Vol.24,

A cold-cathode Penning Ion Gauge (PIG) type ion source as the internal ion source of an 11 MeV cyclotron is designed and tested at Institute of Fluid Physics. The design considerations and some testings are presented. Experimental results of Balmer-line-Emission show that the discharge characteristic, which is mainly determined by gas-flow rate, is not very sensitive to arc current and magnetic field in the operation ranges of the cyclotron. The arc power decreases and ascends while the gas-flow rate goes up from 0.5 SCCM to 20 SCCM. By improving the sealing design and reducing the machine tolerance of the source, the minimum power consumption reduces from 9 SCCM to 4 SCCM, thus having better energy efficiency and benefiting for the pumping system. Preliminary DC extractions show that H^– microampere current ranges from several tens to hundreds under different operation conditions. Some problems during the experiments and future plan are discussed in the end.

567

The computed tomography was applied to setting STIM (Scanning Transmission Ion Microscopy) projections recorded at the Fudan Ion Beam Laboratory. In this work, in order to visualize the three-dimensional mass density distribution in several specimens, example for a test structure of hollow gold cyliner was presented together with a detailed description of the developed system, including data reconstruction code (Tomorebuild 2) and image display software (AMIRA^®). Future development will allow the particle induced X-ray emission tomography for elemental analysis of micrometer-sized samples.

426

In order to separate Zr(IV) and Hf(IV) in acidic solution, several kinds of silica-based macroporous adsorbents were synthesized. Their adsorption selectivity for Zr(IV) and Hf(IV) in HCl solution was investigated, and the TODGA adsorbent for the two elements had the largest adsorption difference. The effects of acid type, HCl concentration, and temperature on the adsorption behavior of Zr(IV) and Hf(IV) onto the TODGA adsorbent were conducted by batch experiments. It was found that H⁺ exhibited a quite strong influence on adsorption capacity of Zr(IV) and Hf(IV). Isotherm fitting showed that the Langmuir model agrees well with the experimental data. The thermodynamic parameters indicate that the adsorption processes for both elements are endothermic reactions. The TODGA adsorbent had the higher adsorption selectivity for Zr(IV) over Hf(IV) and could be promising for their mutual separation.

571

CBCT scanners have been widely used in angiography, radiotherapy guidance, mammography and oral maxillofacial imaging. To cut detector size, reduce manufacturing costs and radiation dose while keeping a reasonable FOV, the flat panel detector can be placed off-center horizontally. This scanning configuration extends the FOV effectively. However, each projection is transversely truncated, bringing errors and artifacts in reconstruction. In this paper, a simple but practical method is proposed for this scanning geometry based on truncation compensation and the modified FDK algorithm. Numerical simulations with jaw phantom were conducted to evaluate the accuracy and practicability of the proposed method. A novel CBCT system for maxillofacial imaging is used for clinical test, which is equipped with an off-center small size flat panel detector. Results show that reconstruction accuracy is acceptable for clinical use, and the image quality appears sufficient for specific diagnostic requirements. It provides a novel solution for clinical CBCT system, in order to reduce radiation dose and manufacturing cost.

452

Because of ³He shortage, sintillator is a promising alternative choice for neutron detection in the field of thermal neutron scattering and imaging. Also, the neutron detection efficiency is difficult to be determined. In this paper, the efficiency for thermal neutron detection is presented by inorganic scintillator using probability principles, supposed that the material of scintillator is uniform in element distribution, and that attenuation length of scintillation light is longer than that of its thickness in the scintillator. The efficiencies for two pieces of lithium glass are determined by this method, indicating the method is useful for determining efficiency of thermal neutron detections.

492

The characteristics of the best known defect centers E' in silica optical fiber material irradiated with γ ray were investigated by ESR at room temperature. A mechanism model of production of the E' center defect was established. The production of E' center includes two processes creation and activation. The strained bonds (or oxygen replacement) in silica networks lead to the creation of new defects whose concentration increases linearly with the dose. The pre-existing defects produce the activation, which tends to saturation. According to this model, the relation of E' center concentration changing with irradiation dose was obtained theoretically. The results are in good agreement with the experimental results.

