Content uploaded by Tsvetan Dachev
Author content
All content in this area was uploaded by Tsvetan Dachev on Oct 12, 2018
Content may be subject to copyright.
This article appeared in a journal published by Elsevier. The attached
copy is furnished to the author for internal non-commercial research
and education use, including for instruction at the authors institution
and sharing with colleagues.
Other uses, including reproduction and distribution, or selling or
licensing copies, or posting to personal, institutional or third party
websites are prohibited.
In most cases authors are permitted to post their version of the
article (e.g. in Word or Tex form) to their personal website or
institutional repository. Authors requiring further information
regarding Elsevier’s archiving and manuscript policies are
encouraged to visit:
http://www.elsevier.com/authorsrights
Author's personal copy
Profile 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 Sofia, 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 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.
&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 field 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 flux and spectra of GCR particles are
strongly influenced 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 field. 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 9–10 Earth radii in the anti-sun direction.
The outer belt mostly consists of electrons whose energy is not
larger than 10 MeV. The electron flux 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
Contents lists available at SciVerse ScienceDirect
journal homepage: www.elsevier.com/locate/jastp
Journal of Atmospheric and Solar-Terrestrial Physics
1364-6826/$ - see front matter &2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.jastp.2013.05.015
n
Tel.: +359 878366225.
E-mail addresses: tdachev@bas.bg,tdachev59@gmail.com
Journal of Atmospheric and Solar-Terrestrial Physics 102 (2013) 148–15 6
Author's personal copy
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
74–215 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 flares, sudden sporadic
eruptions of the chromosphere of the Sun. High fluxes 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 field frozen into the
ejected mass. There is a transition (shock) region between the normal
sectored magnetic structure of interplanetary space and the fields
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 flux intensity is
observed to increase dramatically (Mertens et al., 2007). The time
profile of a typical SEP starts off with a rapid exponential increase in
flux, 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 field 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 flares 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 field arises
as a result of the interaction of primary GCR particles with the
Earth's atmosphere. An additional flux of albedo secondary
GCR is observed at altitudes below 3 km, which contributes to
the forming of the flux 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 field, 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 field provides a different kind of shielding, by
deflecting low-momentum charged particles back to space.
Because of the orientation of the geomagnetic field, 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 flux 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 flux is
low, and vice versa. The dynamic balance between the outward
convective flux of solar wind and the inward diffusive flux 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 preamplifier, 2 or more
microcontrollers and flash 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 flux in
the silicon detector. The unit is managed by the microcontrollers
through specially developed firmware. Plug-in links provide the
transmission of the data stored on the flash 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 profiles 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 flight 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 certification flight 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 flown 31
May–16 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 filling the total 1.0 MB
flash 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) 148–156 14 9
Author's personal copy
altitude of 380 km, as part of an EU-financed scientific 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 May–August, 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 preamplifier, 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 defini-
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 coefficient. 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-flight 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 field (Spurný, 2005;Silari et al., 2009).
According to the “neutron induced nuclear counter effect”intro-
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 first 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. Scientific 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.spaceflight.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 flash 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 finally 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 flux and dose rate measured with 1-min
resolution, and the calculated dose to flux ratio or specific dose
(SD) between 25 May and 3 June 2005. Totally 25,405 points are
presented for the dose rate and SD. The flux 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), flux
(dotted line) and SD (heavy line) are plotted in the figure. During
the first 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 flights from Amsterdam
to Samara, Russia and from Samara to Baikonur, Kazakhstan.
The highest dose rate values obtained during the flights were
about 3.2 μGy h
−1
for the first flight and 2.3 μGy h
−1
for the second
T.P. Dachev / Journal of Atmospheric and Solar-Terrestrial Physics 102 (2013) 148–156150
Author's personal copy
flight. The difference is most probably due to different altitudes of
the flights. 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 figure, denoted with the
label “Gamma”were 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 fire before the touchdown of the
capsule.
