共查询到20条相似文献,搜索用时 15 毫秒
1.
M. Östling C.S. Petersson 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》1984,4(1):88-91
A study of backscattering analysis of AlxGa1?xAs layers using 16O ions at 30 MeV is described.We have found that by using calibration samples of well defined composition, we can use the technique to determine the composition of AlxGa1?xAs thin layers to an accuracy within a few percent. The method can resolve the composition of the first 1 μm of a thin layer. By using sample tilting, films of 300 nm thickness on top of a GaAs substrate can be analysed. 相似文献
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利用为模拟荷能重离子在组织等效气体中能量沉积分布研究而设计的无壁正比计数器系统对25MeV/u ^40Ar^14+离子在组织等效气体中沿其径向及纵向的相对能量沉积分布进行了研究,分别在6.4kPa及0.5kPa气压下模拟了细胞核大小及超螺线管大小的分布情况,并讨论了实验结果。 相似文献
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对人肝癌细胞SMMC-7721细胞和黑色素瘤细胞A375细胞,进行80.55MeV 12C6 离子、X射线和γ射线照射,通过克隆存活实验获剂量-存活曲线,以X射线或γ射线为标准,计算重离子的相对生物学效应(Relative biological effectiveness,RBE ).结果显示,两种细胞的重离子RBE值都大于1,且分次照射的RBE大于单次照射.重离子照射SMMC-7721细胞的RBE高于A375细胞,分次照射的差异更明显.重离子具有独特的物理特性及高传能线密度(Line energy transfer,LET)下的强杀伤作用,可有效杀伤不同肿瘤细胞,减弱了细胞间的敏感性差异.临床的分次照射重离子治疗时,细胞的亚致死修复明显降低,可采取较少的照射次数达到杀伤肿瘤的目的,提高肿瘤治疗效率,减轻病人痛苦. 相似文献
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Jianming Xue Yanbo Xie Long Chen Ke Jing Yugang Wang 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2009,267(6):1007-1010
In order to study the mechanism of the nucleotide directly damaged by energetic heavy ions, the residual ratio of uridine molecules after irradiation was measured by means of High Performance Liquid Chromatography (HPLC). The experimental results show that the irradiation damage probability depends on the electronic energy loss rate (Se) of incident ions: first it increases quickly with Se, then becomes stable when Se reaches 800 eV/nm. The contribution of the nuclear collisions can be neglected compared with that of the electronic process. This is not only because that the nuclear energy loss rate (Sn) is much smaller than Se for MeV heavy ions, but also because the energy deposition through the electronic process is more efficient in damaging molecules than through the nuclear process. 相似文献
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A perturbed hard core equation of state, applicable to both spherical and non-spherical cores, is described and tested with both molecular fluids and liquid metals (Na and U). The theory was found to be particularly accurate in describing the vapour pressure curve of molecular fluids but provides only a qualitative picture for liquid metals. The applicability of the equation to describe the thermodynamic properties of liquid UO2 has been studied and a full set of thermodynamic data is reported. 相似文献
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R. Brenier B. Canut S. M. M. Ramos P. Thevenard 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》1994,90(1-4):339-343
-Al2O3 single crystals were bombarded with MeV xenon ions from 1015 to 1017 ions cm−2 and GeV uranium ions from 1011 to 1013 ions cm−2 to study the surface swelling of sapphire at 77 and 300 K due to atomic collision processes (Xe) and electronic energy loss processes in the 20–45 keV/nm regime (U). The induced damage was studied by channeling Rutherford backscattering. Surface swelling was measured with a profilometer. The step height induced by nuclear cascades of MeV xenon increases with the ion fluence and saturates. With GeV uranium, an electronic stopping power threshold for surface swelling was observed and the step height increased with the damage for dE/dx higher than this threshold. 相似文献
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Kjeld J. Olsen Johnny W. Hansen 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》1984,5(3)
Relative radiation effectiveness, RE, of 21 MeV 7Li and 64 MeV 16O ions being completely stopped in a tissue equivalent film dose meter has been measured as a function of penetration depth and energy, and the results have been compared with calculations based on a δ-ray theory for heavy charged particles developed by Katz et al. The experiment was designed to test calculations particularly in the Bragg-peak region of the slowing down particles where significant deviation between theory and experiment was found. Fitting of the characteristic D37 dose and the size of the radiation sensitive element in the detector, which are important parameters in the theoretical model, does not improve the overall correlation between theory and experiment. It is concluded that disagreement between theoretical and experimental RE-values below 1.5 MeV/amu is partly due to lack of equivalence between the δ-ray spectrum and the slowing down spectrum of electrons from low-LET radiation, and partly from approximations in the calculated distribution of energy deposition of the δ-rays. 相似文献
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Stopping powers for Ge ions (3.5MeV-8.0MeV) in Al foil were measured with RBS (Rutherford backscattering )technique and determined with a new method .Our results are much smaller than the values predicted by the TRIM code and LSS theory. 相似文献
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K. Inoue M. Takai K. Matsunaga M. Izumi K. Gamo S. Namba M. Satou 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》1988,30(4):580-591
A microprobe for Rutherford backscattering (RBS) and particle-induced X-ray emission (PIXE) measurements has been realized by focusing 1.5 MeV helium-ion or proton beams with a demagnification system consisting of piezo-driven objective slits and a magnetic quadrupole doublet. Minimum beam spot sizes of 1.3 × 2.2 μm2 for helium ions and 2.2 × 4.0 μm2 for protons have been achieved. The factors which may limit the minimum spot size are discussed using a Monte Carlo simulation procedure. Rutherford backscattering image mapping of 3-dimensional structures is demonstrated. 相似文献
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R. Bimbot A. Khoumri A. Fahli S. Barbey T. Benfoughal M. Mirea A. Hachem G. Fares R. Anne H. Delagrange C. Tribouillard Y. Georget J. C. Foy 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2000,170(3-4):329-335
