Kamiokannen Experiment

    Muons in a Thermos Flask


      The Kamiokannen-Experiment offers high school and university students an independent study of cosmic particles. It consists of components also used in large experiments, which gives a direct insight into scientific work of astroparticle physics.

      The experiment was developed at the University of Mainz. Within the Cosmic Project of the Netzwerk Teilchenwelt, DESY has produced an advanced version using the identical data acquisition (DAQ) card, as well as the steering and analysis program muonic, which is also used in the CosMO-Experiment. DESY and many other astroparticle physics institutes connected through Netzwerk Teilchenwelt provide the Kamiokannen Experiment for student projects in institutes and in schools.

      The term “Kamiokanne” is derived from the names of the Japanese Kamiokande Experiment and the German name for can "Kanne". Kamiokande uses the Cherenkov effect in a large water volume surrounded by photomultipliers to detect muons and electrons produced by neutrino interactions. The Kamiokannen Experiment is a miniature version of Kamiokande. A photomultiplier observes a water-filled thermos flask to detect muons produced in the atmosphere.

       
      Setup


        The Kamiokannen Experiment consists of:

        • two thermos flasks filled with purified water
        • two PMTs with an internal high voltage supply mounted on top of the cans
        • a DAQ card produced by Fermilab which also provides the 5V input voltage for the PMT's
        • a notebook to operate the DAQ card, as well as store and analyse the data using the measurement and analysis software muonic.
        • a GPS device (optional), which can be connected to the DAQ card.

        Cosmic muons move at almost the absolute speed of light, however in dielectric median such as air and water they move faster than light in that medium, producing the so-called Cherenkov Radiation. Since these Cherenkov light flashes are very weak, a thermos flask with a mirrored interior wall is used so as not to lose light. A PMT observes the water registering the light flash and transforming the optical signal into an amplified electrical pulse. This pulse will be amplified, filtered and digitised in the DAQ board. Then the board sends a data string with the relevant information to the notebook.

         
        Preparation and Experimentation


          As for all experiments the two Kamiokannen detectors have to be calibrated before the measurement can be started:

          • Check the high voltage by connecting a multimeter to the "HV Monitor" output socket of the PMT. The standard value should be around 1600 V.
          • Check that the detector is light-proof. Measure the particle rate at your normal light conditions. Repeat the measurement after covering the detector with a black cloth. If there is a difference in the rate, check that the PMT is immersed in water and that the PMT tube is really fixed at the can. In case of problems use the black cloth.
          • Measure the particle rate by varying the threshold voltage, upon which it is dependent. The reference value for the rate of muons at sea level is: 1 particle per cm2 and per minute. Assuming an inner diameter of the thermos flasks of 10cm, the expected rate can be calculated for the Kamiokannen detector.
          • Choose the corresponding threshold voltage for the expected rate. If the rates are too small for reasonable threshold values (>20mV), increase the high voltage in steps of 50V and repeat.
          With the calibrated detectors one can undertake various investigations, such as those proposed below. The data, stored in the notebook, can be analysed using the program muonic.

           
          Possible Student Exercises


            The Kamiokannen Experiment offers a wide variety of possible exercises with cosmic particles:

              • In rate measurements, one records the number of particles passing the flask in a given period of time (e.g. N particles per second, per minute or per hour).
                With just one flask the shielding effect of different materials can be studied (e.g. by comparing the particle rates on top of a building and in the cellar or by surrounding the can with lead bricks).
                With two flasks and the coincidence requirement, the rate can be investigated for different particle directions. It is essential that the distance between the two flasks' centres is identical for all angle positions.

                • To measure the mean lifetime of muons, one flask is checked for events which have two independent signals with a time difference of 1-20 microseconds. The first signal is caused by a muon and the second one by one of its decay products – either an electron or a positron. The other decay particles, two neutrinos, cannot be detected. Displaying the number of events versus the time difference between the two signals allows to estimate the muon's mean lifetime.

                  • Investigate if the Cherenkov light output can be increased by the use of liquids other than purified water or by putting additives into the water. Measure the rate and amplitude with reasonable statistics (1-2 hours) for every filling. Since the differences are rather small, other influences on the measurement should be avoided (use a black cloth, do not switch on/off neon lamps, perform the measurements within a day)


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