EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Hisparc cosmic ray detector’s response to heavy rain

Alexander P. J. van Deursen1, David Fokkema2, Kasper van Dam2, and Bob van Eijk2
Alexander P. J. van Deursen et al.
  • 1Eindhoven University of Technology, Electrical Engineering, Flux 3.134, POB513, 5600MB Eindhoven, Netherlands
  • 2NIKHEF, Science Park 105, 1098 XG Amsterdam, Netherlands

Cosmic ray particles have extreme energies, 1016 eV/nucleon and up. Upon arrival at the higher atmosphere and collisions with the gas molecules there, the cosmic ray particles convert into an cascade of different secondary particles that finally arrive at soil level in the form of an extensive air shower (EAS): high-energy gamma’s, electrons and muons. In the HIgh School Project on Astrophysics Research with Cosmics (Hisparc, about 100 EAS detector stations are distributed over the Netherlands and several neighboring countries. These stations are mostly placed on the roof of secondary schools, where they have been built by pupils to attract them towards STEM studies.

Each station consists of two or four detectors with 0.5 m2 plastic scintillator plates to record the passage of the EAS. At coincidence, the scintillator signals are individually recorded, accurately timed with GPS. All data are sent to and collected at the NIKHEF institute ( and made available (open-access) for further analysis by pupils and scientists.

The sensitivity of the detectors is commonly adjusted such that each detector records a few hundred hits per second. The number of coincidences within 1.5 μs is then about 1 in 3 seconds, in part due to an actual EAS, in part due to random local radioactive processes.

During intense rainfall of a particular summer storm several two-detector systems recorded an increase in the coincidence frequency of up to a factor of 7. When comparing different stations we could follow the associated storm front moving northwards over NL. Within the coincidence interval of 1.5 μs the increased individual signals of both detectors were evenly distributed. Actual EAS signals tend to be synchronous to within 100 ns. We therefor attribute the increase to random signals. As possible source we suggest gamma radiation due to radon daughters in the atmosphere that are washed out by the rain and accumulate on the roof close to the detectors. The delay between rain and signal increase is noted and in accordance with the washing process time.

How to cite: van Deursen, A. P. J., Fokkema, D., van Dam, K., and van Eijk, B.: Hisparc cosmic ray detector’s response to heavy rain, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10888,, 2020

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Presentation version 1 – uploaded on 17 Apr 2020
  • CC1: Comment on EGU2020-10888, Martino Marisaldi, 04 May 2020

    The event shown on page 11 looks like a gamma-ray glow, on top of a longer duration transient due to radon washout. Did you consider this? Do you have electric field measurements, or other meteo measurements that show the atmospheric conditions on top of the detectors during this event?

    • AC1: Reply to CC1, A. P. J. van Deursen, 04 May 2020

      In fact there are a few possible causes, and indeed gamma ray glow as you suggested could be an option.  I did not consider this up to now, because the detection occurs at ground level and the high altitude (and high energy) photons or their collision products have to travel over the full height of the atmosphere. Perhaps a geant4 simulation could help? If positive, we could think about an extension of the hardware.

      The data we have is local rainfall as 15 minutes average (small at the moment of the surge) and the rate and waveform of the hit records. The analysis of Kasper of 2019 data shows that he can fit the single rate with the decay timeconstants of the radon daugthers. The resulting hit rate shows similar in those of 2010.

      What I am investigating at the moment it whether the single rates, and rate of hits are related via the expected square law behavior, for instance on the sudden storm front of June 4, 2019.

      • AC2: Reply to AC1, Kasper van Dam, 05 May 2020

        I am not familiar gamma ray glows but if they can indeed be detected from the ground (sea level) we can search for similar events. In more recent data we also have additional information ('singles rates') which can be valuable. The royal Dutch meteorology institute (KNMI) provides information on lightning strikes. Is there a proper scientific cause to search for such events? Or could it just be an explanation for the unexpected signal.

        • CC2: Reply to AC2, Martino Marisaldi, 05 May 2020

          glows can well be seen at sea level although it is more common on high-altitude sites (less gamma-ray absorption). Of course it depends on the path length from the cloud charge region to the detectors. Since it was raining there was probably a cloud passing over the detector site during the measurements. Radar reflectivity measurements would be great to assess the geometry of the cloud in conjunction with the (presumed) glow

  • AC3: Comment on EGU2020-10888, A. P. J. van Deursen, 05 May 2020

    Indeed there are good scientific reasons to search the Hisparc database for such events, and I would strongly recommend it. Gamma glows have been observed earlier (in mountains, from aircraft etc.) , but there is a paucity of experimental data for lower regions. We could limit the search to days with extreme weather, if these can be obtained from KNMI. The tsv files would then suffice for an initial search.