[en] A fesibility study to explore the capability of the WILLI detector to observe the solar events/activity by recording the muon intensity at ground level is presented.The WILLI detector, set up in National Institute of Physics and Nuclear Engineering, Bucharest, is a 1 m² incident area sampling calorimeter. It can measure simultaneously muon events with the muon energy ≥0.4 GeV and, if the muons are stopped in the detector, and muon energy between 0.4< E_μ<0.6 GeV, if the muons pass the minimum of 2 plates of the detector stack.Taking into account muon events with energy ≥0.4 GeV, a modulation of the muon intensity as a diurnal variation is observed. Muon events for a smaller energy range (0.4-0.6 GeV) seem to exhibit an aperiodic variation of the muon intensity, which could be correlated with magnetic activity indicated by the planetary K_p index.

[en] Precise measurements of the muon flux are important for different practical applications, in environmental studies and for the estimation of the water equivalent depths of underground sites. A first configuration of the mobile detector was composed of two 1 m² scintillator plates, each viewed by wave length shifters and read out by two PMTs (Photomultiplier Tubes). A more recent configuration of the mobile muon detectors, set up in IFIN-HH, Romania, consists of two 1 m² detection layers, each one including four 1×0.25 m² large scintillator plates. The light output in each plate is collected by twelve optical fibers and then read out by one PMT. The calibration has been made by comparing the energy deposit spectrum of minimum ionizing particles with the spectra simulated with the GEANT4 code. The device is used to measure the muon flux on different locations at the surface and underground.

[en] The WILLI detector, installed in the National Institute of Physics and Nuclear Engineering - Horia Hulubei Bucharest has been devised for studies of atmospheric muons, in particular of the muon charge ratio. We report on the results of studies for various muon energies (pμ < 1 GeV/c). The results are compared with Monte-Carlo simulations performed with the CORSIKA and GEANT codes. We are exploring the potential of a small detector array to be set up nearby the actual WILLI detector for triggering the muon charge ratio measurements by Extended Air Shower (EAS) events

[en] A new mobile detector was developed in IFIN-HH, Romania, for measuring muon flux at surface and in underground. The measurements have been performed in the salt mines of Slanic Prahova, Romania. The muon flux was determined for 2 different galleries of the Slanic mine at different depths. In order to test the stability of the method, also measurements of the muon flux at surface at different altitudes were performed. Based on the results, the depth of the 2 galleries was established at 610 and 790 m.w.e. respectively.

[en] The primary and secondary components of the cosmic radiation are influenced by the geomagnetic field. This leads - in addition to the variation with the zenith angle - to an azimuth dependence, in particular of the ratio of positive and negative muons, pronounced as East-West effect of muon charge ratio for low energy muons. The compact scintillator detector arrangement, WILLI, able to register incident muons with different azimuth and zenith angles (E< 1 GeV), has been used to study the azimuth dependence of the muon charge ratio. Positive and negative muons are discriminated by observing the different lifetimes when being stopped in matter, in the WILLI case by Al absorbers. We are considering the development of a mini array, installed close to the WILLI detector, for triggering the muon charge ratio measurements in extended air shower events

[en] The WILLI detector, built in IFIN-HH, Bucharest, is used to measure the muon flux and the muon charge ratio at low energy (< 1 GeV/c). The results are compared with detailed Monte-Carlo simulations performed with the CORSIKA code which takes into account the influence of the geomagnetic field. Two different hadronic interaction models (DPMJET and QGSJET) are used for the simulations. The semi-analytical formulae of Nash and Gaisser are also compared with experimental data and with Monte-Carlo simulations using DPMJET model. An investigation of the azimuth and zenithal variation of the muon flux is performed. Good agreement between the simulations and the experimental data is reported. The comparison between the simulations using DPMJET and QGSJET models indicates only small differences between them. To check the hadronic interaction models for high energy interactions, new experimental facilities are under development for getting new experimental data.

[en] A concept of an experiment for investigating the muon charge ratio in EAS has been proposed based on the existing WILLI detector designed for measurements of the atmospheric muon charge ratio. A mini-array surrounding WILLI for measuring EAS is presently under construction. This array will serve as a core-finder system consisting of 12 stations of 1 m², each unit containing 4 plastic scintillator sheets (50x50x3) cm³, seen by wave length shifters and 2 photomultipliers. Using CORSIKA and GEANT codes, simulation studies have been performed for H and Fe generated showers (10¹⁴-10¹⁵) eV to optimize the configuration of the WILLI-EAS arrangement. By this device, measurements of the charge ratio can be performed for both in parallel, inclusive muons and EAS muons.

[en] We report in this paper on an analysis of 20 months of data taken with LOPES. LOPES is radio antenna array set-up in coincidence with the Grande array, both located at the Karlsruhe Institute of Technology, Germany. The data used in this analysis were taken with an antenna configuration composed of 30 inverted V-shape dipole antennas. We have restricted the analysis to a special selection of inclined showers - with zenith angle θ>40^∘. These inclined showers are of particular interest because they are the events with the largest geomagnetic angles and are therefore suitable to test emission models based on geomagnetic effects.The reconstruction procedure of the emitted radio signal in EAS uses as one ingredient the frequency-dependent antenna gain pattern which is obtained from simulations. Effects of the applied antenna model in the calibration procedure of LOPES are studied. In particular, we have focused on one component of the antenna, a metal pedestal, which generates a resonance effect, a peak in the amplification pattern where it is the most affecting high zenith angles, i.e. inclined showers. In addition, polarization characteristics of inclined showers were studied in detail and compared with the features of more vertical showers for the two cases of antenna models, with and without the pedestal.

[en] In the present study, we analyze the radio signal from inclined air showers recorded by LOPES-30 in coincidence with KASCADE-Grande. LOPES-30 consists of 30 East-West oriented digital antennas, which are amplitude calibrated by an external source. Radio emission from air showers is considered a geomagnetic effect. Inclined events provide a larger range of values for geomagnetic angle (angle between shower axis and geomagnetic field direction) than vertical showers and thus more information on the emission processes can be gathered. In order to have the geometry of the air shower we use the reconstruction provided by the KASCADE-Grande particle detectors array. Analyzing events observed by both LOPES and the extended part of the KASCADE array, Grande, gives the possibility to test in particular the capability and efficiency of radio detection of more distant events. The results are compared with a previous analysis of inclined events recorded by the initial 10 antenna set-up, LOPES-10, in coincidence with the Grande array.