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Slow positron beam and nanoindentation study of irradiation-related defects in reactor vessel steels
No full textIn order to understand the nature of the hardening after radiation in reactor vessel steels, China A508-3 steels were implanted by proton with an energy of 240 keV up to 2.5 x 10(16), 5.5 x 10(16), 1.1 x 10(17), and 2.5 x 10(17) ions cm(-2), respectively. Vacancy type defects were detected by energy-variable positron beam Doppler broadening technique and then nanoindentation measurements were performed to investigate proton-induced hardening effects. The results showed that S-parameter increased as a function of positron incident energy after irradiation, and the increasing rate of the S-parameter near the surface was larger than that in the bulk due to radiation damage. The size of vacancy type defects increased with dose. Irradiation induced hardening was shown that the average hardness increased with dose. Moreover a direct correlation between positron annihilation parameter and hardness was found based on Kasada method. (C) 2014 Elsevier B.V. All rights reserved
Structural and optical characterization of SiO2 under irradiation with swift heavy ions
No full textSiO2 single crystals irradiated with 600 key, 4 and 5 MeV Kr ions using the 320 kV High Voltage Experimental Platform (IMP, Lanzhou) were investigated with infrared, fluorescence spectroscopes and TEM. In the low-energy regime, single ion tracks are well separated and the damage process is dominated by the formation of simple color centers such as F+ rand F-2 centers. For the high energy ions, the energy density in ion tracks produced at a high stopping power is larger, and consequently the defect concentration increases significantly. At higher defect densities, the distance between single defects is smaller facilitating the aggregation of individual electron center to defect cluster and defect annihilation by recombination of hole and electron centers. The latter process determines the limited efficiency of color-center creation under heavy-ion irradiation. Using the unified thermal spike model, a combination of the elastic collision spike model and the inelastic thermal spike model based on electronic energy losses, it is possible to fully describe the experimental data, which clearly demonstrate a synergy between the nuclear energy loss and the electronic energy loss processes. (c) 2013 The Authors. Published by Elsevier B.V. All rights reserved
Role of autophagy in high linear energy transfer radiation-induced cytotoxicity to tumor cells
No full textHeavy-ion radiotherapy has a potential advantage over conventional radiotherapy due to improved dose distribution and a higher biological effectiveness in cancer therapy. However, there is a little information currently available on the cellular and molecular basis for heavy-ion irradiation-induced cell death. Autophagy, as a novel important target to improve anticancer therapy, has recently attracted considerable attention. In this study, the effect of autophagy induced by high linear energy transfer (LET) carbon ions was examined in various tumor cell lines. To our knowledge, our study is the first to reveal that high-LET carbon ions could induce autophagy in various tumor cells effectively, and the autophagic level in the irradiated cells increased in a dose-and LET-dependent manner. The ability of carbon ions to inhibit the activation of the PI3K/Akt pathway rose with increasing their LET. Moreover, modulation of autophagy in tumor cells could modify their sensitivity to high-LET radiation, and inhibiting autophagy accelerated apoptotic cell death, resulting in an increase in radiosensitivity. Our data imply that targeting autophagy might enhance the effectiveness of heavy-ion radiotherapy
Fluorescence and HPLC Detection of Hydroxyl Radical by a Rhodamine-Nitroxide Probe and its Application in Cell Imaging
No full textA rhodamine nitroxide probe was designed to detect the hydroxyl radical (center dot OH), which presented high selectivity for center dot OH over other reactive oxygen species (ROS) and linear fluorescence response to center dot OH produced by Fenton reaction. The product was detected by HPLC-MS, indicating that the main product of the reaction was O-methylhydroxylamine and the product peak areas measured by HPLC-UV/vis and HPLC-FLD both enhanced proportionally with the increase of center dot OH concentration. The application of the probe in biological system was explored to trace the production of center dot OH in cells under oxidative stress condition induced by rotenone which can inhibit the mitochondria respiratory chain complex I and we found that appropriate rotenone may induce the normal human liver cells (L02) and human hepatoma cells (HepG2) to produce center dot OH at different degrees
Design and beam test of a high intensity continuous wave RFQ accelerator
No full textA four-vane continuous wave (CW) RFQ has been designed for the injector II LINAC of China ADS project. To acquire the experience of a CW RFQ on design, tuning, conditioning, running, etc., a 1-m-long RFQ accelerator prototype has been built. Working at 162.5 MHz, the RFQ prototype accelerates protons of 10 mA from 20 keV to 560 keV in one meter length with a low inter-vane voltage of 65 kV and a safe Kilpatric factor of 1.3. Conditioning and beam test of the accelerator prototype have been completed, and it shows the transmission efficiency can reach 90% with a 10 mA CW proton beam. Design, fabrication and tests of the RFQ prototype will be presented in detail in the paper. (C) 2014 Elsevier B.V. All rights reserved. 'Strategic Priority Research Program' of the Chinese Academy of Sciences；NSF
RF and field measurements of the SSC-LINAC RFQ
No full text<span style="color: rgb(51, 51, 51); font-family: arial, helvetica, sans-serif; font-size: 13px; line-height: 22px; background-color: rgb(248, 248, 248);">The 53.667 MHz continuous-wave heavy ion RFQ has been designed and manufactured for the SSC-LINAC project. This four-rod RFQ accelerates ions with maximum mass to charge ratio of 7 from 3.728 keV/u to 143 keV/u. Measurements have been carried out to check the RF performance of the cavity and the quality of the electric field. The S-11 of the power coupler is adjusted to better than -44 dB, and the Q (0) of the cavity is 6440. The quality of the electric field is evaluated by the perturbation method. The measurement procedure and data analysis will be discussed in detail. The error due to gravity of the perturbation bead has been corrected by averaging the fields in different quadrants. As a result, the unflatness of the electric field is +/- 2.5%, and the dipole field component distributes from 0% to 20% in different longitudinal positions, which indicates the asymmetry of the quadrupole field. The unflatness of the quadrupole field distribution represents a good agreement with the simulation results. High power RF test and beam commissioning of the RFQ are on schedule in early 2014</span
A simulation study of a dual-plate in-room PET system for dose verification in carbon ion therapy
No full text<span style="color: rgb(51, 51, 51); font-family: arial, helvetica, sans-serif; font-size: 13px; line-height: 22px; background-color: rgb(248, 248, 248);">During carbon ion therapy, lots of positron emitters such as C-11, O-15, C-15 are generated in irradiated tissues by nuclear reactions, and can be used to track the carbon beam in the tissue by a positron emission tomography (PET) scanner. In this study, an dual-plate in-room PET scanner has been designed and evaluated based on the GATE simulation platform to monitor patient dose in carbon ion therapy. The dual-plate PET is designed to avoid interference with the carbon beamline and with patient positioning. Its performance was compared with that of four-head and full-ring PET scanners. The dual-plate, four-head and full-ring PET scanners consisted of 30, 60, 60 detector modules, respectively, with a 36 cm distance between directly opposite detector modules for dose deposition measurements. Each detector module consisted of a 24 x 24 array of 2 mm x 2 mm x 18 mm LYSO pixels coupled to a Hamamatsu H8500 PMT. To estimate the production yield of positron emitters, a 10 cm x 15 cm x 15 cm cuboid PMMA phantom was irradiated with 172, 200, 250 MeV/u C-12 beams. 3D images of the activity distribution measured by the three types of scanner are produced by an iterative reconstruction algorithm. By comparing the longitudinal profile of positron emitters along the carbon beam path, it is indicated that use of the dual-plate PET scanner is feasible for monitoring the dose distribution in carbon ion therapy.</span