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21st ECRS
Kosice, 9-12 September 2008
Characteristics of muon flux
distribution in the atmosphere
during solar activity minimum
V.S. Makhmutov1, Y. I. Stozhkov1, G.A. Bazilevskaya1,
N. S. Svirzhevsky1, L. Desorgher2, E. Flueckiger2
1 Lebedev Physical Institute Russian Academy of Sciences, Moscow, Russia
2 Physicalishes Institut, University of Bern, CH-3012 Bern, Switzerland
OUTLINE OF THE TALK:
•
EXPERIMENT & DATA
•
GEANT4 /PLANETOCOSMICS based simulation on
GCR transport in the Earth’s atmosphere
•
EXPERIMENT + SIMULATION
- spatial and spectral feautures
- muon flux distribution in the atmosphere
- latitude effect
Long-term balloon CR measurements in the
Earth’s atmosphere since 1957:
investigations of the variations of primary
CRs in the energy range E ~ 108 - 2В·1010 eV
(Y.I. Stozhkov, this morning)
Additionally, several latitudinal surveys (mainly
in sea expeditions from St-Petersburg to the
Antarctic were carried out during periods of
minima and maxima of solar activity.
1975
1976
Antarctic sea expedition in 1975 - 1976
Geomagnetic Locations of the Balloon CR Measurements in
November 1975 - March 2006
Rc,
mean value
(GV)
Geomagnetic cuttoff rigidity of muon
measurement locations (Rc, GV) and balloon
flight number.
1
1.0
2
2.4
3
4.5
4
7.6
8.0 (2);
7.3 (1);
8.3
7.02 (1);
7.3 (1);
9.44 (1);
11.3
11.09 (1);
11,39 (1); 11.79 (2);
13.6
13.17 (2);
13.43 (1); 13.98 (1);
5
6
7
1.14 (2);
0.88 (2)
2.4 (1)
4.81 (2);
4.7 (1);
4.49 (2)
7.02 (1);
7.64 (2);
9.75 (2)
7.64 (2)
8.0 (2)
12.62 (1)
14.17 (1)
Altitude range is 0-30 km (X ~ 10 – 1000 gсm-2).
•
The detector was composed of 8
gas-discharge Geiger counters STS-6
(Г� - 1.9 СЃm, L - 9.8 СЃm, thickness 0.05 gпѓ—СЃm-2).
• The counters are separated by Pb
absorber (2.5 СЃm, x ~28.4 gпѓ—СЃm-2).
1
2
3
4
Pb
5
6
7
8
• Each counter detects > 0.2 MeV
, > 5 MeV protons and photons
above 20 keV with an efficiency of ≤
Front view of the detector
1 %.
Front view of the detector
• Counters 2 (UP) and 7 (LOW)
constitutes a telescope (coincidence
scheme). A telescope mainly records
> 70 MeV muons and protons, but is
not sensitive to пЃ§-rays
e-
• The sum of the signals from the counter 2
located above the Pb plate is called the CH1
signal,
1
2
3
CH2 - number of coincidence signals in
counters 2 and 7
4
Pb
5
6
7
8
CH3 - number of coincidence signals in
counters 2, 7 and in any 1, 3, 4 –6 or 8
counter (cascade particles record).
We used difference of РЎРќ2 - РЎРќ3 at selected
atmospheric
depth x to
Front view
of the detector
calculate Ntot(С…) = Muons + Protons = N(С…) + Npr(С…).
The proton flux decreases ~ exponentialy in the atmosphere with a
characteristic attenuation lenghts of about С…o=120 gпѓ—СЃm-2,
Npr(С…) = Noпѓ—exp(-С…/С…o), where No=100 cРј-2пѓ—СЃ-1пѓ—СЃСЂ-1 at Rc=13.6 GV).
Finally, muon flux is N(С…) = Ntot(С…) - Npr(С…) !
Muon flux distribution in the atmosphere
at geomagnetic location with Rc=13.6 GV.
1
J (>70 MeV), cm-2 s-1
Rc= 13.6 GV
0,1
0,01
0,001
1
10
100
X, g cm-2
1000
Geant4 / Planetocosmics
based simulation on GCR transport
in the Earth’s atmosphere
we used the Monte Carlo PLANETOCOSMICS code based on Geant4
(Bern University). The code takes into account the following processes:
bremsstrahlung, ionization, multiple scattering, pair production, compton
scattering, photoelectric effect, elastic and inelastic nuclear interaction,
and the decay of particles.
• the GCR proton component is considered as isotropic at the top of the
atmosphere and their energy spectra at solar activity minimum was
described by equation J(E)[#/s*m2*sr*MeV] =D*EО±/(0.01*E+B)4 +
C*exp(- 0.01*E), where E proton kinetic energy [MeV], D=16, B=8, О±=1.3
and C=1.1.
• the primary proton energy range is 500 – 106 MeV was chosen
in simulation.
• we compute the upward and downward fluxes of secondary p, e-, e+,
photons (gamma), pions and muons (пЃ­+, пЃ­-) for 28 atmospheric depth levels
from the ground up to the top of the atmosphere.
Earth’s atmosphere model is a NRLMSISE00
1E-01
I(E), #/cm2В· sВ· РњeV
gР°mma
1E-03
e+
e
1E-05
1E-07
Вµ+,Вµ-
p
1E-09
1E-11
E, MeV
1E-13
1E-01
1E+00
1E+01
1E+02
1E+03
1E+04
1E+05
1E+06
Differential Energy Spectra of Secondaries - p, e-, e+, Вµ +, Вµand gamma at atmospheric depth X=800 gВ·cРј-2 (Rc=13.6 GV).
Angular distribution of > 70 MeV muons
at atmospheric levels X=50 and 100 gВ·cm-2 (Rc=13.6 GV).
1,E-03
douwnword
downwardflux
flux
J, # / cm2*s
1,E-04
upward flux
1,E-05
-1,00
-0,75
-0,50
-0,25
1,E-06
0,00
COS (TETA)
0,25
0,50
0,75
1,00
Distribution of secondaries p, e-, e+, Вµ +, Вµin the atmosphere at Rc=13.6 GV.
0.1
+/-
e
0.01
*
J, #/cm2 СЃ
p
mu
+/-
0.001
0.0001
1
10
100
-2
X, g cm
*
1000
>70 MeV m+ / mu-
1,2
1,15
1,1
0
200
400
600
-2
X, g cm
*
800
1000
Comparison of experimental data and simulation results
1
J (>100 MeV), cm-2 s-1
Rc=13.6 GV
experiment
0.1
+
simulation
0.01
0.001
1
10
100
X, g cm-2
1000
x= 2 0 0 g В·c m
0,16
-2
J , cm
-2
s
-1
Latitude effect of > 70 MeV muon flux
5 0 0 g В·c m
0,08
-2
(~ 5.5 km)
0
0
3
6
9
R
c,
GV
12
15
SUMMARY
• The data on muon flux as function of atmospheric
depth (X~ 10-1000 g cm-2) were obtained during solar
activity minimum (1975/11 – 1976/03; Rc ~ 1 - 14 GV).
*
• On the other hand based on GEANT4 facilities we have
calculated the secondary muon fluxes produced by
GCRs
in the atmosphere at different geomagnetic
locations.
• The experimental and calculation results are in
satisfactory agreement.
Thank you very much
for your attention!
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