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Profile of the ionizing radiation exposure between the Earth surface and free space

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Since 2000 scientists from the former Solar-Terrestrial Influences Institute at the Bulgarian Academy of Sciences contributed Bulgarian-build instruments to a number of experiments for measurements of the incoming space radiation fluxes and dose rates from the Earth surface up to the free space and 100 km Moon orbit. The purpose of this paper is to summarize the data obtained by different instruments on the ground and in aircraft, balloon, rocket, and on spacecraft. Dose rate, flux and specific dose (SD) data are analyzed, compared and plotted. The result is a unified picture how the different ionizing radiation sources contribute and build the space exposure altitudinal profile from the Earth surface to the free space.
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Prole of the ionizing radiation exposure between the Earth surface
and free space
Tsvetan P. Dachev
n
Space Research and Technology Institute, Bulgarian Academy of Sciences, Acad. G. Bonchev Str. Block 1, 1113 Soa, Bulgaria
article info
Article history:
Received 8 April 2013
Received in revised form
21 May 2 013
Accepted 21 May 2013
Available online 31 May 2013
Keywords:
Space radiation
Radiation belts
Balloon aircraft spacecraft ISS
abstract
Since 2000 scientists from the former Solar-Terrestrial Inuences Institute at the Bulgarian Academy of
Sciences contributed Bulgarian-build instruments to a number of experiments for measurements of the
incoming space radiation uxes and dose rates from the Earth surface up to the free space and 100 km
Moon orbit. The purpose of this paper is to summarize the data obtained by different instruments on the
ground and in aircraft, balloon, rocket, and on spacecraft. Dose rate, ux and specic dose (SD) data are
analyzed, compared and plotted. The result is a unied picture how the different ionizing radiation
sources contribute and build the space exposure altitudinal prole from the Earth surface to the
free space.
&2013 Elsevier Ltd. All rights reserved.
1. Introduction
Humans are exposed to ionizing radiation all the time at all
altitudes above the Earth surface, and it is known that it can
induce a variety of harmful biological effects. Consequently, it is
necessary to quantitatively assess the level of exposure to this
radiation as the basis for estimating risks due to ionization
radiation.
The radiation eld around the Earth is complex, composed of
galactic cosmic rays (GCR), trapped radiation of the Earth radiation
belts, solar energetic particles, albedo particles from the Earth's
atmosphere and secondary radiation produced in the shielding
materials of the aircraft and spacecraft and in biological objects.
1.1. Galactic cosmic rays
The dominant radiation component in the near Earth and free
space environment are the galactic cosmic rays (GCR). The GCR are
charged particles that originate from sources beyond our solar
system. They are thought be accelerated at the highly energetic
sources like neutron stars and supernovae within our Galaxy. GCR
are the most penetrating of the major types of ionizing radiation.
The distribution of GCR is believed to be isotropic throughout
interstellar space. The energies of GCR particles range from several
tens up to 10
12
MeV nucleon
1
. The GCR spectrum consists of 98%
protons and heavier ions (baryon component) and 2% electrons
and positrons (lepton component). The baryon component is
composed of 87% protons, 12% helium ions (alpha particles) and
1% heavy ions (Simpson, 1983). Highly energetic particles in the
heavy ion component, typically referred to as high Z and energy
(HZE) particles, play a particularly important role in space dosi-
metry (Benton and Benton, 2001). HZE particles, especially iron,
possess high-LET (Linear energy transfer) and are highly penetrat-
ing, giving them a large potential for radiobiological damage (Kim
et al., 2010). Up to 1 GeV, the ux and spectra of GCR particles are
strongly inuenced by the solar activity and hence show modula-
tion which is anti-correlated with solar activity.
1.2. Trapped radiation belts
Radiation belts are the regions of high concentration of the
energetic electrons and protons trapped within the Earth's mag-
netosphere. There are two distinct belts of toroidal shape sur-
rounding the Earth where the high energy charged particles get
trapped in the Earth's magnetic eld. Energetic ions and electrons
within the Earth's radiation belts pose a hazard to both astronauts
and spacecraft. The inner radiation belt (IRB), located between
about 0.1 to 2 Earth radii, consists of both electrons with energies
up to 10 MeV and protons with energies up to 700 MeV.
The outer radiation belt (ORB) starts from about 4 Earth radii
and extends to about 910 Earth radii in the anti-sun direction.
The outer belt mostly consists of electrons whose energy is not
larger than 10 MeV. The electron ux may cause problems for
components located outside a spacecraft (e.g. solar cell degrada-
tion). They do not have enough energy to penetrate a heavily
shielded spacecraft such as the International space station (ISS)
wall, but may deliver large additional doses to astronauts
during extra vehicular activity (Dachev et al., 2009a,2012a). The
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http://dx.doi.org/10.1016/j.jastp.2013.05.015
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South-Atlantic Anomaly (SAA) is an area where the radiation belt
comes closer to the Earth surface due to a displacement of the
magnetic dipole axes from the Earth's center. The daily average SAA
doses reported by Reitz et al. (2005) inside of the ISS vary in the range
74215 μGy d
1
for the absorbed dose rates and in the range 130
258 μSv d
1
for the averaged equivalent daily dose rates.
1.3. Solar energetic particles (SEP)
The SEP are mainly produced by solar ares, sudden sporadic
eruptions of the chromosphere of the Sun. High uxes of charged
particles (mostly protons, some electrons and helium and heavier
ions) with energies up to several GeV are emitted by processes of
acceleration outside the Sun. It is now generally understood that SEP
events arise from coronal mass ejections (CME) from active regions of
the solar surface. The CME propagates through interplanetary space
carrying along with it the local surface magnetic eld frozen into the
ejected mass. There is a transition (shock) region between the normal
sectored magnetic structure of interplanetary space and the elds
frozen into the ejected mass, which forms a transition region (shock)
where the interplanetary gas is accelerated forming the SEP. As the
accelerated region passes an observation point, the ux intensity is
observed to increase dramatically (Mertens et al., 2007). The time
prole of a typical SEP starts off with a rapid exponential increase in
ux, reaching a peak in minutes to hours. The energy emitted lies
between 15 and 500 MeV nucleon
1
and the intensity can reach
10
4
cm
2
s
1
sr
1
. Electrons with energies of 0.5 to 1 MeV arrive at
the Earth, usually traveling along interplanetary eld lines, within tens
of minutes to tens of hours. Protons with energies of 20 to 80 MeV
arrive within a few to 10 h, although some high energy protons can
arrive in as early as 20 min. SEP are relatively rare and occur most
often during the solar maximum phase of the 11-year solar cycle. In
the years of maximum solar activity up to 10 ares can occur, during
the years of minimum solar activity only one event can be observed on
average (Lantos, 1993).
1.4. Atmospheric ionizing radiation
The natural radiation level at cruising aircraft altitudes is much
higher than it is at ground level. The radiation eld arises
as a result of the interaction of primary GCR particles with the
Earth's atmosphere. An additional ux of albedo secondary
GCR is observed at altitudes below 3 km, which contributes to
the forming of the ux minimum around 1.6 km altitude
(Bazilevskaya et al., 2013). The intensity of the atmospheric
radiations, composed of GCR primary and secondary particles
and their energy distribution vary with altitude, location in the
geomagnetic eld, and the time in the sun's magnetic activity
(solar) cycle (Mertens et al., 2007). The atmosphere provides
shielding, which depends on the overhead atmospheric depth.
The geomagnetic eld provides a different kind of shielding, by
deecting low-momentum charged particles back to space.
Because of the orientation of the geomagnetic eld, which is
predominately dipolar in nature, the Polar Regions are susceptible
to penetrating GCR (and SEP) particles. At each geographic loca-
tion, the minimum momentum per unit charge (magnetic rigidity)
a vertically incident particle can have and still reach a given
3 location above the Earth is called the geomagnetic vertical cutoff
rigidity (Shea and Smart, 2001). The local ux of incident GCR at a
given time varies widely with geomagnetic location and the solar
modulation level. When the solar activity is high, the GCR ux is
low, and vice versa. The dynamic balance between the outward
convective ux of solar wind and the inward diffusive ux of GCR
is responsible for the anti-correlation between the incident GCR
and the level of solar activity (Mertens et al., 2007).
1.5. Natural radioactivity
The larger fraction of the Earth's surface where people live and
work has as natural soil cover resulting from weathering pro-
cesses. The lower atmospheric radiation and the associated exter-
nal exposure are mainly from gamma rays emitted from the top
25 cm of the surface layer of the Earth and the construction
materials of the buildings (Wilson et al., 2003). At ground level
the space radiation (originating from outside the Earth's atmo-
sphere, including solar radiation) generate about 11% of the
effective dose which the average US population, is exposed to,
while the terrestrial one (radiation emitted by radionuclides in soil
and rocks) is 7%. The major amount of the effective dose is
produced by inhaled Radon and ingested Potassium, Thorium
and Uranium (Wahl, 2010).