453

In order to confirm whether the rice sample was exposed to gamma radiation, the changes in starch pasting viscosity of rice irradiated by different absorbed doses with additive acid solution and distilled water were investigated. The peak viscosity of irradiated rice sample was significantly decreased with the increment of absorbed doses even for the samples stored over 360 days. Irradiation samples can be distinguished from non-irradiated samples by their RVA profile as in the acid solution (pH=2.5), the starch pasting viscosities of irradiated rice samples were apparently higher while the starch pasting viscosities of non-irradiated rice samples were lower than that in distilled water (pH=7.0). The irradiation absorbed dose can be estimated accurately by the regression equation constructed with peak viscosity and absorbed doses.

433

In recent years, several RGD (Arg-Gly-Asp)-based radiotracers have already been successfully tested in human for the visualization of integrin αvβ3, demonstrating its feasibility in tumor diagnosis. In this paper, we evaluated the ^99mTc-3P₄-RGD₂ single photon emission computed tomography/computerized tomography (SPECT/CT) in patients suffering from space occupying disease of esophagus. 40 patients (34 males and 6 female; mean age: 58.3 years) with a suspected space occupying lesion of esophagus were included, thus finally obtaining their definite pathologic diagnosis (malignant, n=32; benign, n=8). All patients underwent endoscopic, barium esophagography and SPECT/CT imaging preoperatively. The chest SPECT was performed at 4 h after administration of ^99mTc-3P₄-RGD₂ with a dose of 939±118 MBq. The diagnosis precision, sensitivity and specificity among these methods were compared. The relationship between radioactive uptake and clinical pathological stage of esophageal carcinoma was discussed by calculating the tumor to normal esophagus (T/N). Meanwhile, the integrin αvβ3 expression was assessed immunohistochemically in postoperative esophageal tissues. 31 patients were diagnosed as esophageal carcinoma; and 1, leiomyosarcoma; and 6. leimyoma; and 2, esophageal tuberculosis. The accuracy, sensitivity and specificity of barium esophagography, endoscopic and SPECT/CT imaging are 92.5/93.8/87.5%, 97.5/96.9/100%, and 90/90.6/87.5%, respectively. Abnormal accumulation of radiotracer in 29 malignant lesions is observed. The SPECT/CT imaging displayed the region of radioactive uptake and lesions matched extremely with the T/N ratio from 1.31 to 2.79 (mean 2.04). A case with pulmonary metastases and a case with mediastinal lymph node metastases were found which were missed by barium esophagography and endoscopic. The ^99mTc-3P₄-RGD₂ uptake of the esophageal carcinoma masses had no relevance to the tumor pathologic classification (P>0.05). There was a significant positive correlation between T/N ratio and positive cell percentage of integrin αvβ3 (r=0.976), demonstrating the certain clinical potential in the diagnosis of esophageal carcinoma.

639

Whether extrapulmonary lesions are avid for ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) could help to differentiate the benign or malignant lung lesions. In this trial, the 199 consecutive patients with newly diagnosed lung lesions (169 malignant and 36 benign lesions) were imaged by whole body ¹⁸F-FDG PET/CT. Histopathology and clinic results served as the reference standard. The malignancy likelihood were conducted by CT_scores; the maximum standardized uptake value (SUV_max) of lung lesions, and PET on FDG negative or positive, as well as metastasis index (MI), by PET combined with CT findings. The data were analyzed by stepwise logistic regression and receiver-operating- characteristic. The malignancy predictive probability (P) was obtained by P =e^x/(1+e^x), where x= –1.16+0.87 (CT_score) +0.15(SUV_max)+0.27(MI). The area under curve (AUC) for the fitted logistic model was 0.82±0.04, this was superior and significantly different from SUV_max(AUC, 0.73±0.05) and CT_scores(AUC, 0.71±0.05). The fitted logistic model could improve the diagnostic performance. The MI could help for differential diagnosis.

