摘要:

AbstractThe spatial intensity distribution of neutrons emerging from a curved guide is far from uniform, particularly at short wavelengths, and curved guides are sometimes followed by a straight section of guide to make the intensity distribution more uniform. The behavior of neutrons within curved-straight neutron guide systems is examined using both ray-tracing and analytical approaches to the problem. The intensity distribution within the straight guide tends to wash from one side of the guide to the other. The amplitude of this transverse wave decreases with increasing guide length, and the characteristic length of the wave decreases with increasing neutron wavelength.

ISSN:0029-5639    

DOI:10.13182/NSE92-A23870

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractA recently developed stacked neutron guide system, installed at the Interfaculty Reactor Institute in Delft, The Netherlands, is described. It comprises two 3-m-long stacks of curved narrow neutron guides. This system is designed to transmit thermal neutrons by means of total reflection and, at the same time, attenuate fast neutrons and gamma radiation strongly. Comparison of calculated and measured flux densities shows an excellent transmission of the thermal neutrons. The measured fast neutron and gamma radiation dose-equivalent rates are consistent with the design values.

ISSN:0029-5639    

DOI:10.13182/NSE92-A23871

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractCalculation of physically realistic radiation dose distributions for boron neutron capture therapy (BNCT) is a complex, three-dimensional problem. Traditional one-dimensional (slab) and two-dimensional (cylindrical) models, while useful for neutron beam design and performance analysis, do not provide sufficient accuracy for actual clinical use because the assumed symmetries inherent in such models do not ordinarily exist in the real world. Fortunately, however, it is no longer necessary to make these types of simplifying assumptions. Recent dramatic advances in computing technology have brought full three-dimensional dose distribution calculations for BNCT into the realm of practicality for a wide variety of routine applications. Once a geometric model and the appropriate material compositions have been determined, either stochastic (Monte Carlo) or deterministic calculations of all dose components of interest can now be performed more rapidly and inexpensively for the true three-dimensional geometries typical of actual clinical applications of BNCT.Demonstrations of both Monte Carlo and deterministic techniques for performing three-dimensional dose distribution analysis for BNCT are provided. Calculated results are presented for a three-dimensional Lucite canine-head phantom irradiated in the epithermal neutron beam available at the Brookhaven Medical Research Reactor. The deterministic calculations are performed using the three-dimensional discrete ordinates method. The Monte Carlo calculations employ a novel method for obtaining spatially detailed radiation flux and dose distributions without the use of flux-at-a-point estimators. The calculated results are in good agreement with each other and with thermal neutron flux measurements taken using copper-gold flux wires placed at various locations in the phantom.Three-dimensional dose distribution calculations using both techniques are also presented for the same canine phantom irradiated in the proposed epithermal neutron beam in the Power Burst Facility (PBF) reactor located at the Idaho National Engineering Laboratory. Again, calculated results obtained using the two methods are in good agreement. This exercise allows a direct comparison of the performance of the two epithermal neutron beams for a realistic three-dimensional BNCT application. The PBF beam has a lower level of fast neutron contamination and is much better collimated, resulting in a significantly higher therapeutic ratio (tumor dose relative to normal tissue dose), especially for deep-seated tumor locations.

ISSN:0029-5639    

DOI:10.13182/NSE92-A23872

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractThe fast neutron facility at the Munich Research Reactor [Forschungsreaktor München (FRM)] is briefly described, and data about the beam quality are given. After a listing of the biological experiments performed before and in parallel to the clinical irradiations, the treatment scheme, selection of cases and results of the reactor neutron therapy are reported. More than 80% of patients—all with poor prognosis—show complete remission of the tumor or stoppage of growth for at least several months. Possibilities for a support by boron neutron capture therapy are outlined. Preliminary data of an upgraded thermal-to-fast neutron converter for the planned 20-MW reactor FRM-II are given.