2. Material and methods
The main purpose of the Liulin type Deposited Energy Spectro-
meter (DES) is to measure the spectrum (in 256 channels) of the
deposited energy in a silicon detector from primary and secondary
particles at the aircraft altitudes, at low Earth orbits, outside of the
Earth magnetosphere on the route and on the surface of the
planets of the solar system. The DES is a Liulin type (Dachev et al.,
2002,2011a) miniature spectrometer-dosimeter containing one
semiconductor detector (Hamamatsu S2744-08) PIN diode, 2 cm
2
area, 0.3 mm thick), one charge-sensitive preamplier, 2 or more
microcontrollers and ash memory or telemetry. Pulse analysis
technique is used to obtain the deposited energy spectrum, which
is further used for the calculation of the absorbed dose and ux in
the silicon detector. The unit is managed by the microcontrollers
through specially developed rmware. Plug-in links provide the
transmission of the data stored on the ash memory via standard
interfaces (parallel, serial or USB) of a personal computer or to the
telemetry system of the carrier.
For the analysis of altitudinal proles of space exposure since
2000 the following DES were used in near Earth and free space
radiation environments on different carriers:
A mobile dosimetry unit (MDU) MDU-5 of Liulin-4C instrument
(100 110 45 mm, 410 g including 2 80 g Li-Ion D size
batteries) was used for more than 12,000 ight hours between
2001 and 2008 on Czech Airlines (CSA) aircraft on different
routes with 10 min resolution. In this paper the data between
March 22 and May 7 2001 are used (Spurny and Dachev, 2009).
Mobile dosimetry unit MDU#1 of Liulin-4U instrunent
(100 64 24 mm, 210 g including 80 g Li-Ion rechrgeable
battery pack) was used on the Deep Space Test Bed (DSTB)
balloon during the 8 June 2005 certication ight from Ft.
Sumner, New Mexico, USA up to 37.3 km altitude with 60-s
resolution (Benton, 2005). It was part of the NASA Space
Radiation Shielding Program, Marshall Space Flight Center
(Adams et al., 2007).
Radiation Risks Radiometer-Dosimeter (R3D) (82 57 25,
129 g.) for Biopan (R3D-B) with 256 channels ionizing radiation
monitoring spectrometer and 4 channels visible and UV spec-
trometer known as R3D-B2 which was successfully own 31
May16 June 2005 inside of the ESA Biopan 5 facilities on a
Foton M2 satellite. The operation time of the instrument
started on 24 April for about 20 days lling the total 1.0 MB
ash memory with 60-s resolution (Häder et al., 2009).
Liulin-R spectrometer-dosimeter (11040 20 mm, 92 g) was
successfully launched on the HotPay2 rocket from Andoya
Rocket Range (ARR), Norway, on 31 January 2008, rising to an
T.P. Dachev / Journal of Atmospheric and Solar-Terrestrial Physics 102 (2013) 148156 14 9
Author's personal copy
altitude of 380 km, as part of an EU-nanced scientic pro-
gramme called ALOMAR eARI project (Tomov et al., 2008).
R3DE instrument (76 76 36 mm, 110 g) with 256 channels
ionizing radiation monitoring spectrometer and 4 channels UV
spectrometer which worked on the ESA European Technology
Exposure Facility (EuTEF) platform inside of EXPOSE-E facility
outside of the European Columbus module of the ISS between
20 February 2008 and 1 September 2009 with 10-s resolution
behind 0.45 g cm
2
of shielding (Dachev, 2009;Dachev et al.,
2012a,2012b).
RADOM spectrometer-dosimeter (110 40 20 mm, 98 g) suc-
cessfully used on the Indian Chandrayaan-1 satellite from 22
October 2008 to 30 August 2009. It started working 2 h after
the launch with 10 s resolution behind about 0.45 g cm
-2
shielding. The instrument sent data for a number of crossings
of the Earth radiation belts and continued to work on 100 and
200 km circular lunar orbits measuring mainly the GCR envir-
onment (Dachev et al., 2009b,2011b).
The instruments was successors of the MDUs developed and used
in the Dosimetric Mapping-E094 experiment (Reitz et al., 2005)onthe
US Laboratory module of the ISS as a part of the Human Research
Facility in MayAugust, 2001 (Dachev et al., 2002). The main purpose
of this experiment was to investigate the dose rate distribution inside
the ISS. The obtained data were used for statistical validation of the
high-charge and energy (HZE) transport computer (HZETRN) code
(Wilson et al., 2007;Nealy et al., 2007;Slaba et al., 2011). A
comprehensive modeling of the microdosimetric spectra of the
absorbed dose and dose equivalent due to exposure of tissue
and silicon at the International Space Station was presented by Beck
et al. (2009).
The main measurement in the DESs is the amplitude of the
pulse after the preamplier, generated by particles or quanta
hitting the detector (Dachev et al., 2002). The amplitude of the
pulse is proportional by a factor of 240 mV MeV
1
to the energy
loss in the detector and to the dose, respectively. By 12 bit analog
to digital conversion (ADC) these amplitudes are digitized and
organized in a 256-channel deposited energy spectrum. By deni-
tion the dose in the silicon detector D
Si
[Gy] is one Joule deposited
in 1 kg of matter. The absorbed dose is calculated by dividing the
summarized energy deposition in the spectrum in Joules to the
mass of the detector in kilograms:
D
Si
¼K
255
i¼1
ik
i
A
i
MD
1
ð1Þ
where MD is the mass of the detector in kg, k
i
is the number of
pulses in channel i,A
i
is the amplitude in volts of pulses in channel
i,ik
i
A
i
is the deposited energy (energy loss) in Joules in channel i.
Kis a coefcient. All 255 deposited dose values, depending on the
deposited energy for one exposure time, form the deposited
energy spectrum. The energy channel number 256 accumulates
all pulses with amplitudes higher than the threshold energy of the
spectrometer of 20.83 MeV. The methods for characterization of
the type of incoming space radiation are described by Dachev
(2009).
The boxes for most of the instruments described in this paper
consist of less than 1.0 mm thick aluminum shielding before the
detector. The total external and internal shielding before the
detector (Hamamatsu PIN diode of type S2744-08) of the devices
is less than 0.41 g cm
2
. The calculated stopping energy of nor-
mally incident particles to the detector is 0.78 MeV for electrons
and 15.8 MeV for protons (Berger et al., 2013). This means that
only protons and electrons with energies higher than the above
mentioned values can reach the detector. The detector of the R3D-
B2 device was behind 1.75 g cm
2
shielding; that is why the
calculated minimum energies are 2.81 MeV for electrons and
35.6 MeV for protons.
DES was calibrated with protons in the Louvain la-Neuve
cyclotron facility (Dachev et al., 2002) and with protons and heavy
ions at HIMAC facility in Japan (Uchihori et al., 2002,2003). In both
cases good agreement was found between the measured and the
spectra predicted by the GEANT model. Post-ight calibrations
with Liulin-E094 MDUs were performed on HIMAC heavy ion
accelerator during the 1st ICCHIBAN run (Uchihori et al., 2003)in
Chiba Japan in February 2002 with 400 MeV/u Carbon ions.
Spectra obtained with all MDUs show a sharp maximum in the
deposited energy close to 6.1 MeV, which is in good agreement
with theoretical prediction and with measurements of the same
source with the DOSTEL-1 instrument (Burmeister et al., 2003).
The calibrations revealed that except for charged energetic
particles, the DES has high effectivity towards gamma rays, which
allowed monitoring the natural background radiation (Spurny and
Dachev, 2002). The neutron effectivity of the detectors depends on
their energy being minimal for neutrons with energy 0.5 MeV and
has a maximum of a few percent for neutrons with an energy of
50 MeV in the CERN eld (Spurný, 2005;Silari et al., 2009).
According to the neutron induced nuclear counter effectintro-
duced for the Hamamatsu PIN diodes of type S2744-08 by Zhang
et al. (2011) neutrons could be observed in all channels of the
spectrum with a probability at least one order of magnitude higher
in rst 14 channels. The method of converting D
Si
to an ambient
dose equivalent H
n
(10) for measurements onboard an aircraft was
described in Spurny and Dachev (2002). Later this method was
improved by Ploc et al. (2011).