The recorded maxima in the right side part of Fig. 1 denoted
with the label “In space”were 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 10–300 MeV as in the inner radiation belt
can delivery specific doses per particle always above 1 nGy cm
2
-
particle
−1
, while the specific doses by electrons in the range
1–10 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 figure 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 flights 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 influenced 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
10–11 h in the morning. In the best way the dynamics of the dose
rate and SD or dose to flux 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 fluxes 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 figure 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 profiles of the space radiation exposure between the
Earth surface and free space
Fig. 2 presents the synthesized altitudinal profiles of the
moving averages (over 4 points) of 3 parameters: absorbed dose
rate in μGy h
−1
(heavy line), flux in cm
−2
s
−1
(long (red) dashed
line) and specific dose (SD) in nGy cm
2
particle
−1
(short (blue)
dashed line). On the left side of the figure 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 flights 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, flux 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
airport—D¼0.075 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 flux, 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) 148–156 151
Author's personal copy
3.2.2. Flux minimum at 1.6 km altitude
The next interesting point in Fig. 2 is the flux 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 flights 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
0.03–2.4 GV.
Fig. 2. Variations of the absorbed dose rate, flux and specific dose for altitudinal range from 0.1 to 250,000 km. (For interpretation of the references to color in this figure
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 flux 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
0.026–0.212 0.0028–0.111 0.213–1.15
Flux minimum, 10, 22/03-04/05/20 01 1.6 4 51N, 511W 0.073 0.052 0.386
1.56–1.7 0.049–0.114 0.04–0.072 0.325–0.645
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 flight 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
10.36–10.67 0.85–2.33 0.534–1.068 0.40–0.64
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
18.3–19.01 2.66–5.94 1.28–1.48 0.87–1.22
HotPay2 rocket trajectory, 14 31/12/2008 312 70.71N, 141E 8.99 1.9 1.3
211–376–204 4.8–11.8 1.68 –2.15 0.79–1.89
South-Atlantic Anomaly maximum (Ascending node
orbits), 116 22/02/2008-23/0 6/2009
360 311S, 511W 948 113 2.33 (38 MeV)
347–371 626–119 5 7 6–140 2.04–2.53
South-Atlantic Anomaly maximum (Descending node
orbits), 122 22/02/2008-04/06/2009
361 311S, 511W 1310 154 2.37 (37 MeV)
349–371 882–1640 104–192 2.24–2.51
Inner radiation belt maximum, (Flux maximum),
2, 26/10/2008
2730 15.31S, 1651E 35,489 3279 3.0 (26 MeV)
2707–2753 34,811–36,167 3274–3284 2.95–3.06
Inner radiation belt maximum, (Dose rate max.),
2, 26/10/2008
3007 15.31S, 1651E 37,279 3127 3.28 (24 MeV)
2984–3030 37,254–37,305 3099–3156
Outer radiation belt maximum, (Flux maximum),
7, 26/10/2008
20,300 15.81S, 1491W 44,200 16,021 0.766
20,180–20,436 43,745–44,642 15,976–16,053 0.757–0.773
Outer radiation belt maximum, (Dose rate max.),
8, 26/10/2008
21,260 15.81S, 1491W 46,090 14,978 0.86
21,111–21,409 42,462–47,132 13,460–15,539 0.823–0.883
Free space, 8710, 06/11/2008 230,000 12.87 3.16 1.13 (169MeV) 0.51–3.25
200,000–
252,000
4.6–41.3 1.71–4.71
T.P. Dachev / Journal of Atmospheric and Solar-Terrestrial Physics 102 (2013) 148–156152
Author's personal copy
The averaged flux 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 flux 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
certification flight from Ft. Sumner, New Mexico, USA up to
37.3 km altitude with 60-s resolution (Benton, 2005). The averaged
flux value observed by us in the altitude range 1.7–2.4 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 flare 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 flight from Prague to New
York at an altitude of 35,000 ft (10.67 km) (Spurny and Dachev,
2001). The usual dose rates and fluxes observed at this altitude on
flights 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 flux values before, during and after the GLE
are summarized in Table 1.
3.2.4. Civil aircraft flight level at 35,000 ft
At altitudes above the point of minimal flux the dose rate and
flux start to increase rapidly because of the dominant cosmic
radiation component. As seen in Fig. 2 the dose rate and flux in the
altitudinal range 1–12 km gives strong variations of the measured
values. The R-squared value for the flux 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
flux at flight 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 2001–5 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 flight 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 flights from Prague to
New York and Montreal and back were used. Some data cover the
low latitudes by flights 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 figure 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 251E–501E. The maximum dose rates are in the
high latitudes in the longitudinal range 251W–751W. 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 field 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 fluxes and larger dose
rates are observed.