409

The experimental muon source on China Spallation Neutron Source (CSNS) is expected to be a high intensity (10⁵ μ⁺/s) surface muon source with a small beam spot of 4-cm diameter. For a practical application of this muon source, we are devoting to develop the first pulsed μSR spectrometer in China. In this paper, the performance of plastic scintillators in the μSR spectrometer is studied by Monte Carlo simulation. The processes such as positron energy deposition, scintillation photons production, light propagation and photon-electron conversion are carefully considered. According to the results, an optimal dimension of the plastic scintillator is proposed using for our future spectrometer, which has a long-strip shape with the dimension variation range of 50–60 mm length, 5–8 mm height, and 10–12 mm width. Finally, we can build a spectrometer with a count rate up to 10⁴e⁺/s by 100–120 forward and backward segmental detectors in total. The simulation could serve as an important guide for spectrometer construction.

637

As a key part of the diagnosis system in the International Thermonuclear Experimental Reactor (ITER), the neutron flux monitor (NFM), which measures the neutron intensity of the fusion reaction, is a Counting-Campbelling system with a large dynamic counting range. A dynamic linear calibration method is proposed in this paper to solve the problem of cross-over between the different counting and Campbelling channels, and improve the accuracy of the cross-calibration for long-term operation. The experimental results show that the NFM system with the dynamic linear calibration system can obtain the neutron flux of the fusion reactor in real time and realize the seamless measurement area connection between the two channels.

615

In this paper, a high precision vernier delay line (VDL) TDC (Time-to-Digital Convertor) in an actel flash-based Field-Programmable-Gate-Arrays A3PE1500 is implemented, achieving a resolution of 16.4-ps root mean square value or 42-ps averaged bin size. The TDC has a dead time of about 200 ns while the dynamic range is 655.36 μs. The double delay lines method is employed to cut the dead time in half to improve its performance. As the bin size of the TDC is dependent on temperature, a compensation algorithm is adopted as temperature drift correction, and the TDC shows satisfying performance in a temperature range from –5°C to +55°C.

746

The AP1000 with high safety is a generation III pressurized water reactor (PWR), its significant feature is passive safety system. However, its passive cooling can only maintain for 72 h and requires additional support from inside or outside the plant. To solve this problem, this study utilized the WGOTHIC software to calculate and analyze the water inventory in the passive containment cooling water tank under different conditions. The results show that when the cooling water inventory is 6553.78 m³, the AP1000 nuclear power plants can achieve long-term, completely passive cooling without any inside or outside the plant. The same outcomes occur when 65-mm-thick containment wall increases the design pressure rating to 0.6 MPa at the cooling water inventory of 5673 m³. Also, the AP1000 shield building was accordingly improved. An ANSYS analysis of the structural stability of the shield building with a 6000 m³ cooling water inventory confirmed that the new design can meet the requirements of the seismic design and the safe residual heat removal requirements of a large-scale PWR.

594

Small long-life transportable high temperature gas-cooled reactors (HTRs) are interesting because they can safely provide electricity or heat in remote areas or to industrial users in developed or developing countries. This paper presents the neutronic design of the U-Battery, which is a 5 MWth block-type HTR with a fuel lifetime of 5–10 years. Assuming a reactor pressure vessel diameter of less than 3.7 m, some possible reactor core configurations of the 5 MWth U-Battery have been investigated using the TRITON module in SCALE 6. The neutronic analysis shows that Layout 12×2B, a scattering core containing 2 layers of 12 fuel blocks each with 20% enriched ²³⁵U, reaches a fuel lifetime of 10 effective full power years (EFPYs). When the diameter of the reactor pressure vessel is reduced to 1.8 m, a fuel lifetime of 4 EFPYs will be achieved for the 5 MWth U-Battery with a 25-cm thick graphite side reflector. Layouts 6×3 and 6×4 with a 25-cm thick BeO side reflector achieve a fuel lifetime of 7 and 10 EFPYs, respectively. The comparison of the different core configurations shows that, keeping the number of fuel blocks in the reactor core constant, the annular and scattering core configurations have longer fuel lifetimes and lower fuel cost than the cylindrical ones. Moreover, for the 5 MWth U-Battery, reducing the fuel inventory in the reactor core by decreasing the diameter of fuel kernels and packing fraction of TRISO particles is more effective to lower the fuel cost than decreasing the ²³⁵U enrichment.

617