3. Scientic results
3.1. Unique single instrument (R3D-B2) measurements of the space
radiation on the ground, on aircraft and in space between 24 May
and 3 June 2005
The doses of ionizing radiation were measured continuously
from 24 May to 12 June 2005 with the R3D-B2 instrument (Häder
et al., 2009). It was mounted inside the Biopan 5 facility (Demets
et al., 2005;http://www.spaceight.esa.int/documents/foton/expo
sure-experiments.pdf) on 24 May 2005 and was powered ON at
16:00 UT (all time data are in UT) in ESA's space research and
technology centre ESTEC. Since this moment the radiation data
were measured and collected in the ash memory of the instru-
ment. The Biopan 5 facility was transported on ground from ESTEC
to Amsterdam and then by aircraft to Samara, Russia and nally to
Baikonur, Kazakhstan on 25th and 26th of May. The facility was
integrated in the Foton M2 satellite in the early UT hours of 29
May. The launch of the Foton M2 satellite occurred on 31 May
about noon (Häder et al., 2009).
Fig. 1 presents the ux and dose rate measured with 1-min
resolution, and the calculated dose to ux ratio or specic dose
(SD) between 25 May and 3 June 2005. Totally 25,405 points are
presented for the dose rate and SD. The ux single points of
measurements are not plotted.
In addition to directly measured values, moving averages
curves over 30 points for dose rate (heavy dashed line), ux
(dotted line) and SD (heavy line) are plotted in the gure. During
the rst time span between 00:00 on 25 May and 03:00 on 29
May the measurements were performed mainly in the natural
background radiation environment. Two maxima occurred on 25th
and 26th of May during the two aircraft ights from Amsterdam
to Samara, Russia and from Samara to Baikonur, Kazakhstan.
The highest dose rate values obtained during the ights were
about 3.2 μGy h
1
for the rst ight and 2.3 μGy h
1
for the second
T.P. Dachev / Journal of Atmospheric and Solar-Terrestrial Physics 102 (2013) 148156150
Author's personal copy
ight. The difference is most probably due to different altitudes of
the ights. The different natural background radiation conditions
in Nederland, Russia and Kazakhstan produced different aver-
age values below 0.1 μGy h
1
, which are comparable with the
world mean value of natural background radiation of about
0.0585 μGy h
1
(Ghiassi-nejad et al., 2002).
The doses in the central part of the gure, denoted with the
label Gammawere obtained after the integration of the Biopan
5 facility with the returnable capsule of the Foton M2 satellite. The
increase of the dose rates up to 0.196 μGy h
1
in this part of the
recording is the result of additional radiation produced by a
gamma ray source on the Foton M2 capsule used for the determi-
nation of automatic rockets re before the touchdown of the
capsule.
The recorded maxima in the right side part of Fig. 1 denoted
with the label In spacewere obtained during the crossings of the
South-Atlantics magnetic anomaly (SAA) region where the inner
radiation belt populated with high-energy protons is encountered
and from the crossings of the outer radiation belt populated by
relativistic electrons (Dachev et al., 2009a,2012a).
The values of the SD (heavy curve in Fig. 1 plotted against the
right Yaxes) gives some information of the type of predominant
radiation sources measured by the instrument. This methodology
is based on the experimental formulas published by Heffner (1971)
and recently described for the Liulin type dosimeters (Dachev,
2009). The experimental formula (Heffner, 1971) shows that
protons in the range 10300 MeV as in the inner radiation belt
can delivery specic doses per particle always above 1 nGy cm
2
-
particle
1
, while the specic doses by electrons in the range
110 MeV are less than 1 nGy cm
2
particle
1
. The same is true for
muons and electromagnetic radiation as Roentgen and gamma. It
is seen that the SD value in the left part of the gure is stable with
values around 0.5 nGy cm
2
particle
1
. These low values are indi-
cator of small energy depositing events in the instrument which
are generated mainly by muons and gamma rays. During the two
aircraft ights the SD value increased up to 0.63 nGy cm
2
parti-
cle
1
because the increased amount of protons in the dose rate at
altitudes above 10 km. The SD values drop to about 0.42 nGy cm
2
-
particle
1
when the doses start to be strongly inuenced by the
gamma radiation source on board of the capsule.
After the launch on 31 May about noon the SD mean values
increased and resided at about 0.9 nGy cm
2
particle
1
most of the
time in orbit. These values are interpreted as caused by GCR
particles (Dachev, 2009). Crossings of the regions of SAA increased
these values to above 1 nGy cm
2
particle
1
, where protons pre-
dominate, and decreased below it during the crossings of the other
radiation belt regions populated mainly by relativistic electrons.
This behavior is repeatedly seen on 2 and 3 June when before and
after noon SAA crossings occurred and inner belt crossings about
1011 h in the morning. In the best way the dynamics of the dose
rate and SD or dose to ux ratio was investigated on ISS in 2008
2009 by the R3DE instrument and presented by Dachev et al.
(2012a); see Figure 5 there.
The result of the uxes measured with the R3D-B2 instrument
during the orbital phase of the Foton-M2 satellite in dependence
of the Lvalue (McIlwain, 1961;Heynderickx et al., 1996)is
presented in Figure 7 in Häder et al. (2009). Bearing in mind that
the Lparameter is the Earth radius (6378 km) and using the data
from the gure mentioned above we may conclude that the IRB
maximum appeared in the Foton-M2 data at L¼1.57 (3635 km
above the surface of the Earth), while the outer belt maximum
appeared at L¼3.82 (17,986 km above the surface of the Earth).
The value for the IRB is comparable with values described in the
next section of the paper, while the value for the altitude of the
ORB is smaller than the values predicted by the models AP/AE-
8MIN and CRESS/ELE/PRO (SPENVIS (http://www.spenvis.oma.be/)
reported by Dachev et al. (2011b) because larger shielding of the
detector of the R3D-B2 instrument.
3.2. Altitudinal proles of the space radiation exposure between the
Earth surface and free space
Fig. 2 presents the synthesized altitudinal proles of the
moving averages (over 4 points) of 3 parameters: absorbed dose
rate in μGy h
1
(heavy line), ux in cm
2
s
1
(long (red) dashed
line) and specic dose (SD) in nGy cm
2
particle
1
(short (blue)
dashed line). On the left side of the gure are listed the carriers,
instruments, time, averaged geographic coordinates of the mea-
sured values and their altitudinal range in km. On the right side
are listed the conditions and predominant radiation sources for
the places pointed with the arrows.
3.2.1. Ground natural radiation dose rate
The data in the bottom part of Fig. 2 were collected between 22
March and 7 May 2001 by a Liulin-4C MDU-5 instrument during
commercial (CSA airlines) aircraft ights mainly between Prague
and airports in North America (Spurny and Dachev, 2002); that is
why the average coordinates are (501N, 301W). The data acquisi-
tion time was chosen to be 10 min.
The lowest point at 100 m altitude in Fig. 2 represents the
values of the dose rate, ux and SD obtained by averaging of 2431
points with 10-min resolution (totally about 405 h) obtained
during the measurements in the airports at elevations above the
mean sea level (AMSL) between 2 and 1123 m (Bahrain 2 m, Dubai
19 m, New York (JFC 4 m and Newark 5.5 m), Montreal 38 m,
Prague 1123 m and Toronto 173 m). We accept these values as
average elevation of 100 m above the AMSL. The obtained average
dose rate value over all airports is 0.073 μGy h
1
. Other parameter
values and their ranges are given in Table 1. Different airports
shows different mean dose rate values being maximal in Prague
airportD¼0.075 μGy h
1
(the Prague airport coordinates are
50.151N, 14.371E, 1123 m AMSL and minimal in the Dubai airport
D¼0.058 μGy h
1
(25.251N, 55.361E, 19 m AMSL). The smaller dose
rates in the Dubai airport can be explained by: (i) smaller altitude
and latitude and (ii) longitudinal position (please see Fig. 3).
The averaged value of 0.073 μGy h
1
is in good agreement with
the world average natural background radiation dose rate, which is
0.0585 μGy h
1
with a minimum dose rate of 0.018 and maximum
of 0.095 μGy h
1
(Ghiassi-nejad et al., 2002).
Fig. 1. Variations of the ux, dose rate and SD measured with the R3D-B2
instrument between 25 May and 3 June 2005.
T.P. Dachev / Journal of Atmospheric and Solar-Terrestrial Physics 102 (2013) 148156 151
Author's personal copy
3.2.2. Flux minimum at 1.6 km altitude
The next interesting point in Fig. 2 is the ux minimum
observed around 1.6 km altitude. This is the point where the
terrestrial and albedo components of the background radiation
can be neglected but the cosmic radiation component is still at
very low levels. This minimum was discovered at about 1 km
altitude by Victor Hess during balloon ights up to 5.3 km altitude,
and this was explained by radiation coming from outer space. The
GEANT4 simulations made by Sloan et al. (2009) found the
minimum at 850 g cm
2
atmospheric depth (1.6 km altitude),
independent of the effective cutoff rigidity (Rc) in the range
0.032.4 GV.
Fig. 2. Variations of the absorbed dose rate, ux and specic dose for altitudinal range from 0.1 to 250,000 km. (For interpretation of the references to color in this gure
legend, the reader is referred to the web version of this article.)
