摘要:

AbstractThe interaction of neutrons over a wide energy range with matter can be applied in computerized tomography (CT) to obtain nondestructive insight into objects, which is highly complementary to the information obtained by the classical method of X-ray tomography.Systematic tomography studies with thermal neutrons, fast neutrons of different spectral composition, and mixed neutron and gamma fields have been done in recent years. The experiments were performed at the Munich research reactor [Forschungsreaktor München (FRM)] of the Technical University of Munich. Examples of CT measurements demonstrate the manifold possibilities of the interdisciplinary cooperation of neutron physics and materials research.The necessary equipment and some specific problems in the processing of measured transmission rates for image reconstruction are described.

ISSN:0029-5639    

DOI:10.13182/NSE92-A23905

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractPolarized neutron scattering from clusters of polarized proton spins in solid material provides a new contrast variation method. Frozen solutions of apoferritin and of the large subunit of Escherichia coli ribosomes in a mixture of heavy water and deuterated glycerol have been studied at the conditions of dynamic nuclear spin polarization (H = 2.5 T, T< 1K, 4-mm microwave irradiation). The three basic scattering functions of contrast variation were derived by varying polarized neutron scattering with the polarization of target nuclei. They agree with results obtained from neutron scattering in H2O/D2O mixtures at room temperature. Furthermore, the proton spins appear to be polarized uniformly, at least to a structural resolution of 40Å. This is an important prerequisite for the in situ structure determination of macromolecular labels in larger host particles.

ISSN:0029-5639    

DOI:10.13182/NSE92-A23906

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractCurrent research in boron neutron capture therapy (BNCT) and radiation synovectomy at the Massachusetts Institute of Technology Research Reactor is reviewed. In the last few years, major emphasis has been placed on the development of BNCT primarily for treatment of brain tumors. This has required a concerted effort in epithermal beam design and construction as well as the development of analytical capabilities for10B analysis and patient treatment planning. Prompt gamma analysis and high-resolution track-etch autoradiography have been developed to meet the needs, respectively, for accurate bulk analysis and for quantitative imaging of10B in tissue at subcellular resolutions. Monte Carlo-based treatment planning codes have been developed to ensure optimized and individualized patient treatments. In addition, the development of radiation synovectomy as an alternative therapy to surgical intervention in joints that are affected by rheumatoid arthritis is described.

ISSN:0029-5639    

DOI:10.13182/NSE92-A23907

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractThe basic principles of boron neutron capture therapy (BNCT) are described. At the Jülich external neutron laboratory ELLA, the FRJ-2 research reactor delivers a pure beam of“cold”neutrons. It is discussed here in connection with the possible use of cold neutrons for experimental BNCT of melanoma of the skin.

ISSN:0029-5639    

DOI:10.13182/NSE92-A23908

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractNeutron spectrum measurements are performed on the aluminum-oxide-filtered neutron beam at the Brookhaven Medical Research Reactor (BMRR). Two independent measurement techniques are used in the spectrum characterization: (a) foil activation spectrometry and (b) proton-recoil spectrometry.Activation foil assemblies are irradiated at the exit port of the beam facility. Dominant resonances in selected activation reactions are used to measure the epithermal neutron spectrum. The intermediate and fast energy ranges of the neutron spectrum are measured by threshold reactions and the10B-filtered235U fission reaction. Neutron spectral data are derived from the activation data by two approaches: (a) an analysis that yields neutron flux values at the energies of the dominant or primary resonances in the epithermal activation reactions and (b) an analysis that utilizes all the activation data simultaneously in a spectrum unfolding process using the FERRET data adjustment code.Hydrogen-filled proton-recoil proportional chambers are used at the beam port exit to acquire data of a higher energy resolution than that obtainable through foil activation techniques. These measurements are made to determine if structure in the aluminum scattering cross section would produce significant structure in the filtered spectrum in the fast neutron region.

