Cosmic rays studied with a hybrid high school detector array

Abstract

C osmic rays" is the generic name for different types of particles that hit the Earth's atmosphere with about the speed of light, varying in energy over a wide range. It was found that with increasing energy the number of cosmic rays arriving at the Earth drops sharply, see the flux-power spectrum in Fig. 1. The cosmic ray (CR) composition consists of protons (86%), α-particles (11%), nuclei of heavier elements (1%), electrons (2%) and neutrinos (<1%) [1]. Most cosmic rays up to Gev energies are thought to be produced in our galaxy by stars and beyond these energies in supernova remnants (SNR); however the origin of the highest energetic particles is still unclear. An upper limit to the energy has been observed around 100 EeV (GZK cutoff [2], [3]). A uniform distribution on the sky strongly indicates that the highest energy CRs are produced in a variety of distant extra-galactic sources. Source candidates are collimated relativistic matter streams (jets) associated with galaxies emitting powerful radio emission (radio galaxies), as well as radio-loud young galaxies called quasi-stellar objects (quasars). Furthermore, bursts of high frequency electromagnetic emission called gamma ray bursts (GRBs) and magnetars, which are very compact stars with strong magnetic fields, are also candidates for the origin of the high energy CRs since they may be capable of the extreme particle acceleration required.In the Earth's atmosphere these CRs initiate a cascade of particle collisions in which a large multiplicity of secondary particles of all kinds are produced. The creation and annihilation of particles in the cascade establishes a so-called air shower pancake traveling through the atmosphere. Additionally, the charged particles in the pancake -mainly the electrons and their counterparts the positrons -get deflected in the Earth's magnetic field and emit beamed coherent radiation called geosynchrotron emission [4]. The number of particles in the air shower and the peak voltage of the radio emission detectable on the ground depend approximately linearly on the energy of the primary particle. The radio emission increases with increasing angle between the cosmic ray trajectory and the Earth's magnetic field [5]. Why air showers?Every second, one low energy cosmic ray particle is hitting every square meter of the Earth's atmosphere. The resulting shower is attenuated in the atmosphere before reaching the ground and can, however, only be detected directly by a detector on a plane or balloon. The latter is the way cosmic rays have been discovered in 1912 by Victor F. Hess [6]. High energy cosmic rays hit an area of a square kilometer only once per year, thus requiring an expensive detector covering a large area for an effective measurement. On the other hand, from the air shower initiated by the primary particle, several hundred thousands of particles reach the ground within a radius of a few hundred meters, depending on the energy of the cosmic ray. Therefore, analyzing the shower to infer information ••• " ᭡ Fig. 1: Cosmic ray...