Table 1
Tabulated data concerning points of interest in Fig. 2.
Point description, number of the measurements
used, time [dd/mm/yyyy]
Averaged
altitude, and
range [km]
Averaged geographic
coordinates [long,
lat]
Averaged dose
rate and range
[µGy h
1
]
Averaged ux and
range [cm
2
s
1
]
Averaged SD and range
[nGy cm
2
particle
1
]
Ground, 2431, 22/03-07/05/2001 0.1 481N, 21W 0.073 0.059 0.346
0.0260.212 0.00280.111 0.2131.15
Flux minimum, 10, 22/03-04/05/20 01 1.6 4 51N, 511W 0.073 0.052 0.386
1.561.7 0.0490.114 0.040.072 0.3250.645
SEP on 15 April 2001 (Maximum exposure),
1,13:42 15/04/2001
Fixed at 10.67 531N, 261W 3.66 1.46 0.696
Civil aircraft ight level between 34,000 and 36,000 ft
(10.67 km), 559 points, 22/03/2001-05/05/2001
10.55 521N, 311W 1.62 0.921 0.49
10.3610.67 0.852.33 0.5341.068 0.400.64
Photzer maximum (Flux maximum), 1, 08/06/2005 14.7 441N, 1071W 2.9 1.46 0.55
Photzer maximum (Dose rate maximum), 4, 08/06/2005 18.65 441N, 1071W 4.38 1.36 0.89
18.319.01 2.665.94 1.281.48 0.871.22
HotPay2 rocket trajectory, 14 31/12/2008 312 70.71N, 141E 8.99 1.9 1.3
211376204 4.811.8 1.68 2.15 0.791.89
South-Atlantic Anomaly maximum (Ascending node
orbits), 116 22/02/2008-23/0 6/2009
360 311S, 511W 948 113 2.33 (38 MeV)
347371 626119 5 7 6140 2.042.53
South-Atlantic Anomaly maximum (Descending node
orbits), 122 22/02/2008-04/06/2009
361 311S, 511W 1310 154 2.37 (37 MeV)
349371 8821640 104192 2.242.51
Inner radiation belt maximum, (Flux maximum),
2, 26/10/2008
2730 15.31S, 1651E 35,489 3279 3.0 (26 MeV)
27072753 34,81136,167 32743284 2.953.06
Inner radiation belt maximum, (Dose rate max.),
2, 26/10/2008
3007 15.31S, 1651E 37,279 3127 3.28 (24 MeV)
29843030 37,25437,305 30993156
Outer radiation belt maximum, (Flux maximum),
7, 26/10/2008
20,300 15.81S, 1491W 44,200 16,021 0.766
20,18020,436 43,74544,642 15,97616,053 0.7570.773
Outer radiation belt maximum, (Dose rate max.),
8, 26/10/2008
21,260 15.81S, 1491W 46,090 14,978 0.86
21,11121,409 42,46247,132 13,46015,539 0.8230.883
Free space, 8710, 06/11/2008 230,000 12.87 3.16 1.13 (169MeV) 0.513.25
200,000
252,000
4.641.3 1.714.71
T.P. Dachev / Journal of Atmospheric and Solar-Terrestrial Physics 102 (2013) 148156152
Author's personal copy
The averaged ux value we observed on aircrafts at the altitude
of 1.6 km was 0.052 cm
2
s
1
, while the predicted one by the
GEANT-4 model (Bazilevskaya et al., 2009) is 0.025 cm
2
s
1
.
On the other hand the measured average value for 1976 is
0.052 cm
2
s
1
(Bazilevskaya et al., 2009). The exact values for this
point and their ranges are summarized in Table 1.
Another observation of the ux minimum was performed with
the Mobile dosimetry unit MDU#1 of the Liulin-4U instrunent on
the Deep Space Test Bed (DSTB) balloon during the 8 June 2005
certication ight from Ft. Sumner, New Mexico, USA up to
37.3 km altitude with 60-s resolution (Benton, 2005). The averaged
ux value observed by us in the altitude range 1.72.4 km was
found to be 0.033 cm
2
s
1
at an altitude of 2 km. This value is
closer to the GEANT-4 model (Bazilevskaya et al., 2009).
3.2.3. Solar proton event on 15 April 2001
On 15 April 2001 around noon a solar are and a SEP event was
observed. The Ground level event (GLE) was designated as GLE 60.
During the time of the event the Liulin-4C MDU-5 instrument was
operated on a CSA airlines commercial ight from Prague to New
York at an altitude of 35,000 ft (10.67 km) (Spurny and Dachev,
2001). The usual dose rates and uxes observed at this altitude on
ights before or after the SEP increase by a factor of 2 (Lantos and
Fuller, 2003). This increase is well seen in Fig. 2 and the exact
average dose rate and ux values before, during and after the GLE
are summarized in Table 1.
3.2.4. Civil aircraft ight level at 35,000 ft
At altitudes above the point of minimal ux the dose rate and
ux start to increase rapidly because of the dominant cosmic
radiation component. As seen in Fig. 2 the dose rate and ux in the
altitudinal range 112 km gives strong variations of the measured
values. The R-squared value for the ux is R
2
¼0.9115, while for the
dose rate it is R
2
¼0.8301, obtained by polynomial approximation,
which is a relatively low value. The average values of dose rate and
ux at ight levels between 34,000 and 36,000 ft (10.67 km) are
1.62 μGy h
1
and 0.921 cm
2
s
1
, respectively, by averaging 559
measurements in the time interval 22 March 20015 May 2001, i.e.
during the maximum of solar activity. During the rising phase of
the solar activity cycle the aircraft dose rates at 10.67 km slowly
increased and reached values of 2.5 μGy h
1
(Dachev et al., 2010a).
The dose rate value ranges are between 0.85 and 2.33 μGy h
1
(Table 1). The reason is that a large amount of data was obtained at
standard nominal altitudes at different latitudes and longitudes.
3.2.5. Geographic map of dose rate at a ight level of 35,000 ft
Fig. 3 aims to answer the question how the values of dose rate
were distributed in latitudes and longitudes for the period 6 May
28 June, 2002. Data obtained mainly during ights from Prague to
New York and Montreal and back were used. Some data cover the
low latitudes by ights from Prague to Dubai and Bahrain and
back. The dose rate data obtained at standard nominal altitude of
35,000 ft are plotted in Fig. 3b in dependence of the geographic
latitude and longitude. The grid was obtained from 1043 measure-
ments by the method of minimum curvature, which was with 51
and 101spacing in latitude and longitude, respectively. The linear
gray level scale on the left side of the gure is with minimal and
maximal values of 0.7 and 2.1 μGy h
1
. It is well seen that the
minimum dose rate values are obtained at low latitudes in the
longitudinal range 251E501E. The maximum dose rates are in the
high latitudes in the longitudinal range 251W751W. The reason
for this distribution is seen in Fig. 3a where the vertical cosmic ray
cut-off rigidity at 20 km altitude for the geomagnetic conditions in
1990 in GV is plotted (Shea and Smart, 2001). As expected,
following the shape of the geomagnetic eld lines, the cut-off
rigidity has its maximal values where the dose rates has minima
and in reverse at the places with minimal rigidity the maximal
dose rates were observed. The higher cut-off rigidity means that
the particles from the GCR and their secondary particles have to
have a higher energy to penetrate the atmosphere. That is why at
the areas with low cut-off rigidity larger uxes and larger dose
rates are observed.
3.2.6. Photzer maximum
The altitude of maximum ux in the atmosphere is the Pfotzer
Maximum (Regener and Pfotzer, 1935;Pfotzer, 1936). It is for-
matted at the altitude at which the showers or cascades of
secondary particles produced by primary cosmic rays interacting
with the constituent nuclei of the atmosphere are most intense.
The interaction of the primary cosmic radiation with the atoms
and molecules of the atmosphere produces a broad spectrum of
different secondary particles with varying energy and linear
energy transfer (LET): protons, neutrons, electrons, muons, pions,
gamma-quanta and bremsstrahlung. With increasing depth in the
atmosphere, the primary cosmic radiation component decreases,
whereas the secondary radiation component increases.
