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Predictions of Total Ionizing Dose made using full 3-D Monte Carlo and simplified sector-shielding techniques for simple and complex geometries in a space environment are compared and differences between them analyzed in detail. Index Terms--Monte Carlo methods, radiation effects, ray tracing, shielding.

The enhancement of displacement damage energy deposition due to secondary neutrons, pions, deuterons, and alphas resulting from high-energy (100--1000 MeV) proton interactions with aluminum and tungsten shielding are examined in this paper. The results obtained using a comprehensive Monte Carlo charged particle transport code, MCNPX Version 2.1.5, indicated that the dominant secondary particle is neutrons. The additional contribution to the displacement damage energy produced by secondary pions, deuterons, and alphas turned out to be less than 5 %. Index Terms--Displacement damage, nonionizing energy loss, proton, secondary particles.

We report experimental measurements of neutron production from collisions of neutron beams with polyethylene blocks simulating tissue at the Los Alamos National Laboratory Neutron Science Center and 1 GeV/amu iron nuclei with spacecraft shielding materials at the Brookhaven National Laboratory AGS. Index Terms--High-energy neutrons, neutron moderation, polyethylene.

Radiation transport codes are applied to calculate the influence of aircraft structure and loads on the internal environment from galactic cosmic rays. Significant shielding effects are predicted, while thermalization of the neutron flux can lead to enhanced single-event upset rates in devices containing boron. The enhanced environments due to large solar particle events are calculated and shown to be very important for both single-event effects in electronics and dose to crew and passengers.

An investigation of the shielding constants and nuclear quadrupole coupling constants of nitrogen atoms in a complete set of parent structures of N-methyl-substituted azoles is presented. Multiconfiguration SCF wave functions provide a good description of the investigated molecular properties.

The shielding effectiveness of laser-induced breakdown from focused, visible laser pulses from 5 ns to 125 fs is determined from measurements of transmission of energy through the focal volume. The shielding efficiency decreases as a function of pulse duration from 5 ns to 300 fs and increases from 300 fs to 125 fs. The results are compared with past studies at similar pulse durations. The results of the measurements support laser-induced breakdown models and may lead to an optimization of laser-induced breakdown in ophthalmic surgery by reduction of collateral effects. Key words: Laser-induced breakdown, optical breakdown, plasma, shielding, intraocular photodisruption.

GaAs heterojunction bipolar transistor 1/f noise performance is demonstrated to be unaffected by dose rate and total dose. This is believed to be due to shielding provided by the [N.sup.+] collector from the GaAs substrate.

Commercial CMOS analog/digital processes are considered for spaceborne applications. Total dose hardness of three processes is compared by the testing of analog multiplexers. Parts were irradiated at 18 and 1.8 rad(Si) per sec. The total dose results are then compared with the requirements for a low earth and a geosynchronous orbital design. Shielding thicknesses for each of the orbital designs are suggested.

Shielding for space microelectronics needs to provide an acceptable dose rate with minimum shield mass. The analysis presented here shows that the best approach is, in general, to use a graded-Z shield, with a high-Z layer sandwiched between two low-Z materials. A graded-Z shield is shown to reduce the electron dose rate by more than sixty percent over a single-material shield of the same areal density. For protons, the optimal shield would consist of a single, low-Z material layer. However, it is shown that a graded-Z shield is nearly as effective as a single-material shield, as long as a low-Z layer is located adjacent to the microelectronics. A specific shield design depends upon the details of the radiation environment, system model, design margins/levels, compatibility of shield materials, etc. Therefore, we present here general principles for designing effective shields and describe how the computer codes are used for this application.

In this paper, we have pioneered a new direction concerning the shielding of electronic devices (at a micro-circuit-packaging or a larger level) in a radiative environment. As a matter of fact, this work not only considers the role of the material itself on the shielding efficiency but also the effect of the structure of the shield. By simulations with the NOVICE Code, we have explored the possibility of combining the specific attenuation properties of given materials in an optimized multilayer (and multimaterial) structure. This study is based on a brief theoretical overview of interaction of space radiation with material. Then, the results of simulations are presented. The workframe of these calculations is a worst-case geosynchronous orbit (160 [degrees] West) for a period of 15 years (trapped electrons and protons from 4 anomalously large solar particle events). We found that it is possible to improve the shielding properties of a monomaterial absorber by using an optimized multilayer, multimaterial shield.

Realistic models of satellite shielding have been used to calculate SEE rates for Galactic Cosmic Rays (GCR) and solar flare protons. The results are compared with those obtained with a nominal 0.1 inch spherical shield. The rates for GCR (solar minimum) are systematically lower than those calculated with the nominal shield. The ratio of rates is greater than 75% for lightly shielded devices, but may be as high as a factor of two where there is shielding by other circuit boards. A more nearly realistic estimate of the rates would be obtained with a spherical shield with a thickness of at least 0.4 inches (3 gm/[cm.sup.2]) for the typical satellites considered. The calculation of the SEE rate due to protons was reformulated to expedite shielding calculations. When the method was applied to the 93L422 RAM for various flare spectra, it was apparent that shielding has a first order effect on rate predictions. The calculated flare upset rates for the TDRS satellite were within 20% of the observed rates. A spherical shield of thickness 0.3 inches (2 gm/[cm.sup.2]) would reproduce the rates. The method was also applied to a trapped proton environment predicted from standard models for CRRES. The predicted rate was consistent with the uncertainties of the environment.

