Shields

About: Shields is a research topic. Over the lifetime, 1456 publications have been published within this topic receiving 10896 citations.

Effects of pseudo-lensing and pseudo-dispersion in curved radiation shields and collimators - Effects on measurements

Abstract: The use of collimators and shields for measurements and imaging with X- and γ -rays requires a well-defined collimation for the pixels and well-determined formula for the effect of the collimators. We analyze the geometric effects of tubular and pinhole collimators and the effects of curved shields for the case of omni-directional fluxes. These effects can affect measurements of X- and γ-rays as well as UV rays behind the shield and collimators. On the other hand, such effects can be used to enhance the capability of multi-spectral sensors by using appropriate covers in front of them.

Superconducting magnet for a traveling wave maser

Abstract: A superconducting magnet has been developed to supply the magnetic field necessary to operate a 4 Gc traveling wave ruby maser. The field required by the maser is about 3000 oersteds uniform throughout the volume of the ruby to one part in a thousand. The field is directed across a gap of about 0.8 inches whose cross section is 5 inches by 0.5 inches. A close approach to the ideal magnetic circuit has been achieved by placing superconducting shields adjacent to the pole pieces. Circulating currents are set up in the shields which prevent the existence of leakage and fringing flux. Since there is no loss mechanism in the shields, the currents persist and the air-gap field remains everywhere uniform. With the absence of leakage and fringing flux, the size and weight of the magnetic circuit is considerably reduced. Superconducting coils allow the use of a persistent current to generate the field. A heater element encased in a glass sleeve is used to initiate the persistent current. The switching procedure is simple and involves no moving parts in the cryostat.

Measuring the Magnetic Field Attenuation of Nonlinear Shields

Abstract: The problem of a low-frequency shielding of a loop placed inside a coaxial torus shield is analyzed by the application of the Schelkunoff transmission theory of shielding. Copper and iron torus shields are considered. In the case of ferromagnetic material, the losses inside the medium are evaluated by new analytic formulations. One method reduces the full nonlinear diffusion problem to a linear problem through an optimization procedure. A second formulation attempts to approximate the differential magnetic permeability by a complete set of functions. The results of such a theory are adapted to the problem of measuring the shielding effectiveness of nonlinear shields. In particular, this measurement is reduced to the experimental characteriza- tion of the electric conductivity and of the B(H) dynamic hysteresis cycle of the shielding material. Direct shielding effectiveness measurements are obtained and compared with results obtained through the proposed procedure at different frequencies showing a substantially good agreement.