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

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

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

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

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

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

Bern Cosmic Ray Group University of Bern, Switzerland operates 3 NMs: 18-IGY NM at Jungfraujoch, 3570 m asl, since 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

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

3-NM64 Neutron Monitor Jungfraujoch Roof of Research Station

IGY NM64 Jungfraujoch

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

Effects of wind on pressure measurements Gusty winds cause short-time fluctuations Strong winds cause diminished readings of conventional barometers Bernoulli effect: p meas = p eff – ρv 2 /2

1-minute pressure data

NM count rate atmospheric pressure wind speed

Snow Effect

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

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

Δ N IGY vs. Snow Thickness ~0.5% / 10 cm snow ~0.2% / 10 cm snow

NM Operating Only Part of Interval

Only Part of Monitor Operating

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

Monthly Graph

Monthly Data

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

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

Cosmic Rays in the Atmosphere

Principle of Neutron Monitor Reflector (Paraffin/Polyethylen) Producer (Lead) Moderator (Paraffin/Polyethylen) Counter Tube (B 10 F 3 ) B 10 + n → Li 7 + α

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

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

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Visualisation of particle interactions