3.2.6. Photzer maximum
The altitude of maximum flux 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 certification
flight 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 first the flux 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 fluxes 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) 148–156 15 3
Author's personal copy
rate and flux 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 profile
As seen in the upper half of Fig. 2 the dose rates and fluxes, stay
at almost fixed low GCR levels up to the bottom side of the IRB
maximum at about 1700 km altitude. This profile 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, flux and SD as moving average
lines. The first 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 flight 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 flux 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 flux 2.0 cm
−2
s
−1
. Close to the apogee of 377 km the measured
dose was 10.18 μGy h
−1
and the flux 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
,
flux¼1.92 cm
−2
s
−1
and SD¼1.3 nGy cm
2
particle
−1
. These much
larger dose rate and flux values are caused by the larger Earth
magnetic field 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 flux values (see Table 1) coincide
well with the latitudinal profiles 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, flux
and SD moving average lines, is denoted with an label “ISS”. Two
short lines below the label present the dose rate and flux 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 flux 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 profile of the ISS descending node
orbits for the time interval mentioned above. Very rough approx-
imations of the dose rate and flux profiles show best results for the
linear fitting of the curves. Nevertheless the exponential fitting is
expected to be the best one. The obtained linear coefficients are for
the dose rate and flux 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
1805–2263 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 fluxes
(Ersmark et al., 2007;Easley, 2007;Chernykh et al., 2008) the
ascending orbits dose rate and fluxes 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 fluxes 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 fluxes
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
fluxes 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 flux in the ORB was observed at
22,500 km. The comparison of our RADOM ORB flux 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 flux is 3.16 particles cm
−2
s
−1
, while
the real flux 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 flux 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 space”region can be
considered at altitudes above 70,000 km.
3.2.12. Analysis of the SD profile
The SD values seen in Fig. 2 are low at the ground with values
of 0.3–0.5 nGy cm
2
particle
−1
. In the altitudinal range 1–8 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 profile 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 confirmed 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 flight 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) 148–156154
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 388–1572 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 flux (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 2.33–2.37 nGy
cm
2
particle
−1
correspond to protons with energies 37–38 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 first observed
at lower altitudes in the flux values at next in the dose rate values.
The transformation of the SD values to protons energy values gives
26 MeV in the flux 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 0.6–0.8 nGy cm
2
particle
−1
, which
indicates a change of the predominant radiation source from
protons to electrons—as 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 flux of GCR particles exists. It is remarkable that around
the ORB maximum the flux 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 profile 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 unified picture how the
different ionizing radiation sources contribute and build the space
radiation exposure altitudinal profile from the Earth surface up to
the free space. The dose rate and flux 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 first 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.
References
Adams, J.H., Adcock, L., Apple, J., Christl, M., Cleveand, W., Cox, M., Dietz, K.,
Ferguson, C., Fountain, W., Ghita, B., Kuznetsov, E., Milton, M., Myers, J., O'Brien,
S., Seaquist, J., Smith, E.A., Smith, G., Warden, L., Watts, J., 2007. Deep space test
bed for radiation studies. Nuclear Instruments and Methods in Physics Research
Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
579 (21), 522–525 1.
Bagshaw, M., F.A. Cucinotta, 2007. Fundamentals of aerospace medicine cosmic
radiation. Available online at: 〈http:/ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.
gov/20070028831_2007025868.pdf〉.
Bazilevskaya, G.A., Makhmutov, V.S., Stozhkov, Y.I., Svirzhevskaya, A.K., Svirzhevsky,
N.S., Usoskin, I.G., Kovaltsov, G.A., Sloan, T., 2009. Dynamics of the ionizing
particle fluxes in the Earth's atmosphere. In: Proceedings of the 31st ICRC, Lodz,
1-4. Available online at: 〈http:/icrc2009.uni.lodz.pl/proc/pdf/icrc0228.pdf〉.
Bazilevskaya, G.A., Stozhkov, Y.I., Svirzhevskaya, A.K., Svirzhevsky, N.S., 2013.
Cosmic rays and radioactivity in the near-ground level of the atmosphere.
