Download Ionizing particle fluxes in the near

32 ND I NTERNATIONAL C OSMIC R AY C ONFERENCE , B EIJING 2011
Ionizing particle fluxes in the near-ground atmosphere
BAZILEVSKAYA G.A., K RAINEV M.B., K VASHNIN A.N., M AKHMUTOV V.S., S TOZHKOV
S VIRZHEVSKAYA A.K., S VIRZHEVSKY N.S.
Lebedev Physical Institute, RAS, Leninsky prospect, 53, 119991, Moscow, Russia
[email protected]
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Y.I.,
Abstract: Nowadays, a role of ionizing particles in the atmospheric processes is widely discussed. Especially important
for the weather and climate formation are the processes in the troposphere, in particular, at altitude below 5 km. Measurements of charged particle fluxes at different levels of the atmosphere are performed by the Lebedev Physical Institute at
the polar and middle latitudes since 1957. There are also results of X-ray flux measurements in the atmosphere. Several
latitude surveys were fulfilled. At altitudes above 3 km the results of observations are successfully reproduced by the
Monte-Carlo simulations of cosmic ray propagation through the atmosphere. At the near-ground levels the calculations
predict lower fluxes. To some extent, it may be explained by a contribution of natural radioactivity in the charged particle
flux and by cosmic ray albedo due to transition effect between the air and an underlying surface. This work based on the
results of observations tries to separate contributions of cosmic rays and radioactivity in the near-ground atmosphere.
Keywords: Cosmic rays, radioactivity, near-ground atmosphere
1 Introduction
cosmic rays and radioactivity. We focus on the atmospheric
depth more than 700 g/cm2 (altitude <≈3 km).
Galactic cosmic rays (GCRs) impinge upon the Earth’s atmosphere and create the cascades of secondary particles
while interacting with the air nuclei. Geomagnetic field
and the atmosphere are the energy analyzers of particles:
higher energy is required to access the lower latitudes as
well as primary particles of higher energy provide the particle fluxes at lower layers of the atmosphere. Time series of
charged particle fluxes at altitudes above ≈20 km (residual
atmospheric pressure P =55 g/cm2 ) correlate very well with
the GCRs arriving at the same latitude (correlation coefficient r ≈0.98), but this correlation decreases with increase
of P . At altitudes below ≈3 km r ≤ 0.2. That means influence of atmospheric factors and natural radioactivity on
the ionization in the lower atmosphere. In this work, we
use the data of the long-term observations of ionizing particle fluxes in the atmosphere undertaken by the Lebedev
Physical Institute, Russia, (LPI) from IGY (1957) to now
at several latitudes [1]. Monte-Carlo simulations of particle
fluxes fulfilled by L. Desorgher [2], and V.S. Makhmutov
[3] reproduce fairly well the observed values at altitudes
between 4 and 22 km, but predict significantly lower fluxes
in the near-ground level [4]. It is rather expected since calculations do not take into account a soil radioactivity available in the near-ground air layer. However, the discrepancy
is also kept in the data of Antarctic measurements where
the radioactivity should be depressed by the ice cover. The
aim of this work is to analyze the observational data available and to attempt to separate contributions of secondary
2 Observations
The LPI group uses the radiosondes with particle detectors
which are carefully preflight calibrated during the whole
period of observations. Features of the detectors are given
in Table 1.
Table 1: Threshold energy (MeV) for ionizing particle detectors being lifted to the atmosphere.
Detector
Protons Electrons
X-rays
Geiger tube
5
0.2
0.02–0.5
Telescope of 2 tubes
30
5
none
NaI(Tl) scintillator
8.75
0.8
0.02
All detectors record charged particles including muons
with efficiency of about 100%. Geiger counter is sensitive to X-rays but with efficiency <1%. Telescope is not
sensitive to X-rays at all.
