14.11.2011

New Helmholtz-Russia research group on the hunt for cosmic radiation

With innovative technologies, a German-Russian research group is in Siberia on the hunt for high enery cosmic gamma rays as well as for so-called cosmic rays. The latter are forming a continuous shower of high-energy atomic nuclei from outer space, its origin still being mysterious to a large extent, even a hundred years after its discovery. This coming project is funded within the framework of the Helmholtz-Russia Joint Research Groups (HRJRG), with an annual sum of about 150 000 euros for a period of three years.

Entrance to the Tunka National Park. Courtesy of the Tunka Collaboration

In the Tunka valley, not far from Lake Baikal, physicists are installing a test array of so-called Cherenkov detectors to identify cosmic gamma rays of highest energies (from 10 Tera- up to Peta-electronvolts). This gamma radiation may point to the sources of cosmic particle radiation as gamma rays – unlike electrically charged atomic nuclei – are not deflected by cosmic magnetic fields on their way to earth.

The projected detectors will record the Cherenkov light of fast secondary particles which are produced by cosmic particles and gamma radiation in the Earth's upper atmosphere. Cherenkov light is some kind of an ultrasonic bang of superluminal particles: cosmic rays generate cascades of secondary particles in the atmosphere which rain down from the sky as so-called air showers. Many of these secondary particles travel faster than light in the air (but not faster than the speed of light in vacuum which is regarded as the upper speed limit). This produces the characteristic blue glow of Cherenkov radiation which are detected in moonless nights with sensitive instruments (photomultipliers).

The air showers are not only detectable through particles and Cherenkov light; they also emit radiation at radio frequency. Therefore, in another experiment in the Tunka valley, scientists will test how well air showers can be measured by an array of radio antennas. The advantage of this method: it is not restricted to clear and moonless nights but allows collecting data round the clock.

Cooperating partners of the new Helmholtz-Russia Joint Research Group are the Institute for Nuclear Research of the Russian Academy of Sciences, the Universities of Moscow (MSU), Irkutsk and Hamburg, the Karlsruhe Institute of Technology, and DESY. The location was chosen because it already runs another air shower detector array named Tunka-133 which – a worldwide unique air shower Cherenkov facility. With its precise shower energy measurements, Tunka-133 provides a perfect basis for the test of new experimental technologies.

Altogether, the Helmholtz Association and the Russian Foundation for Basic Research (RFBR) are funding six new groups in the current fourth round of the common programme. According to the Helmholtz Association, 20 joint projects have already been funded in the first three rounds. “With the newly selected groups, we will set further priorities in the cooperation with Russia and systematically extend research in strategically relevant areas,” Professor Jürgen Mlynek, President of the Helmholtz Association, stresses out.

Further reading

• Project HiSCORE at the University of Hamburg:
  http://wwwiexp.desy.de/groups/astroparticle/score/
• Project LOPES:
  http://www.astro.ru.nl/lopes/

A cherenkov detector against the night sky. Courtesy of the Tunka Collaboration