Journal of Physics 409, 012213, http://dx.doi.org/10.1088/1742-6596/409/1/
012213, Conference Series〈http:/iopscience.iop.org/1742-6596/409/1/012213〉.
Beck, P., Berger, T., Reitz, G., Latocha, M., Rollet, S., Zechner, A., Luszik-Bhadra, M.,
Jaksic, A., Vuotila M., 2009. Modeling Microdosimetric Spectra of Absorbed
Dose and Dose Equivalent due to Exposure of Tissue and Silicon at International
Space Station (EuCPADs). 14th WRMISS Workshop on Radiation Monitoring for
the International Space Station, Dublin, 8–10 September 2009.
Benton, E.R., Benton, E.V., 2001. Space radiation dosimetry in low-Earth orbit and
beyond. Nuclear Instruments and Methods in Physics Research Section B: Beam
Interactions with Materials and Atoms 184 (1–2), 255–294.
Benton, E., 2005. Deep Space ICCHIBAN: An International Comparison of Space
Radiation Dosimeters aboard the NASA Deep Space Test Bed.10th Workshop for
Radiation Monitoring on ISS, Chiba, Japan, 7-9 September 2005. Available
online at: 〈http:/wrmiss.org/workshops/tenth/pdf/08_benton.pdf〉.
Berger, M.J., Coursey, J.S., Zucker, M.A., Chang, J., 2013. Stopping-power and range
tables for electrons, protons, and helium ions. NIST Standard Reference
Database 124. Available online at: 〈http:/www.nist.gov/pml/data/star/index.
cfm〉.
Burmeister, S., Beaujean, R., Petersen, F., Reitz, G., 2003. Post Flight, Calibration of
DOSTEL with Heavy Ions During the First and Third, ICCHIBAN Run at HIMAC,
Chiba. 8th Workshop on Radiation Monitoring for the International Space
Station 3–5 September 2003, LBNL, Berkeley, USA. Available online at: 〈http:/
wrmiss.org/workshops/eighth/burmeister.pdf〉.
Chernykh, I., Petrov, V., Shurshakov, V., et al., 2008. Workshop on Radiation
Measurements on ISS, Krakow, Poland, 2008. Available online at: 〈http:/www.
wrmiss.org/workshops/thirteenth/Chernykh.pdf〉.
Dachev, Ts., Tomov, B., Matviichuk, Yu., Dimitrov, Pl., Lemaire, J., Gregoire, Gh.,
Cyamukungu, M., Schmitz, H., Fujitaka, K., Uchihori, Y., Kitamura, H., Reitz, G.,
Beaujean, R., Petrov, V., Shurshakov, V., Benghin, V., Spurny, F., 2002. Calibra-
tion results obtained with Liulin-4 type dosimeters. Advances in Space
Research 30, 917–925 〈http://dx.doi.org/10.1016/S0273-1177(02)00411-8〉.
Dachev, Ts.P., 2009. Characterization of near Earth radiation environment by Liulin
type instruments. Advances in Space Research, 1441–1449, http://dx.doi.org/
10.1016/j.asr.2009.08.007.
Dachev, Ts.P., Tomov, B.T., Matviichuk, Yu.N., Dimitrov, P.G., Bankov, N.G., 2009a.
Relativistic electrons high doses at international space station and foton M2/M3
T.P. Dachev / Journal of Atmospheric and Solar-Terrestrial Physics 102 (2013) 148–156 15 5
Author's personal copy
satellites. Advances in Space Research 44, 1433–1440, http://dx.doi.org/10.1016/
j.asr.2009.09.023.
Dachev, Ts.P., Tomov, B.T., Matviichuk, Yu.N., Dimitrov, Pl.G., Spurny, F., 2009b.
Monitoring lunar radiation environment: RADOM instrument on Chandrayaan-
1. Current Science0011-389196 (4), 544–546.
Dachev, Ts., Plock, O., Tomov, B., Spurny, F., 2010a. Analysis of the GCR dose rate
increase onboard spacecraft and aircraft in the declining phase of the 23rd solar
cycle. Fundamental Space Research, Suplement of Comptes Rend. Acad. Bulg.
Sci., Available online at〈http:/www.stil.bas.bg/FSR2009/pap139.pdf〉.
