X-ray astronomy detector - AbsoluteAstronomy.com

X-ray astronomy detectors are instruments that detect X-rays for use in the study of X-ray astronomy

X-ray astronomy

X-ray astronomy is an observational branch of astronomy which deals with the study of X-ray observation and detection from astronomical objects. X-radiation is absorbed by the Earth's atmosphere, so instruments to detect X-rays must be taken to high altitude by balloons, sounding rockets, and...

.

X-ray astronomy

X-ray astronomy

is an observational branch of astronomy

Astronomy

Astronomy is a natural science that deals with the study of celestial objects and phenomena that originate outside the atmosphere of Earth...

which deals with the study of X-ray

X-ray

X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...

emission from celestial objects. X-radiation is absorbed by the Earth's atmosphere

Earth's atmosphere

The atmosphere of Earth is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention , and reducing temperature extremes between day and night...

, so instruments to detect X-rays must be taken to high altitude by balloon

Balloon

A balloon is an inflatable flexible bag filled with a gas, such as helium, hydrogen, nitrous oxide, oxygen, or air. Modern balloons can be made from materials such as rubber, latex, polychloroprene, or a nylon fabric, while some early balloons were made of dried animal bladders, such as the pig...

s, sounding rocket

Sounding rocket

A sounding rocket, sometimes called a research rocket, is an instrument-carrying rocket designed to take measurements and perform scientific experiments during its sub-orbital flight. The origin of the term comes from nautical vocabulary, where to sound is to throw a weighted line from a ship into...

s, and satellite

Satellite

In the context of spaceflight, a satellite is an object which has been placed into orbit by human endeavour. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon....

s. X-ray astronomy is part of space science

Space science

The term space science may mean:* The study of issues specifically related to space travel and space exploration, including space medicine.* Science performed in outer space ....

.

X-ray astronomy detectors have been designed and configured primarily for energy and occasionally for wave-length detection using a variety of techniques usually limited to the technology of the time.

Detection and imaging of X-rays

X-rays span 3 decades in wavelength (~8 nm - 8 pm), frequency (~50 PHz - 50 EHz) and energy (~0.12 - 120 keV). In terms of temperature, 1 eV = 11,604 K. Thus X-rays (0.12 to 120 keV) correspond to 1.39 × 10⁶ to 1.39 × 10⁹ K. From 10 to 0.1 nanometers (nm) (about 0.12 to 12 keV

Kev

Kev can refer to:*Kev Hawkins, a fictional character.*Kevin, a given name occasionally shortened to "Kev".*Kiloelectronvolt, a unit of energy who symbol is "KeV".* Krefelder Eislauf-VereinKEV can refer to:...

) they are classified as soft X-rays, and from 0.1 nm to 0.01 nm (about 12 to 120 keV) as hard X-rays.

Closer to the visible range of the electromagnetic spectrum is the ultraviolet

Ultraviolet

Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...

. The draft ISO standard on determining solar irradiance

Irradiance

Irradiance is the power of electromagnetic radiation per unit area incident on a surface. Radiant emittance or radiant exitance is the power per unit area radiated by a surface. The SI units for all of these quantities are watts per square meter , while the cgs units are ergs per square centimeter...

s (ISO-DIS-21348) describes the ultraviolet as ranging from ~10 nm to ~400 nm. That portion closest to X-rays is often referred to as the "extreme ultraviolet" (EUV

Extreme ultraviolet

Extreme Ultraviolet radiation is high-energy ultraviolet radiation, generally defined to be electromagnetic radiation in the part of the electromagnetic spectrum spanning wavelengths from 120 nm down to 10 nm, and therefore having photons with energies from 10 eV up to 124 eV...

or XUV). When an EUV photon is absorbed, photoelectrons

Photoelectric effect

In the photoelectric effect, electrons are emitted from matter as a consequence of their absorption of energy from electromagnetic radiation of very short wavelength, such as visible or ultraviolet light. Electrons emitted in this manner may be referred to as photoelectrons...

and secondary electrons

Secondary electrons

Secondary electrons are electrons generated as ionization products. They are called 'secondary' because they are generated by other radiation . This radiation can be in the form of ions, electrons, or photons with sufficiently high energy, i.e. exceeding the ionization potential...

are generated by ionization

Ionization

Ionization is the process of converting an atom or molecule into an ion by adding or removing charged particles such as electrons or other ions. This is often confused with dissociation. A substance may dissociate without necessarily producing ions. As an example, the molecules of table sugar...

