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261.
262.
Wen-li Wu William J. Orts John H. Van Zanten Bruno M. Fanconi 《Journal of Polymer Science.Polymer Physics》1994,32(15):2475-2480
The density profiles of polymethylmethacrylate (PMMA) thin films on silicon (111) single crystal wafers were investigated via neutron reflectivity measurements. Films were prepared by spin casting PMMA onto silicon wafers from o-xylene solution followed by annealing under vacuum at 90°C for 5 h. A ~45 Å thick layer at the free polymer surface was observed in the as-prepared samples that has a density about half the value of bulk PMMA. After heating above 110°C, this diffuse layer disappeared and the thin film density profile was transformed to one with a sharp free polymer surface. This transition was found to be irreversible. © 1994 John Wiley & Sons, Inc. 相似文献
263.
Characterization of polymer materials by scattering techniques,with applications to block copolymers
Tim Lodge 《Mikrochimica acta》1994,116(1-3):1-31
The application of six techniques—static and dynamic light scattering, small-angle neutron and X-ray scattering, neutron and X-ray reflectivity—to the characterization of polymer materials is summarized. Emphasis is placed on the similarities and differences among the various techniques, and on recent advances in experimental practice. Twelve examples from the recent literature are described, most of which concern block copolymers. A brief introduction to block copolymer properties is also provided. 相似文献
264.
在中能重离子反应中出射的En>20MeV中子在出射总中子中占有相当大的比例,因此,当用雷姆计测量剂量当量时,由于仪器的能量响应,雷姆计的直接读数低于真实的中子剂量当量值,本文从重离子反应出射中子能谱入手,理论上计算了在屏蔽墙内用10in,直径单球雷姆计和标准A-B雷姆计测量41.7MeV/u 12C+Fe和100MeV/u 12C+C反应出射中子剂量当量的修正因子. 它可以近似应用于中能重离子反应出射中子的剂量当量测量. 相似文献
265.
The α-phase in Zr-2.5 Nb pressure tubes has been analysed after irradiation with neutrons for temperatures between 523 and 573 K. The α-phase contains Nb in supersaturated solid solution (about 0.5−1 wt% Nb) in the as-fabricated condition. Irradiation results in the formation of small discrete precipitates having diameters of about 5 nm. Energy Dispersive X-ray (EDX) analysis using a scanning transmission electron microscope (STEM) was complicated by the presence of a self-generated X-rays in the irradiated material and by the fact that the precipitates were small relative to the foil thickness (typically 100–200 nm). Techniques developed to measure segregation of impurities at interfaces were employed to show that the precipitates were Nb-rich, their formation being consistent with a decrease in Nb concentration in the matrix. 相似文献
266.
Discovery of the neutron in 1932 by Chadwick ushered in a new era of scientific research and technology. The neutron is endowed
with unique properties in its mass, life time, spin and magnetic moment etc and every important property has been used in
the study of condensed matter, biological molecules, nuclear forces, stellar objects and other fields. Neutron has a wide
range of applications in power production, breeding of fissile fuel, radiography, medicine and others. 相似文献
267.
A polarised neutron study of the ferromagnetic Heusler alloy Cu2Mn0.863Al1.057 has been made. It has been concluded that the magnetic moment density is primarily situated on the Mn ions. On assigning
the Mn-moment value, the observed magnetic form factor is found to be in good agreement with the Mn2+ free ion form factor calculated by Watson and Freeman. A slight asphericity has been observed in the moment density. It is
estimated that there are about 3% excess 3d-electrons in the Eg states compared to spherical distribution. There is evidence of a very small positive polarisation of
the Cu atoms. No appreciable conduction electron polarisation is found. 相似文献
268.
The yield and energy distribution of long-range alpha-particles (lra) emitted from neutron-induced fission of235U have been measured at neutron energies; thermal, 125±12, 155±11, 185±10, 210±9, 240±9, 365±50 and 480±45 keV. The long-range
alpha-particles were detected in cellulose nitrate track detector foils. Results showed an increase of about 50% in the yield
at neutron energies in the region 150 keV≤E
n≤220 keV as compared to that of thermal neutrons. A calculation has been carried out to extract thelra to binary fission ratio forp-wave neutron induced fission. 相似文献
269.
270.