ISSN:0029-5639    

DOI:10.13182/NSE92-A23909

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractSeveral radioisotope generator systems exist in which the carrier-free daughter product would precipitate if present in macro amounts at pH levels at which the parent is soluble. Included among these are the68Ge/68Ga,90Sr/90Y, and47Ca/47Sc pairs. In these systems, chemical separation can be achieved by Fajans adsorption of the radiocolloidal daughter products onto surfaces such as activated glass microspheres at an appropriate pH, followed by washing to remove the parent solution and desorption of the daughter crop by acid washes. Investigation of the Ge/Ga and Sr/Y systems demonstrated that this solid-phase extraction method is erratic, but can give daughter yields as high as 89% with separation factors up to∼10000 from parent isotope. This method has the potential for producing daughter isotopes with a minimum of metal and organic impurities for labeling cells, receptor binding ligands, and antibodies for diagnostic and radiotherapeutic purposes.

ISSN:0029-5639    

DOI:10.13182/NSE92-A23910

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractDuring thermal annealing, amorphous Fe40Ni40P20becomes brittle via a two-step process at 220 and 300°C. The first step results from a loss of excess free volume. This embrittlement is reversible: During subsequent neutron irradiation, a swelling of the alloy is observed, which corresponds to an increase in excess volume and a complete restoration of the ductility. Small-angle neutron scattering reveals that the second step of embrittlement, during which the specimen remains fully amorphous, is induced by phase separation into regions enriched and depleted in phosphorus. If amorphous Fe40Ni40P20is exposed to neutron irradiation prior to the heat treatment, a similar phase separation into amorphous phosphorus-enriched and phosphorus-depleted regions occurs. While the radius of the phosphorus-rich regions is about the same regardless of whether or not the specimen has been irradiated, the onset of phase separation occurs at lower temperatures for preirradiated samples; under identical annealing conditions, the volume fraction of phosphorus-rich clusters is much larger in preirradiated FeNiP than in unirradiated material. The faster phase separation kinetics are a consequence of the irradiation-induced excess volume that allows for an increased mobility of individual atoms.

ISSN:0029-5639    

DOI:10.13182/NSE92-A23911

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractHelium trapping and release are studied for the nickel-rich amorphous alloys Ni75.1Cr14.0-P10.1C0.08, Ni63.5Zr36.5, and Ni87.7P12.3. Helium-3 is introduced into the samples by implantation at 150-keV energy. The depth distribution of the implanted helium is observed by neutron depth profiling employing the reaction3He(n, p)3H. Two implantation doses are used: 1×1016and 5×1016 3He/cm. Both implantation doses were chosen to be low enough to avoid blistering or flaking of the surface of the samples. The helium release behavior of the samples is studied by taking depth profiles after each annealing stage. At the same time, electron diffraction is used on parallel samples to observe the microstructure of the samples as a function of annealing. The annealing sequence for each material is broken off when electron diffraction indicated the existence of relatively large crystals in a sample. Only a small fraction of the implanted helium is released in most cases, and a clear correlation between helium release and recrystallization can be found in only one case.

ISSN:0029-5639    

DOI:10.13182/NSE92-A23912

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractThree spinodally strengthened copper alloys were irradiated with fast neutrons to 34 displacements per atom (dpa) at 414°C, 50 dpa at 411°C, and 32 dpa at 529°C in order to assess their suitability for high-temperature service in neutron environments. Density, electrical conductivity, tensile property, and fracture behavior changes were determined with emphasis on the microstructural reasons for the changes observed. These spinodally strengthened alloys were found to exhibit improved properties following irradiation, and they show merit for use in high-temperature neutron environments, although their low initial conductivity may be a limitation. The results are compared to those of high-purity, unalloyed copper.

ISSN:0029-5639    

DOI:10.13182/NSE92-A23913

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractNeutron diffraction has been of fundamental importance for the determination of the structure of high-temperature superconductors and for understanding the influence of structure on the critical temperature. This is because the new superconductors are heavy metal oxides; X rays are mainly scattered by the metal atoms, but thermal neutrons are scattered as strongly by oxygen, which is the atom of most interest in these materials. In fact, for the past 20 yr, neutron diffraction has been steadily gaining ground as an important technique in structural inorganic chemistry.

ISSN:0029-5639    

DOI:10.13182/NSE92-A23914

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor