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. 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 to ensure consistent data acquisition across different experiments. The configuration included five scintillation counters and a lead-glass Cherenkov counter providing a total of seven radiation lengths of material. The lead-glass counter detected Cherenkov radiation, enabling precise measurement of particle energy. The scintillation counters, arranged in layers, recorded the passage of charged particles and facilitated the discrimination between protons and electrons. A lead layer was included to initiate cascade showers in electrons, while a thin aluminum layer helped differentiate nuclear interactions from electromagnetic processes. The pulse-height information from each counter was telemetered digitally to ground stations.

The detectors were carefully calibrated using accelerator beams in the energy range of 0.2 to 6 GeV to establish their response to electrons of known energy. The system's response function, empirically determined, allowed researchers to interpret observed spectra in terms of the true energy distribution of primary electrons. The instrument's sensitivity to electrons was significantly higher than to protons, achieving an electron-to-proton sensitivity ratio of approximately 1,000 to 1. Data collected during flights were analyzed to extract the primary electron spectrum, correcting for secondary electrons generated in the atmosphere and other environmental factors.

The findings from the balloon flights revealed significant features in the energy spectrum, including a distinct bend around 2-3 GeV and a power-law behavior above this range. These results contributed to the understanding of cosmic-ray propagation and solar modulation, providing valuable insights for future astrophysical studies.

Balloon launched on: 7/20/1965
Launch site: De Bilt, Netherlands  
Balloon launched by: Royal Netherlands Meteorological Institute (KNMI)
Balloon manufacturer/size/composition: Zero Pressure Balloon  
End of flight (L for landing time, W for last contact, otherwise termination time): 7/20/1965
Balloon flight duration (F: time at float only, otherwise total flight time in d:days / h:hours or m:minutes - ): F 1 h 30 m

• A balloon observation of high energy electrons 9th International Cosmic Ray Conference, Vol. 1, p.327