Polarstern Project


      The Alfred-Wegener-Institut's German research vessel "Polarstern" crosses all latitudes from Arctic to Antarctic waters at yearly intervals. DESY has installed different scintillation counter experiments to measure the rate of cosmic muons: a first setup from 2010-2012, an improved detector from 2012-2016, a larger detector with new read-out electronics and higher sensitivity since 2017. Towards the end of 2011 a mini neutron monitor was taken into operation together with the universities Kiel (Germany) and Potchefstroom (South Africa).

      The measurement of cosmic particles on board of the "Polarstern" has many advantages. Due to the Earth's magnetosphere, the fraction of cosmic particles with lower energy will be distracted to the poles. This results in a lower particle rate around the equator. The measurement of this latitude effect is a simple but efficient method to estimate the detector sensitivity. The main advantage is however that these detectors are the only ones taking data at almost all latitude positions on sea, and therefore are an excellent supplement to the worldwide cosmic weather observations.

      The current position of the "Polarstern" can be found here. Since 2012 a scintillation detector and a mini neutron monitor are also installed at the German Neumayer Station III in the Antarctica.

       
      Setup of the Muon Detector (2012-2016)


        The experiment measures muons, which are decay products of particles generated by the interaction of primary cosmic particles with atoms of the atmosphere. The muons are detected using two scintillator plates similar to the CosMO Experiment. The setup consists of the following components (see the numbering on the photo):


          1. two scintillation detectors at a distance of 40 cm,
          2. a DAQ card (by Fermilab QuarkNet Experiment),
          3. a Netbook with a special program that not only stores the data but also analyses it so that it can be transmitted to DESY once a day via the internal Polarstern network.


          Muons passing the 25x25 cm2 scintillator generate a signal read-out by a PMT. Only if both scintillators show a signal at the same time, the event will be accepted as a traversing muon. This coincidence condition ensures the reduction of false signals.

           
          Setup of the Muon Detector (since 2017)


            The new experiment consists of two detector planes arranged one over the other at a distance of 50cm. A plane contains 4 independent scintillator plates. To suppress false signals every scintillator is read-out by two pmt's. The new data acquisition electronics allows to define the coincidence condition of the two signals of one scintillator and then to require coincidences between the scintillators of the upper and lower plane. For a single muon one receives 16 possible directional combinations. Since the swell causes a rolling and stamping of the "Polarstern" the directional information makes no sense. Therefore, only two variables will be stored: the total number of muons per hour (sum of all 16 combinations) and the number of shower events, where all 8 scintillators show a signal at the same time.

             
            Setup of the Mini Neutron Monitor


              Neutron monitors measure the nuclear component of cosmic particles reaching the Earth's surface. The North-West University of Pochefstroom (South Africa) has developed a light, portable version consisting of the following components:
              • the neutron detector,
              • an electronics box for the data acquisition,
              • a notebook to control the settings for the data taking and for data storage and transfer.

              A detailed description of neutron monitors and how they work is given in the glossary.

               
              Data Structure


                The datasets available via Cosmic@Web contain: time, particle rates per hour for the muon detector and the neutron monitor, air pressure and temperature. More detailed information can be found in the description of the dataset.

                 
                Possible Student Exercises


                • Analyse existing dependencies between particle rate and latitude position for both detectors (key word: geomagnetic cut-off).
                • Visualise the position of the "Polarstern" using the latitude and longitude variables. With the given information on the vessels's time and position, its velocity can be calculated and its path recreated.
                • Investigate the particle rate's dependency on weather conditions.
                • Compare the weather conditions in different areas (equator, Arctic, Antarctica) for different years.
                • Search for strong solar eruptions which can lead to a sudden increase of the particle rate.
                • Compare the particle rates with data from other experiments (neutron monitors, satellites) measuring the particle flux of the Sun.
                • Compare the data with the data from the muon detector and the mini neutron monitor at the Neumayer III station.

                Example Diagrams


                  At Cosmic@Web some example diagrams will be shown if you use the Session-ID Polarstern.
                   

                  Visualisation of the "Polarstern" Position


                   

                  Diagram Muon Rate versus Latitude