PROPORTIONAL COUNTERS

The objective of the flight was to perform measurements of the intensity and spectral distribution of high-energy X-rays from the Crab Nebula and Cyg X-l.

The detector consisted of eleven proportional counters containing a mixture of 90% xenon and 10% nitrogen at a pressure of 2 atmospheres. Each tube was 2 inches in diameter by 65 inches long with aluminum walls of thickness 0.015 or 0.022 inches. The detector was surrounded by a graded shield of tin and copper, as can be seen in the figure at left. The collimator was constructed from 1/16 inch brass slats assembled in egg-crate fashion to provide a pyramidal response function whose base was 38º by 38º. Outside the passive shield was an anticoincidence shield of twenty-five argon-filled proportional counters to eliminate effects due to penetrating charged particles.

Pulses from the detector were amplified and fed to a thirty-channel pulse-height analyzer which in turn fed thirty scalers. The last stages of the latter were connected to indicator lights which turned on or off every 128 counts. A camera containing 300 feet of 35-mm film driven at 3 inches per minute by a chronometric timing motor continuously photographed these lights. The resulting image on the film consisted of parallel trails of dashes and gaps, the length of each dash or gap being proportional to the time required to accumulate the preset number of counts set by the scanning factors. Every 20 seconds a flash caused a Wallace and Tiernan aneroid altimeter, an Accutron watch, and a thermometer to be photographed. The outputs of two horizontal crossed magnetometers were fed to two meters blackened except on the tips of their needles. Azimuthal information was recorded in the form of the continuous trails produced when these meters were illuminated by a dim light. Additional indicator lights registered anticoincidence rates, provided timing marks derived from the Accutron, displayed the output of a solar sensor, indicated analyzer dead time, number of pulses of height outside the range of interest, and in-flíght calibration on-off status.

The apparatus was suspended with the detector axis at 21º from the vertical. A line twister rotated the detector by 360º in azimuth with respect to the balloon at a rate of one revolution every 10 minutes.

Balloon launched on: 9/8/1967 at 00:44 cdt
Launch site: Columbia Scientific Balloon Facility, Palestine, Texas, US  
Balloon launched by: National Center for Atmospheric Research (NCAR)
Balloon manufacturer/size/composition: Zero Pressure Balloon Winzen 10.600.000 cuft (0.5 mil. Stratofilm)
Flight identification number: 343P
End of flight (L for landing time, W for last contact, otherwise termination time): 9/8/1967
Balloon flight duration (F: time at float only, otherwise total flight time in d:days / h:hours or m:minutes - ): 5 h
Landing site: In Teague, Texas, US
Payload weight: 1054 lbs.

The balloon was launched at 0:44 cdt on September 8, 1967. Ascent from ground to 30,000 feet was at a speed of 788 feet per minute (fpm), 30,000 to 50,000 feet was 740 fpm and from 50,000 to 85,500 feet was 251 fpm. At that altitude (with all ballast expended) it started to slowly loss altitude reaching 68.700 feet three hours later. The balloon was observed from the ground after sunrise and had the cylindrical shape caracteristic of this type of failure so was decided to terminate it. This was the second balloon failure for this experiment after a first attempt performed in August 9th.

A third mission -this time succesful- finally allowed to perform the planned observations in October 1st (see below in the table).

• NCAR Scientific Balloon Facility Annual Report, 1967 National Center for Atmospheric Research, January 1968