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 owever, 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.

Issued by Sandia National Laboratories, operated for the United States Department of Energy by San&a Corporation. NOTICE This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government, nor any agency thereof, nor any of their employees, nor any of their contractors, subcontractors, or their employees, make any warranty, express or implied, or assume any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, o r process disclosed, or represent that its use would not infringe privately owned rights. Reference herein t o any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government, any agency thereof, or any of their contractors or subcontractors. The views and opinions expressed herein do not necessarily state or reflect those of the United States Government, any agency thereof, o r any of their contractors.

1do not work for charged-particle beams. It is hoped, however, that the methods presented here provide some progress toward a multidimensional, deterministic electron-transport capability.Coupled electron-photon transport capability is needed for an ever-increasing number of applications, including the response of electronics components to space and man-made radiation environments, medical radiation therapy, industrial curing, and food sterilization. Currently, powerful Monte Carlo codes are available for electron transport*. While some problems are well suited for a Monte-Carlo approach, other problems are more efficiently solved with a deterministic method, e.g. computing distributions, modeling deep penetration, and low-probability events.Deterministic electron transport capability has been available for one-dimensional geometries, with the CEPXS/ONELD code package5. Unfortunately, the CEPXS/ONELD approach is not easily extendable to multidimensional geometries. Bill Filippone and his students at the University of Arizona developed the multidimensional, deterministic charged-particle code, SMARTEPANTS'.This code is presently under active development.The work presented here combines the CEPXS/ONELD and SMARTEPANTS approaches, resulting in SMARTEPANTS-like cross sections that are compatible with production discreteordinates codes. The resulting cross sections have a number of desirable properties: 1) positivity, 2) much smaller than the true interaction cross sections, 3) low-order Legendre expansion, 4) and not tied to a particular quadrature set. These desirable properties will be further explained, with limitations given, later in this article. BOLTZMANN-FOKKER-PLANCK OPERATORThe Boltzmann operator, L, describing the distribution in space, direction, and energy of a field of either charged or neutral particles is defined by7 L@(r, 52, E) = -52 0 V@(r, 52, E ) -at(r, E)@(r, 52, E) + JJ as(r, 521 + 52, E' + E)a(r, a', E')~oz'~E'.(1)The scattering cross section, as(r,O' -+ 52, E' + E), is the probability per unit energy and solid angle that a particle of energy E' moving in direction 52' will be scattered to energy E in direction 52. The total cross section is at(r, E). For neutral-particle applications, the Boltzmann equation is normally solved by expanding the scattering cross section in a low-order Legendre polynomial expansion and the discretizing the spatial, energy, and angular dependence of the fluence.For scattering that is highly forward peaked, which is characteristic of charged-particle scattering, the Legendre polynomial angular expansion of the cross sections that is normally used in discrete ordinates codes is inadequate. The Boltzmann-Fokker-Planck (BFP) operator is an approximation to the Boltzmann-transport operator for scattering interactions that are highly forward peaked.In order to model electron transport with a BFP formulation, the scattering cross section is separated into three components, 1) the elastic-scattering part (for directional change without energy loss), 2) a soft inelastic-s...

SummaryThis paper reports on the processing steps in a silicon foundry leading to improved performance of the Radiation Sensing Field Effect Transistor @&ET) and the use of multiple RadFETs in a handheld, battery operated, combination spectrometer/dosimeter.

A novel solution method has been developed to solve the linear Boltzmann equation on an unstructured triangular mesh. Instead of tackling the first-order form of the equation, this approach is based on the even/odd-parity form in conjunction with the conventional multigroup discreteordinates approximation. The finite element method is used to treat the spatial dependence. The solution method is unique in that the spacedirection dependence is solved simultaneously, eliminating the need for the conventional inner iterations, and the method is well suited for massively parallel computers.