The Gamma-Ray Imaging Spectrometer (GRIS) was a

gamma-ray spectrometer A gamma-ray spectrometer (GRS) is an instrument for measuring the distribution (or spectrum—see Gamma spectroscopy#Scintillation detectors, figure) of the intensity of gamma radiation versus the energy of each photon. The study and analysis of ...

instrument on a

balloon A balloon is a flexible membrane bag that can be inflated with a gas, such as helium, hydrogen, nitrous oxide, oxygen, or air. For special purposes, balloons can be filled with smoke, liquid water, granular media (e.g. sand, flour or rice), ...

-borne

airborne observatory An airborne observatory is an airplane or airship with an astronomical telescope. By carrying the telescope to a sufficiently high altitude, the telescope can avoid cloud cover, pollution, and carry out Observational astronomy, observations in the ...

. It used

germanium Germanium is a chemical element; it has Symbol (chemistry), symbol Ge and atomic number 32. It is lustrous, hard-brittle, grayish-white and similar in appearance to silicon. It is a metalloid or a nonmetal in the carbon group that is chemically ...

detectors to achieve high resolution spectroscopy. GRIS was operated from 1988 to 1995 by

NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the federal government of the United States, US federal government responsible for the United States ...

Goddard Space Flight Center The Goddard Space Flight Center (GSFC) is a major NASA space research laboratory located approximately northeast of Washington, D.C., in Greenbelt, Maryland, United States. Established on May 1, 1959, as NASA's first space flight center, GSFC ...

, which called it "arguably one of the most successful gamma-ray balloon programs in history".

History

GRIS followed earlier gamma ray spectroscopy work by

Bell Labs Nokia Bell Labs, commonly referred to as ''Bell Labs'', is an American industrial research and development company owned by Finnish technology company Nokia. With headquarters located in Murray Hill, New Jersey, Murray Hill, New Jersey, the compa ...

Sandia National Laboratories Sandia National Laboratories (SNL), also known as Sandia, is one of three research and development laboratories of the United States Department of Energy's National Nuclear Security Administration (NNSA). Headquartered in Kirtland Air Force B ...

and co-investigators Marvin Leventhal and Bonnard Teegarden, including the LEGS spectrometer. GRIS was selected for a balloon program after the removal of a high-resolution gamma-ray spectrometer from the payload of what would become the

Compton Gamma Ray Observatory The Compton Gamma Ray Observatory (CGRO) was a space observatory detecting photons with photon energy, energies from 20 kElectronvolt#Properties, eV to 30 GeV, in Earth orbit from 1991 to 2000. The observatory featured four main tel ...

. GRIS first flew in May 1988 from

Alice Springs Alice Springs () is a town in the Northern Territory, Australia; it is the third-largest settlement after Darwin, Northern Territory, Darwin and Palmerston, Northern Territory, Palmerston. The name Alice Springs was given by surveyor William ...

, Australia. During its first several flights, the instrument definitively measured the gamma ray lines from

Supernova 1987A SN 1987A was a Type II supernova in the Large Magellanic Cloud, a dwarf satellite galaxy of the Milky Way. It occurred approximately from Earth and was the closest observed supernova since Kepler's Supernova in 1604. Light and neutrinos f ...

, including that of ⁵⁶Co, and the

positron annihilation The positron or antielectron is the particle with an electric charge of +1'' e'', a spin of 1/2 (the same as the electron), and the same mass as an electron. It is the antiparticle (antimatter counterpart) of the electron. When a positron col ...

line from the

Galactic Center The Galactic Center is the barycenter of the Milky Way and a corresponding point on the rotational axis of the galaxy. Its central massive object is a supermassive black hole of about 4 million solar masses, which is called Sagittarius A*, a ...

at 511 keV, elucidating the nature of these emissions. These measurements resulted in two letters in ''

Nature Nature is an inherent character or constitution, particularly of the Ecosphere (planetary), ecosphere or the universe as a whole. In this general sense nature refers to the Scientific law, laws, elements and phenomenon, phenomena of the physic ...

'' and three in ''

The Astrophysical Journal ''The Astrophysical Journal'' (''ApJ'') is a peer-reviewed scientific journal of astrophysics and astronomy, established in 1895 by American astronomers George Ellery Hale and James Edward Keeler. The journal discontinued its print edition and ...

