Download Deexcitation NSS 2004

Models for the Simulation of X-Ray
Fluorescence and PIXE
A. Mantero, S. Saliceti, B. Mascialino, Maria Grazia Pia
INFN Genova, Italy
NSS, Rome, 21 October 2004
http://www.ge.infn.it/geant4/lowE/index.html
Alfonso Mantero, INFN Genova
Fluorescence Emission
Cosmic rays,
jovian electrons
Original motivation from astrophysics requirements
X-Ray Surveys of Asteroids and Moons
Solar X-rays, e, p
Geant3.21
ITS3.0, EGS4
Courtesy SOHO EIT
Induced X-ray line emission:
indicator of target composition
(~100 mm surface layer)
Alfonso Mantero, INFN Genova
Geant4
C, N, O line emissions included
Wide field ofCourtesy
applications
beyond& astrophysics
ESA Space Environment
Effects Analysis Section
X-ray fluorescence and Auger effect
Calculation of shell cross sections
– Based on Livermore (EPDL) Library for photoelectric effect
– Based on Livermore (EEDL) Library for electron ionisation
– Based on Penelope model for Compton scattering
Detailed atom description and calculation of the energy of
generated photons/electrons
– Based on Livermore EADL Library
– Production threshold as in all other Geant4 processes, no photon/electrons
generated and local energy deposit if the transition predicts a particle
below threshold
Alfonso Mantero, INFN Genova
Test process
Unit, integration and system tests
Verification of direct physics results against established references
Comparison of simulation results to experimental data from test beams
– Pure materials
– Complex composite materials
Quantitative comparison of simulation/experimental distributions with
rigorous statistical methods
– Parametric and non-parametric analysis
Alfonso Mantero, INFN Genova
Verification: X-ray fluorescence
Comparison of monocromatic photon lines generated by Geant4 Atomic
Relaxation w.r.t. reference tables (NIST)
Transitions (Fe)
K transition
K transition
Alfonso Mantero, INFN Genova
Transition
Probability
Energy (eV)
K L2
1.01391 -1
6349.85
K L3
1.98621 -1
6362.71
K M2
1.22111 -2
7015.36
K M3
2.40042 -2
7016.95
L2 M1
4.03768 -3
632.540
L2 M4
1.40199 -3
720.640
L3 M1
3.75953 -3
619.680
L3 M5
1.28521 -3
707.950
Verification: Auger effect
Auger electron lines from
various materials w.r.t.
published experimental results
428.75, 429.75 eV
(430 unresolved)
366.25 eV (367)
436.75, 437.75 eV
(437 unresolved)
Precision: 0.74 % ± 0.07
Cu
Auger
spectrum
Alfonso Mantero, INFN Genova
Test beam at Bessy
Advanced Concepts and Science Payloads
A. Owens, A. Peacock
Complex geological materials
Hawaiian basalt
Icelandic basalt
Anorthosite
Dolerite
Gabbro
Hematite
FCM beamline
Si reference
GaAs
Alfonso Mantero, INFN Genova
Si
XRF chamber
Comparison with experimental data
Pearson correlation analysis:
r>0.93
p<0.0001
Effects of detector response function
+ presence of trace elements
Anderson Darling test
Beam Energy
4.9
6.5
8.2
9.5
A2
0.04
0.01
0.21
0.41
Ac (95%) = 0.752
Experimental and simulated X-ray spectra are
statistically compatible at 95% C.L.
Alfonso Mantero, INFN Genova
PIXE
Calculation of cross sections for shell ionization induced by
protons or ions
Two models available in Geant4:
– Theoretical model by Grizsinsky – intrinsically inadequate
– Data-driven model, based on evaluated data library by Paul & Sacher
(compilation of experimental data complemented by calculations from
EPCSSR model by Brandt & Lapicki)
Generation of X-ray spectrum based on EADL
– Uses the common de-excitation package
Alfonso Mantero, INFN Genova
PIXE – Cross section model
Fit to Paul & Sacher data library; results of the fit are used to predict the
value of a cross section at a given proton energy
– allow extrapolations to lower/higher E than data compilation
First iteration, Geant4 6.2 (June 2004)
–
–
–
–
The best fit is with three parametric functions for different groups of elements
6 ≤ Z ≤ 25
26 ≤ Z ≤ 65
66 ≤ Z ≤ 99
Second iteration, Geant4 7.0 (December 2004)
– Refined grouping of elements and parametric
functions, to improve the model at low energies
Alfonso Mantero, INFN Genova
Next: protons, L shell
ions, K shell
Quality of the PIXE model
How good is the regression model adopted w.r.t. the data library?