ISSN:0029-5639    

DOI:10.13182/NSE92-A23873

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractLong-range order in materials can be aperiodic. Quasi-periodic lattices are mathematically derived from cross sections of objects that are periodically arranged in a higher dimensional space. Experimental investigations of these structures require the specification of more parameters than for classical crystallography. Neutron diffraction, with the special technique of contrast variation, allows a reasonable approach to this problem.

ISSN:0029-5639    

DOI:10.13182/NSE92-A23874

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractThe low-temperature irradiation facility, Tieftemperatur-Bestrahlungsanlage (TTB), at the 4-MW Munich Research Reactor (Forschungsreaktor München—FRM) makes it possible to perform neutron irradiations at liquid helium temperature. Two irradiation positions exhibiting different neutron spectra are available. The possible integration of suitable measuring or transfer cryostats into the liquid helium circuit of the TTB allows the use of this facility for the study of a large variety of neutron irradiation effects in basic research as well as in materials sciences. Besides a description of the general experimental setup, some topics of current TTB research are briefly summarized.

ISSN:0029-5639    

DOI:10.13182/NSE92-A23875

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractIn-core absolute neutron spectra are measured for high-enriched uranium (HEU) and low-enriched uranium (LEU) materials test reactor fuel using multiple foil activation. The measurements were made in special fuel elements configured to simulate a regular fuel element but that permitted reproducible insertion of a wide range of samples. The measured subcadmium LEU flux was 14% less than the HEU fuel, which is within the experimental uncertainty of the 19% calculated value. There was no observed difference between the fast spectra. A separate spectral unfolding of just the LEU fast flux yielded reasonable agreement with proton-recoil measurements.

ISSN:0029-5639    

DOI:10.13182/NSE92-A23876

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractTo test the recent advances in receptor modeling for the identification of long-range transport of regional source signatures of airborne particulate matter, an epithermal irradiation facility to determine indium has been specifically constructed. Analysis of filter samples collected weekly over a 5-yr period has indicated that indium in the arctic atmosphere is strongly dependent on season. Typical detection limits were 0.1 ng per one-eighth of a 20.3-×25.4-cm Whatman filter. The airborne concentrations of indium are extremely elevated in the winter and spring months, and they almost disappear in the summer months. The application of the potential source contribution function has indicated that the indium originates from several areas in Eurasia as well as from known“hot spots”in North America.

ISSN:0029-5639    

DOI:10.13182/NSE92-A23877

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractThe method of backscattering that is applied in neutron spectroscopy in the microelectron-volt region is described, as is its development at the Jülich Research Reactor FRJ-2, and at the Institut Laue-Langevin in Grenoble. Selected examples of experiments are presented. The backscattering principle can be applied for high-precision measurements of lattice parameters (Δa/a≃10−7) as developed at the Jülich reactor.

ISSN:0029-5639    

DOI:10.13182/NSE92-A23878

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractBoron neutron capture therapy (BNCT) is an experimental radiation therapy that is being developed for the treatment of malignant tumors. One requirement for successful BNCT is that a sufficient amount of10B concentrates in the tumor while clearing from normal tissues and blood. Many pharmaceuticals are currently being developed to selectively deliver10B to a tumor. To evaluate the effectiveness of various10B delivery agents, the concentrations of boron in blood, tumor, and normal tissues must be known. Using the solid-state nuclear track detector CR-39, a tissue assay technique has been developed to spatially determine10B concentrations in tissue samples. The technique has been used to quantify10B concentrations in tumor and normal tissue on lines across rat brain tissue sections. This was done by combining10B concentrations measured on lines across the CR-39 with color digital images of the tissue section. Coupling the methodology that was developed for tissue samples with an existing analytical technique for blood-10B concentration measurements allows for complete evaluation of10B distributions in blood, tumor, and normal tissues and should be useful in evaluating various10B delivery agents for use in BNCT.

ISSN:0029-5639    

DOI:10.13182/NSE92-A23879

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor