HIGH RESOLUTION SPECTROMETER

Objective of the flight was to obtain high-resolution measurements of gamma-ray emission produced during solar flares using a High Resolution Spectrometer. Main goal of the initiative was to investigate the acceleration, confinement, transport, and interaction of energetic protons and ions in the solar atmosphere. Particular emphasis was placed on the precise measurement of gamma-ray line energies and line profiles, since these features contained critical information about the energy spectra of accelerated particles and the composition of the ambient solar material in which they interacted. The project also sought to demonstrate that a balloon platform could support long-duration observations with sufficient spectral resolution, gain stability, and sensitivity to detect solar gamma-ray emissions that had previously proven difficult to observe. The payload was developed by the Laboratory for Astronomy and Solar Physics at NASA Goddard Space Flight Center, in collaboration with The Catholic University of America and Computer Sciences Corporation.

In the image at left we can see an schematic view of the instrument (click for more details). The spectrometer was centered on a high-purity germanium (HPGe) detector manufactured by Princeton Gamma-Tech. The detector measured 58 mm in diameter by 45 mm in height, operated at 3300 V bias, and achieved an energy resolution better than 2.5 keV FWHMFWHM (Full Width at Half Maximum)Common metric used across physics, engineering, and data analysis to measure the spread or width of a curve, peak, or pulse. It is calculated as the horizontal distance between the exact two points where the amplitude of the function reaches half of its maximum value. at 1.17 MeV. The detector and preamplifier field-effect transistor were cooled to approximately 77 K using a 30-liter liquid nitrogen dewar with a seven-day operating capacity.

Background rejection was provided by an active anticoincidence system consisting of a CsI(Na)Sodium-doped cesium iodideSodium-doped cesium iodide is a widely used, high-performance inorganic scintillator crystal. When high-energy radiation (like gamma or X-rays) strikes the crystal, it converts that energy into blue light. This makes it a vital component for medical imaging, space research, and geological well-logging. shield and a plastic scintillator aperture detector. The CsI(Na) shield surrounded the detector laterally and from below and was divided into three independent sections monitored by seven photomultiplier tubesPhotomultiplier TubePhotomultiplier tubes (or PMTs for short) are extremely sensitive detectors of light in the ultraviolet, visible, and near-infrared ranges of the electromagnetic spectrum. They are members of the class of vacuum tubes, more specifically vacuum phototubes. These detectors multiply the current produced by incident light by as much as 100 million times, enabling individual photons to be detected when the incident flux of light is low.. The aperture scintillator was 6 mm thick and was viewed by four photomultiplier tubes. Together, these systems reduced charged-particle and atmospheric gamma-ray background. The instrument field of view was approximately 120° FWHM and the detector axis was aligned with the zenith.

Signal processing was performed using NIMNIMA NIM (Nuclear Instrumentation Module) is a standardized electronic module primarily used in experimental particle and nuclear physics for high-resolution signal processing and data acquisition. Modules slide into a powered chassis (NIM bin) and include amplifiers, discriminators, logic units, and high-voltage power supplies. and CAMACCAMACA CAMAC (Computer Automated Measurement and Control) module is a standardized, plug-in electronic hardware unit used primarily for data acquisition, particle detection, and instrument control in nuclear, high-energy physics, and industrial applications. electronics. Valid events were digitized by an 8192-channel ADC, while shield signals were recorded through dedicated ADC and TDC systems. Data acquisition and payload control were managed by a DEC LSI-11/23 microcomputer. Telemetry operated at 20 kbps and transmitted detector events, timing information, count rates, temperatures, pressures, voltages, and system status. Power was supplied by twenty-eight lithium batteries feeding regulated ±6 V, ±12 V, and ±24 V electronics buses, with separate circuits for heaters and fans.

The entire instrument was enclosed within a thermally stabilized pressure gondola measuring approximately 1.3 m in diameter that contained the spectrometer and electronic subsystems while maintaining environmental conditions suitable for laboratory-grade instrumentation operating in the stratosphere. The gondola maintained an internal pressure of approximately 10^5 Pa throughout flight, preventing electrical arcing and thermal failures in sensitive components. The structure incorporated pressure-relief valves, thermal insulation, frozen thermal reservoirs, circulation fans, and controlled heaters. These systems maintained temperatures within operational limits despite the extreme thermal environment encountered at altitudes between 35 and 40 km. Internal temperatures remained between 12 °C and 34 °C during flight.

Balloon launched on: 6/10/1982 at 12:16 utc
Launch site: Donaldson Center, Greenville, South Carolina, US  
Balloon launched by: National Scientific Balloon Facility (NSBF)
Balloon manufacturer/size/composition: Zero Pressure Balloon Raven 785.797 m3 (15.24 microns X-124)
Balloon serial number: R27.75-2-101
Flight identification number: 188N
End of flight (L for landing time, W for last contact, otherwise termination time): 6/11/1982 at 19:40 utc
Balloon flight duration (F: time at float only, otherwise total flight time in d:days / h:hours or m:minutes - ): F 33 h 10 m
Landing site: 25 miles NW of El Paso, Texas, US
Payload weight: 1473 kgs.

This was the second flight of the instrument which had to be rebuilt after an accident during recovery from the first flight. The balloon was launched from Greenville, South Carolina, on 10 June 1982. The balloon remained at float altitude for 29.5 hours between approximately 35 and 40 km altitude. The mission included both day-night and night-day transitions and demonstrated stable operation of all subsystems.

The spectrometer recorded high-resolution atmospheric and cosmic gamma-ray spectra. The CsI(Na) shield rejected approximately 75% of events above 500 keV. The 511 keV positron-annihilation line was measured with a width of about 3 keV, while gain stability remained better than 0.15% during the entire flight.

Two solar flares were detected during the mission: an M1.9 event on 10 June 1982 and an M3.6 event on 11 June 1982. Both produced detectable hard X-ray emission up to approximately 130 keV. Although no nuclear gamma-ray lines were observed, the measurements verified the sensitivity, stability, and operational capability of the payload for future long-duration solar gamma-ray observations.

• A balloon-borne high-resolution spectrometer for observations of gamma-ray emission from solar flares NASA Technical Memorandum 86069 (1984)
• A balloon-borne high-resolution spectrometer for observations of gamma-ray emission from solar flares Nuclear Instruments and Methods in Physics Research, Sect. A, Vol. 225, No. 1, p. 195 - 208 (1984)
• National Scientific Balloon Facility Annual Report FY 1982 National Center for Atmospheric Research, February 1983