Goodness of model verified with analysis of residuals and of
regression deviation
Regression deviation
Residual deviation
– Multiple regression index R2
– ANOVA
– Fisher’s test
Total deviation
Test
statistics
Results (from a set of elements covering the periodic table)
– 1st version (Geant4 6.2): average R2 99.8
– 2nd version (Geant4 7.0): average R2 improved to 99.9 at low energies
– p-value from test on the F statistics < 0.001 in all cases
Alfonso Mantero, INFN Genova
Fisher
distribution
Bepi Colombo
Mission to Mercury
Study of the elemental composition
of Mercury by means of
X-ray fluorescence and PIXE
Insight into the formation of the
Solar System
(discrimination among various models)
Alfonso Mantero, INFN Genova
A Library For Simulated X-Ray
Emission form Planetry Surfaces
A. Mantero, S. Saliceti, B. Mascialino, Maria Grazia Pia
INFN Genova, Italy
A.Owens, ESA
NSS, Rome, 21 October 2004
Alfonso Mantero, INFN Genova
The BepiColombo Mission to Mercury
HERMES
Composed of 2 orbiters carrying a total
of 25 scientific experiments:
●
Magnetic Field Study
●
Planet Surface Mapping
●
Planet Surface Composition study
●
4 spectrometer (IR, X, , n)
●
1 laser altimeter
Alfonso Mantero, INFN Genova
Is an X-Ray spectrometer to
measure the composition of
the upper layers of planetary
surface
X-Ray Detectors
Solid State Detectors
Gas Detectors
• Better Resolution
• Poor resolution
- 140 eV @ 5.89 KeV”
- “< 1KeV @ 5.95 KeV”
• Greater Efficiency at low Energies
• Faster count speed
• Poor efficiency at low
energies
Basalt fluorescence spectrum
Only for some
elements K lines can
be detected (Mg, Al,
Si, S, Ca, Ti, and Fe)
Counts
Beam Energy 9.5 KeV
Energy (KeV)
Alfonso Mantero, INFN Genova
Rocks X-Ray Emission Library
Space missions are risky, so solid strategies for risk
mitigation are to be undertaken
●
HERMES is an X-Ray spectrometer studying Mercury's
surface composition
●
Solid state detector have a better definition than “normal”
gas-filled proportional counters
●
We will measure detailed X-Ray spectra leading to
detailed elemental composition of the crust of the planet
●
We need to study possible responses of the
instruments before they are in flight with a very good
precision for all the possible situations they can find
Alfonso Mantero, INFN Genova
Rocks X-Ray Emission Library
Test beams at BESSY labs have been
undertaken in order to provide a set of X-Ray
spectra from PSSL rocks that could be found
rocky planets (Mars, Venus, Mercury)
A total of 8 rocks have been irradiated
and by now 5 of them have been
simulated.
• Basalt (Hawaii, Madagascar and Iceland)
• Anorthosite
• Ematite
• Gabbro
• Dolerite (Whin Sill, Java)
•Obsidian
Alfonso Mantero, INFN Genova
FCM beamline
GaAs
Si
Si
reference
XRF
chamber
Rocks Spectra Simulation
Geant4 provides advanced
instruments for the description of
geometry and materials
Thanks to a Geant4 simulation
we can simulate any rock of
known composition with a high
degree of confidence
Alfonso Mantero, INFN Genova
Rocks Spectra Simulation
Alfonso Mantero, INFN Genova
Summary
Geant4 provides precise models for detailed processes at the
level of atomic substructure (shells)
X-ray fluorescence, Auger electron emission and PIXE are
accurately simulated
Rigorous test process and quantitative statistical analysis for
software and physics validation have been performed
A new generation of X-Ray detectors will be used shortly for
planetary investigations, giving precise results
A library of rocks X-Ray spectra is needed for accurate physic
reach and risk mitigation studies
Geant4 is capable of generating X-Ray spectra for any rock of
known composition and a library is under production.
Alfonso Mantero, INFN Genova