Showing papers on "Shields published in 1976"

Non-combustible nuclear radiation shields with high hydrogen content

Abstract: This invention relates to compositions, methods of production and uses of non-combustible nuclear radiation shields, with particular emphasis on those containing a high concentration of hydrogen atoms, especially effective for moderating neutron energy by elastic scatter, dispersed as a discontinuous phase in a continuous phase of a fire resistant matrix.

Glassy metal fabric: A unique magnetic shield

Abstract: Metallic glass ribbon of the composition Fe 40 Ni 40 P 14 B 6 , METGLAS® alloy 2826, has been produced in kilogram quantities with controlled magnetic properties. Cylindrical shields have been made by interlacing such ribbons using three different methods. Shielding ratios have been measured at 60 Hz for the cylindrical shields and compared with an equal weight shield wrapped from polycrystalline 80/20 NiFe foil. Shielding ratios of woven metallic glass compare favorably with equal weight polycrystalline foil shields. The woven metallic glass shield also has the important advantage of being flexible and less sensitive to mechanical strain.

Prediction and Measurement Results of Radiation Damage to CMOS Devices on Board Spacecraft

Abstract: The CMOS Radiation Effects Measurement (CREM) experiment is presently being flown on the Explorer-55. The purpose of the experiment is to evaluate device performance in the actual space radiation environment and to correlate the respective measurements to on-the-ground laboratory irradiation results. The experiment contains an assembly of CMOS and P-MOS devices shielded in front over 2? steradian by flat slabs of aluminum of 40, 80, 150, and 300 mils (1.02, 2.04, 3.81, and 7.62mm) thicknesses, and by a practically infinite shield in the back. This paper presents initial results obtained from the CREM experiment. Predictions of radiation damage to C-MOS devices are based on standard environment models and computational techniques. A comparison of the shifts in CMOS threshold potentials, that is, those measured in space to those obtained from the on-the-ground simulation experiment with Co-60, indicates that the measured space damage is smaller than predicted by about a factor of 2-3 for thin shields (t < 100 mils), but agrees well with predictions for thicker shields. It is not clear at this time how the trapped particle environment models or the computational methods should be modified in order to achieve better agreement between experimental results and predicted damage curves. A subsequent paper will present some considerations along these lines as well as an evaluation of performance of C-MOS devices located in a typical electronic subsystem box within the spacecraft.

Impulse voltage distribution improving partial-turn electrostatic shields for disc windings

Abstract: A disc wound winding formed of a plurality of spirally wound, disc coil sections and having series capacitance increasing electrostatic shields in less than all of said sections, incorporates partial-turn electrostatic shields in disc coil sections adjacent that portion of said winding not having electrostatic shields. With this arrangement, a substantial reduction in the change in series capacitance between the shielded and unshielded portions of a disc wound winding is effected which minimizes unsatisfactory impulse voltage build-up at the beginning of the unshielded portion of said winding.

Radiation shielding means for radiant coolers

Abstract: The improved passive radiation shielding means for radiant coolers as illustrated and described herein involves a device wherein one or more radiation shields having open, externally viewing end areas are positioned in a housing between stages of a radiant cooler. Mechanical low conductive supports hold the various elements, including the device to be cooled, the cooling stages and the radiant shields in place. In one practical embodiment of the device of this invention for use in cooling detector means aboard a satellite, the housing includes first radiant cooler stage is composed of a radiator surface, an optically polished and aluminized cone, two gold plated radiation shields and eight tubular low conductance insulating supports which mount the first stage to the vacuum housing. In addition there is hinged earth shield which may be deployed on command, whether the device is being tested or its in position in orbit. The second stage is made up of the patch, the detector package, two gold plated radiation shields and four tubular low conductance insulating supports which mount this assembly to the first stage of the cooler.

Method of manufacturing structural honeycomb with integral heat radiation shields, and the resulting product thereof

Abstract: A method of manufacturing structural honeycomb with superior insulation effectiveness, by the incorporation of integral heat radiation shields into the current process of manufacturing honeycomb hexagonal cells as formed by expanding a block of flat laminations. The heat radiation shields are initially in the form of flat ribbons of thin low emissivity metal coated plastic film, which are bonded between each lamination, in a direction normal to either the adhesive lines, strips, or stripes, or unmasked stripes, strips, or lines, used to bond the honeycomb nodes. The ribbons are formed of compressed pleats, which open up when the flat laminated block is expanded, closing off each hexagonal cell with spaced heat radiation shields.