The data above 11.9 km and up to 37 km altitude in Fig. 2 were
obtained with a Mobile dosimetry unit MDU#1 of the Liulin-4U
instrument, which is battery operated, during the certication
ight of the NASA Deep Space Test Bed (DSTB) balloon on 8 June
2005 at Ft. Sumner (34.471N 104.241W), New Mexico, USA
(Benton, 2005;Adams et al., 2007).
In Fig. 2 it is seen that rst the ux reached a maximum with a
value of 1.46 cm
2
s
1
at about 15 km altitude. Because the relative
low latitude (34.471N and Rc¼5.18 GV (Rc has been calculated by
SPENVIS, Magnetocosmics model (http://www.spenvis.oma.be/))
the observed uxes in the Pfotzer maximum are smaller than the
average value for 2005 at the mid northern latitude (Rc ¼2.4 GV)
station of 2.4 cm
2
s
1
presented by Stozhkov et al. (2011).
The dose rate maximum (see Fig. 2) was reached at about
19 km altitude with an average value of 4.38 μGy h
1
. This value is
higher than the absorbed dose rate derived from the balloon
cosmic rays measurements during the solar activity minimum at
Rc¼2.4 GV, which was obtained to be about 3.0 μGy h
1
at 20 km
altitude (Makhmutov et al., 2009). The displacement of the dose
Fig. 3. (a) Vertical cosmic ray cut-off rigidity at 20 km altitude for the geomagnetic
conditions in 1990 in GV (Shea and Smart, 2001). (b) 2D variations of the absorbed
dose rate for regions in Northern hemisphere between 751W and 501E longitude at
altitude around 35,000 ft (10.67 km).
T.P. Dachev / Journal of Atmospheric and Solar-Terrestrial Physics 102 (2013) 148156 15 3
Author's personal copy
rate and ux maximum we interpret with differences in the
energies of the GCR protons penetrating into the atmosphere.
The lower energy protons were stopped at higher altitudes but
they deposited higher dose rates than the higher energy GCR
protons, which penetrate deeper into the atmosphere.
3.2.7. HotPay2 rocket prole
As seen in the upper half of Fig. 2 the dose rates and uxes, stay
at almost xed low GCR levels up to the bottom side of the IRB
maximum at about 1700 km altitude. This prole was adequate for
the RADOM instrument measurements on the Indian Chan-
drayaan-1 satellite in October 2008 (Dachev et al., 2011b), which
was obtained at low latitudes and far away from the region of the
SAA maximum.
With a purpose of presenting the radiation conditions out of
these single low latitude point two additional data sets are plotted
in Fig. 2 showing the dose rate, ux and SD as moving average
lines. The rst one is the data set from the HotPay2 rocket.
The HotPay2 rocket was launched at 19:14:00 UT on 31 January
2008 from Andoya Rocket Range (69.291N, 16.031E) (Tomov et al.,
2008). After 323 s ight time the rocket reached an apogee of
380 km altitude and coordinates (70.671N, 14.041E). The impact
distance of the payload was 343 km (at 71.871N, 12.191E).
The Liulin-R data are shown in Fig. 2 as dose rate ux and SD
moving average lines at altitudes between 211 and 376 km. For the
different values the same line attributes as in the main graphics
are used. It is seen that on the ascending part of the trajectory at
about 212 km altitude the measured dose was 9.28 μGy h
1
and
the ux 2.0 cm
2
s
1
. Close to the apogee of 377 km the measured
dose was 10.18 μGy h
1
and the ux 1.87 cm
2
s
1
. From 14
experimental points with 30-s resolution on the ascending and
descending trajectories above 200 km altitudes the follow-
ing average values were obtained: dose rate¼8.99 μGy h
1
,
ux¼1.92 cm
2
s
1
and SD¼1.3 nGy cm
2
particle
1
. These much
larger dose rate and ux values are caused by the larger Earth
magnetic eld latitude and resulting lower geomagnetic cutoff
rigidity (Rc¼0.27 (Rc has been calculated by SPENVIS, Magneto-
cosmics model (http://www.spenvis.oma.be/)), which allowed a
larger amount of GCR particles to reach these altitudes. The
obtained average dose rate and ux values (see Table 1) coincide
well with the latitudinal proles shown by Dachev et al. (2011c);
see Fig. 2.
3.2.8. SAA region maximum
The second data set plotted in Fig. 2, showing the dose rate, ux
and SD moving average lines, is denoted with an label ISS. Two
short lines below the label present the dose rate and ux data
obtained by the R3DE instrument outside the Columbus module of
the ISS during descending node orbits at altitudes between 349
and 371 km. The SD data are not plotted to avoid mismatch with
data in Fig. 2.
The ISS dose rate and ux data were selected from a rectan-
gular geographic coordinate region with 21size (331Solatitu-
deo311S and 511Wolongitudeo491W). Preliminary analysis of
the data showed that the SAA maximum dose rate values are
situated inside this rectangle. The time span of the data is between
22 February 2008 and 4 June 2009.
The two short lines in Fig. 2 actually present the whole
dynamics of the altitudinal prole of the ISS descending node
orbits for the time interval mentioned above. Very rough approx-
imations of the dose rate and ux proles show best results for the
linear tting of the curves. Nevertheless the exponential tting is
expected to be the best one. The obtained linear coefcients are for
the dose rate and ux of 27.3 μGy h
1
and 3.2 cm
2
s
1
for 1 km
altitude, respectively. The Chandrayaan-1 data in the range of
18052263 km values are larger, being 47.9 μGy h
1
and
5.2 cm
2
s
1
for 1 km altitude, respectively. This behavior is also
seen in Fig. 2.
Because of the East-West asymmetry in the SAA uxes
(Ersmark et al., 2007;Easley, 2007;Chernykh et al., 2008) the
ascending orbits dose rate and uxes for the same location and
time span shows much smaller values (see Table 1).
3.2.9. Inner radiation belt maximum
Starting from about 1500 km altitude (see Fig. 2) the dose rates
and uxes increase sharply by more than 4 orders of magnitude
and reach their maxima at the position of the IRB maximum at
about 3000 km altitude. The major radiation source in the lower
part of the IRB are high energy protons (Dachev et al., 2011b).
At altitudes above the IRB maximum the dose rates and uxes
decrease and reach minimum values at about 11,000 km altitude
in the slot region.
3.2.10. Outer radiation belt maximum
Up than the slot region at 11,000 km altitude the dose rates and
uxes raised again to reach a new maximum in the region of the
outer radiation belt (ORB) maximum. Fig. 2 shows that the
ORB starts from 14,000 km and extends up to 54,000 km.
The maximal particle ux in the ORB was observed at
22,500 km. The comparison of our RADOM ORB ux data with
the predicted ones by the models AE-8MIN and CRESS/ELE/PRO
(SPENVIS (http://www.spenvis.oma.be/) shows relatively large
discrepancies. The differences between the observed data and
the model data can be explained by the fact that the RADOM
observations were made during relatively very low solar activity
and quiet geomagnetic conditions, which was never observed
before Dachev et al. (2011b).
3.2.11. Free space
The average dose rate from 8314 measurements (see Fig. 2)in
the altitudinal range between 200,000 and 251,000 km from the
Earth was 12.87 μGy h
1
. The range of the real measured dose
rates is between 3.34 and 41.34 μGy h
1
with a standard deviation
of 4.25 μGy h
1
. The average ux is 3.16 particles cm
2
s
1
, while
the real ux range is between 1.71 and 4.82 particles cm
2
s
1
with
a standard deviation of 0.41 cm
2
s
1
. These values of the dose rate
and ux may be used as reference values for the free space
radiation conditions at this very low level of solar activity. As seen
in Fig. 2 the lower boundary of the free spaceregion can be
considered at altitudes above 70,000 km.
3.2.12. Analysis of the SD prole
The SD values seen in Fig. 2 are low at the ground with values
of 0.30.5 nGy cm
2
particle
1
. In the altitudinal range 18 km the
SD slowly increase. Further the SD rise up to values of about 0.9
1.1 nGy cm
2
particle
1
at the altitude of 37 km. We interpret this
behaviour of the SD prole with the change of the mass of the
radiation source components from predominantly light particles
such as electrons, pions and muons at altitudes up to 8 km toward
heavier ones such as protons and neutrons at altitudes up to 37 km
(Bagshaw and Cucinotta, 2007).
This hypothesis is conrmed with the increase of the SD values
up to 0.7 nGy cm
2
particle
1
in the maximum of the SEP on 15
April 2001. As seen from Table 1 the average value for 10.67 km is
0.49 nGy cm
2
particle
1
.
