Advances in Space Research 37 (2006) 1770–1776
www.elsevier.com/locate/asr
Simulation of the ALTEA experiment on the International
Space Station with the Geant 3.21 program
R. Scrimaglio a, G. Nurzia a,*, E. Rantucci a, E. Segreto a, N. Finetti a,
A. Di Gaetano a, A. Tassoni a, P. Picozza b, L. Narici b, M. Casolino b,
L. Di Fino b, A. Rinaldi b, V. Zaconte b
b
a
Department of Physics, University of LÕAquila, Via Vetoio (Coppito 1), 67010 Coppito, LÕAquila, Italy
Department of Physics, University ‘‘Tor Vergata’’ and INFN Sez, Roma2, Via della Ricerca Scientifica 1, 00133 Roma, Italy
Received 30 September 2004; received in revised form 25 November 2004; accepted 29 November 2004
Abstract
The ALTEA (Anomalous Long Term Effects in Astronauts) project is aimed at the study of the transient and long term effects of
cosmic particles on the astronautsÕ cerebral functions. The detector will fly on the International Space Station in 2005. Due to the
complexity of the detector (12 double silicon detector boxes arranged around the head of the astronaut) it is necessary to have a
detailed simulation of the apparatus response to cosmic ray nuclei in order to assess the detector response and its observational
capabilities. The ALTEA detector was therefore simulated by using the Geant 3.21 program, by the astronautsÕ head described
by 64 cubes of water. By using Creme96 program to evaluate the cosmic rays fluxes within the International Space Station we
obtained the events distribution and the energy lost in the cubes of water, as well as the expected interaction rates. Furthermore,
we calculated the triggered events number per unit of time in the detector. The simulation was also used to develop a technique
to recognize the cosmic rays nuclei.
2004 COSPAR. Published by Elsevier Ltd. All rights reserved.
Keywords: Light flash; Cosmic rays; Biological effects
1. Introduction
In the next few years the average time stay on the
International Space Station of human beings will
strongly increase. For this reason the safety issue in
space environment is crucial. There is a need to study
the effects of particles on the human body and particularly on the functionality of the CNS.
The visual system has been chosen to ‘‘probe’’ the
CNS because it is particularly sensitive to space environment. In missions Apollo missions 11 through 17, Skylab 4, Apollo-Soyuz, Mir, Iss, the astronauts, after
some minutes of dark adaptation, observed brief flashes
*
Corresponding author.
E-mail address: giampietro.nurzia@aquila.infn.it (G. Nurzia).
of white light with the shape of thin or thick streaks, single or multiple dots, clouds, etc. (Osborne et al., 1975;
Pinsky et al., 1974, 1975).
The experiments hint linking these perceptions to the
passage of heavy ionizing nuclei through the retina. The
specific mechanism of the interaction, and its site, remain uncertain. In order to evaluate the LF phenomenon it is necessary the simultaneous determination of
time, nature, energy and trajectory of the particle passing through the cosmonautÕs eyes, as well as the cosmonautÕs LF perception time. Some previous experiments
are described in (Casolino et al., 2002, 2003a,b).
The ALTEA project is aimed at the study of the transient and long term effects of cosmic particles on the
astronautsÕ cerebral functions. It has been funded by
the Italian Space Agency (ASI) and by the National
0273-1177/$30 2004 COSPAR. Published by Elsevier Ltd. All rights reserved.
doi:10.1016/j.asr.2004.11.029
R. Scrimaglio et al. / Advances in Space Research 37 (2006) 1770–1776
Institute for Nuclear Physics (INFN) and ‘‘Highly recommended’’ by the European Space Agency (ESA).
The experiment is an international and multidisciplinary
collaboration.
The basic instrumentation is composed by a series of
active particles telescopes, an ElectroEncephaloGrapher
(EEG) and a visual stimulator, arranged in a helmet
shaped device. This instrumentation is able to measure
simultaneously the dynamics of the functional status
of the visual system, the cortical electrophysiological
activity, and the passage through the brain of those
particles whose energy is included in a predetermined
window. The three basic instruments can be used
separately or in any combination, permitting several
different experiments.
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arranged perpendicular each other. The distance between two sensors of each detector is 3.75 cm. Each
SDU is placed inside an aluminium box 1.3 mm thick.
The set-up of the detector is shown in Fig. 1.
The astronauts will used two push buttons to mark
the perception of a light flash. All information will be
stored via an integrated data handling system which will
also allow the transmission of the data to ground.
In our simulation particles are generated in random
way and isotropically on a big spherical surface with
the ALTEA detector in the centre.
The energy of a particle is chosen in random way
within the cosmic ray spectrum obtained by using the
Creme96 program (Fig. 2), so that events are distributed
according to this spectrum.
The direction of a particle is isotropically generated
in random way.
