Measurement of the delayed neutron fraction and correction of small angle scattering data from a pulsed spallation source
Abstract The fraction of delayed neutrons in a moderated beam from the enriched uranium, pulsed spallation source at the intense pulsed neutron source at Argonne National Laboratory has been measured and found to be 0.0283 for 450-MeV protons. Delayed neutrons produce a sample-dependent background in time-of-flight instruments. Because of the distribution of neutron wavelengths in the prompt pulse, the significance of the delayed neutron contribution to the observed scattering profile is strongly dependent on the wavelength and therefore on the magnitude of the momentum transfer. This effect is demonstrated, and a general correction procedure in current use for small angle neutron scattering data is described.
Neutron-scattering techniques
Neutrons have been available to scientists for about sixty years but it is only in the last 25 years that they have been widely exploited as a tool in condensed matter research. This is largely due to the advent of high-flux beam reactors such as those at the Institut Laue Langevin in Grenoble, France, and at Brookhaven National Laboratory in New York. It is not feasible to review all the literature relating to solid polymers even given the finite number of laboratories equipped for such investigations. Reference will be made particularly to those papers that describe advances in the technique and to some review articles on specific applications. The description of theory will be limited to definition of the terminology and a few of the most basic equations.
Measurement and Demonstration of Thermal Expansion Coefficient
There are many classroom demonstrations, such as the ball-and-ring experiment, for showing the existence of thermal expansion of solids. The coefficient of linear expansion α (= increase in length divided by the original length times the change in temperature) may be measured in high school laboratories using a number of methods.1–4 In this paper we describe an especially simple experiment for determining α for a metal rod. It is based on the well-known optical lever method and is suitable for either a laboratory experiment or a classroom exercise.