ELECTRON DETECTOR

This flight was part of an experiment to determine the energy spectrum of primary cosmic-ray electrons in the range of 0.5 to 30 GeV to support theoretical studies on cosmic-ray propagation and interactions in astrophysical environments. The experiment involved institutions such as the Cosmic Ray Working Group at the Kamerlingh Onnes Laboratorium in Leiden, Netherlands, with additional contributions from Nagoya University in Japan and technical support from the Kiruna Geophysical Observatory. The observations were conducted in 1965 and 1966 on balloon flights launched from Kiruna, Sweden and De Bilt, Netherlands, during a period of solar minimum activity, to minimize solar modulation effects.

The detector system which can be seen in the image at left was standardized for consistency across flights and was calibrated using accelerator beams in the energy range of 0.2 to 6 GeV. The configuration included five scintillation counters and a lead-glass Cherenkov counter, providing seven radiation lengths of material. The system recorded pulse-height information from each counter digitally via telemetry. It allowed for the discrimination of minimum ionizing particles, primarily relativistic protons and electrons, and enabled electron identification through cascade shower initiation in a lead layer.

To improve accuracy, the detector incorporated layers of aluminum and lead for comparative event analysis, reducing nuclear interaction contributions. Its sensitivity to electrons was approximately three orders of magnitude higher than for protons. The response function, determined empirically, facilitated the extraction of energy spectra from observed data. Flights were conducted at various altitudes and geomagnetic cutoffs to capture different aspects of the electron spectrum and to study the atmospheric and geomagnetic effects.

The results showed a distinct bend in the spectrum at around 2-3 GeV and a power-law distribution above this energy range, with implications for the understanding of solar modulation and galactic cosmic-ray dynamics. The collaborative effort and methodology provided a robust dataset contributing to ongoing studies of high-energy astrophysical phenomena.

Balloon launched on: 8/13/1967
Launch site: Kiruna Geophysical Observatory, Sweden  
Balloon manufacturer/size/composition: Zero Pressure Balloon  
End of flight (L for landing time, W for last contact, otherwise termination time): 8/13/1967
Balloon flight duration (F: time at float only, otherwise total flight time in d:days / h:hours or m:minutes - ): 15 h

• Long-Term Time Variations of the Cosmic-Ray Electron Flux above 500 MeV Physical Review Letters, vol. 22, Issue 24, pp. 1325-1326
• Time variations in the cosmic ray electron spectrum above 500 MeV Vol. 1. Acta Physica, Supplement to Volume 29. p.209