With these results, we have illustrated how these peptides interacted differently with the lipid membrane because of the modification of their sequences. Although these peptides didn’t relate to disease and antibiosis, we hope these results still could provide some clues for partly understanding the working mechanism of amyloidogenic peptides and antimicrobial peptides.

338

The gap parameter of the standard BCS model is replaced by the order parameter of the modified Ginzburg-Landau theory. Using this new form of the BCS model, the energy, entropy, and heat capacity of ^93,94,95Mo nuclei are calculated. The results are compared with the experimental data and standard BCS results. Since the order parameter does not drop to zero at a critical temperature, our results for thermal properties are free of singularities. We have shown that the heat capacity as a function of temperature behaves smoothly and it is highly in agreement with the experimental heat capacity, while heat capacity behaves singularly and discontinuously in the standard BCS model. A smooth peak in the heat capacity is observed which is interpreted as a signature of the transition from the superfluid to the normal phase.

461

Measurement of dose distribution in patients during radiotherapy is impossible. The Monte Carlo simulation is an alternative method for dose calculations. In routine radiotherapy, the Source-to-Surface Distance (SSD) method is not practical for an isocentric unit because it requires numerous values of Tissue-Air Ratios (TARs) and inverse square law. Therefore, this method is time consuming. In this paper, the curves of relative depth doses were obtained for three different SSDs using the MCNP4C Monte Carlo simulation and approximated with a single curve called calibration curve. This curve was compared to the curve obtained by published data, differing in approximately 5% in the worst case. It was also observed that the obtained results were more accurate for distances between -5 cm and 10 cm from Source-to-Axis Distance (SAD).

514

The RF system of CYCIAE-100 cyclotron has two cavities, which are driven separately by two identical 100kW RF amplifiers. Due to the power on sequence issue of the three DDSs in the LLRF systems, each time when the system is individually switched on, the phase relationship may not satisfy the requirements of beam acceleration. Instead of adding an extra reset logic to the system, a search and validation algorithm based on the decision tree has been carried out to make sure the phase of the two cavities is correct right after applying power to the cavities, taking advantage of existing hardware resources. In the first year of operation, there are more than 20 times of scheduled shut down of the cyclotron system. For each time when the cyclotron RF system is completely shutdown and powered on again, the operator confirmed that the phase matching of the two cavities can be done automatically within 30 seconds. The related work, including the optimization of the phase detector and the development and validation of the algorithm are reported in this paper.

546

This paper is to achieve a gamma-ray source with the lowest rate of buildup factor, which is of great importance in medical, industrial and agricultural sciences. The flux buildup factor of gamma-rays is calculated by the MCNP code for point, linear, surface and volume sources with shield layers of lead, iron and aluminum. The results show that for the high Z shielding material, the flux buildup factor of coaxial cylindrical sources is the lowest (1.6-2.3) of all sources, while for low Z shielding materials, the coaxial disk surface sources have smaller buildup factor (1.45 -1.6).

580

Electron beam (EB) degradation of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) in aqueous solutions was studied. Their degradation followed the pseudo-first-order kinetics. The decomposition efficiencies were 95.7% for PFOA and 85.9% for PFOS, by EB irradiation in an anoxic alkaline solution (pH=13). In presence of different radical scavengers, this work indicated hydrated electron and hydrogen radical were important in the electron beam degradation of PFOA and PFOS, especially hydrated electron. The potential degradation pathways of PFOA and PFOS by electron beam irradiation through defluorination and the removal of CH₂ unit were proposed.