The standard radiosonde contains a telescope of two Geiger
tubes with a 0.05 g·cm−2 steel walls and a 2 g·cm−2 thick
Aluminum filter inserted between the counters. Count rates
of both an omnidirectional counter and a telescope are
recorded throughout the atmosphere and transmitted to the
ground-level receiver. This work employs the data of following observations:
Vol. 11, 330
BAZILEVSKAYA et al. I ONIZING PARTICLE FLUXES IN THE NEAR - GROUND ATMOSPHERE
Omnidirectional flux of ionizing particles
10
Mi76
Mo76
Mo90
Mu76
GEANT4 [2]
1
-2 -1
GEANT4 [3]
F, cm s
(1) several times a week balloon launching at Murmansk
(geomagnetic cutoff Rc =0.6 GV), Moscow (Rc =2.4 GV)
during 1957-2010, and Mirny (Antarctica, Rc =0.03 GV)
during 1963-2009;
(2) sea survey with the same devices undertaken in 1987
[5];
(3) X-ray measurements with scintillation counters in
1965-1969 at several latitudes [6];
(4) high precision measurements with a balloon-borne
instrument B1 consisting of 240 Geiger tubes of the
same type supplemented with scintillation counters (highlatitude Arkhangelsk and mid-latitude Saratov regions) [7].
It should be emphasized that the data of telescopes are free
from the radioactivity contribution and that radioactivity is
low over the oceans and in the Antarctic.
0.1
0.01
0
200
400
600
800
1000
2
Atmospheric depth, g/cm
3 Ionizing radiation in the near-ground atmosphere
Figure 1 demonstrates the results of observations of the particle flux as measured by a LPI omnidirectional counter in
1976 and simulations [2, 3]. Here we focus on disagreement between the calculated and observed values at atmospheric depth more than 700 g/cm2 . It should be noted that
some inconsistency between the simulated results [2] and
[3] is available which probably may be due to different primary GCR spectra used. However, the [3] fluxes should be
higher than those of [2] because the former refer to minimum and the latter to the maximum of solar activity. It is
really the case for high altitudes, but at P > 700 g/cm2
the situation is opposite. Nevertheless, both sets of simulation show the decline relative to observations. On the other
hand, it is clear from Fig. 1 that the observational data
taken at Moscow region in 1976 (min of solar activity) and
in 1990 (max of solar activity) coincide for P > 700 g/cm2
within the error bars for the yearly averaged data. Thus, in
order to get better accuracy, thereafter we average the observational data over the whole period of observation, i.e.
more than 50 years for the Murmansk and Moscow regions
and 48 years for Mirny (in total, more than 83,000 balloon
launchings).
The results of measurements of omnidirectional radiation
at P > 700 g/cm2 are summarized in the upper panel of
Fig. 2. The results of the sea survey are averaged over all
latitudes of the northern and southern hemispheres since
no latitude effect was found at P > 700 g/cm2 . More than
300 launchings from a ship were treated. In spite of not
high accuracy a trend toward lower particle fluxes is seen
comparing with observations over land. Natural Earth’s radioactivity should lead to particle flux enhancement in the
near-ground level. However, the data of the permanent observations at Murmansk, Moscow and Mirny show somewhat retarded decrease but no clear enhancement down to
P ≈ 950 g/cm2 . Statistics is not sufficient at lower altitudes. Such enhancements are seen in the data of B1 at
Figure 1: Average fluxes of charged particles in the atmosphere: observational and simulated results.
P > 950 g/cm2 due to contribution of the ground radioactivity [7].
Lower panel of Fig. 2 presents the results of X-ray measurements. The X-ray fluxes at Murmansk and Moscow
regions do not differ at P > 700 g/cm2 and are averaged
in Fig. 2 (lower panel). Data taken over Antarctica (Mirny)
prove that radioactivity is low. Both upper and lower panels
argue that the radioactivity at P > 950 g/cm2 depends on
the site of measurements and varies with time. It confirms
the results [8].
