COSMIC RAY DETECTOR

Developed by NASA - Goddard Space Flight Center (GSFC)

Balloon launched on 8/15/1973, from Thompson, Manitoba, Canada

Purpose of the flight and payload description

The instrument was a balloon-borne Cosmic-Ray telescope designed to measure the isotopic composition of nuclei from lithium to iron by combining charge determination, trajectory reconstruction, velocity measurement, residual range determination, and total energy-loss measurements within a single detector system. For nuclei below approximately Z = 12 the instrument operated primarily as a range and total-energy detector, while for heavier nuclei the Cherenkov detector provided the principal velocity measurement because scintillation saturation reduced the accuracy of conventional energy-loss measurements. The instrument was developed by the NASA Goddard Space Flight Center.

In the image at left we can see an schematic drawing of the telescope (click to enlarge). The detector assembly consisted of a charge scintillator, a Cherenkov detector, a spark chamber, a totally active scintillator stack, and a penetration counter. The upper detector was a 75 × 75 × 1 cm Pilot Y plastic scintillator viewed through four light guides by four 3-inch photomultiplier tubes. It provided the primary charge measurement together with the remaining scintillators. Beneath it was located a Cherenkov detector containing a 50 × 50 × 1 cm ultraviolet-transmitting acrylic radiator enclosed in a diffusion box and viewed by twelve 5-inch photomultiplier tubes. The radiator had a refractive index of approximately 1.49 and provided an independent measurement of particle velocity required for heavy nuclei.

Trajectory reconstruction was performed by an eight-deck multiwire spark chamber with an active area of 50 × 50 cm. Each deck contained four wires per centimetre and determined the particle trajectory through the detector stack. The trajectory measurement provided the path length through every scintillator, determined whether the particle remained inside the detector volume until stopping, and allowed accurate correction of energy-loss measurements for incidence angle.

The active absorber consisted of twelve plastic scintillators with increasing thickness. The upper trigger scintillator measured 50 × 50 × 0.65 cm and was viewed from both ends by photomultiplier tubes. Three subsequent scintillators measured approximately 57.5 × 55 × 1 cm, while the remaining eight scintillators measured approximately 57.5 × 55 × 3.5 cm and were viewed by four photomultiplier tubes each. The increasing detector thickness allowed continuous sampling of the particle energy deposition as it slowed and eventually stopped within the stack. Only two thin aluminium sheets separated successive scintillators, minimizing inactive material. A final penetration scintillator located beneath the stack recorded particles traversing the complete instrument and provided calibration data.

Detector signals were digitized through a dual-gain pulse-height system using paired 256-channel analyzers. High- and low-gain amplifiers provide overlapping dynamic ranges while minimizing digitization uncertainty. The instrument incorporated four trigger modes. The primary trigger selected lithium and heavier nuclei while rejecting the large proton and helium background through variable thresholds dependent on estimated particle range. A second trigger periodically recorded penetrating protons, helium nuclei, and atmospheric muons for calibration. A third trigger enabled Cherenkov measurements of heavy nuclei above the Cherenkov threshold, while a fourth trigger recorded particles traversing the complete detector stack for calibration and performance monitoring.

The entire detector assembly was mounted inside a pressurized gondola.

Details of the balloon flight

Balloon launched on: 8/15/1973 at 5:04 local
Launch site: Thompson, Manitoba, Canada  
Balloon manufacturer/size/composition: Zero Pressure Balloon  
 End of flight (L for landing time, W for last contact, otherwise termination time): 8/16/1973 at 7:00 local
Balloon flight duration (F: time at float only, otherwise total flight time in d:days / h:hours or m:minutes - ): 22 h

The balloon was launched from Thompson, Manitoba, Canada on August 15, 1973, at 5:04 a.m, local time. Data was received at Thompson and Ft. McMurray during the entire flight. The payload floated at altitudes between 3.5 and 5 g cm2 of residual atmosphere for about 22 hours and was cut down at 7:00 a.m. on August 16.

External references

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