URL: https://www.desy.de/school/school_lab/zeuthen_site/cosmic_particles/experiments/e288814/index_eng.html
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Polarstern Project
Polarstern Project
The measurement of cosmic particles from the North Pole to the South Pole is of great scientific interest, as the strength of the Earth's magnetic field with which the cosmic particles interact changes between the poles. Especially in marine areas, where there are so far only few data on cosmic particles, the measurement of those very particles is particularly interesting.
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.
Muon Detector Setup 2012-2016
- two scintillation detectors at a distance of 40 cm,
- a DAQ card (by Fermilab QuarkNet Experiment),
- 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.
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.
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.
The setup consists of the following components (see the numbering on the photo):
Muon Detector Setup 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 PMTs. 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: mu_rate, the total number of muons per hour (sum of all 16 combinations), and sh_rate, the number of shower events, where all 8 scintillators show a signal at the same time.
Mini Neutron Monitor Setup
- 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.
Neutron monitors measure the nuclear component of cosmic particles reaching the Earth's surface. A detailed description of neutron monitors and how they work is given in the glossary.
The North-West University of Pochefstroom (South Africa) has developed a light, portable version consisting of the following components:
Data Structure
Possible Student Exercises
Example Diagrams
- How can this diagram be interpreted? What is the physical explanation for this distribution?
At Cosmic@Web some example diagrams will be shown if you use the Session-ID Polarstern.
This xy diagram shows the muon rates that were measured at different latitudes in 2015. An additional z-axis illustrates the corresponding air pressure.
The exact settings can be found on the session ID Polarstern.
Visualisation of the Polarstern's Position
Each dataset contains longitude and latitude information. With the help of those coordinates, maps can be created.
In addition, one can choose a third variable which will be displayed in color gradiants. As an example, the time is illustrated in this diagram. This allows to retrace the ship's position at a certain time.