Dachev, T., Tomov, B., Matviichuk, Y., Dimitrov, P., Ploc, O., Vadawale, S., Goswami, J.,
Angelis, G., 2011c. Characterization of the GCR flux and dose rate during the
2001–2009 time interval. In: Proceedings of Sixth Scientific Conference with
International Participation SES, Sofia, 2–4 November 2010, ISSN 13131-3888,
70-75. Available online at: 〈http:/www.space.bas.bg/sens/SES2010/1_SpPh/10.
pdf〉.
Dachev, Ts.P., Tomov, B.T., Matviichuk, Yu.N., Dimitrov, Pl.G., Spurny, F., Ploc, O.,
Brabkova, K., Jadrnickova, I., 2011a. Liulin type spectrometry-dosimetry instru-
ments. Radiation Protection Dosimetry 144, 675–679.
Dachev, Ts.P., Tomov, B.T., Matviichuk, Yu.N., Dimitrov, Pl.G., Vadawale, S.V.,
Goswami, J.N., Girish, V., Angelis, G., 2011b. An overview of RADOM results
for Earth and Moon radiation environment on Chandrayyan-1 Satellite.
Advances in Space Research 48 (5), 779–791, http://dx.doi.org/10.1016/j.
asr.2011.05.009.
Dachev, Ts.P., Tomov, B.T., Matviichuk, Yu.N., Dimitrov, Pl.G., Bankov, N.G., Reitz, G.,
Horneck, G., Häder, D.-P., Lebert, M., Schuster, M., 2012a. Relativistic electron
fluxes and dose rate variations during April–May 2010 geomagnetic distur-
bances in the R3DR data on ISS. Advances in Space Research 50, 282–292
〈http://dx.doi.org/10.1016/j.asr.2012.03.028〉.
Dachev, Ts., Horneck, G., Häder, D.-P., Lebert, M., Richter, P., Schuster, M., Demets, R.,
2012b. Time profile of cosmic radiation exposure during the EXPOSE-emission:
the R3D instrument. Journal of Astrobiology 12 (5), 403–411 〈http:/eea.space
flight.esa.int/attachments/spacestations/ID501800a9c26c2.pdf〉.
Demets, R., Schulte, W., Baglioni, P., 2005. The past, present and future of Biopan.
Advances in Space Research 36, 311–316 〈http://www.dx.doi.org/10.1016/〉.
Easley, S.M., 2007. Anisotropy in the South Atlantic Anomaly, Master Thesis, Report
Number A618464, 2007. Available online at: 〈http:/www.stormingmedia.us/61/
6184/A618464.html〉.
Ersmark, T., Carlson, P., Daly, E., et al., 2007. Influence of geometry model
approximations on Geant4 simulation results of the Columbus/ISS radiation
environment. Radiation Measurements 42 (8), 1342–1350.
Ghiassi-nejad, M., Mortazavi, S.M.J., Cameron, J.R., Niroomand-rad, A., Karam, P.A.,
2002. Very High Background Radiation Areas of Ramsar. 82. Preliminary
Biological Studies. Health Physics, Iran, pp. 87–93 〈http:/www.probeinterna
tional.org/Ramsar.pdf〉, Available online at.
Häder, D.P., Richter, P., Schuster, M., Dachev, Ts., Tomov, B., Georgiev, Pl., Matvii-
chuk, Yu., 2009. R3D-B2—Measurement of ionizing and solar radiation in open
space in the BIOPAN 5 facility outside the FOTON M2 satellite. Advances in
Space Research 43 (8), 1200–1211, http://dx.doi.org/10.1016/j.asr.2009.01.021.
Heffner, J., 1971. Nuclear radiation and safety in space. M, Atomizdat, 115, in
Russian.
Heynderickx, D., Lemaire, J., Daly, E.J., 1996. Historical review of the different
procedures used to compute the
L
-parameter. Radiation Measurements 26,
325–331.
Kim, M.-H.Y., Angelis, G., De Cucinotta, F.A., 2010. Probabilistic assessment of
radiation risk for astronauts in space missions. Acta Astronautica 68 (7–8),
747–759.
Lantos, P., Fuller, N., 2003. History of the solar particle event radiation doses on-
board aeroplanes using a semi-empirical model and concorde measurements.
Radiation Protection Dosimetry 104 (3), 199–210.
