X-RAY DETECTOR

Developed by Cosmic Ray Working Group, The Royal Dutch Academy of Sciences, Delft, Netherlands

Balloon launched on 12/17/1965, from De Bilt, Netherlands

Purpose of the flight and payload description

The objective of the flight was to study the isotropic component of celestial X-rays up to 90 keV to measure and analyze the spectrum of these X-rays and determine whether their origin was thermal radiation. It was part of a collaboration between scientists from the Cosmic Ray Working Group of The Royal Dutch Academy of Sciences in Delft, Netherlands, and the Nagoya University from Japan.

The detector system can be seen in the scheme at left. It consisted of a 2-inch sodium iodide crystal (NaI(Tl)) with a thickness of 5 mm. This crystal was housed inside a cylindrical cup made of tin with 2 mm wall thickness, which served both as a collimator and shield. The cup defined a geometrical factor of 8 cm² steradian for X-ray detection, with a half angle of 20 degrees. The entire detector assembly was surrounded by a plastic scintillator that functioned as a guard counter, designed to reject background events associated with charged particles. The guard counter's anti-coincidence threshold was set at 200 keV.

A key feature of the detection system was a rotating shutter made of 2 mm thick tin plate that periodically blocked the detector's opening angle. This design allowed the researchers to distinguish between cosmic-ray induced background radiation (measured when the shutter was closed) and the combined signal from celestial and atmospheric X-rays entering through the opening angle (measured when the shutter was open). The difference between these measurements provided a clear separation of "forward X-rays" from the cosmic-ray induced background. The detector's pulse height information was digitally transmitted via telemetry.

Details of the balloon flight

Balloon launched on: 12/17/1965
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): 12/17/1965

The balloon was launched from De Bilt, Netherlands, on December 17, 1965, reaching a ceiling altitude corresponding to 7 g/cm² of residual atmosphere at 10:30 AM local time.

External references

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