.
Measurement of the Sidereal Variation
of the Cosmic Radiation
at the University Freiburg, Germany
Early (before 1945) measurements of the direction of incidence of the cosmic
radiation by Prof. Steinke, who used continuously operated ionization
chambers for this purpose, were continued by his successor,
Prof. Wolfgang Gentner.
Wolfgang Gentner (see photos), one of the great
nuclear physicicst of our time, became Dean of the Physics Faculty of the
University of Freiburg shortly after WWII, built up the completely destroyed
Physics Institute and led the research efforts of the institute into two
directions: study of the cosmic radiation and the elementary particles,
and age determination of minerals by the decay products of their radioactive
isotopes.
Experimental studies of cosmic radiation and elementary particles at the
University Freiburg were expanded by Dr. Citron and Dr. Sittkus
(see photos),
who later became involved in the planning (with Prof. Gentner) of the CERN
accelerators.
Investigations of Extensive Air Showers of the Cosmic Radiation were led by
Dr. Citron, who guided the design of EAS equipment and investigation
of EAS properties by graduate students working on their thesis. The EAS
instrumentation was built by A. Langenbacher and consisted of an array of
ten groups of glass-walled Geiger Müller counters that were read in
various coincidence combinations. The detector array was installed in the
attic of the dormitory of the Sun Observatory of the Fraunhofer Institute
(under Prof. Kiepenheuer) on the Schauinsland (elevation 1150 m) in the
Black Forest.
One-year measurements of the Extensive Air Showers were first performed by
Paul Kehler
(see photos) and then continued by
Gerhard Stiller. The measurements by Kehler yielded the more significant
data and were published in the Zeitschrift für Naturforschung
(see Reference). The main result of his investigation was the measurement
of sidereal variation of extensive air showers, as shown in the following
Figure:
This Figure shows the hourly intensities measured for the two conditions K5
and K3, plotted versus local sidereal time in tenths of percent difference
from the average intensity. The frequencies of K5 and K3 were 64/hr and
123/hour, respectively. The average particle density of the K5 and K3
showers was 30/m2 and 18/m2, which
corresponds to average energies of the primary particles of
1013 eV and 5x1013 eV.
The amplitudes were 0.9% and 0.6%, and occured around 23 hr of local siderial
time, which corresponds to the time at which the aperture of the equipment
passed through the equatorial plane of the galaxy.
If one assumes that only high-energy showers contribute to the siderial
variation, then it can be calculated from the measured amplitudes and the
density distributions of the K5 as well as the K3 showers that only showers
with particle densities over 130/m2 were causing the
measured anisotropy, which corresponds to primary energies of over
5x1014 eV. This is the energy where the well-known
"kink" is found in the energy spectrum of the primary cosmic
radiation.
Reference: A. Citron und P. Kehler: Untersuchung großer Schauer
auf Sternzeitgang, Zeitschrift für Naturforschung, Band 10a, Heft 6,
page 499 (1955).
www.nucleonics-online.com/6f1341.html
Edited on 10 July 2002 - E-mail to the
Webmaster