Lantos, P., 1993. The Sun and its effects on the terrestrial environment. Radiation
Protection Dosimetry 48 (1), 27–32.
Makhmutov, V.S., G.A. Bazilevskaya, Y.I. Stozhkov, N.S. Svirzhevsky, A.K. Svirzhevs-
kaya, 2009. Ionisation state of the Earth's stratosphere during powerful solar
proton events. In: Proceedings of the 31st ICRC, Lodz, 2009.
McIlwain, C.E., 1961. Coordinates for mapping the distribution of magnetically
trapped particles. Journal of Geophysical Research 66, 3681–3691.
Mertens, C.J., Wilson, J.W., Blattnig, S.R., Solomon, S.C., Wiltberger, M.J., Kunches, J.,
Kress, B.T., Murray, J.J. 2007. Space weather nowcasting of atmospheric ionizing
radiation for aviation safety, NASA Langley Research Center. Available online at:
〈http:/ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/
20070005803_2007005368.pdf〉.
Nealy, J.E., Cucinotta, F.A., Wilson, J.W., Badavi, F.F., Zapp, N., Dachev, T., Tomov, B.T.,
Semones, E., Walker, S.A., Angelis, G.De, Blattnig, S.R., Atwell, W., 2007. Pre-
engineering spaceflight validation of environmental models and the 2005
HZETRN simulation code. Advances in Space Research 40 (11), 1593–1610,
http://dx.doi.org/10.1016/j.asr.2006.12.030.
Pfotzer, G., 1936. Dreifachkoinzidenzen der Ultrastrahlung aus vertikaler Richtung
in der Stratosphäre. Zeitschrift für Physik A Hadrons and Nuclei, 102. Springer,
Berlin/Heidelberg, pp. 23–40 〈http://dx.doi.org/10.1007/BF01336829〉, Available
online at.
Ploc, O., Spurny, F., Dachev, Ts.P., 2011. Use of energy depositing spectrometer for
individual monitoring of aircrew. Radiation Protection Dosimetry 144 (1–4),
611–614 〈http:/rpd.oxfordjournals.org/content/early/2010/12/24/rpd.ncq505.
abstract〉.
Regener, E., Pfotzer, G., 1935. Vertical intensity of cosmic rays by threefold
coincidences in the stratospher. Nature 136, 718–719, http://dx.doi.org/
10.1038/136718a0.
Reitz, G., Beaujean, R., Benton, E., Burmeister, S., Dachev, T., Deme, S., Luszik-Bhadra,
M., Olko, P., 2005. Space radiation measurements on-board ISS-The DOSMAP
experiment. Radiation Protection Dosimetry 116 (1–4), 374–379.
Shea M.A., Smart D.F., 2001. Vertical cutoff rigidities for cosmic ray stations since
1955. In: 27th International Cosmic Ray Conference. Contributed Papers, 10,
4063–4066.
Silari, M., Agosteo, S., Beck, P., Bedogni, R., Cale, E., Caresana, M., Domingo, C.,
Donadille, L., Dubourg, N., Esposito, A., Fehrenbacher, G., Fernández, F.,
Ferrarini, M., Fiechtner, A., Fuchs, A., García, M.J., Golnik, N., Gutermuth, F.,
Khurana, S., Klages, Th., et al., 2009. Intercomparison of radiation protection
devices in a high-energy stray neutron field. Part III: Instrument response.
Radiation Measurements 44 (7–8), 673–691.
Simpson, J.A., 1983. Composition and origin of cosmic rays. In: Shapiro, M.M. (Ed.),
NATO ASI Series, Series C Mathematical and Physical Sciences, 107. Reidel,
Dordrecht.
Slaba, T.C., Blattnig, S.R., Badavi, F.F., Stoffle, N.N., Rutledge, R.D., Lee, K.T., Zapp, E.N.,
Dachev, T.P., Tomov, B.T., 2011. Statistical validation of HZETRN as a function of
vertical cutoff rigidity using ISS measurements. Advances in Space Research 47,
600–610, http://dx.doi.org/10.1016/j.asr.2010.10.021.
Sloan, T., Bazilevskaya, G.A., Makhmutov, V.S., Stozhkov, Y.I., Svirzhevskaya, A.K.,
Svirzhevsky, N.S., 2009. Ionization in the atmosphere, comparison between
measurements and simulations. Atmospheric and Oceanic Physics, Available
online at〈http:/arxiv.org/abs/1012.0250v2〉.
