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

Rolf Bütikofer, Erwin O. FlückigerUniversity 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 GroupUniversity 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

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 BernRoof 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: pmeas = peff – ρv2/2

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

ΔNIGY 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

YYYY MM DD HHMM Uncorr Press Corr ******************************************* 2007 2 1 100 5244/ 492.7 5808.8/ 2007 2 1 200 0 492.7 0.0 2007 2 1 300 5252/ 492.7 5818.2/ 2007 2 1 400 5256 492.6 5818.4 2007 2 1 500 5264 492.5 5825.1 2007 2 1 600 5257 492.5 5813.6 2007 2 1 700 5239 492.6 5801.4 2007 2 1 800 5252 492.8 5824.8 2007 2 1 900 5250 492.8 5825.3 2007 2 1 1000 5242 493.0 5825.2 2007 2 1 1100 5263- 493.1 5856.5- 2007 2 1 1200 5251 493.3 5850.9 2007 2 1 1300 5222 493.5 5830.3

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 (B10F3)

B10 + n → Li7 + 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

View from top

Visualisation of particle interactions