Consideration of the telescope data (Fig. 3, upper panel)
shows that the results at various sites of measurements coincide with each other within the error bars and do not
contradict the value obtained at the ground with account
of barometric effect [7]. Ratio of count rates of an omnidirectional counter and a telescope k depends on particle composition and their angular distribution. These ratios are calculated for each month and then averaged over
time. This procedure gives more precise k than if the ratio
would be taken for averaged data of omnidirectional counters and telescopes. The k behaviour at P > 400 g/cm2
is expected to depend on P weakly because the cosmic
ray initiated cascades are just absorbed in this part of the
atmosphere and energy spectra are equilibrium. Value of
k increases at P > 750 g/cm2 being indicative of existence of some additional particle flux with properties other
than those of cosmic rays. However, k of Murmansk and
Moscow are consistent down to 900 g/cm2 while the Mirny
k is slightly lower. At P > 900 g/cm2 the k values are different for Murmansk, Moscow, and Mirny. This is due to
the ground radioactivity which depends on the site and is
lower at Mirny. In the P range between 600 - 750 g/cm2 ,
where only small contribution of radioactivity is expected,
k is almost constant (see lower panel of Fig. 3) and may
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32 ND I NTERNATIONAL C OSMIC R AY C ONFERENCE , B EIJING 2011
40
0.1
0.09
Sea_surv87
Mo 1960-2009
Mu 1957-2010
Mu 1960-2009
Mi 1963-2010
0.08
Count rate, min -1
2 -1
F, cm- s
0.07
B1 Saratov
B1 Arkhang
0.06
0.05
Sea survey 1987
Ground
20
10
0.04
0.03
700
Mi 1964-2008
30
Mo 1957-2010
750
800
850
900
950
1000
1050
0
600
2
Atmospheric depth, g/cm
700
1965-69
X-ray B1
Ratio of omnidir to telescope
-1
0.8
-2
1000
4.75
Mirny 1967
F, cm s
900
5
equat,68-69
1
0.6
0.4
0.2
0
700
800
Atm . depth, g/cm 2
1.2
4.5
4.25
4
3.75
Mu1960-2009
3.5
Mo 1960-2009
Mi 1964-2008
3.25
Extrapolation
750
800
850
900
950
1000
1050
3
600
2
Atmospheric depth, g/cm
700
800
900
1000
Atm. depth, g/cm 2
Figure 2: The results of ionizing particle observations at
different sites. Upper panel: omnidirectional fluxes of
charged particles, lower panel: X-rays.
be extrapolated to larger P values as shown by the dotted
line. Knowing k(P ), it is possible to get the omnidirectional particle flux using the data of telescopes. This flux
may represent the omnidirectional particle flux due to cosmic rays in the lower atmosphere. The result is shown on
the upper panel of Fig. 2 by the grey circles alongside with
the similar result from [7] (grey solid curve). Note that the
both sets are in excellent agreement.
4 Discussion and conclusion
Upper panel of Fig. 4 demonstrates the observed omnidirectional fluxes (averaged over Murmansk, Moscow, Mirny
results and Arkhangelsk results down to P = 1010 g/cm2 ),
the expected from cosmic rays flux (obtained from telescope data) and the results of simulation [2, 3]. It is clear
that the measured fluxes are higher than both the expected
from cosmic rays and simulated fluxes. Displayed on the
middle panel of Fig. 4 are differences between the observed
Figure 3: Upper panel: charged particle fluxes as measured
with telescopes. Lower panel: ratio of count rates of an
omnidirectional counter and of a telescope.
fluxes and the GEANT 4 results (symbols and line 1) and
the observed fluxes and expected from cosmic rays (symbols and lines 2, 3). Bottom panel of Fig. 4 presents the
result of subtraction of X-ray fluxes in the Antarctic (where
low if any radioactivity is expected) from the values of Xray fluxes measured by B1 [7]. The X-ray fluxes behave
similar to charged particles at P > 750 g/cm2 (curves 4
and 5), but ratios of X-ray fluxes to charged particle fluxes
Rxc are different. Between 400 and 600 g/cm2 i.e. for
GCR secondaries, Rxc decreases from 9.5 to 8.8; it is almost constant for populations presented by curves 2 and 4
in Fig. 4 (average Rxc = 33 ± 0.7), then Rxc increases
rapidly toward the ground level and reaches values > 200,
although the latter changes depending on time and site.
An excess of the observed fluxes over expected from cosmic rays consists of two populations. That at P > 950
g/cm2 (lines 3 and 5) is certainly due to the ground radioactivity, the origin of the excess fluxes between 750 and
950 g/cm2 (lines 2 and 4) is not so clear. Charakhchyan
Vol. 11, 332
BAZILEVSKAYA et al. I ONIZING PARTICLE FLUXES IN THE NEAR - GROUND ATMOSPHERE
0.09
G4, Desorgher
G4, Makhm utov
Observ.
