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21 st ECRS Kosice, 9-12 September 2008

21 st ECRS Kosice, 9-12 September 2008 Characteristics of muon flux distribution in the atmosphere during solar activity minimum V.S. Makhmutov 1 , Y. I. Stozhkov 1 , G.A. Bazilevskaya 1 , N. S. Svirzhevsky 1 , L. Desorgher 2 , E. Flueckiger 2

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21 st ECRS Kosice, 9-12 September 2008

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  1. 21st ECRSKosice, 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

  2. 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

  3. 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 - 2·1010 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.

  4. 1975 - 1976 Antarctic sea expedition in 1975 - 1976

  5. 1.14 (2); 0.88 (2) 4.81 (2); 4.7 (1); 4.49 (2) 8.0 (2); 7.3 (1); 7.02 (1); 7.64 (2) Geomagnetic Locations of the Balloon CR Measurements in November 1975 - March 2006 Geomagnetic cuttoff rigidity of muon measurement locations (Rc, GV) and balloon flight number. Rc, mean value (GV) 1 1.0 2 2.4 (1) 2.4 3 4.5 4 7.6 5 7.02 (1); 7.3 (1); 7.64 (2); 8.0 (2) 8.3 9.44 (1); 9.75 (2) 6 11.3 11.09 (1); 11,39 (1); 11.79 (2); 12.62 (1) 7 13.6 13.17 (2); 13.43 (1); 13.98 (1); 14.17 (1) Altitude range is 0-30 km (X ~ 10 – 1000 gсm-2).

  6. 3 2 1 5 4 Pb 8 7 6 Front view of the detector • The detector was composed of 8 gas-discharge Geiger counters STS-6 (Ø - 1.9сm, L - 9.8 сm, thickness -0.05 gсm-2). • The counters are separated by Pb absorber (2.5 сm, x~28.4 gсm-2). • Each counter detects > 0.2 MeV e-, > 5 MeV protons and photons above 20 keV with an efficiency of ≤ 1 %. • 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 -rays Front view of the detector

  7. 3 2 1 5 4 Pb 8 7 6 Front view of the detector • The sum of the signals from the counter 2 located above the Pb plate is called the CH1 signal, • CH2 - number of coincidence signals in counters 2 and 7 • 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 СН2 - СН3at selected atmospheric depth x to calculate Ntot(х)= Muons + Protons = N(х) + Npr(х). The proton flux decreases ~ exponentialy in the atmosphere with a characteristic attenuation lenghts of about хo=120 gсm-2, Npr(х) = Noexp(-х/хo), where No=100 cм-2с-1ср-1 at Rc=13.6 GV). Finally, muon flux is N(х)=Ntot(х)-Npr(х) !

  8. Muon flux distribution in the atmosphere at geomagnetic location with Rc=13.6 GV.

  9. Geant4 / Planetocosmics based simulation on GCR transport in the Earth’s atmosphere

  10. 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*Eα/(0.01*E+B)4 + • C*exp(- 0.01*E), where E proton kinetic energy [MeV],D=16, B=8, α=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 (+, -) for 28 atmospheric depth levels • from the ground up to the top of the atmosphere. • Earth’satmosphere model is a NRLMSISE00

  11. 1E-01 gаmma 1E-03 e- + e 1E-05 I(E), #/cm2·s· МeV µ+ , µ- 1E-07 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+, µ+, µ- and gamma at atmospheric depth X=800 g·cм-2 (Rc=13.6 GV).

  12. Angular distribution of > 70 MeV muons at atmospheric levels X=50 and 100 g·cm-2 (Rc=13.6 GV). douwnword flux downward flux upward flux

  13. Distribution of secondaries p, e-, e+, µ+, µ- in the atmosphere at Rc=13.6 GV.

  14. Comparison of experimental data and simulation results

  15. Latitude effect of > 70 MeV muon flux (~ 5.5 km)

  16. 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.

  17. Thank you very muchfor your attention!

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