Barghouty, Nasser

NASA Technical Reports Server

National Aeronautics and Space Administration
SCIENCE & TECHNOLOGY OFFICE
Nasser Barghouty 
Astrophysics Office, NASA-MSFC
AMS Sectional Meeting, march 28, 2015, Huntsville, AL
Modeling the radiation quality factor as a linear 
'time'-dependent Ornstein-Uhlenbeck process
https://ntrs.nasa.gov/search.jsp?R=20150011127 2019-08-31T07:33:03+00:00Z
2AMS, March 28, 2015
The Main Points
 The drive
Capture the uncertainties in the Q factor for 
more robust exposure and risk estimates
 A brief introduction to space radiation
The sources; the expected exposure; the risk; 
mitigation strategies
 Modeling the Q factor
Namely Monte Carlo
 The Q factor as a linear stochastic process
‘time’-dependent Ornstein-Uhlenbeck
 Benefits
Bracketing the risk?
3AMS, March 28, 2015
Space Radiation: The Drive & The Challenges
Effective shielding against the combined 
effects of GCRs and SEPs can be mass 
prohibitive
Shielding effectiveness of new, potential 
shielding materials (or combinations 
thereof) is not well characterized
Little data to guide dose and risk 
assessment models 
Known, large uncertainties and 
variabilities in radiobiological effects
Other uncertainties and variabilities?
(e.g., in generalization and scale-up of 
shielding or protection solutions)
A NASA strategic radiation protection 
guideline is the:
“Demonstration of shielding concepts 
providing radiation protection focusing on 
light-weight multi-functional structure-
capable materials that can provide 
GCR/SPE protection while providing other 
functionalities such as thermal insulation, 
structural integrity, and/or MMOD 
protection.” 
The Drive
4AMS, March 28, 2015
Space Radiation: The Drive & The Challenges
(From http://hacd.jsc.nasa.gov)
Radiobological uncertainties 
dominate!
These large uncertainties 
can frustrate -even defeat-
any mitigation solution
5AMS, March 28, 2015
Two main sources of ionizing radiation:
Galactic Cosmic Rays (GCR)
Protons + almost all other nuclei
Low intensity (~ 1 cm-2)
High-energy (peaks at 500 MeV/N)
Sun-modulated by a factor ~4
Isotropic
Solar Energetic Particles (SEP)
Mostly protons
High intensity (~ 107 cm-2)
Lower energy (~ 100-200 MeV)
Random 
Directional
Space Radiation: Natural Sources
6AMS, March 28, 2015
Space Radiation: Uncertainties in radiobiological effects
Large uncertainties -and variabilities-
in the radiation quality factor is seen 
as a main hindrance toward reliable 
dose and risk estimates 
These can be captured mathematically
if we model the quality factor as an 
Ornstein-Uhlenbeck process, 
with a corresponding PDF of the form,
7AMS, March 28, 2015
Space Radiation: Shielding effectiveness (how certain?)
Materials vary in their ability to shield 
against GCR nuclei
Polymeric based materials tend to 
be most effective - but their 
structural and safety properties 
remain poor or poorly known
Aluminum, like all metals, is a poor 
GCR shield
Regolith is not that much better 
either!
8AMS, March 28, 2015
Distribution of terrestrial                       
exposure of few cSv/yrIn-Space expected levels and limits
Use of regolith as a shield 
material in the presence of a 
small nuclear-power ource
Space Radiation: Regolith as a shield material
9AMS, March 28, 2015
Space Radiation at Marshall
• Monitoring & Detection
protons- TaSEPS
neutrons- ANS
• Forecasting
Mag4
• Modeling & Simulation
Geant4-based
• Radiation-Smart Structures
Geant4-informed
Bastille Day (2000 July 14) Flare, Coronal Mass 
Ejection and Solar Energetic Particle Event
10AMS, March 28, 2015
Space Radiation: Monitoring & Detection
11AMS, March 28, 2015
Space Radiation: Monitoring & Detection
12AMS, March 28, 2015
Space Radiation: Monitoring & Detection
13AMS, March 28, 2015
Space Radiation: Monitoring & Detection
• Marshall scientists and engineers develop state-of-the-art charged 
particle and neutral particle detectors suitable for the harsh 
environments of space:
-Advanced Neutron Spectrometer (ANS): is a new instrument technique being 
developed to meet NASA’s requirements to monitor the radiation exposure due to 
secondary neutrons for future crewed missions. New instrument designs are 
needed to achieve the measurement performance requirements that fit within the 
resource limits of exploration missions beyond Earth’s protective magnetic field
Plastic and Li-Gd-B scintillator
n + 6Li  → 3H + 4He
Q  = 4.78 
n + Gd → Gd* + γ
Q  = [0,2]
n + 10B → 7Li + 4He
Q  = 2.73 (93%) 
or 2.25 (7%) 
Planned for an ISS flight demonstration
14AMS, March 28, 2015
Space Radiation: Magnetic-based Forecasting (Mag4) 
• Marshall scientists and engineers developed an automated prediction 
system that downloads and analyzes magnetograms from the HMI 
(Helioseismic and Magnetic Imager) instrument on NASA SDO (Solar 
Dynamics Observatory), and then automatically converts the rate (or 
probability) of major flares (M- and X-class), Coronal Mass Ejections 
(CMEs), and Solar Energetic Particle Events
[Present cadence of new forecasts: 96 min; Vector magnetogram actual cadence: 12 min]
A magnetogram of an active region on the Sun
For each Active Region: 
The integral of the gradient 
along the neutral line is the 
free-energy proxy
When the transverse 
gradient of the vertical 
(or line-of-sight) magnetic 
field is large, there is more 
free-energy stored in the 
magnetic field
15AMS, March 28, 2015
Mag4: A Comparison of Safe and Not Safe Days
June 26, 2013
C1, C1.5 flares
March 7, 2012
X5.4, X1.3, C1.6
CME 2684, 1825 km/sec,
Solar Energetic Proton Event reaches 
6530 ‘particle flux unit’ >10 MeV
16AMS, March 28, 2015
Space Radiation: Modeling & Simulation
• Marshall scientists and engineers use Geant4 for the design, analysis, 
and development of
particle detector systems
exposures at accelerators and in-situ
dose estimates
shielding solutions 
• Marshall scientists and engineers collaborate
with experimental and theoretical and 
computational groups at Oak Ridge National                           
Laboratory, Berkeley’s Lawrence National                               
Laboratory, Brookhaven National 
Laboratory, Indiana University’s Cyclotron                                       
Facility, Japan’s HIMAC facility, and others for basic and applied 
nuclear modeling, simulation, and exposure and shielding studies   
17AMS, March 28, 2015
Space Radiation: Modeling & Simulation
●p1 ● p2
Δz Δz
Z-direction≈
Complex geometry and material composition -in the presence of 
known physical uncertainties- are expected to produce sizable 
errors in any radiation protection solution.
A 2-D illustration:
} }
18AMS, March 28, 2015
Space Radiation: Modeling & Simulation
A 3-D illustration:
Unlikely?
19AMS, March 28, 2015
Radiation-Smart Structures and Designs?
A B
C
D
E
A: Adaptive Structures
B: Sensory Structures
C: Controlled Structures
D: Active Structures
E: Intelligent Structures


Modeling the Radiation Quality Factor as a Linear 'Time'-Dependent Ornstein-Uhlenbeck Process

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server