Fast Burst Reactor Neutron Damage in Silicon Transistors

Abstract: An experiment was performed to assess the magnitude of the differences in neutron damage to silicon transistors under various conditions encountered in fast burst reactor testing. Transistors were subjected to free-field pulse and free-field power run exposures, and to exposures shielded by lead and by paraffin. These tests provided data to compare to damage results obtained under routine test conditions, i.e., relatively unperturbed field but with the experiment table in place. Fission foils and an activation foil were exposed with each group of transistors. The objectives of the experiment were: 1) to determine if perturbations in the reactor testing environment would produce measurable differences in the relative damage in silicon transistors--greater than the statistical variations characteristics of the test groups, and 2) to determine if the observed differences in damage could be correlated with the results of fission and activation foil neutron fluence measurements. Neutron exposures were performed at the White Sands Missile Range (WSMR) Fast Burst Reactor (FBR). Thin fission foils were exposed adjacent to lexan plastic discs to record the resulting fission tracks. The fission foils were exposed inside cadmium shields which were placed inside 10B shields. Sulfur pellets were exposed both inside and outside the boron shields. The fission track and sulfur counter data were evaluated using techniques similar to those specified in ASTM standard procedures. Relative silicon damage measurements were obtained by exposing groups of carefully characterized transistors.

Thermal radiation shields for radiant coolers.

Abstract: Thermal radiation shields in the form of low-emissivity surfaces spaced on low-conductance supports can be used to advantage as a replacement for multilayer insulation in radiant coolers. A view factor between adjacent shields of less than unity increases the insulation factor when the surfaces terminate with an external view. An analytical model that accounts for unequal areas as well as the reduced view factor is shown to be in good agreement with experimental measurements when the end area absorption and emission are small. The modifications to both the analytical model and the experimental evaluation are discussed for the case of significant end absorption or emission.

Rejection of Radio-Frequency Noise with a Wide-Band Differential Preamplifier and Solid-Shielded Coaxial Input Cables

Abstract: Radio-frequency signals simulating electrical interference ranging from 50 Hz to 50 MHz were applied to the shields of the input cable system (two solid- shielded, mineral-insulated cables approximately 6 m long) of a wide-band (approximately 60 MHz) differential preamplifier for use with fission counters as input devices as part of in-vessel, low-level flux monitors in future liquid- metal fast breeder reactors (LMFBRs) to determine the common-mode rejection Results show that differences in electrical properties and shielding characteristics of the two input coaxial cables along with end effects produced by an unbalanced sensor severely degrade the rejection capability of the differential preamplifier At 1 MHz, the common-mode rejection without input cables is approximately -70 dB; this is reduced to approximately -10 dB when measured with the rf signal applied to the surface of the input cable shields Measurements of the shielding characteristics of the input cables showed resonances at test frequencies greater than 2 MHz A ferrite core was installed in the input assembly to increase the impedance of the shields and to permit termination of the coaxial line consisting of the input cable shields and the protective metal conduit for the input cables This assembly eliminated all resonances below 20more » MHz The increased impedance also reduced the amplitude of the shield currents, resulting in an increase in the shielding effectiveness of the input cables without affecting the signal transmission of the cables (auth)« less

A theoretical investigation of gas conduction effects on multilayer insulation performance

Abstract: The thermal performance of multilayer insulation hlankets depends on three (interacting) modes of energy transfer: radiation between the radiation shields, gas conduction in the residual interstitial gas and solid conduction via the contacting interfaces. The contribution of the gas conduction depends on the interstitial gas and its pressure, that are determined mainly by the temperature dependent outgassing of the shield and spacer materials. Special attention has been given to the actual problems of the insulation of the storage of cryogenic licpiids in vessels, the insulation of black boxes from space environment and the effect of gas sources surroimded by multilayer insulation. The results indicate that perforation of the shields reduces the insulation properties of a blanket considerably. Hence for cryogenic storage non-perforated shields are to be preferred. In space cutted shields are to be preferred, because they allow fast depressurisation without impairing the radiation properties.

Natural thermal radiation of heat-absorbing thermal vacuum chamber shields

Abstract: A simplified method for computing the natural thermal radiation of heat-absorbing shields of vacuum chambers is elucidated; computational dependences are presented for shields of herringbone outlines and the influence of the geometric profile characteristics on the magnitude of the natural radiation is shown.