GCR Methods in Radiation Transport. F.A. Cucinotta And M.Y. Kim NASA Johnson Space Center

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1 GCR Methods in Radiation Transport F.A. Cucinotta And M.Y. Kim NASA Johnson Space Center

2 Overview CRÈME used in HZETRN and other codes Badhwar and O Neill Model developed for HZETRN applications in 1993 Elemental spectra for H, He, C, O, Si, Fe Crème formula for other elements New version by Pat O Neill in 2004 fit to ACE and includes LSS spectra Elemental spectra for all elements Isotopic composition integrated into HZETRN in 2005 using historical data including Ulysses

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6 GCR Environment at Solar Minimum 1.E+09 1.E+08 1.E+07 1.E+06 Φ (>E) 1.E+05 1.E+04 Z=1 Z=2 1.E+03 Z= E+02 New GCRENV Old GCRENV Z=11-20 Z= E+01 1.E+00 1.E-02 1.E-01 1.E+00 1.E+01 1.E+02 1.E+03 1.E+04 1.E+05 E, MeV/u

7 Free Space at Solar Minimum H, csv/y Old_GCRENV New_GCRENV X(Al), g/cm 2

8 Isotopic Composition Historical data used to re-distribute Badhwar-O Neill elemental flux into isotopic fractions Energy-independent

9 Table 1a: Isotopic Composition of GCR Elements Z=3 to 12. Isotope Near-Earth Fraction Source Fraction Z=3 6 Li* Li Z=4 7 Be* Be Be Z=5 10 B B Z=6 12 C C Z=7 14 N N Z=8 16 O O O Z=10 20 Ne Ne Ne Z=12 24 Mg Mg Mg Table 1b: Isotopic Composition of GCR Elements Z=13 to 20. Isotope Near-Earth Fraction Source Fraction Z=13 26 Al Al Z=14 28 Si Si Si Z=16 32 S S S Z=17 35 Cl Cl Cl Z=18 36 Ar Ar Ar Ar Z=20 40 Ca Ca Ca Ca Ca *Data on solar modulation was not found and thus near-earth and source composition are set equal.

10 10 2 φ(e), 1/(cm 2 MeV/u yr) Ne 21 Ne+ 22 Ne 28 Si 29 Si+ 30 Si 56 Fe 54 Fe+ 55 Fe+ 57 Fe E, MeV/u

11 %Error in Mass Fluence from Isotopic Grid g/cm 2 of aluminum 20 g/cm 2 of aluminum Solar Min Mass Number, A Figure 10a: Comparisons of the error that results from the HZETRN Code for the mass fluence distribution near solar minimum when using a reduced 59-isotope grid compared to transport with a 170-isotope grid

12 20 %Error in Elemental Flux from Isotopic Grid g/cm 2 Aluminum 20 g/cm 2 Aluminum Solar Min Charge Number, Z Figure 10b: Comparisons of the error that results from the HZETRN Code for the elemental fluence distribution near solar minimum when using a reduced 59-isotope grid compared to transport with a 170-isotope grid.

13 Table 3b: Elemental (Z) and Neutron excess (Y) dependence on GCR dose equivalent behind 5 g/cm 2 of Aluminum Shielding. GCR Dose Equivalent per Year near Solar Minimum Z Y<0 Y=0 Y=1 Y=2 Y=3 Y>3 Total-Z Total-Y

14 Solar Modulation of GCR Badhwar and O Neill use self-consistent solution to transport Local Intersteller source (LIS) for each element using Fokker-Plank radial diffusion equation based on Parker (1965) Neutron monitor counts Sun-spot number Kim et al. use a statistical model to predict probability distribution for level of future GCR modulation

15 Future GCR Modulation- Approach Sunspot number is well correlated with many observable space quantities and represents variation in the space radiation environment. A solar cycle statistical model (1-3) was developed based on the accumulating cycle sunspot data. A predictive model for GCR radiation environment (4,5) represented by GCR deceleration potential (φ) was derived from GCR flux and ground-based Climax neutron monitor rate measurements over the last four decades. Prediction of radiation environments and doses for future space exploration missions. Relationship between large SPE occurrence and φ A probability of SPE in mission period.

16 Population Group of Declining Phase of Cycle 23 (Cumulative Mean Value and Statistical Fluctuation) 1 Trend at solar cycle 23, percentile Standard deviation Up-to-date average Level of measured sunspot number Monthly index from solar max 23

17 Projections of Solar Cycles 23 and 24 A basis for estimating of exposure in future space missions Sunspot number Cycle 23 Cycle 24 Population distribution level, percent Measured sunspot number Smoothed sunspot number Projected smoothed sunspot number at level, percent Year

18 4500 Climax Neutron Monitor Rate Measurements and Projection to Solar Cycles 23 and Climax NM Time

19 GCR Environments and Point Dose Equivalents inside Spacecraft 2000 GCR Deceleration Potential 20 Φ, MV 0 Free Space LEO Point Dose Equivalent (5 g/cm 2 Al) Point Dose Equivalent, csv/month Time

20 60 13 C 15 N Isotopic Ratio (%) Modulation Parameter, Φ(MV)