The stopping powers of six gaseous media have been measured for incident 40 MeV/u 125Te heavy ions. The energy losses of ions in various “thicknesses” of gas have been accurately determined. The gases were confined in a cell. The amount of matter traversed by the ions was determined from temperature and pressure measurements. The beam energy before and after slowing down were measured using the LISE magnetic spectrometer at GANIL. These experimental gas stopping powers are lower by about 10% than the corresponding tabulated values for solid media. This means that the gas–solid effect is still significant at 40 MeV/u for Te ions. The projectile effective charges derived from these measurements depend on the target atomic number, thus confirming the trend observed in previous experiments performed with lighter ions or at lower energies. 相似文献
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Kieran J. McCarthy J. Garc?&#x;a López Bernardo Zurro M.A. Respaldiza 《Journal of Nuclear Materials》2003,321(1):78-83
We have characterised the response of a chromium-doped alumina screen ‘Chromox’ to light ions (H+ and He+) accelerated to keV and MeV energies. In particular, we have determined the absolute luminosity in terms of the number of photons emitted per incident ion from the front and back faces of such a screen. This work has been motivated by the application of this material to a diagnostic for measuring fast ion losses, close to the plasma edge, from the hot plasmas in fusion devices, where its radiation hardness, compared to that of standard phosphors, makes it very attractive. We also discuss the persistent afterglow observed after removal of the ion beam in terms of its cause and possible repercussions for this diagnostic. 相似文献
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A. Denker K. H. Maier 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》1999,150(1-4):118-123
The elemental composition of realistic thick samples has been measured with PIXE by 68 MeV protons. Heavy elements can be well detected much deeper below the surface, than with other methods. Measurements on objets d'art are presented. Large and complicated objects can be measured easily. 相似文献
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Yoshikazu Fujii Shinsuke Fujiwara Kazumasa Narumi Kenji Kimura Michi-hiko Mannami 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》1994,90(1-4):212-215
Inelastic interaction of fast ions at glancing angles of incidence on a low index crystal surface is described by the probabilities, which depend on the distance of the ion from the surface; the charge state and energy distributions of the scattered ions are found to result from position-dependent interactions along their trajectories in vacuum. A stochastic equation to describe the charge exchange and energy loss of specularly reflected ions is proposed. Taking account of ion scattering at surface steps, the theory is applied to derive the position-dependent probabilities of electron loss and electron capture of MeV ions from the observed charge state and energy distributions of the scattered ions at glancing angle incidence on the (100) surface of SnTe. 相似文献
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MIAO Qi LAI Jiang-Nan XUE Jian-Ming QIN Huai-Li WANG Wei-Dong QIN Guang-Yong WANG Yu-Gang 《核技术(英文版)》2006,17(5):272-275
A study of the fragments of DNA irradiated with MeV ions is important for the understanding of the DNA damage mechanism and the subsequent biological effects (induced by heavy ions). In this experiment, the products of calf thymus DNA (CT DNA) irradiated with MeV fluorine ions were analyzed using agarose gel electrophoresis, modified time-of-flight mass spectrometer (MALDI-TOF), and high-performance liquid chromatography (HPLC). The results showed that the molecular mass of the fragments were concentrated around 831 bp with agarose gel electrophoresis, there was no observable product in the range of 1,000- 30,000 (m/q) using MALDI-TOF, and small biomolecules were separated from the products. The results of this study indicated that the strand breaks of calf thymus DNA induced by MeV fluorine ions were nortrandom. 相似文献
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F. D. McDaniel B. L. Doyle C. H. Seager D. S. Walsh G. Vizkelethy D. K. Brice C. Yang P. Rossi M. Nigam M. El Bouanani G. V. Ravi Prasad J. C. Schwartz L. T. Mitchell J. L. Duggan 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2002,190(1-4):1-10
A new ion beam analysis-based, single ion technique called the time to first photon has been developed to measure the decay of the luminescence signal of phosphors. Such measurements are currently needed to study luminescence decay mechanisms following high-density excitations and to identify strongly luminescent phosphor coatings with short lifetimes for ion photon emission microscopy (IPEM). The samples for this technique consist of thin phosphor layers placed or coated on the surface of PIN diodes. Single ions from an accelerator strike this sample and simultaneously create ion beam induced luminescence (IBIL) from the phosphor that is measured by a single-photon-detector, and an ion beam induced charge collection (IBICC) signal in the PIN diode. In this case, the IBICC signal provides the start pulse and the IBIL signal the stop pulse to a time to amplitude converter. It is straightforward to show that this approach also measures a signal proportional to activity versus time with an accuracy of 5% as long as the number of detected photons per ion is less than 0.1, which usually requires the use of absorbers for the IBIL detector or electronic discrimination for the IBIL signals. Details of the new analysis are given together with examples of luminescence decay measurements of several ceramic phosphors being considered to coat IPEM samples. IPEM is currently being developed at Sandia National Laboratory (SNL), the University of North Texas in Denton, and the Universities and INFN of Padova and Torino. 相似文献