During the HotPay2 rocket ight the averaged SD value was
1.3 nGy cm
2
particle
1
, which is a typical GCR value (Dachev et al.,
2012a), showing a predominant population of high energy pro-
tons. Nevertheless that the launch occurred inside an aurora
T.P. Dachev / Journal of Atmospheric and Solar-Terrestrial Physics 102 (2013) 148156154
Author's personal copy
(Tomov et al., 2008), there were no observed electrons with
energies above 0.78 MeV at altitudes above 200 km.
In the altitudinal range 3881572 km the SD values measured
by the RADOM instrument on the Chandrayaan-1 satellite were
very low with an average value of 0.6 nGy cm
2
particle
1
. This
region being below the IRB maximum is characterized by a very
low ux (0.74 cm
2
s
1
), which is out of the application range of
the Heffner's formulas.
The averaged SD values observed with the R3DE instrument on
the ISS inside of the SAA maximum was almost equal for ascend-
ing and descending nodes. The observed values of 2.332.37 nGy
cm
2
particle
1
correspond to protons with energies 3738 MeV
(Heffner, 1971;Dachev, 2009).
Similar values of SD were observed with the RADOM instru-
ment at the bottom of the IRB (see Fig. 2). Further with increasing
altitude the SD values raised and reached values of about
4.6 nGy cm
2
particle
1
at 9000 km altitude which correspond to
energies of about 15 MeV (Heffner, 1971;Dachev, 2009). The IRB
maximum as well as in the Photzer maximum were rst observed
at lower altitudes in the ux values at next in the dose rate values.
The transformation of the SD values to protons energy values gives
26 MeV in the ux and 24 MeV in the dose rate maximum.
In general the protons energy decreased across the IRB maximum.
The crossings of the slot region led to a dramatical decrease of
the SD values down to about 0.60.8 nGy cm
2
particle
1
, which
indicates a change of the predominant radiation source from
protons to electronsas expected when the satellite reached the
outer radiation belt. The SD values are larger than the ones
predicted by the Heffner's formulas because in the ORB one
additional ux of GCR particles exists. It is remarkable that around
the ORB maximum the ux maximum occurred at a lower altitude
(20,300), while the dose rate maximum was observed at
21,260 km altitude.
Finally, when the satellite reached the free space at 230,000 km
altitude the averaged SD value of 1.13 nGy cm
2
particle
1
is ade-
quate for the GCR particles with an energy of 169 MeV (Heffner,
1971;Dachev, 2009).
4. Discussion
The paper analyzes the obtained results for the exposure to
different radiation environments at aircraft, balloon and spacecraft
altitudes obtained with Bulgarian-built instruments.
It is understand that the obtained prole of exposure does not
have a global coverage because of limited distribution of the IRB,
which maximum extent up to L¼1.6.
The limitation of the paper is that the aircraft and the balloon
data in the low altitudes were collected mainly at mid latitudes at
relatively high solar activity, while the high altitude data of the
Chandrayaan-1 satellite was obtained at low latitudes and low
solar activity.
The strong point of this paper is that original experimental data
are compared and plotted to reveal a unied picture how the
different ionizing radiation sources contribute and build the space
radiation exposure altitudinal prole from the Earth surface up to
the free space. The dose rate and ux data cover 7 orders of
magnitude and can be used for educational purposes and also as
reference values for new models. The presentation of data in
kilometers above the Earth surface instead in Lvalues allows space
agencies medical staff and that not specialized in the geophysics
support to use them for a rst approach for the expected human
exposure at different altitudes and also the general public and
students to have a simple knowledge about the position of the
most common maxima of exposure around the Earth and up to
free space.
Acknowledgements
The author would like to thank B. Tomov, P. Dimitrov and Y.
Matviichuk from the Space Research & Technology Institute at the
Bulgarian Academy of Sciences for their cooperation in the devel-
opment of the Liulin type spectrometers and for the assistance
with data analysis; F. Spurny, and O. Ploc from Nuclear Physics
Institute, Czech Republic for the aircraft data and work on the
interpretation procedure; G. Horneck and G. Reitz from DLR,
Institute of Aerospace Medicine, Germany, D.-P. Häder, M. Lebert
and M. Schuster from Department für Biology der Friedrich-
Alexander-Universität, Germany for the leadership and coopera-
tion in the experiments on Foton-M2 spacecraft and ISS; E. Benton
from Department of Physics, Oklahoma State University,USA for
the balloon data from MDU#1 of Liulin-4U instrument; ISRO staff
and more specially to: Mr. M. Annadurai, Project Director and J. N.
Goswami, Project scientist of Chandrayaan-1 satellite, P. Sreeku-
mar and V. Sharan, Space Astronomy & Instrument Div., and Dr. J D
Rao, ISTRAC/ISRO Bangalore for the RADOM instrument support.
The author acknowledges with thanks the help of D.-P. Häder for
editing this paper.
This work is partially supported by the Bulgarian Academy of
Sciences and contract DID 02/8 with the Bulgarian Science Fund.
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... Relative humidity levels can drop below 1%, and temperatures in the lower stratosphere regularly reach -100°C. Stratospheric radiation is substantially higher (Kylling et al., 2003;Adams et al., 2007;Dachev, 2013) than doses at other frequently visited Mars analog environments, including the McMurdo Dry Valleys of Antarctica (Wynn-Williams and Edwards, 2000) and the Atacama Desert . Laboratory environmental chamber experiments have been employed in the past to simulate martian conditions (Schuerger et al., 2003;Diaz and Schulze-Makuch, 2006;Tauscher et al., 2006;de la Vega et al., 2007;Moores et al., 2007;Osman et al., 2008;Fendrihan et al., 2009;Smith et al., 2009;Gómez et al., 2010;Peeters et al., 2010;Johnson et al., 2011;Kerney and Schuerger, 2011), but artificial illumination sources do not realistically represent the dynamic nature of sunlight. ...
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... The exposure of varied biological samples to the stratospheric conditions opens up the possibility to observe changes in the functioning of the cell, e.g., decreased viability, dysfunction of cellular organelles and their localization, cell cycle arrest, changes of gene expression, and DNA damage (Moan and Peak, 1989;Cadet et al., 2005). In addition, ionizing and nonionizing radiation in the stratosphere (Dachev, 2013) affects the cells both directly and indirectly [water radiolysis, therefore exacerbating the oxidative stress (Desouky et al., 2015)], causing effects such as mitochondrial impairment (Anand et al., 1997), DNA damage, protein and lipid peroxidation correlated with disruption of the cell membrane (Cohen-Jonathan et al., 1999) that altogether may lead to cell death (Cohen-Jonathan et al., 1999;Desouky et al., 2015) (Figure 1A). Furthermore, stratospheric flights provide unique cyclic changes of linked environmental factors, including radiation, overload, pressure, temperature, wind (high velocities, rapidly varying wind direction), and vibrations, which are impossible to be simulated altogether in laboratory. ...
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The current age of dynamic development of the space industry brings the mankind closer to routine manned space flights and space tourism. This progress leads to a demand for intensive astrobiological research aimed at improving strategies of the pharmacological protection of the human cells against extreme conditions. Although routine research in space remains out of our reach, it is worth noticing that the unique severe environment of the Earth’s stratosphere has been found to mimic subcosmic conditions, giving rise to the opportunity to use the stratospheric surface as a research model for the astrobiological studies. Our study included launching into the stratosphere a balloon containing mammalian normal and cancer cells treated with various compounds to examine whether these substances are capable of protecting the cells against stress caused by rapidly varying temperature, pressure and radiation, especially UV. Due to oxidative stress caused by irradiation and temperature shock, we used natural compounds which display antioxidant properties, namely - catechin isolated from green tea, honokiol derived from magnolia, curcumin from turmeric and cinnamon extract. “After-flight” laboratory tests have shown the most active antioxidants as potential agents which can minimize harmful impact of extreme conditions on human cells.
... Above that, only a limited amount data exists which were measured on board a high-altitude aircraft [16] or the Concorde aircraft [17,18] up to altitudes of approximately 20.4km. At these altitudes the ionization of the air reaches a maximum [19] owing to the interplay between particle production and absorption as a function of the atmospheric density. The maximum is named the Pfotzer Maximum, in accordance with its discovery by Pfotzer in the 1930s [20]. ...
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Monitoring the ambient dose equivalent rate at aviation altitudes is an ambitious task, which requires sophisticated dosemeter systems and the possibility to carry out such measurements on board aircraft. A rather simple approach has been investigated in this study: soundings with weather balloons up to an altitude of 30 km. This paper summarises the measurements carried out between 2011 and 2016. The results indicate that annual measurements of the ambient dose equivalent rate at altitudes of around 20 km are a reliable tool to monitor the variation of the dose rate in the atmosphere owing to the solar activity.
