GEANT4 Based Assessment of the Cosmic Radiation Transport in Space:

Examples of International Space Station and Apollo Missions

NETS Presentation

2/23/2015 By: Matthew Lund

Prof. Tatjana Jevremovic Utah Nuclear Engineering Program, University of Utah, Salt Lake City

Outline • Introduction • Radiation Environment in

Space • Introduction to GEANT4 • Developing Spacecraft

Simulations – Geometry – New Detector Models – Spectrum Files – Physics Processes – New Dose Equivalent Scorers – Normalizing Results

• Benchmarking with the DESIRE study of ISS

• Simulating the Apollo Moon Missions- Comparing Apollo 11 & 14

• Conclusion

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Introduction • Radiation shielding for Apollo consisted of the

aluminum hull compared to ISS’s shielding • DESIRE Project4 modeled dosimetric data for

astronauts using the complete spacecraft geometry and post simulation processing.

• Dose rates on Apollo mission varied dramatically with a higher dose rate on Apollo 14. Apollo spaceflights were the only human manned mission to leave Low Earth Orbit (LEO).

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Galactic Cosmic Rays

Earth’s Radiation Belts

Solar Particle Events Albedo Neutrons and Protons

Composition 87% Protons 12% Alpha Particles 1% Heavy Ions 2% Electrons and Positrons

Electrons <6 MeV Protons <250 MeV

Protons and Electrons, mostly low energy with some heavy ions

Neutrons and protons

Solar Cycle Effect Decreases with solar max.

Solar max creates temporary radiation belts and changes altitude. East/West Anisotropy changes with cycle.

Increases frequency and magnitude with solar max.

Earth’s Magnetic Field Effect

In LEO protected by cutoff rigidity of magnetosphere varying with latitude and particle direction.

Caused by magnetic field with a higher area over Brazil known as South Atlantic Anomaly.

In LEO protected by cutoff rigidity of magnetosphere varying with latitude and particle direction.

Caused by magnetosphere trapping neutrons and protons from GCR collision with atmospheric atoms.

Models Badhwar/O’Neill CREME96

AE-8 AP-8 AE-9 AP-9

NOAA Space Environment Monitoring Goes Satellites Neutron Ground Monitoring

AE-8 AP-8 AE-9 AP-9

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Space Radiation Environment

Introduction to GEometry ANd Tracking (GEANT4) • Developed by CERN and GEANT4 collaboration team.

• Monte Carlo code written in C++. • Requires following aspects to model radiation environment:

– Geometry – Particle Sources and Spectrums – Physics Processes – Scoring – Normalization – Error Analysis – High Performance Computing

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Geometry • Geometry Descriptive Markup Language (GDML)5 • Developed models of TEPC, CPD, and ICRU sphere

detectors for modeling radiation in Spacecraft. • Developed Apollo Command Module Geometry

6 ISS Models from DESIRE Study

TEPC

TLD

Comparison of ICRU, TEPC, TLD Detectors

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Energy Deposition Vs.

Energy of Proton

Normalized Deposition vs.

Energy of Proton

Difficulty in Creating Geometry Models

8 Thickness of Stainless Steel Logger Pro Photo Analysis

• Plans were hand drafted, no CAD drawings available. • Original drawings are lost. • Exact material information was lost. • Alternative sources of information were used for details:

• Photo Analysis to determine dimensions. • NASA Technical Database of original reports. • Posts from scientists, engineers, and enthusiasts with memorabilia from Apollo.

Geometry Layout

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• Broken into four sections: – Central Heat Shield – Aft Heat Shield – Forward Heat Shield – Top Hatch

• Consisting of multiple layers: – Kapton – Ablator – Stainless Steel Plates and Honeycomb – Insulation – Aluminum Plates and Honeycomb – Interior – Equipment Racks

Allday, Johnathan. Apollo in Perspective: Spaceflight Then and Now.

