From real-time to final data — Some thoughts on quality control

1. From real-time to final data — Some thoughts on quality control Rolf Bütikofer, Erwin O. FlückigerUniversity of Bern, Switzerland

2. Measurements at NM Station • Time tag • NM count rate • Atmospheric pressure • Temperature, rel. humidity, wind speed ... • Observation of snow accumulation on and around detector housing

3. Time Tag • Accuracy of clock (mechanical clock, clock with quartz oscillator, radio clock, GPS, time server) • Time shift of clock • Local time, UT, winter/summer time • Start or end of interval

4. NM Count Rates (1) • Electronic problems: • Power cut • Rel. humidity (condensation  leakage current  spurious counts) • Stability of HV power supply • Temperature effects on electronic components • Drifts in power supply, amplifier and discriminator • Static charging • Change in counter tube characteristics (broken counters) • Replacement of counter tubes, amplifier

5. NM Count Rates (2) • Environment: • Change in material close to the NM (detector housing) • Relocation of NM • Accumulation of snow on roof or around detector housing

6. Atmospheric Pressure Measurements • Effects of winds on atmospheric pressure measurements: gusty and high wind speeds • Drift of barometer

7. Bern Cosmic Ray Group • University of Bern, Switzerland operates 3 NMs: • 18-IGY NM at Jungfraujoch, 3570 m asl, since 1958 • 3-NM64 NM at Jungfraujoch, 3475 m asl, since 1986 • Special Neutron Monitor at Bern, 570 m asl, since 1977 • Main interest of Bern group: • Analysis of solar cosmic ray events (GLEs) • Analysis of Forbush decreases • Space Weather

8. 18-IGY Neutron Monitor Jungfraujoch Roof of Sphinx building IGY NM

9. 3-NM64 Neutron Monitor Jungfraujoch Roof of Research Station

10. Jungfraujoch IGY NM64

11. Special Neutron Monitor Bern Roof of Physics Institute, University of Bern

12. Effects of wind on pressure measurements • Gusty winds cause short-time fluctuations • Strong winds cause diminished readings of conventional barometers Bernoulli effect: pmeas = peff – ρv2/2

13. 1-minute pressure data

14. NM count rate atmospheric pressure wind speed

15. Snow Effect

18. Precipitation mm/hour CEST (UTC+2) Meteo station at Interlaken, 18 km NNW from Jungfraujoch

20. Count rate vs. Snow Accumulation on Roof First preliminary results NM64: ~1% / 10 cm snow

21. ΔNIGY vs. Snow Thickness ~0.2% / 10 cm snow ~0.5% / 10 cm snow

22. NM Operating Only Part of Interval

23. Only Part of Monitor Operating

24. Normalisation Factors • One section of NM not in operation • Change in number of counter tubes • Change in NM type IGY  NM64 • Significant change in the environment of NM (change of detector housing, moving NM) Scaling factors

25. Monthly Graph

26. Monthly Data

27. Conclusions • Automatic data processing is OK for real-time data, however data must be controlled carefully by operators of NM before publishing final data • For preparation of final data corrections of measurements can be made for some effects, wheras some effects should only be mentioned with a comment in final dataset • Postprocessing of NM data within database by cross-correlation with nearby NM stations is possible

32. Effect of Atmosphere • Change in air mass has large effect on count rate • This change is the only significant meteoro-logical factor • Barometric pressure is used as a proxy for the air mass • Barometric pressure coefficient ~1 % / mmHg→ pressure must be measured very accurately

33. Cosmic Rays in the Atmosphere

34. Principle of Neutron Monitor • Reflector (Paraffin/Polyethylen) • Producer (Lead) • Moderator (Paraffin/Polyethylen) • Counter Tube (B10F3) B10 + n → Li7 + α

35. NM Simulation with Monte Carlo • Simulation of interactions of neutrons with material (detector housing, detector, ground, snow) • Simulation of detection of slow neutrons in the counter tubes • Geant4 software package

36. Detector and material in the environment Snow on the roof Roof (copper, wood) Snow around detector housing Ground (concrete) NM64 neutron monitor

37. View from top

38. Visualisation of particle interactions