Cosmic rays are high energetic particles like protons, electrons, ions created a large variety of different processes in the universe. Particles up to a few billion eV come usually from the sun; particles with energies above are caused by sources within our galaxy or even beyond.
While entering the higher atmosphere these particles do react with the atoms of our atmosphere creating showers of new particles like muons, protons and neutrons. About 63% of the flux of cosmic rays are Muons. Muon are electrically charged particles which are created by processes outside of earth atmosphere with a relatively high energy. Passing through an scintelator they create an rather intensive signal compared to the background radiation which is observed by particle detector as well. Specifically the electrically charged particles are easy to observe by using plastic scintillator and photo multipliers.
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The fact that CR particles are interacting with the atmosphere is providing the arguments to identify them. Lets assume that the secondary particles like muons are absorbed following a simple Beer Lambert Law, then the intensity of the CR particles will depend on the angle of the entry measured against the surface normal since the path length of such articles become longer with with increasing entry angle.
This leads to the following dependency between entry angle and intensity:
This gives a first estimate how the intensity of cosmic rays depends on the entry angle dependency of cosmic rays.
In order to measure the intensity of CR depending on the entry angle, the detector needs to be sensitive to directions.
The idea is to operate two particle detectors in a coincident setup in order to detect particles which are passing through both detector volumes by correlating the signals of both detectors.
Since cosmic rays and the corresponding secondary particles are of quite high energy, a particle passing through both detectors will cause in both detectors a signal at virtually the same time. Using this coincidence we can count the number of particles passing through both detectors at the same time.
Each detector comprises of an PMT (R1477 from Hamamatsu) and a plastic scintillator (BC412). Charged particles passing through the plastic scintillator will cause impulses of light to be emitted which is detected by the PMT's. In order to sort out low energetic events, the signal from the PMT's is fed into adjustable discriminators (Schmidt Triggers). The discriminator level is set manually in such a way that only the events with the highest amplitudes are taken into accounts. The output of both PMT's is fed into the correlation circuit which is implemented by means of a simple AND logic module.
An experiment controller is connected to the PMT and the discriminators which allows to adjust the PMT gain and discriminator levels manually via the front plane of the controler or remotely from a computer. The experiment controller has been specificially designed for this purpose my using a PSoC from Cypress.
The data analysis is has been done a few weeks after the collection of the data. For this purpose the relevant data sets are exported from the SVN into the file system and loaded in the an relational database (MimerSQL). Additional information like the air pressure, the data of the NMDB are imported from the Internet into the CI data base as well.
For each major aspect in this work an result evaluation script is written which provides the diagrams shown in this work by using the gnuplot tool.
he measurement of the CI rate for different azimuth tilts of the detector has been executed over 3/4 of a year. The results and the comparison with the estimation given in this first chapter are shown in the picture below:
In the above diagram shows the measurements taken (red points) and the estimation formular fitted to the measured data. There is a fairly good agreement between expected intensity and the measured values. From this we can conclude that the detecor setup may in fact detect muons.
The project has not produced any artefact but the a tar ball of the CI controler project may be downloaded here.
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