... The exposure of varied biological samples to the stratospheric conditions opens up the possibility to observe changes in the functioning of the cell, e.g., decreased viability, dysfunction of cellular organelles and their localization, cell cycle arrest, changes of gene expression, and DNA damage (Moan and Peak, 1989;Cadet et al., 2005). In addition, ionizing and nonionizing radiation in the stratosphere (Dachev, 2013) affects the cells both directly and indirectly [water radiolysis, therefore exacerbating the oxidative stress (Desouky et al., 2015)], causing effects such as mitochondrial impairment (Anand et al., 1997), DNA damage, protein and lipid peroxidation correlated with disruption of the cell membrane (Cohen-Jonathan et al., 1999) that altogether may lead to cell death (Cohen-Jonathan et al., 1999;Desouky et al., 2015) (Figure 1A). Furthermore, stratospheric flights provide unique cyclic changes of linked environmental factors, including radiation, overload, pressure, temperature, wind (high velocities, rapidly varying wind direction), and vibrations, which are impossible to be simulated altogether in laboratory. ...
Conference Paper
The aim of the study was the verification how the external environment can affect the functioning of cells. The experiment was carried out to send a stratospheric balloon to a height of 35 km above the surface of the Earth with human gingival fibroblasts, SKOV-3 and CHO cells. In this way, the research material got into the stratosphere, where the low temperature, pressure and UV radiation levels are similar to these currently presenting on the surface of Mars. This enabled the determination of the effect of subcosmic conditions on the functioning of human cells. There was examined whether the type of freezing medium (DMSO+FBS; Bambanker®; sucrose solution) in which the cells were suspended effects on the cells’ properties and whether preincubation with various antioxidants protect cell membranes from damage and disintegration in the stratosphere. The results were compared with the data obtained from laboratory-simulated low temperature effects on cells’ properties in vitro, which revealed that cells from different tissues respond differently to subcosmic conditions. Significant differences in the results after laboratory simulation and after the balloon flight indicate that various parameters of the extra-terrestrial environment – the pressure, radiation and the overload associated with the balloon flight have a significant effect on the functioning of cells. ACKNOWLEDGEMENTS: The study was supported by funds from the project “Budowa mini aparatury naukowo-badawczej na pokladzie balonu stratosferycznego” financed by Wroclaw University of Science and Technology, partially from Statutory Funds of the Wroclaw Medical University No.: ST.E130.16.060 (PI prof. J. Zalewski) and from Student Scientific Club of Cancer Cell Biology.
... The absorbed dose rates and specific doses obtained by the RDR2 instrument during the whole monitoring period (from 23 October to 25 November 2014) are plotted in Fig. 2. The black points against the left axis in the upper part of the figure correspond to the observed dose rates in μGy h −1 . The specific dose (SD) variations calculated from the dose rate to flux ratio in nGy cm 2 particle −1 (Heffner, 1971, Dachev, 2009, Dachev, 2013b) are plotted in red color against the right axis in the lower part of the figure. On the horizontal axis we choose the geomagnetic dipole latitude (Fraser-Smith, 1987), which, similar to the L value (McIlwain, 1961), organizes well the geomagnetic dependent parameters of the space radiation but allows understanding the differences in both geomagnetic hemispheres. ...
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Space radiation was monitored using the R3DR2 spectrometer-dosimeter during the flight outside the Russian “Zvezda” module of ISS in October-November 2014. The instrument was mounted on the ESA EXPOSE-R2 platform. The R3DR2 instrument was first developed and used during the flight of ESA EXPOSE-R platform in 2009-2010 (Dachev et al, 2015a). It is a low mass, small dimension automated device that measures solar visible and ultraviolet (UV) radiation in four channels and ionizing radiation in 256 channels of a Liulin-type energy deposition spectrometer (Dachev et al, 2002). Ionizing radiation was measured and separated in 256 deposited energy spectra, which were further used for determination of the absorbed dose rate and flux. The main results obtained by the R3DR2 instrument are: (1) three different radiation sources were detected and quantified - galactic cosmic rays (GCR), energetic protons from the inner radiation belt (IRB) in the region of the South Atlantic anomaly and energetic electrons from the outer radiation belt (ORB); (2) for the first time in the history of using of the Liulin-type energy deposition spectrometers (Dachev et al, 2015b) an observable flux from solar energetic particles (SEP) was detected in the period 1-4 November 2014; (3) the obtained SEP energy deposition spectra were compared with other spectra to confirm their shape.
... Energetic particle radiation from space continuously bombards the Earth's atmosphere. Cosmic radiation has sufficient energy to penetrate deep within the atmosphere and adversely affect human health to crew and passengers on aircraft [Reitz, 1993;Dachev, 2013]. There are two sources of cosmic rays: (1) the ever-present galactic cosmic rays (GCR), with origins outside the solar system and (2) the transient solar energetic particles (SEP) (or solar cosmic rays), which are associated with eruptions on the Sun's surface lasting several hours to days. ...
Article
Full-text available
The NASA Radiation Dosimetry Experiment (RaD-X) stratospheric balloon flight mission addresses the need to reduce the uncertainty in predicting human exposure to cosmic radiation in the aircraft environment. Measurements were taken that characterize the dosimetric properties of cosmic ray primaries, the ultimate source of aviation radiation exposure, and the cosmic ray secondary radiations that are produced and transported to aviation altitudes. In addition, radiation detectors were flown to assess their potential application to long-term, continuous monitoring of the aircraft radiation environment. RaD-X was successfully launched from Fort Sumner, New Mexico (34.5∘ N, 104.2∘ W) on 25 September 2015. Over 18 hours of science data were obtained from a total of four different type dosimeters at altitudes above 20 km. The RaD-X flight mission was supported by laboratory radiation exposure testing of the balloon flight dosimeters and also by coordinated radiation measurements taken on ER-2 and commercial aircraft. This paper provides: the science background and motivation for the RaD-X flight mission, a brief description of the balloon flight profile and the supporting aircraft flights, and a summary of the articles included in the RaD-X special collection and their contributions to the science goals of the RaD-X mission.
Chapter
The effects from ionizing radiation exposure are a concern faced by aircrew, high‐altitude pilots, frequent flyers, and commercial space travelers. This chapter describes the physics of atmospheric radiation's primary sources, including galactic cosmic rays (GCRs) and solar energetic particles (SEPs), as well as the possibility of a newly identified third source of secondary radiation caused by precipitating radiation belt charged particles. The primary radiation processes of transport through the heliosphere, modulation by the solar wind, and magnetic shielding by the Earth's geomagnetic field are described. The SEP primary radiation differential energy spectrum is described, and radiation belt precipitated charged particles are discussed with information from a large database of atmospheric radiation measurements. The transport of charged particles from all sources through the magnetic shielding from the Earth's geomagnetic field is described and the concept of geomagnetic cutoff rigidity is thoroughly explained. The transport of radiation through the atmosphere from precipitating charged particles below the mesopause is presented from a theoretical perspective, including the interactions of neutrons and charged particles with target species in the atmosphere. Radiation dosimetry is described, including dose quantities and quality factor. Additional discussions are presented with an introduction on radiation effects on avionics, the models capable of reporting the aviation radiation environment, the measurements that have been made of the atmospheric radiation by specific instruments, and introductory remarks on the regulatory activity internationally and in the US related to the effects of radiation faced by aircrew, high‐altitude pilots, frequent flyers, and commercial space travelers.
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Full-text available
The paper presents the solar modulation of the long-term galactic cosmic rays (GCR) flux and dose rates variations, observed during 14 space experiments by 10 Bulgarian build Liulin-type spectrometers (LTS) (Dachev et al., 2015a). They worked in near Earth space and in the interplanetary radiation environment between January 1991 and January 2019. Data were collected by LTS in the low Earth orbit (LEO) in the L range between 4 and 6.2 or outside the magnetosphere. The major advantage of the data sets are that they are obtained by the electronically identical LTS. The Liulin measurements of about monthly averaged flux and dose rate data are compared with the monthly values of the modulation parameter, reconstructed from the ground based cosmic ray data (Usoskin et al., 2017). A good correlation between the two data sets is observed. The most important achievement of the paper is that for the first time a proof of the solar modulation of the long-term variations of the monthly averaged dose rates is obtained. These long-term experimentally obtained dose rate data could be used for modelling of the GCR space radiation risks to humans in the near Earth radiation environment. Parallel to the long-term dose rate varitions, the monthly averaged flux variations are also presented.
