EMMREM Framework

Figure 1: EMMREM is a flexible module with well-defined interfaces for predicting radiation exposure in the Earth, Moon, Mars and interplanetary space environments based on input of an energy spectrum, composition and angular distribution of energetic particles and cosmic rays.

The EMMREM framework consists of four pieces:

• The interplanetary source input provides the energy spectrum, composition and angular distributions (SEPs, ACRs and GCRs) based on simulations, observed events and interplanetary conditions, or user-specified files. We are developing a database (available online) of simulated and observed events and time-series.

• The Scenario/Environment sub-module transforms the interplanetary source energy spectra, composition, and angular distributions based on shadowing by the planetary body and deflection/trapping by planetary magnetic fields.

• The Radiation Transport sub-module describes the interaction of incident ionized particles with atmospheres, shielding material and tissue, including production of secondary forms of radiation including neutrons, protons and heavy ion recoil atoms, utilizing output from the Scenario sub-module.

• EMMREM outputs include time-dependent dose-related quantities. Events, time-series, and case-studies for validation are also collected into the online data-base.

Figure 2:A three-dimensional system of nodes is followed with the evolving solar wind to solve the particle transport and acceleration equations in the Energetic Particle Radiation Environment Module. In the node-mesh used here, we have focused on the ecliptic plane in which the Cassini spacecraft traveled through the inner solar system en route to Saturn.

We have developed the Energetic Particle Radiation Environment Module (EPREM) which traces individual nodes along magnetic field lines, as they are carried out with the Solar Wind, and solves the energetic particle transport equations in the Lagrangian field aligned grid. The energetic particle solutions include both the field aligned transport solutions and contributions from cross-field diffusion and drift. A snapshot of this evolving node-mesh is shown in Figure 2. Along each fieldline (a connected list of nodes), we solve for particle transport, adiabatic focusing, adiabatic cooling, convection, pitch-angle scattering, and stochastic acceleration.

Figure 3:BFO (Blood Forming Organ) doses (top row) near Earth during the 2003 Halloween events.

The EMMREM specific version of the BRYNTRN code (Looping BRYNTRN) has been installed at the University of New Hampshire and is running on the UNH operating systems using the UNH Fortran compilers. The code is capable of performing near real-time simulations of SEPs that provide organ doses and dose equivalents (Figure 3), using computerized anatomical models of the shielding of radio-sensitive organs, for thinly shielded spacecraft. The code has been used for various studies involving several large historical SEP events.

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This material is based upon work supported by the NASA/LWS under Grant No. NNX07AC14G.

Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of NASA.