169 Matching Results

Search Results

Advanced search parameters have been applied.

Advanced biomolecular materials based on membrane-protein/polymer complexation

Description: This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The goal of this project was to apply neutron reflectometry and atomic force microscopy to the study of lipid membranes containing proteins. Standard sample preparation techniques were used to produce thin films of these materials appropriate for these techniques. However, these films were not stable, and a new sample preparation technique was required. Toward this goal, the authors have developed a new capability to produce large, freely suspended films of lipid multi-bilayers appropriate for these studies. This system includes a controlled temperature/humidity oven in which the films 5-cm x 5-cm are remotely drawn. The first neutron scattering experiments were then performed using this oven.
Date: December 1, 1998
Creator: Smith, G.S.; Nowak, A. & Safinya, C.
Partner: UNT Libraries Government Documents Department

Overview of the Target Systems for the Spallation Neutron Source

Description: The technologies that are being utilized to design and build the target systems for a state-of-the-art accelerator- based neutron source, the Spallation Neutron Source (SNS), are discussed. Emphasis is given to the technology issues that present the greatest challenges. The present facility configuration, ongoing analysis, and planned research and development program are also described.
Date: October 15, 1998
Creator: Gabriel, T.A.; Haines, J.R. & McManamy, T.J.
Partner: UNT Libraries Government Documents Department

On the Rossi-{alpha} measurement of {beta}{sub eff} in reflected reactors

Description: In unreflected reactors, the probability of detecting chain-related counts is given by the well known Rossi-{alpha} expression. Using this the author derives an expression for the effective delayed neutron fraction, {beta}. He demonstrates that this expression for {beta} is equally applicable for a reflected systems in which two alphas are experimentally observed.
Date: March 13, 1997
Creator: Doulin, V.A. & Spriggs, G.D.
Partner: UNT Libraries Government Documents Department

SNS moderator design

Description: The pulsed-neutron source SNS facility will start operation at 1 MW. A later upgrade to 5 MW is planned. The facility consists of a linear accelerator, an accumulator ring, and a target station. The protons from the accumulator ring will be injected into the target station at 1 GeV. The subsequent spallation process will then produce low-energy thermal neutrons that may be used for a wide variety of experiments. In this paper the authors discuss neutronic calculations which address various aspects of the moderate design. The computer codes HETC and MCNP were used for these calculations with the former code performing the high-energy transport. Neutrons which fell in energy to 20 MeV or less were then passed to MCNP for further transport.
Date: December 1, 1997
Creator: Charlton, L.A.; Barnes, J.M.; Gabriel, T.A. & Johnson, J.O.
Partner: UNT Libraries Government Documents Department

{beta}{sub eff} measurements in reflected reactors using a Rossi-{alpha} technique

Description: In this report the authors calculate the effective delayed neutron fraction equation for reflected reactors using the Rossi-{alpha} technique. They determine that the equation for the delayed neutron fraction is just as valid for reflected systems as it is for unreflected systems.
Date: January 20, 1998
Creator: Doulin, V.A. & Spriggs, G.D.
Partner: UNT Libraries Government Documents Department

The performance of reflectometers at continuous wave and pulsed-neutron sources

Description: To quantify gains from time-of-flight (TOF) methods, identical reflectometers viewing a continuous wave (CW) neutron source and a variety of pulsed-neutron sources were simulated using a Monte Carlo technique. Reflectivity profiles obtained for a simple thin-film, reflecting,sample were nearly identical in all simulations, and models fitted to the simulated data yielded parameters (film thickness, surface roughness, and scattering length density) that were equally accurate and precise in all cases. The simulations confirm the power of the TOF method and demonstrate that the performance of pulsed sources for reflectometry does not scale simply as the inverse duty factor of the source. In the case of long-pulse sources, the simulations suggest that pulse tails have little effect on results obtained from specular reflectometry and that maximum brightness of the neutron source should be the primary design criterion.
Date: December 1995
Creator: Fritzsimmons, M. R. & Pynn, R.
Partner: UNT Libraries Government Documents Department

K Reactor moderator distortion study

Description: Irradiation-induced moderator distortion has plagued the Hanford reactors from their earliest days until the present. The first-manifestation of graphite distortion was in the form of expansion of the B, D and F stacks. It was found that expansion was very temperature-dependent and could be reversed by raising the graphite operating temperature. The DR, H, C and K Reactors were designed with provisions to minimize, or accommodate expansion. It was not until after the K Reactors had been designed that graphite contraction was recognized as a threat to stack life. Under the present operating conditions, contraction is largely dependent upon neutron flux levels. To date, this study has been largely concerned with the K Reactors, since the vast bulk of the distortion data available is from the Ks. This study not only attempts to explain the mechanisms by which the K Reactors arrived at their present state of distortion but also provides a basis for forecasting future distortion. An understanding of the nature and magnitude of the forces at work within the stacks will enhance the possibility of devising means of conteracting the present trends.
Date: June 22, 1964
Creator: Alexander, W.K. & Russell, A.
Partner: UNT Libraries Government Documents Department

Effect of reflector location at array criticality

Description: The motion of a thick reflector away from a critical array of subcritical units of fissile material results in an array reactivity loss. The fraction of the total reactivity worth of a reflector is related to the distance a reflector is located from the surfaces of an array. The magnitude of reactivity associated with the reflector location may be used in the assessment of nuclear criticality safety of operations with fissile materials to establish margins of subcriticality. An equivalence is established between the reactivity associated with reflector location and the reactivity associated with the thickness of a water reflector closely fitting an array.
Date: November 1, 1980
Creator: Thomas, J.T.
Partner: UNT Libraries Government Documents Department

Solid angle and surface density as criticality parameters

Description: Two methods often used to establish nuclear criticality safety limits for operations with fissile materials are the surface density and solid angle techniques. The two methods are used as parameters to express experimental and validated calculations of critical configurations. It is demonstrated that each method can represent critical arrangements of subcritical units and that there can be established a one-to-one correspondence between them. The analyses further show that the effect on an array neutron multiplication factor of perturbations to the array can be reliably estimated and that each form of fissile material and unit shape has a specific representation.
Date: October 1, 1980
Creator: Thomas, J.T.
Partner: UNT Libraries Government Documents Department