model-dependent deconvolution of hend neutron data by mcnpx code

2001 Mars Odysseypage 1

W o r k s h o p H E N D - 2003

Institute for Space Research, June 9 - 11, 2003

Model-dependent deconvolution of Model-dependent deconvolution of HEND neutron data by MCNPX HEND neutron data by MCNPX

codecodeM. Litvak, I. Mitrofanov, Charyshnikov, V.

Grinkov, A. Kozyrev, A. Sanin V. Tret’yakov

Institute for Space ResearchD. Drake

Santa Fe, USA




MODELMODEL

Atmosphere

CO2 deposit

Dry regolith

Wet regolith




MODEL PARAMETERSMODEL PARAMETERS

Flux of CGR Atmosphere thickness at different times Chemical composition of atmosphere Thickness of CO2 frost Presence of water (%) in CO2 frost Thickness of dry regolith Chemical composition of regolith Presence of water (%) in dry regolith Presence of water (%) in wet regolith




“Chemical analyses of Martian soil and rocks obtained by the Pathfinder Alpha Proton X-ray spectrometer” Radiation Physics and Chemistry 61 (2001)191 –197

MODEL PARAMETERSMODEL PARAMETERSMartian Soil

Name Na2O MgO Al2O3 SiO2 P2O5 SO3 Cl K2O CaO TiO2 Cr2O3 MnO FeO

SoilsA-2 SoilbyLander 3.1 10.3 10.0 40.9 0.9 6.0 0.7 0.5 6.1 0.8 0.3 0.5 20.0A-4 NexttoYogi 3.1 9.5 10.2 40.9 1.1 7.0 0.8 0.5 5.6 1.3 0.4 0.4 19.2A-5 DarknexttoYogi 3.8 8.4 10.0 40.5 0.5 5.7 0.8 0.5 6.1 0.7 0.5 0.2 22.2A-8 ScoobyDoo 2.4 7.6 10.2 45.4 0.5 5.6 0.9 0.9 7.1 0.9 0.1 0.3 18.2A-9 DistnexttoYogi 2.3 7.7 9.9 41.9 0.7 6.7 1.3 0.7 6.5 1.1 0.2 0.1 21.0A-10 NexttoLamb 2.5 8.8 9.4 41.0 0.6 6.4 0.9 0.4 6.0 1.0 0.3 0.4 22.4A-15 NoName 2.9 8.0 9.6 43.1 0.5 5.3 0.8 0.7 5.6 1.0 0.3 0.3 21.9RocksA-3 Barnacbill 3.4 2.5 12.2 53.5 0.7 2.0 0.5 1.2 5.7 0.7 0.1 0.4 17.3A-7 Yogi 3.6 6.2 10.9 47.2 0.5 4.5 0.9 0.8 6.6 0.9 0.1 0.4 17.8A-16 Wedge 4.3 4.8 11.0 47.5 0.5 3.0 0.7 0.8 6.9 0.9 0.0 0.3 19.3A-17 Shark 2.5 4.6 10.3 53.8 0.4 1.7 0.5 0.9 7.7 0.7 0.1 0.4 16.5A-18 Halfdome 4.3 4.0 11.7 49.2 0.5 3.0 0.7 1.0 5.9 0.9 0.1 0.4 18.5

For model 3.2 6.9 10.5 45.4 0.6 4.7 0.8 0.7 6.3 0.9 0.2 0.3 19.5




MODEL PARAMETERSMODEL PARAMETERSMartian Atmosphere: Chemical composition and

thickness

Major gases: Carbon Dioxide (CO2) - 95.32% ;

Nitrogen (N2) - 2.7%

Argon (Ar) - 1.6%; Oxygen (O2) - 0.13%;

Carbon Monoxide (CO) - 0.08% http://nssdc.gsfc.nasa.gov/planetary/factsheet/marsfact.html

Thickness of atmosphere for given Mars region and season

is taken from the Ames global climate model




HOW TO CALCULATE: HOW TO CALCULATE: GEOMETRYGEOMETRY

The layer produced the neutrons




HOW TO CALCULATE: HOW TO CALCULATE: DATA SELECTIONDATA SELECTION

The Surface of Mars may be divided into the set of regions of interest. The properties of surface should be homogenous inside selected region The size of each region should be more than footprint.




1. Calculation of neutron flux for model of homogeneous sphere with some initial parameters

2. Convolution of model spectra with efficiency functions for different detectors to get model counts

3. Comparison of model count rate and real count rate of HEND sensors for this Martian area of interest and for the same seasons

4. Fitting of parameters of geometry, water percentage in model of homogeneous sphere

hdry%H20dry

%H2Owet

hCO2

HOW TO CALCULATE: HOW TO CALCULATE: ALGORITHMALGORITHM




HOW TO CALCULATE: MINIMIZATIONHOW TO CALCULATE: MINIMIZATION

Search of model best fit parameters based on 2 minimization:

i

ii

ii MCS

22

22value ~

Where: Ci is detector counts, i=1,5 (SD,MD,LD,SC1,SC2). Mi is model counts predicted by MCNPX for (SD,MD,LD,SC1,SC2). i is statistical error for Ci, Mi

SD, MD, LD are integral counts detected in proportional countersSC1 is fast neutron counts in energy range (0.8-2.5 MeV) registered in stilbenSC2 is fast neutron counts in energy range >2.5 MeV registered in stilben




BEST FIT PARAMETERS: CGR fluxBEST FIT PARAMETERS: CGR flux

The selection of HEND data accumulated above large region near Solis Planum. It is driest place on Mars where variation of neutron flux explained only by variations of CGR flux or by Solar activity.

The selection of different time intervals: Ls={ [330o-360o] , [0o -30o ] ,[30o -60o] , [60o-90o], [90o-120o] , [120o-150o]

Applying of the homogenous model to estimate flux of CGR: {Atmosphere +homogenous regolith layer with 2% of water}




BEST FIT PARAMETERS: FROST FREE BEST FIT PARAMETERS: FROST FREE AREASAREAS

The selection of data for summer surface of Mars (season when CO2 frost is absent) First step:Applying of the homogeneous regolith model with one freeparameter describing content of water in the regolith. Second step: If homogeneous model was rejected two layers regolith model should be tested with 2% of water in upper layer and two free parameters: thickness of upper layer and water content inbottom layer.




The best fitting parameters describing summer surface are fixed for given region.

The data for given region are taken for different winter periods of time.

The real data are fitted by model of summer surface with added layer of CO2 frost with variable thickness.

BEST FIT PARAMETERS: COBEST FIT PARAMETERS: CO22 FROST FROST

THICKNESSTHICKNESS

model-dependent deconvolution of hend neutron data by mcnpx code

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