Pete Truscott

An atmospheric radiation model based on response matrices generated by detailed Monte Carlo Simulations of cosmic ray interactions

A comprehensive model of the energetic radiation in the atmosphere has been developed. It is based on the use of a dynamic cosmic ray radiation model, an efficient rigidity cutoff calculation tool, and the use of detailed atmospheric response matrices to monochromatic cosmic ray particle incidences. The response matrices were produced by detailed Monte Carlo (MC) simulations of cosmic ray interactions with the atmosphere. This model can predict the secondary particle (proton, neutron, electron, gamma, charged pion, or charged muon) spectrum at any given location and time in the atmosphere.

Improvements to and Validations of the QinetiQ Atmospheric Radiation Model (QARM)

The QinetiQ atmospheric radiation model (QARM) is a comprehensive model of the energetic radiation in the atmosphere. In this paper we report on the improvement and validation activities for this model. The improvements include the implementation of two additional cosmic ray models, new response matrix, dose rate and flight dose calculation facilities. Tests/validations of the model have been carried out at individual component level as well as at system level. We will also report on the web interface developed to allow easy access to the model.

Single Event Effects in Power MOSFETs and SRAMs Due to 3 MeV, 14 MeV and Fission Neutrons

Various SRAM and MOSFET devices were exposed to 3 MeV and 14 MeV neutrons at a fusion facility and to a fission neutron spectrum with a californium-252 source. Single event burnout (SEB) was observed in several of the MOSFETs in all three environments-the first time this phenomenon has been observed at neutron energies below 10 MeV. In addition to observing single event upsets (SEU) and single event latchup (SEL) in the SRAMs, two devices experienced significant multiple cell upset (MCU) effects which dominated the upset rate. The physical mechanisms underlying these phenomena and the consequences for various radiation environments are discussed.

SEPEM: A tool for statistical modeling the solar energetic particle environment

Solar energetic particle (SEP) events are a serious radiation hazard for spacecraft as well as a severe health risk to humans traveling in space. Indeed, accurate modeling of the SEP environment constitutes a priority requirement for astrophysics and solar system missions and for human exploration in space. The European Space Agencys Solar Energetic Particle Environment Modelling (SEPEM) application server is a World Wide Web interface to a complete set of cross-calibrated data ranging from 1973 to 2013 as well as new SEP engineering models and tools. Both statistical and physical modeling techniques have been included, in order to cover the environment not only at 1u2009AU but also in the inner heliosphere ranging from 0.2u2009AU to 1.6u2009AU using a newly developed physics-based shock-and-particle model to simulate particle flux profiles of gradual SEP events. With SEPEM, SEP peak flux and integrated fluence statistics can be studied, as well as durations of high SEP flux periods. Furthermore, effects tools are also included to allow calculation of single event upset rate and radiation doses for a variety of engineering scenarios.

Update on the use of Geant4 for the Simulation of low-energy protons scattering off X-ray Mirrors at grazing incidence angles

A new physics process has been implemented in the Geant4 Monte Carlo code to treat the scattering of low-energy protons at grazing incidence angles. Experimental data has shown that this is a predominantly surface process where protons are reflected without entering the surface material hence the classical multiple scattering process is not applicable. The new model has been used to revise predictions of proton fluence at the focal plane of the XMM-Newton telescope obtained in earlier simulations.

Analyses of CCD images of nucleon-silicon interaction events

Sets of image frames were captured from a CCD device exposed to continuous beams of high energy neutrons. The tracks of short-range fragments from nuclear spallation interactions in the silicon of the devices pixels have been analyzed in respect of their frequency, intensity, directionality and other pertinent parameters. A comparison between these results and the predictions of computer code models of nucleon interactions in silicon is presented. Comparisons are also made with equivalent images of neutron events in an APS camera.

Influence of beam conditions and energy for SEE testing

The effects of heavy-ion test conditions and beam energy on device response are investigated. These effects are illustrated with two types of test vehicles: SRAMs and power MOSFETs. In addition, GEANT4 simulations have also been performed to better understand the results. Testing to high fluence levels is required to detect rare events. This increases the probability of nuclear interactions. This is typically the case for power MOSFETs, which are tested at high fluences for single event burnout or gate rupture detection, and for single-event-upset (SEU) measurement in SRAMs below the direct ionization threshold. Differences between various test conditions (e.g., “in air” or vacuum irradiations, with or without degraders) are also explored. Nuclear interactions with any materials in the beams path can increase the number of high collected charge events potentially impacting the experimental results. A “species” effect has been observed in the power MOSFET devices examined in this work. When the beam energy increases, the single-event-burnout (SEB) voltage is constant, such that the SEB voltage is determined only by the species of the ion beam. The species effect is shown to be due to high collected charge events induced by nuclear interactions, which can lead to premature SEB. If a device is sensitive to the species effect, the worst-case test conditions will be for the heaviest ion species, which can produce the largest linear-energy-transfer (LET) secondaries. SRAMs can also be sensitive to the species effect below the direct ionization threshold LET. For the devices used in this work, the worst-case energy for SEU characterization is

Assessment of neutron- and proton-induced nuclear interaction and ionization models in Geant4 for Simulating single event effects

sim 10{rm s}~{rm MeV/u}

Analyses of images of neutron interactions and single particle displacement damage in CCD arrays

where the species dominates the device response. In the 10s MeV/u range the heaviest species result in the largest cross sections. However, at very high energies (100s MeV/u), the species is not the dominant parameter because of differences in the population of secondaries created by nuclear interactions. At very high energies the SEU cross section below the direct ionization threshold LET decreases by several orders of magnitude compared to 10s MeV/u SEU data. The results of this work emphasize that there is no such thing as an “ideal” test facility. Nevertheless, these results can be used by experimenters to optimize the integrity of their results for given test conditions.

Single Event Effects in Power MOSFETs Due to Atmospheric and Thermal Neutrons

This paper examines the performance of the Geant4 radiation transport toolkit for the simulation of energy deposition from proton- and neutron-nuclear interactions in silicon microelectronics. The results show that for large (/spl sim/300 /spl mu/m) to small (/spl sim/0.5 /spl mu/m) feature-size devices, the nucleon-nuclear and electromagnetic interaction models within the toolkit provide energy deposition spectra and single event upset rate predictions that are in good agreement with experimental data. The new Binary Cascade and Classical Cascade models, together with the nuclear pre-equilibrium model in Geant4, do not significantly differ in the results they produce. For small feature-size devices, it is shown that it is necessary to consider the effects of ionization by particles produced by nuclear interactions several micrometers above the sensitive volume.