'', and earned the John Lindsay Memorial Award for Science from Goddard Space Flight Center. GRIS was flown a total of nine times between 1988 and 1995, with a total flight time of 223 hours. In a configuration that included a wide-field

collimator A collimator is a device which narrows a beam of particles or waves. To narrow can mean either to cause the directions of motion to become more aligned in a specific direction (i.e., make collimated light or parallel rays), or to cause the spat ...

and blocking crystal mechanism, GRIS measured the diffuse galactic and cosmic gamma-ray spectra, yielding insight into the production of ²⁶Al in the galaxy. During its final two flights from Alice Springs, GRIS carried the PoRTIA instrument, which yielded measurements of the

CdZnTe Cadmium zinc telluride, (CdZnTe) or CZT, is a compound of cadmium, zinc and tellurium or, more strictly speaking, an alloy of cadmium telluride and zinc telluride. A direct bandgap semiconductor, it is used in a variety of applications, including ...

detector background for use in future instrument design. Following the program, the Goddard team proposed transferring the instrument to the

University of Maryland The University of Maryland, College Park (University of Maryland, UMD, or simply Maryland) is a public land-grant research university in College Park, Maryland, United States. Founded in 1856, UMD is the flagship institution of the Univ ...

to be refurbished for the Long Duration Balloon program, which would entail reconfiguring the instrument for wide field-of-view studies of diffuse emissions. The program would involve graduate and undergraduate student researchers, and would address observation regimes inaccessible to the

INTEGRAL In mathematics, an integral is the continuous analog of a Summation, sum, which is used to calculate area, areas, volume, volumes, and their generalizations. Integration, the process of computing an integral, is one of the two fundamental oper ...

mission.

Specifications

The GRIS instrument was flown with a helium-filled balloon to a typical altitude of . The GRIS instrument carried seven n-type germanium detectors with a range of sensitivity between 20 and 8000

keV In physics, an electronvolt (symbol eV), also written electron-volt and electron volt, is the measure of an amount of kinetic energy gained by a single electron accelerating through an electric potential difference of one volt in vacuum. When us ...

and a combined energy resolution of 1.8 keV at an energy of 500 keV. Each detector was in diameter by deep (among the largest in the world at the time), for a total detector area of and a total detector volume of . The

liquid nitrogen Liquid nitrogen (LN2) is nitrogen in a liquid state at cryogenics, low temperature. Liquid nitrogen has a boiling point of about . It is produced industrially by fractional distillation of liquid air. It is a colorless, mobile liquid whose vis ...

-cooled detectors were shielded on all sides by of NaI active anticoincidence shielding for rejection of background events. The instrument had a three-

sigma Sigma ( ; uppercase Σ, lowercase σ, lowercase in word-final position ς; ) is the eighteenth letter of the Greek alphabet. In the system of Greek numerals, it has a value of 200. In general mathematics, uppercase Σ is used as an operator ...

narrow line sensitivity of 1.7 x 10⁻⁴ picohenries per square centimeter per second at 500 keV over 12 hours, and a

field of view The field of view (FOV) is the angle, angular extent of the observable world that is visual perception, seen at any given moment. In the case of optical instruments or sensors, it is a solid angle through which a detector is sensitive to elec ...

(

FWHM In a distribution, full width at half maximum (FWHM) is the difference between the two values of the independent variable at which the dependent variable is equal to half of its maximum value. In other words, it is the width of a spectrum curve ...

) of 17 degrees at 500 keV. The experimental payload had a weight of , and used 350 Watts of power. It relied on a

momentum wheel A reaction wheel (RW) is an electric motor attached to a flywheel, which, when its rotation speed is changed, causes a counter-rotation proportionately through Angular momentum#Conservation of angular momentum, conservation of angular momentum. ...

for

azimuth An azimuth (; from ) is the horizontal angle from a cardinal direction, most commonly north, in a local or observer-centric spherical coordinate system. Mathematically, the relative position vector from an observer ( origin) to a point ...

control, and a magnetic pointing reference, with a

star tracker A star tracker is an optical device that measures the positions of stars using photocells or a camera. As the positions of many stars have been measured by astronomers to a high degree of accuracy, a star tracker on a satellite or spacecraft may ...

and

Sun sensor A Sun sensor is a navigational instrument used by spacecraft to detect the position of the Sun. Sun sensors are used for Spacecraft attitude control, attitude control, solar array pointing, gyroscope, gyro updating, and safe mode (spacecraft), fai ...

for verification. The instrument delivered

telemetry Telemetry is the in situ collection of measurements or other data at remote points and their automatic transmission to receiving equipment (telecommunication) for monitoring. The word is derived from the Greek roots ''tele'', 'far off', an ...

at a rate of 55.2 kbps.

Team

The principal investigator of the GRIS project was Jack Tueller, with co-investigators Scott Barthelmy, Lyle Bartlett,

Neil Gehrels Cornelis A. "Neil" Gehrels (October 3, 1952 – February 6, 2017) was an American Astrophysics, astrophysicist specializing in the field of gamma-ray astronomy. He was Chief of the Astroparticle Physics Laboratory at NASA's Goddard Space Flig ...

, Marvin Leventhal, Juan Naya, Ann Parsons, and Bonnard Teegarden.

References

{{reflist

External links

GRIS scientific results
by co-investigator

Gamma-ray telescopes Spectrometers Balloon-borne telescopes Goddard Space Flight Center