Purpose of the flight and payload description

The objective of the flight was to study the energy spectrum of diffuse primary X-rays up to 180 keV. Their main objective was to determine whether these diffuse X-rays were of celestial or terrestrial origin by conducting balloon flights from locations with significantly different geomagnetic latitudes: De Bilt, Netherlands (53° N) and Taiyomura, Japan (25° N). The researchers aimed to measure the high-energy part of the spectrum (above 20 keV) to better understand the mechanism of origin of these X-rays. The flights were part of a collaboration between scientists from the Cosmic Ray Working Group at Kamerlingh Onnes Laboratory in Leiden, Netherlands, and the Department of Physics at Nagoya University, Japan.

The detector developed for the flights can be seen in the drawing at left. It consisted of a sodium iodide crystal (NaI(Tl)) that measured 50 mm in diameter and 12.5 mm in thickness, equipped with an aluminum window only 0.02 mm thick. This crystal-photomultiplier assembly was enclosed in a sophisticated multilayer cylindrical cup that served as both shield and collimator. The cup's wall comprised three layers from outside to inside: 1 mm of lead, 2 mm of tin, and 0.3 mm of magnetic shield material. This multilayer structure was designed to provide excellent X-ray absorption (95% at 150 keV) while preventing interference from X-rays generated in the lead or tin layers. The cup defined a geometrical factor of 8 cm² sr for X-ray detection.

A key feature of the detector was a rotating disk made of the same multilayer materials as the cup. This disk periodically blocked the opening angle, allowing the researchers to distinguish between cosmic-ray-induced background radiation and "forward" X-rays from both atmospheric and celestial sources. The entire assembly was surrounded by a plastic scintillator that acted as a guard counter, rejecting background events associated with charged particles. The detector was calibrated using radioactive sources (Cadmium-109 and Cerium-139), providing four calibration points across the energy range of interest. The energy resolution ranged from 40% to 20% full width at half maximum throughout the observed energy range, and the guard counter threshold was set at 250 keV. A 32-channel pulse-height analyzer digitized the X-ray events, which were then transmitted via telemetry.

Details of the balloon flight

Balloon launched on: 8/9/1966 at 4:03 jst
Launch site: Taiyo, Ibaraki, Japan  
Balloon launched by: Institute of Space and Astronautical Science (ISAS)
Balloon manufacturer/size/composition: Zero Pressure Balloon 5000 m3
Balloon serial number: T5
Flight identification number: Taiyo 5
End of flight (L for landing time, W for last contact, otherwise termination time): ??/??/1966
Balloon flight duration (F: time at float only, otherwise total flight time in d:days / h:hours or m:minutes - ): F 3 h

Ceiling at 6:20 jst

External references

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