Spurny, F., Dachev, T.P., 2009. New results on radiation effects on human health.
Acta Geophysica 57 (1), 125–140, http://dx.doi.org/10.2478/s11600-008-0070-
6.
Spurny, F., Dachev, T., 2001. Measurements in an aircraft during an intense solar
flare, ground level event 60, on the 15th of April 2001 letter to the editor of.
Radiation Protection Dosimetry 95 (3), 273–275 〈http:/rpd.oxfordjournals.org/
content/95/3/273.full.pdf+html〉.
Spurny, F., Dachev, T., 2002. On board aircrew dosimetry with a semiconductor
spectrometer. Radiation Protection Dosimetry 100, 525–528 〈http:/rpd.oxford
journals.org/cgi/content/abstract/100/1-4/525〉.
Spurný, F., 2005. Response of a Si-diode-based device to fast neutrons. Radiation
Measurements 39 (2), 219–223 〈http://dx.doi.org/10.1016/j.radmeas.2004.05.
006〉.
Stozhkov, Y.I., Svirzhevsky, N.S., Bazilevskaya, G.A., Krainev, M.B., Svirzhevskaya, A.
K., Makhmutov, V.S., Logachev, V.I., Vashenyuk, E.V., 2011. Cosmic rays in the
stratosphere in 2008–2010. Astrophysics and Space Sciences Transactions 7,
379–382 〈http://www.astrophys-space-sci-trans.net/7/379/2011/〉.
Tomov, B., Dimitrov, Pl., Matviichuk, Yu., Dachev, Ts., 2008. Galactic and solar
cosmic rays study by ground and rocketborne space radiation spectrometers-
dosimeters-Liulin-6R and Liulin-R. In: Proceedings of Fundamental Space
Research Conference, ISSBN 978-954-322-316-9, 252-257. Available online at:
〈http:/www.stil.bas.bg/FSR/PDF/TOP5Tomov_Borislav2242058.pdf〉.
Uchihori, Y., Kitamura, H., Fujitaka, K., Dachev, Ts.P., Tomov, B.T., Dimitrov, P.G.,
Matviichuk, Y., 2002. Analysis of the calibration results obtained with Liulin-4J
spectrometer-dosimeter on protons and heavy ions. Radiation Measurements
35, 127–134 〈http:/www.sciencedirect.com/science/article/pii/S135044870100-
2864〉.
Uchihori, Y., Kitamura. H., Fujitaka. K., Yasuda. N., Benton, E., 2003. Comparison of
results from the 1st ICCHIBAN experiment and current status of the 3rd
ICCHIBAN experiment. In: 8th Workshop on Radiation Monitoring for the
International Space Station 3–5 September, LBNL, Berkeley, USA. Available
online at: 〈http:/wrmiss.org/workshops/eighth/uchihori.pdf〉.
Wahl, L.E., 2010. Environmental radiation. Available online at: 〈http:/hps.org/
documents/environmental_radiation_fact_sheet.pdf〉, Fig. 1., reprinted from
http://www.ncrppublications.org/Reports/160).
Wilson, J.W., Maiden, D.L., Goldhagen, P., Tai, H., Shinn, J.L., 2003. Overview of
Atmospheric Ionizing Radiation (AIR). NASA Langley Research Center, Available
online at.
Wilson, J.W., Nealy, J.E., Dachev, T., Tomov, B.T., Cucinotta, F.A., Badavi, F.F., Angelis,
G., de Leutke, N., Atwell, W., 2007. Time serial analysis of the induced LEO
environment within the ISS 6A. Advances in Space Research 40 (11), 1562–1570,
http://dx.doi.org/10.1016/j.asr.2006.12.030.
Zhang, L., Mao, R., Zhu, R., 2011. Fast neutron induced nuclear counter effect in
Hamamatsu silicon PIN diodes and APDs. IEEE Transactions on Nuclear Science
58 (3), 1249–1256 〈http:/www.hep.caltech.edu/ zhu/papers/11_tns_fast_neu
tron.pdf〉.
T.P. Dachev / Journal of Atmospheric and Solar-Terrestrial Physics 102 (2013) 148–156156