2. Description of the detector system
Due to the complexity of the detector it is necessary
to have a detailed simulation of its response to cosmic
rays particles in order to evaluate its observational capabilities. The ALTEA detector was therefore simulated
using the Geant 3.21 program.
The Geant program simulates the passage of elementary particles through the matter. Originally designed
for the High Energy Physics experiments, it has today
found applications also outside this domain in areas
such as medical and biological sciences, radio-protection
and astronautics.
The principal applications of Geant in HEP are:
(1) the transport of particles through an experimental
setup for the simulation of detector response;
(2) the graphical representation of the setup and of the
particle trajectories.
The two functions are combined in the interactive
version of Geant. This in very useful, since the direct
observation of what happens to a particle inside the
detector makes the debugging easier and may reveal
possible weakness of the setup.
The Geant system can be obtained from CERN
(http://cernlib.web.cern.ch/cernlib/version.html) and the
program runs everywhere the CERN Program Library
has been installed.
The detector system consists of an helmet holding 12
active silicon telescopes (Narici et al., 2001a,b,c, 2003),
assembled in six independent units named Silicon Detector Unit or SDU.
Each detector is made of three silicon strip sensors.
The basic sensor is obtained by assembling back to back
two chips each with 32 ion implanted resistive strips,
with a sensitive area of 2 · (8 · 8) cm2 and a thickness
of 380 lm. In order to allow both x and y coordinates
measurement the strips of the two detectors are
3. Cosmic rays fluxes evaluation
We used the Creme96 program to evaluate the cosmic
rays fluxes within the International Space Station.
Creme96 is a suite of programs for creating numerical
models of the ionizing radiation environment in near
Earth orbits and evaluating the resulting radiation effects on electronic systems in spacecraft and in high altitude aircraft (Tylka et al., 1996, 1997a,b).
We used the Creme96 program in four steps::
(1) Because the International Space Station is inside
of geosynchronous orbit, we used a first routine
in order to evaluated the geomagnetic shielding
effect of Earth on some particles found in interplanetary space. This routine averages the geomagnetic transmission function over the entire
orbit of ISS: an orbit-generator routine is used to
step along the specified orbit, which is tracked
for seven days. Geomagnetic access is evaluated
at each point on the orbit, and the results are averaged. The calculation is averaged over all directions, without any preferred ISS orientation or
lookout direction (due to thin shielding, for example) from the ISS. The calculation does take into
account, however, that some lookout directions
are blocked by the solid Earth. Flux calculations
using Creme96 assume that the incoming primary
source flux is isotropic. (Anisotropies in the incoming primary energetic particle fluxes are generally
small, except in the very early stages of solar particle events). The orbit-averaged flux calculation
further assumes that the incoming primary flux
varies slowly compared with the orbital period.
(2) A routine of the Creme96 program evaluates the
geomagnetically trapped proton fluxes. The calculation is orbit-averaged. The program provides
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R. Scrimaglio et al. / Advances in Space Research 37 (2006) 1770–1776
z
y
x
Fig. 1. 3D view of the ALTEA detector.
Fig. 2. Cosmic rays differential fluxes vs. kinetic energy.
omnidirectional trapped proton fluxes, which
means that the fluxes are averaged over the entire
range of arrival directions, covering 4p Sr. Omni-
directional does not imply isotropic, that is, having
the same flux arriving from all directions. In fact,
the low-altitude trapped proton flux is highly
R. Scrimaglio et al. / Advances in Space Research 37 (2006) 1770–1776
anisotropic. (The anisotropies may be important
for orientation-stabilized spacecraft and for some
applications). We evaluated trapped proton fluxes
near solar minimum condition.
(3) The results from previous two routines enter in the
third routine providing a numerical model of the
space ionizing-radiation environment at the surface of the ISS, before transport through shielding.
We chose the Solar Quiet (‘‘no flare’’) Model. This
model represents the ambient environment which
prevails in the absence of solar energetic particle
(‘‘flare’’) events. This environment, which varies
slowly in intensity over the 22-year solar cycle, is
the basic environment in which all space systems
must operate. The model is appropriate for evaluating typical and long-term average particle fluxes.
(4) The last routine of the Creme96 transports the
input particle fluxes through a thickness of shielding. This transport code takes into account both
energy loss and nuclear fragmentation. In
Creme96 the aluminum is the shielding material.
We used a greater value for specifying the shielding thickness.
The next step will be the use of more sophisticate
Low Earth Orbit (LEO) particle environmental models
in order to obtained more realistic results.
The differential fluxes, in minimum solar condition,
are shown in Fig. 2. There is a strong predominance
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of protons and alpha particles with respect to heavier
nuclei and a great predominance of protons with respect
to alpha particles when kinetic energy is below 1 GeV/
nucl. The maximum value for protons flux is near 102
MeV/nucl. The remaining particles have maximum values near 103 MeV/nucl.
