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 figure) of the intensity of gamma radiation versus the energy of each photon. The study and analysis of gamma-ray spectra for scientific and techni ...

instrument on a

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

-borne

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

. It used

germanium Germanium is a chemical element with the symbol Ge and atomic number 32. It is lustrous, hard-brittle, grayish-white and similar in appearance to silicon. It is a metalloid in the carbon group that is chemically similar to its group neighbo ...

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 agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeedi ...

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 emp ...

, 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, originally named Bell Telephone Laboratories (1925–1984), then AT&T Bell Laboratories (1984–1996) and Bell Labs Innovations (1996–2007), is an American industrial research and scientific development company owned by mult ...

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 Bas ...

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 energies from 20 k eV to 30 GeV, in Earth orbit from 1991 to 2000. The observatory featured four main telescopes in one spacecraft, covering X- ...

. GRIS first flew in May 1988 from

Alice Springs Alice Springs ( aer, Mparntwe) is the third-largest town in the Northern Territory of Australia. Known as Stuart until 31 August 1933, the name Alice Springs was given by surveyor William Whitfield Mills after Alice, Lady Todd (''née'' Al ...

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

line Line most often refers to: * Line (geometry), object with zero thickness and curvature that stretches to infinity * Telephone line, a single-user circuit on a telephone communication system Line, lines, The Line, or LINE may also refer to: Art ...

s 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. 1987A's light reached Earth on Febr ...

, including that of ⁵⁶Co, and the

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

line from the

Galactic Center The Galactic Center or Galactic Centre is the rotational center, the barycenter, of the Milky Way galaxy. Its central massive object is a supermassive black hole of about 4 million solar masses, which is called Sagittarius A*, a compact ...

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

Nature Nature, in the broadest sense, is the physical world or universe. "Nature" can refer to the phenomena of the physical world, and also to life in general. The study of nature is a large, if not the only, part of science. Although humans ar ...

'' and three in ''

The Astrophysical Journal ''The Astrophysical Journal'', often abbreviated ''ApJ'' (pronounced "ap jay") in references and speech, is a peer-reviewed scientific journal of astrophysics and astronomy, established in 1895 by American astronomers George Ellery Hale and Ja ...

'', 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 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 university, public Land-grant university, land-grant research university in College Park, Maryland. Founded in 1856, UMD is the Flagship un ...

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 assigns numbers to functions in a way that describes displacement, area, volume, and other concepts that arise by combining infinitesimal data. The process of finding integrals is called integration. Along with ...

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 Kev can refer to: Given name * Kev Adams, French comedian, actor, screenwriter and film producer born Kevin Smadja in 1991 * Kevin Kev Carmody (born 1946), Indigenous Australian singer-songwriter * Kev Coghlan (born 1988), Scottish Grand Prix mot ...

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 low temperature. Liquid nitrogen has a boiling point of about . It is produced industrially by fractional distillation of liquid air. It is a colorless, low viscosity liquid that is wi ...

-cooled detectors were shielded on all sides by of

NaI Nai or NAI may refer to: Music * ''Nai'' (album), an album by singer Anna Vissi * Nai (pan flute), a wind instrument, also known as a pan flute (Romania and Moldova) * "Nai" (song), a 2007 CD single by Irini Merkouri Organizations * National A ...

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; grc-gre, σίγμα) 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 ...

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 extent of the observable world that is 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 electromagnetic radiation. Humans a ...

(

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 mea ...

) 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 used primarily by spacecraft for three-axis attitude control, and does not require rockets or external applicators of torque. They provide a high pointing accuracy, and are particularly useful when the spacecraft must be ...

for

azimuth An azimuth (; from ar, اَلسُّمُوت, as-sumūt, the directions) is an angular measurement in a spherical coordinate system. More specifically, it is the horizontal angle from a cardinal direction, most commonly north. Mathematicall ...

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 attitude control, solar array pointing, gyro updating, and fail-safe recovery. In addition to spacecraft, sun sensors fin ...

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'', "remote", and ' ...

at a rate of 55.2 kbps.

Team

The

principal investigator In many countries, the term principal investigator (PI) refers to the holder of an independent grant and the lead researcher for the grant project, usually in the sciences, such as a laboratory study or a clinical trial. The phrase is also often us ...

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 astrophysicist specializing in the field of gamma-ray astronomy. He was Chief of the Astroparticle Physics Laboratory at NASA's Goddard Space Flight Center (GS ...

, 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