Low Energy Absorbing Research Articles

Effect of Low-Energy Resonance Absorber on Positive Neutron Temperature Coefficient of Dilute Plutonium-Water Solution

The positive neutron temperature coefficient of reactivity of a dilute plutonium-water solution is discussed analytically and numerically. It is explained by the competition of the temperature sensitivity coefficients of microscopic thermal cross sections of fissile materials and absorbers. The use of 176Lu, 180Ta, or 167Er, which have absorption resonances at low energy, in the solution makes it possible for the neutron temperature coefficient of reactivity of a dilute plutonium-water solution to be negative.

The materials science and Laue diffraction beamlines at the European Synchrotron Radiation Facility

This article presents the design of two diffraction beamlines, BL2 and BL3, at the European Synchrotron Radiation Facility. The materials science beamline will produce a monochromatic beam tunable in the energy range 5<E<60 keV and provide an energy resolution of 10−4 < ΔE/E < 3 × 10−4 below ∼40 keV. The radiation is generated by a 24 pole wiggler with critical energy εc = 28.8 keV and K=14.0. It produces 4.9 kW of power over a horizontal fan of 1.5 mrad. The heat load on the first monochromator crystal is controlled by an adaptive premirror set to reflect an energy band exceeding the desired monochromator energy by 20% or by low energy absorbing filters. The first monochromator crystal will be cryogenically cooled. The premirror and a symmetric postmirror will collimate and refocus in the vertical plane. Horizontal focusing will be done by sagittal bending of a rib enforced second monochromator crystal. The white beam station BL3 is optimized for Laue diffraction in the energy range 5<E <60 keV. The source is a 44 pole wiggler with εc = 17.2 keV and K=4.7. It produces a power of 1.8 kW and an integrated flux ∼ 6 × 1017 ph/s. over a horizontal fan of 0.5 mrad. The radiation is focused by a toroidal mirror with fixed sagittal radius.

The ecological and evolutionary interdependence between web architecture and web silk spun by orb web weaving spiders

Spider orb webs are dynamic, energy absorbing nets whose ability to intercept prey is dependent on both the mechnical properties of web design and the material properties of web silks. Variation in web designs reflects variation in spider web spinning behaviours and variation in web silks reflects variation in spider metabolic processes. Therefore, natural selection may affect web function (or prey capture) through two independent and alternative pathways. In this paper, I examine the ways in which architectural and material properties, singly and in concert, influence the ability of webs to absorb insect impact energy. These findings are evaluated in the context of the evolution of diverse aerial webs. Orb webs range along a continuum from high to low energy absorbing. No single feature of web architecture characterizes the amount of energy webs can absorb, but suites of characters indicate web function. In general, webs that intercept heavy and fast flying prey (high energy absorbing webs) are large, built by large spiders, suspended under high tension and characterized by a ratio of radii to spiral turns per web greater than one. In contrast, webs that intercept light and slow flying prey (low energy absorbing webs) are suspended under low tension, are small and are characterized by radial to spiral turn ratios that are less than one. The data suggest that for spiders building high energy absorbing webs, the orb architecture contributes much to web energy absorption. In contrast, for spiders that build low energy absorbing webs, orb architecture contributes little to enhance web energy absorption. Small or slow flying insects can be intercepted by web silks regardless of web design. Although there exists variation in the material properties of silk collected from high and low energy absorbing webs, only the diameter of web fibres varies predictably with silk energy absorption. Web fibre diameter and hence the amount of energy absorbed by web silks is an isometric function of spider size. The significance of these results lies in the apparent absence of selective advantage of orb architecture to low energy absorbing webs and the evolutionary trend to small spiders that build them. Where high energy absorption is not an exacting feature of web design, web architecture should not be tightly constrained to the orb. Assuming the primitive araneoid web design is the orb web, I propose that the evolution of alternative web building behaviours is a consequence of the general, phyletic trend to small size among araneoids. Araneoids that build webs of other than orb designs are able to use new habitats and resources not available to their ancestors.