4. Trigger rate
We define ‘‘trigger signal’’ an event which hits a single
strip along y direction of three silicon plane of a SDU
and release in each plane an energy above the detection
value of 10 mip 1.09 MeV. In fact, 1 mip in 380 lm of
silicon is equal to 109 keV.
In Fig. 3 the energy spectrum of some particle that
yield trigger signals in any SDU is shown. We can see
that the ALTEA detector does not reveal relativistic
protons and alpha nuclei.
We define ‘‘single trigger events’’ a particle that yield a
trigger signal in one SDU and ‘‘double trigger events’’ a
particle that yield a trigger signal in two SDU. The ‘‘double trigger events’’ are very important because they will
permit a better reconstruction of the experimental tracks.
Remembering that the cosmic particle flux is assumed
isotropic, we calculated the mean number of events per
second that yield a single or a double trigger in the ALTEA detector with and without the astronautsÕ head.
The results are shown in Tables 1 and 2. The results
Fig. 3. Energy spectra of ions that yielding trigger signals in any SDU.
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Table 1
Mean number of ‘‘single trigger events’’ per second in the SDU
p
20.3
27.5
10
7
Li3
a
3
0.0249
0.0279
12
B5
3
1.3 · 10
1.3 · 103
14
C6
3
3 · 10
3.2 · 103
10.6 · 10
10.8 · 103
16
N7
O8
3
2.8 · 10
2.9 · 103
9.4 · 103
10.2 · 103
Table 2
Mean number of ‘‘double trigger events’’ per second in the SDU
p
7
a
0
2.45
10
Li3
4
0.0023
0.0054
12
B5
2 · 10
3 · 104
14
C6
3
0.9 · 10
1.1 · 103
shown in the first row are obtained by including the
astronautsÕ head in the computations, whereas the results in the second row do not consider the astronautsÕ
head.
From Table 2, we notice that protons cannot yield
events of double trigger when the astronautsÕ head is
present. In this case, in fact, the protons energy spectra
relative to the first and to the second trigger signal have
not common parts. However, in (Casolino et al., 2003b)
are assumed at least two causes of Light Flash, one due
to protons and one due to heavy nuclei.
The number of events triggered per second in the
SDU is very important because it can have a relation
with the experimentally observed frequency of Light
Flashes.
Considering that ALTEA does not reveal relativistic
protons and that protons can not yield events of double
trigger when the astronautsÕ head is present, we can say
that our experiment allows us to study properly only the
heavy nuclei (see Section 7).
We changed the trigger configuration in order to calculate the mean number of events per second that yield
signals above the detection energy in the outermost silicon plane of the SDU. The results are shown in Table 3.
As before, the results shown in the first row are obtained
by including the astronautsÕ head in the computations,
whereas the results in the second row do not consider
the astronautsÕ head. These values are about 10 times
greater than those of Table 1.
16
N7
3
3.5 · 10
3.6 · 103
O8
3
2.6 · 103
3.4 · 103
0.9 · 10
1 · 103
5. Energy lost in the astronautsÕ head
The astronautsÕ head is simulated with 64 cubes of
water (Fig. 1) because the Geant program does not simulate the human tissues. The approximation is acceptable at this level of calculation. More advanced
simulation programs (Geant 4) will permit to obtain
more realistic results. The length of the side of the cubes
is 4.2 cm.
In Table 4, the mean energy lost in one cube of water
during the passage of a particle for different species of
cosmic rays is shown. The first row includes all events
generated by Geant ð
wÞ; the second row includes only
the events triggered by any SDU ð
wt Þ. In the second case
there is a smaller energy release, except for alpha and
lithium. Obviously, the values increase with the atomic
number of the ionizing nuclei.
We calculated the mean energy lost because, when
there is a Light Flash, a cosmic particle loses energy in
a certain zone of the astronautsÕ head.
6. Rate of events occurring in water cubes
In Table 5, the mean number of interactions occurring in one cube of water per second for different species
of particles is shown. The first row includes all events
generated by Geant ðqÞ; the second row includes only
the events triggered by any SDU ðqt Þ.
Table 3
Mean number of triggered events per second in the outermost silicon plane of the SDU
p
a
7
394.22
412.63
1.26
1.26
1.12 · 102
1.13 · 102
Li3
10
12
14
1.9 · 102
1.92 · 102
6.46 · 102
6.47 · 102
1.72 · 102
1.73 · 102
B5
C6
N7
16
O8
6.05 · 102
6.16 · 102
Table 4
Mean energy lost in one cube of water during one interaction for different species of particles
w
w
t
p
a
7
10
12
14
16
23.5 ± 2.2
21.9 ± 1.5
28.3 ± 2.9
67.1 ± 6.1
62.5 ± 5.9
66.5 ± 6.1
172.1 ± 14.9
170.0 ± 13.8
249.3 ± 22.3
243.1 ± 20.1
341.1 ± 30.0
331.8 ± 26.8
429.2 ± 37.8
422.0 ± 34.2
The values reported in this table are in MeV.
