Cosmic Ray Observatory

Hafelekar (2334 m)
Nordkette
North of Innsbruck behind the Victor Franz Hess Laboratory building (2265 m)

The High Energy Physics group is operating the observatory (muon and neutron counters) to record cosmic ray data like many other observatories around the world. The data are collected at the World Data Centers. The data from the Hafelekar are sent to World Data Center A on Solar-Terrestrial Physics (Boulder Colorado), B (Moscow/Russia) and C2 (Tokyo/Japan).

• Erinnerungen an V.F. Hess und and die ersten Jahre des Betriebes des Hafelekar Labors (partly in German).
• Schauraum mit Gedenktafeln am Hafelekar (in German).

Further links on V.F. Hess and Cosmic Rays:

• V.-F.-Hess Homepage
• Nobelprize.org
• A. Wolfendale on Cosmic Rays
• More articles and pictures on V.F. Hess.

This laboratory was founded by Victor Franz Hess¹ in 1931. It lies north of Innsbruck at an altitude of 2265 m. Today the following equipment is present in a small room kept at a constant temperature :

• Two muon-scintillator telescopes (data not pressure corrected), since 1978. Disc-like plastic scintillators (diameter 1 m) with a photomultiplier on top. Two such devices are connected in coincidence to give one detector.
• A neutron monitor (data pressure corrected), since 1968. It consists of three cylindrical gas counters, 2.25 m long, filled with Bortrifluoride BF₃. Each of them is surrounded by 30 cm paraffin and 4.5 cm lead, which is positioned in a way such that it prevents particles others than muons from going through the muon detector described above. It works in the following way : High energetic nucleons from the cosmic radiation break up lead nuclei, thereby producing fast neutrons. These slow down in the paraffin and then give a signal in the gas counter. The rate is proportional to the density of the primary nucleons.

The data taken at 1 hour intervals are routinely submitted to the World Data Centers for Cosmic Rays (Tokyo, Boulder, Moscow). Up to 1990 this was done by sending paper and now by sending ASCII files. Data taken in 10 minute intervals are available on request. The rate of cosmic particles is about 100.000 h^-1m^-2. Equipment of the old days (1952), phased out in the mid-eighties :

• Apparatus developed by Steinke in Königsberg : It consists of a cylindrical ionisation chamber (80 litres, 10 bar, filled with argon). The cosmic radiation (muons) ionizes the gas and the charge produced is measured electrostatically - the amplitude of an electrometer is registered photographically (analysis of course done by eye !). However the mean value of the collected charge is compensated for by means of a condensator driven by a potentiometer. So the electrometer only shows variations around an absolute value.

¹In 1912 Hess reached a height of 5 km by ballon flights and was able to show that the current in an ion chamber increased with altitude. In addition, he established that there was no difference between the day and the night intensity from which he concluded that a new penetrating radiation from outside was responsible and gave it the name Höhenstrahlung. For the discovery of this cosmic radiation he got the nobel prize in 1936.