B1 Arkhangelsk
Cosm ic rays
0.08
0.07
Flux, cm-2s-1
tain albedo particles which we did not account for while
calculated expected omnidirectional flux from the data of
telescopes. Unfortunately, the present simulations do not
consider ionizing particle propagation near/through the airground boundary. It is necessary to perform such simulations to reproduce cosmic ray albedo from the underlying
surface.
0.06
0.05
Acknowledgements
0.04
This work was partially supported by the Russian Foundation for Basic Research (grants 10-02-00326a, 11-0200095a, 11-02-10018k), and by the Program ”Neutrino
Physics and Astrophysics” of the Presidium of the Russian
Academy of Sciences. This work was to great extent stimulated by the ISSI project ”Study of cosmic rays influence
upon atmospheric processes”.
0.03
0.02
700
800
900
1000
Atm. depth, g/cm2
0.014
Observ-calc. G4
Observ-cosm .rays
0.012
Arkhangelsk
Flux, cm-2s-1
0.01
References
0.008
3
1
0.006
0.004
0.002
2
0
700
800
900
1000
Atm . depth, g/cm 2
1.4
Flux, cm-2s -1
1.2
1.0
0.8
5
0.6
0.4
4
0.2
0.0
700
800
900
Atm. depth, g/cm 2
1000
Figure 4: Upper panel: Omnidirectional fluxes of observed,
expected from cosmic rays, and calculated charged particles. Middle panel: difference between observed and caculated fluxes (line 1) and observed and expected from cosmic rays fluxes (lines 2 and 3) of charged particles. Lower
panel: the same as lines 2 and 3 of middle panel but for
X-rays.
[1] Stozhkov Y.I., Svirzhevsky N.S., Bazilevskaya G.A.,
Kvashnin A.N., Makhmutov V.S. Svirzhevskaya A.K.,
Adv. Space Res., 2009, 44: 1124-1137.
[2] Desorgher L., Flueckiger E.O., Gurtner M., Buetikofer
R., Int. J. Modern Phys., 2005, A20(29): 6802-6804.
[3] Bazilevskaya G.A., Makhmutov V.S., Stozhkov Y.I.,
Svirzhevskaya
A.K.,
Svirzhevsky
N.S.,
Usoskin I.G.,
Kovaltsov G.A.,
Sloan T.,
in:
Proc. 31st ICRC Lodz, Poland, 2009.
http://icrc2009.uni.lodz.pl/proc/pdf/icrc0228.pdf.
[4] Sloan T., Bazilevskaya G.A., Makhmutov V.S.,
Stozhkov Y.I., Svirzhevskaya A.K., Svirzhevsky N.S.,
Astrophys. Space Sci. Transact., 2011, 7(1): 29-33.
[5] Golenkov A.E., Svirzhevskaya A.K., Svirzhevsky
N.S., Stozhkov Yu.I., in: Proc. 21st ICRC, Adelaide,
Australia, 1990 7(1): 14-17.
[6] Charakhchyan A.N., Bazilevskaya G.A., Kvashnin
A.N., Charakhchyan T.N., Trudy FIAN, 1976, 88, 5179, (in Russian).
[7] Charakhchyan A.N., Bazilevskaya G.A., Krasotkin A.F., Charakhchyan T.N., Geomagnetizm i
Aeronomiya, 1976, 15(2), 197-202, (in Russian).
[8] Warburton J.A., Fookes R.A., Watt J.S., Nature, 1965,
207 (4993), 181, doi:10.1038/207181a0.
et al. [7] ascribed it to the radioactivity of the atmosphere.
Now it seems more appropriate to explain it as cosmic ray
albedo from the ground due to transition effect between the
air and an underlying surface.
Difference between the observed and calculated particle
fluxes at P = 750-950 g/cm2 is not explained by the ground
radioactivity which contributes to lower altitudes. It may
refer to the albedo effect since the telescope data also con-
Vol. 11, 333