Li3
B5
C6
N7
O8
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Table 5
Mean number of interactions occurring in one cube of water per second for events which do not trigger the experiment ðqÞ and for those which give a
trigger ð
qt Þ
q
qt
10
p
a
7
440
2.67
2.05
0.0119
0.0099
0.0007
Li3
B5
12
14
16
0.0540
0.0057
0.0144
0.0015
0.0476
0.0047
C6
0.0153
0.0015
N7
O8
Table 6
Mean energy lost per second in one cube of water for different species of particles
E
t
E
E
t
E=
p
a
7
10340
58.7
176
58.0
0.80
72.5
0.62
0.047
13.2
Li3
10
12
14
2.63
0.26
10.1
13.5
1.39
9.71
4.91
0.50
9.7
B5
C6
16
N7
O8
20.4
1.98
10.3
The values reported in this table are in MeV.
We obtain the mean energy lost per second in one
cube of water multiplying the values reported in Table
4 times the values reported in Table 5. The results are
shown in Table 6. Again the first row includes all
the second row inevents generated by Geant ðEÞ;
t Þ. At
cludes only the events triggered by any SDU ðE
last, the third row consist of the ratio between values
at the first row and the second row. The values are
high for protons and alpha and nearly constant for
heavier particles.
In Tables 4–6, only the second rows are important because the ALTEA detector stores only the quantities
triggered. The first rows are written for confrontation.
Fig. 4 shows the energy lost in the 26th cube of water
by a carbon nucleus, considering only the events triggered by any SDU. We can note the presence of a maximum value.
In Table 7, the maximum energy that a particle can
lose in one interaction in one cube of water for some
particles is shown. The maximum values are calculated
using a fit with a gaussian shape and a polynomial of degree 3 of the distribution of the energy in one cube of
water.
7. Recognition of particles
The Geant simulation was also used to develop a
technique to identify cosmic particles. We considered
only one detector of one SDU and studied different
kinds of nuclei by a standard statistical analysis. We
simulated the species of nuclei reported in Table 3 except
nitrogen. The particles flux was isotropic.
We considered the plot shown in Fig. 5. The abscissa
variable is DEud = DE1 + DE2 DE5 DE6, where DEi
is the energy P
lost in the ith silicon plane. On the ordinate
6
axis DEtot ¼ i¼1 DEi , the total energy lost in six silicon
planes, is reported. The statistical analysis is divided in
two complementary phases: h > p/2 (downward particles) and h < p/2 (upward particles), where h is the zenit
angle.
Fig. 4. Energy lost in the cube of water number 26 from a carbon
nucleus considering only the events triggered by any SDU. The values
of energy are in MeV.
Table 7
Maximum energy lost in one cube of water
7
Li3
68.7 ± 0.06
10
12
14
16
213 ± 0.06
301 ± 0.15
411 ± 0.21
532 ± 0.27
B5
C6
N7
O8
The values reported in this table are in MeV.
As shown in Fig. 5, the points relative to different
species of particles are arranged in different zones of
the plane DEtot DEup. It is possible to identify different
species of particles in an efficient way by apply opportune cuts on the values of the variables.
The confusion matrix shows the percentage of particles of a species present in a fixed plane zone as regards
the total number of particles of that species. In this way
we write 4 confusion matrixes.
In Table 8, the conclusive results obtained combining
the 4 cases are shown. When the threshold energy of the
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about 1 MeV, we can distinguish particles with Z P 5.
Further developments in the detector will improve its actual performances.
The ALTEA experiment will allow to evaluate the
risk on the Central Nervous System due to cosmic rays
fluxes in microgravity conditions during long term space
missions. It will provide information to define the causes
of the anomalous phosphenes perception of the
astronauts.
The detector will fly on the International Space
Station in 2005.
References
Fig. 5. Events distribution as a function of DEtot versus DEud.
Table 8
Confusion matrix obtained by combined analysis
p
a
7
Li3
10
B5
12
C6
16
O8
p
(%)
a
(%)
7
Li
(%)
10
B
(%)
12
C
(%)
16
O
(%)
23.3
13.5
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0
10.9
11.7
11
0
0.01
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50.6
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0.01
0
0.02
20.8
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16.2
58.8
0.9
0.01
0
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3.3
35.7
84.5
0.54
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1.1
0.8
5.5
14.6
99.2
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8. Conclusion
This is a preliminary work. The following step will
consist in a more realistic simulation realized with other
programs, which are able to simulate also human tissues
(Geant 4). However, in the ground of tables contained in
this paper, we can conclude that the ALTEA detector
has rates of events statistically significant. Furthermore,
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