360

Molten salt reactor (MSR), with good economics and inherent reliability, is one of the six types of Generation IV candidate reactors. The Basket-Fuel-Assembly Molten Salt Reactor (BFAMSR) is a new concept design based on fuel assemblies composed of fuel pebbles made of TRISO-coated particles. Four refueling patterns, similar to the fuel management strategy for water reactors, are designed and analyzed for BFAMSR in terms of economy and security. The MCNPX is employed to calculate the parameters, such as the total duration time, cycle length, discharge burnup, total discharge quantity of ²³⁵U, total discharge quantity of ²³⁹Pu, neutron flux distribution, and power distribution. The in-out loading pattern has the highest burnup and duration time, the worst neutron-flux and power distribution, and the lowest neutron leakage. The out-in pattern possesses the most uniform neutron-flux distribution, the lowest burnup and total duration time, and the highest neutron leakage. The out-in partition alternate pattern has slightly higher burnup, longer total duration time and smaller neutron leakage than that of the out-in loading pattern at the cost of sacrificing some neutron-flux distribution and power distribution. However, its alternative distribution of fuel elements cut down the refueling time. The low-leakage pattern is the second highest in burnup,and total duration time, and its neutron-flux and power distributions are the second most uniform.

500

We evaluate the hydrogen depletion ability of the hydrogen depletion system for Chinese Pressurized Reactor 1000 (CPR1000), which has been applied in nuclear power plants with pressurized water reactors; Moreover, we introduce a new device that can continuously monitor hydrogen concentration inside the CPR1000 containment building. Experimental studies show that a moveable hydrogen autocatalytic recombiner alone can sufficiently deplete hydrogen under the condition of a design-basis accident, and 33 passive autocatalytic recombiners placed in the areas of high hydrogen concentration satisfy the hydrogen depletion requirements under the condition of a beyond-design-basis accident. Meanwhile, the hydrogen concentration monitoring system is designed and installed based on the approach of detecting the temperature increase caused by the catalytic reaction of hydrogen. In conclusion, the hydrogen depletion capacity of the CPR1000 meets the requirements, and the system’s safety can be enhanced by the improved hydrogen concentration monitoring system.

354

The highest thermal-hydraulic pressure in the containment occurs when reactor coolant in the first loop and steam in the secondary loop discharge simultaneously, and the maximum amount of energy from reactor unit enters to containment volume. In this paper, we investigate temperature and pressure variations in the VVER1000 containment compartments owing to concurrent break in the pipelines of the primary and secondary loops. A two-phase, multicellular model is applied in presence of noncondensable gases. Convection and conduction through the main heat structures inside the containment are also considered. The predicted results agree well with available data. Maximum values of pressure and temperature in the containment are then calculated and compared to the design values. If LOCA and MSLB occur simultaneously, the maximum pressure would exceed the design value and integrity of the containment would be threatened.

386

In order to determine the efficiency of medical devices sterilization by gamma irradiation at the end of source life and to check the dose uniformity, calculations of the absorbed dose were carried out. Monte Carlo simulations, as well as dosimetry measurements, were established to study the radiation processing quality control and to show whether the irradiation facility at third source half life maintains the absorbed dose rate uniformity. Indeed, an isodose chart was created by GEANT4 Monte Carlo code to evaluate the absorbed dose rate uniformity inside the irradiation room from the year of installation until the year of source reload. Likewise, the Dose Uniformity Ratio (DUR) is deduced from maximum and minimum experimental doses in medical devices during the third period of the source half life.

459

The 10 MW_th solid fueled thorium molten salt reactor (TMSR-SF1) is a FLiBe-salt-cooled pebble bed reactor to be deployed in 5–10 years, designed by the TMSR group. Due to a large amount of beryllium in the core, the photoneutrons are produced via (γ, n) reactions. Some of them are generated a long time after the fission event, and therefore are considered as delayed neutrons. In this paper, we redefine the effective delayed neutrons into two fractions: the delayed fission neutron fraction and the delayed photoneutron fraction. With some reasonable assumptions, the inner product method and the k-ratio method are adopted for studying the effective delayed photoneutron fraction. In the k-ratio method, the Monte Carlo code MCNP6 is used to evaluate the effective photoneutron fraction as the ratio between the multiplication factors with and without contribution of the delayed neutrons and photoneutrons. In the inner product method, with the Monte Carlo and deterministic codes together, we use the adjoint neutron flux as a weighting function for the neutrons and photoneutrons generated in the core. Results of the two methods agree well with each other, but the k-ratio method requires much more computing time for the same precision.

360