Thesis
Full-text available
The interaction of radiation with living entities is generally associated with damages of their fundamental structures, i.e. the DNA, which can later induce malignant effects such as chromosome aberrations, cell necrosis or apoptosis. Depending on the amount and type of radiation exposure, on a macroscopic scale this could translate in skin erythema, hair loss, sterility, cataract, fetal decease, teratogenesis, cancer, hereditary defects or death. It appears clear that the exposures to ionizing radiation should be justified, limited if not totally avoided. However, radiation is silent, tasteless, invisible and cannot be perceived in any way by humans before that its effects irremediably occurred. Luckily, with the evolution of science, many devices able to quantify radiation exposures have been developed. Detectors made of luminescent materials represent an elegant example. After a radiation exposure and under controlled conditions, these crystals glow and the emitted light can be correlated with the received amount of radiation dose. As a consequence, this technology has been used for decades to monitor radiation doses received by exposed workers or for retrospective analyses after nuclear incidents. On the other hand, ionizing radiation can be used to cure cancer. The latter is the case of radiotherapy, where finely tuned particle beams are shot against the tumor volume to selectively kill the cancer cells. Also here, due to their small, cheap and passive nature, bunches of luminescent detectors can be used to judge the precision of the treatment and to assess possible changes in its effectiveness within the cancer volume. However, the main drawback of luminescent detectors is that they do not record radiation exposure information independently from the nature of the radiation exposure: for sparsely ionizing radiation as photons they have high efficiency, while a strong efficiency decrease occurs for measuring strongly ionizing particles as the ones present in space or close to the edges of cancer radiotherapy treatments. This has led to a progressive replacement of these detectors with more sophisticated and expensive ones. In this Thesis, an accurate study of the nanoscopic structure of energy deposition gave new insights and a complete description of the efficiency changes of luminescent detectors, a tool to predict the efficiency in known radiation environments and a new methodology to extract radiation quality information within cancer radiotherapy treated volumes.
Chapter
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This chapter addresses long-range dispersion and the survival of microorganisms across a wide range of altitudes in Earth's atmosphere. Topics include mechanisms of dispersion, survivability of microorganisms known to be associated with long-range transport, natural and artificial sources of bioaerosols, residence time estimation through the use of proxy aerosols, transport and emission models, and monitoring assays (both culture and molecular based). We conclude with a discussion of the known limits for Earth's biosphere boundary, relating aerobiology studies to planetary exploration given the large degree of overlapping requirements for in situ studies (including low biomass life detection and contamination control).
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Full-text available
Results on energy deposition and ioni-sation rate in the Earth's atmosphere during solar proton events (SPEs) are presented. The estimations for the most powerful solar proton events recorded in the Earth environment during are given. The solar proton measure-ments in the near-Earth space, in the atmosphere and by the ground-based neutron monitors are used to obtain energy spectra during the maximum phase of each event. The Monte Carlo simulation of the solar proton transport in the atmosphere based on GEANT4 enable us to determine spatial and energy distributions of secondary particles at the different atmospheric levels. The energy deposition and ion production rate in the stratosphere during powerful solar proton events are presented.
Article
Full-text available
Since 1957 the Lebedev Physical Institute has being performed observations of ionizing radiation in the atmosphere from the ground level up to the height of 30-35 km. The time series of charged particle fluxes in the near-ground levels of the atmosphere at polar latitudes and at mid-latitude obtained in the course of the experiment are presented. The measured fluxes include cosmic ray particles and radioactivity. Over the solid ground radioactivity is observed up to the heights of ~ 3 km. Over the sea surface radioactivity level is several times less than over the solid ground. It seems that above the ground surface up to ~1.5 km there is a contribution from the cosmic ray air-soil transition effect.
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Radiation fields on board aircraft contain particles with energies up to a few hundred MeV. Many instruments have been tested to characterise these fields. This paper presents the results of studies on the use of an Si diode spectrometer to characterise the on board field. During a Czech Airlines flight from Prague to New York it was possible to register the effects of an intense solar flare, (ground level even, GLE 60), which occurred on 15 April 2001. It was found that the number of deposition events registered was increased by about 70% and the dose in Si by a factor of 2.0 when compared with the presence of galactic cosmic rays alone. Directly measured data are interpreted with respect to on-earth reference field calibration (photons, CERN high-energy particles); it was found that this approach leads to encouraging results and should be followed up.
Article
This overview of solar-terrestrial relations has been written as a specific introduction to solar activity effects on particles observed on the Earth. Particles emitted during flares travel through interplanetary medium faster than solar wind disturbances. Thus pre-existing conditions, where an interplanetary magnetic field is controlled by a quiet Sun and active regions, are first described. Travelling shock waves that might have been produced by previous flares or by the same flare as the particles are also considered. Finally the effects of solar activity (either under normal conditions or during flares) on non-solar cosmic rays are mentioned.
Article
The latest results on the composition of cosmic rays, and their theoretical implications, were discussed at a conference held in Cambridge during July 16-19. They point to a thermonuclear origin, but it is still a matter of speculation whether cosmic rays in the solar vicinity are produced in galactic objects such as supernovae, or whether they originate in extragalactic "violent events".
Conference Paper
There is a growing concern for the health and safety of commercial aircrew and passengers due to their exposure to ionizing radiation with high linear energy transfer (LET), particularly at high latitudes. The International Commission of Radiobiological Protection (ICRP), the EPA, and the FAA consider the crews of commercial aircraft as radiation workers. During solar energetic particle (SEP) events, radiation exposure can exceed annual limits, and the number of serious health effects is expected to be quite high if precautions are not taken. There is a need for a capability to monitor the real-time, global background radiations levels, from galactic cosmic rays (OCR), at commercial airline altitudes and to provide analytical input for airline operations decisions for altering flight paths and altitudes for the mitigation and reduction of radiation exposure levels during a SEP event. The Nowcast of Atmospheric Ionizing Radiation for Aviation Safety (NAIRAS) model is new initiative to provide a global, real-time radiation dosimetry package for archiving and assessing the biologically harmful radiation exposure levels at commercial airline altitudes. The NAIRAS model brings to bear the best available suite of Sun-Earth observations and models for simulating the atmospheric ionizing radiation environment. Observations are utilized from ground (neutron monitors), from the atmosphere (the METO analysis), and from space (NASA/ACE and NOAA/GOES). Atmospheric observations provide the overhead shielding information and the ground- and space-based observations provide boundary conditions on the OCR and SEP energy flux distributions for transport and dosimetry simulations. Dose rates are calculated using the parametric AIR (Atmospheric Ionizing Radiation) model and the physics-based HZETRN (High Charge and Energy Transport) code. Empirical models of the near-Earth radiation environment (GCR/SEP energy flux distributions and geomagnetic cut-off rigidity) are benchmarked against the physics-based CMIT (Coupled Magnetosphere-Ionosphere-Thermosphere) and SEP-trajectory models.
Article
Space radiation has been monitored successfully using the Radiation Risks Radiometer-Dosimeter (R3D) installed at the ESA EXPOSE-R (R3DR) facility outside of the Russian Zvezda module of the International Space Station (ISS) between March 2009 and January 2011. R3DR is a Liulin type spectrometer–dosimeter with a single Si PIN detector 2 cm2 of area and 0.3 mm thick. The R3DR instrument accumulated about 2 million measurements of the absorbed dose rate and flux of 10 s resolution. The total external and internal shielding before the detector of R3DR device is 0.41 g cm−2. The calculated stopping energy of normally incident particles to the detector is 0.78 MeV for electrons and 15.8 MeV for protons. After the Coronal Mass Ejection (CME) at 09:54 UTC on 3 April 2010, a shock was observed at the ACE spacecraft at 0756 UTC on 5 April, which led to a sudden impulse on Earth at 08:26 UTC. Nevertheless, while the magnetic substorms on 5 and 6 of April were moderate; the second largest in history of GOES fluence of electrons with energy >2 MeV was measured. The R3DR data show a relatively small amount of relativistic electrons on 5 April. The maximum dose rate of 2323 μGy day−1 was reached on 7 April; by 9 April, a dose of 6600 μGy was accumulated. By the end of the period on 7 May 2010 a total dose of 11,587 μGy was absorbed. Our data were compared with AE-8 MIN, CRESS and ESA-SEE1 models using SPENVIS and with similar observations on American, Japanese and Russian satellites.
Article
Dipole representations of the earth's magnetic field have insufficient accuracy for the study of magnetically trapped particles. A coordinate system consisting of the magnitude of the magnetic field B and the integral invariant I was organized adequately, measurements made at different geographic locations. A parameter L = f(B,I) is defined that retains most of the desirable properties of I and that has the additional property of organizing measurements along lines of force. Since the parameter L is the analog of a physical distance in a dipole field (the equatorial radius of a magnetic shell), it usually presents fewer conceptual difficulties than the integral invariant I. (auth)