The optical reflectance and transmittance spectra of complete windows for near normal and oblique angles of incidence are calculated from spectra of the individual panes taking multiple reflections into account. Calculated and experimental spectra are compared for triple and quadruple glazed windows with different combinations of low-e coatings. For the annual energy balance of a window the total solar transmission at oblique incidence is more relevant than the near normal performance. It is shown that, owing to the experimental difficulties involved in optical measurements at oblique incidence, great care must be taken when evaluating the annual performance. A simple equation for the annual energy balance of the window taking solar radiation and thermal heat losses into consideration is presented. Annual meteorological data for the insolation and outside temperature are used together with the optical performance to evaluate the net energy heat flow through a window. This can be performed for the complete heating season to evaluate the heat load needed for the building as well as for the warm season to evaluate the cooling load needed owing to solar overheating. This model provides a simple way of comparing the thermal performance of windows with different combinations of advanced glazings in both cold and hot climates, and makes it possible to estimate the cost efficiency of such windows.

The use of a sacrificial carbon surface layer deposited on the target surfaceto protect it from sputtering during a high dose heavy ion implantation processwas investigated. The results showed that the carbon layer effectively shieldedthe target from sputtering damage. However, as the implantation energy was increased, a significant degree of carbon mixing was observed at the C/Cu interface.

The derivation of derived intervention level (DIL) for sheltering in the event of a nuclear accident relies heavily on the effectiveness of shielding provided by the shelters. Different types of buildings having different external wall materials will exhibit tremendous variation in the effective shielding capability. Shielding factors for concrete and glass based on the equivalent dose build-up factors in the materials have been calculated and these factors are applicable for estimating the protection against a radioactive plume. The [gamma] emitters normally present in the plume are divided into 3 groups for the convenient choosing of appropriate shielding factors. A case study on the application of shielding factors for protection against a design based accident occurring at the Guangdong Daya Bay nuclear power plant was also described. Discussion was also focused on the practical application and meaning of the DIL.

The binding free energies and complexation-induced NMR shifts of complexes in water between 16 nucleic acid components and lipophilic receptor models with positively charged nitrogen atoms are investigated. Electrostatic contributions to nucleotide binding may be measured separately based on constant salt bridge increments. Binding constants and binding geometry reveal the selectivity of van der Waals contributions for adenine. Moreover, pyrimidine derivatives are not encapsulated.

A study was conducted to calculate the change in chemical shielding of the terminal oxygen atoms in five different functional groups. The results showed that for the small selection of molecules, the direction of change in [[sigma].sub.iso] (deshielded or shielded) upon substitution is not dependent on the change in charge on oxygen, but on the change in charge due to forced torsion without perturbing substituents on the aromatic ring.

Results from the Cosmic Radiation Environment Monitors (CREAM and CREDO) have been reported from a range of platforms during the declining phase of solar cycle 22 and a number of implications drawn for radiation environment and shielding models. Since these reports, the CREAM monitor has flown on a number of Shuttle visits to MIR during 1997-1998 with an extended deployment on MIR during January to May 1998. In all cases an active monitor measured charge-deposition spectra at various locations, while passive packages comprising neutron activation foils, neutron bubble detectors and thermoluminescent dosimeters obtained integrated data at these and other sites. Movement of the South Atlantic Anomaly is observed and cannot be fitted by simply updating the geomagnetic field model. The data from MIR are compared with those from previous Shuttle missions and show comparable secondary neutron fluencies and dose rates. Meanwhile a CREDO-3 particle telescope has been included in the Microelectronics and Photonics Test Bed in highly eccentric, high inclination orbit and has been returning data since November 1997. This experiment measures proton fluxes greater than 38 MeV and linear energy transfer spectra of cosmic rays and solar particle events in the range 100-20 000 MeV/(g cm-2). The data have been extended to July 2000 and are used both to correlate with device behavior and to compare with models of trapped radiation, cosmic rays and solar particles. A number of solar particle events have been observed as cycle 23 builds up. Following a relatively quiet year in 1999, the recent event of July 14, 2000 is observed to compete with the October 1989 events in terms of proton fluency but has a somewhat lower heavy ion fraction.

A previously proposed method was applied to a heterogeneity shield calculation and showed some remarkable results. In the present work, more extensive study of the dose distributions near a shield heterogeneity, were performed. As a result of this investigate, a calculation-experimental method was developed for dose field calculations with complex geometry, and a typical scale much greater than a mean free path of gamma radiation. Experimental data can be readily used to verify other codes.