Particle Sources and Spectrums • General Particle Source

– Point, Surface, Volume – Beam, Isotropic, Cosine – Ions and Particles

• SPENVIS – Creates Spectrum Files

from Databases – Web Based Interface

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GCR for Apollo

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Integral Flux Differential Flux

Trapped Protons

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Trapped Electrons Trapped Radiation Belts for Apollo

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Sunspots per Year

SPE Flux for Apollo at 1 AU Free Space

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Physics Processes • Contains All Possible Interactions for:

– Hadrons (Particle Interactions) – Electromagnetic Processes – Radioactive Decay

• GEANT4 Uses: – Theoretical Atomic Models – Cross Section Data

• Current Research Focuses on Comparing – QBBC – QGSP_BIC_HP – QGSP_BERT_HP 15

Trapped Protons for ISS at 380 km

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Scoring (Tallying Radiation) • New sensitive detectors

for scoring. – Equivalent Dose based

on: • ICRP 60 Weighting Factor • ICRP 90 Weighting Factor • ICRP 103 Weighting

Factor

– Created Human Phantom GDML.

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Comparison between DESIRE Study and Current Work (Dose Estimation by Simulation of the ISS Radiation Environment)

DESIRE Study • Used 10 AMD Athlon 1667

MHz, single thread. • LHEP_BIC_HP model (replaced

by QGSP_BIC_HP in current GEANT4 version).

• Used 15 ICRU spheres. • Scored energy deposition and

calculate dose and equivalent dose by post processing.

• ROOT package used for data analysis.

• Error was calculated as RMS.

Current Work • Using 40 simultaneous threads on

2.8 GHz Intel Xeon. • Using new QBBC comparing with

other Physics Lists. • Used 15 ICRU spheres and human

phantom. • Score dose and equivalent dose,

no post processing. • Data analysis done within code. • Error calculated with more

extensive error package: relative error, standard deviation, figure of merit. 18

ISS Dosimetry for Solar Minimum

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ISS Dosimetry for Solar Maximum

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ISS Dosimetry for GCR

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Apollo Radiation Detectors13 • Craft had

– Nuclear Particle Detection System (NPDS). – Van Allen Belt Dosimeter (VAPD). – 3 Personal Radiation Dosimeters (RSM). – Portable Radiation Survey Meter (PRD). – Each Astronaut Carried Four TLD’s.

• NPDS and VAPD sent telemetry to earth. PRD and RSM were read twice a day by astronauts to ground.

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Apollo Dose Rates Apollo Mission Skin dose (rads)

7 0.16 8 0.16 9 0.20

10 0.48 11 0.18 12 0.58 13 0.24 14 1.14 15 0.30

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Image from: Apollo 11's Translunar Trajectory and how they avoided the radiation belts by Robert A. Braeunig

Map of Dose Rate in Van Allen Belts

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Trapped Radiation Belt Dose

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Apollo GCR Dose by Element

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Apollo Radiation Belt Dose to Human Organs

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Dose from Solar Particle Events Model Spectrum Dose (mGy) Relative Error Figure of Merit

CM 1 ESP-PYSCH Total 13.82 0.4% 0.0348

CM 2 ESP-PYSCH Total 4.52 0.5% 0.0356

CM 1 ESP-PYSCH Worst 521.36 0.5% 0.0240

CM 2 ESP-PYSCH Worst 169.41 0.7% 0.0236

CM 1 JPL 884.31 0.3% 0.0546

CM 2 JPL 319.42 0.3% 0.0411

CM 1 King 8.51 3.7% 0.0005

CM 2 King 1.54 2.8% 0.0009

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Total Simulated Dose to Apollo Astronauts Apollo

Mission Trapped

(mGy) GCR (mGy)

Total (mGy)

Measured (mGy)

11 .093 1.28 1.37 1.8 14 .081 1.44 1.52 11.4

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Standard deviation between ICRU spheres in cabin was 0.00750 mGy.

Apollo Mission

Trapped (mGy)

GCR (mGy)

SPE (King) (mGy)

Total (mGy)

Measured (mGy)

14 .081 1.44 8.506 10.027 11.4

Conclusion • ISS dose simulations estimates were smaller than

measured, but Equivalent dose simulations were higher with higher quality factor.

• Apollo 11 and 14 mission simulation produced similar values; however, only Apollo 11 was close to measured value.

• Apollo 14’s high dose rate was likely caused by a SPE from a solar flare the week before launch. 29

Acknowledgments

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I would like to thank the Center for High Performance Computing at the University of Utah for their support in providing computational time at the Ember cluster. I would also like to thank Dr. Tori Ersmark for his GDML models of ISS from DESIRE project and Dr. Eric Benton from Oklahoma State University for Apollo mission dose data. This research is partially funded by the Utah Nuclear Engineering Program and partially by a Nuclear Regulatory Commission fellowship.

References

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