, much like what happens when X-rays or electron beams are absorbed by matter.

The distinction between X-rays and gamma ray

Gamma ray

Gamma radiation, also known as gamma rays or hyphenated as gamma-rays and denoted as γ, is electromagnetic radiation of high frequency . Gamma rays are usually naturally produced on Earth by decay of high energy states in atomic nuclei...

s has changed in recent decades. Originally, the electromagnetic radiation emitted by X-ray tube

X-ray tube

An X-ray tube is a vacuum tube that produces X-rays. They are used in X-ray machines. X-rays are part of the electromagnetic spectrum, an ionizing radiation with wavelengths shorter than ultraviolet light...

s had a longer wavelength

Wavelength

In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...

than the radiation emitted by radioactive nuclei

Atomic nucleus

The nucleus is the very dense region consisting of protons and neutrons at the center of an atom. It was discovered in 1911, as a result of Ernest Rutherford's interpretation of the famous 1909 Rutherford experiment performed by Hans Geiger and Ernest Marsden, under the direction of Rutherford. The...

(gamma rays). So older literature distinguished between X- and gamma radiation on the basis of wavelength, with radiation shorter than some arbitrary wavelength, such as 10⁻¹¹ m, defined as gamma rays. However, as shorter wavelength continuous spectrum "X-ray" sources such as linear accelerators and longer wavelength "gamma ray" emitters were discovered, the wavelength bands largely overlapped. The two types of radiation are now usually distinguished by their origin: X-rays are emitted by electrons outside the nucleus, while gamma rays are emitted by the nucleus.

Although the more energetic X-rays, photon

Photon

In physics, a photon is an elementary particle, the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic radiation. It is also the force carrier for the electromagnetic force...

s with an energy greater than 30 keV

Kev

(4,800 aJ), can penetrate the air

Earth's atmosphere

at least for distances of a few meters, the Earth's atmosphere is thick enough that virtually none are able to penetrate from outer space all the way to the Earth's surface (they would have been detected and medical X-ray machines would not work if this was not the case). X-rays in the 0.5 to 5 keV (80 to 800 aJ) range, where most celestial sources give off the bulk of their energy, can be stopped by a few sheets of paper

Paper

Paper is a thin material mainly used for writing upon, printing upon, drawing or for packaging. It is produced by pressing together moist fibers, typically cellulose pulp derived from wood, rags or grasses, and drying them into flexible sheets....

; 90% of the photons in a beam of 3 keV (480 aJ) X-rays are absorbed by traveling through just 10 cm of air.

To detect X-rays from the sky, X-ray detectors must be flown above most of the Earth's atmosphere. There are three main methods of doing so: sounding rocket flights, balloons, and satellites.

Proportional counters

A proportional counter

Proportional counter

A proportional counter is a measurement device to count particles of ionizing radiation and measure their energy.A proportional counter is a type of gaseous ionization detector. Its operation is similar to that of a Geiger-Müller counter, but uses a lower operating voltage. An inert gas is used to...

is a type of gaseous ionization detector that counts particle

Charged particle

In physics, a charged particle is a particle with an electric charge. It may be either a subatomic particle or an ion. A collection of charged particles, or even a gas containing a proportion of charged particles, is called a plasma, which is called the fourth state of matter because its...

s of ionizing radiation

Ionizing radiation

Ionizing radiation is radiation composed of particles that individually have sufficient energy to remove an electron from an atom or molecule. This ionization produces free radicals, which are atoms or molecules containing unpaired electrons...

and measures their energy

Energy

In physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...

. It works on the same principle as the Geiger-Müller counter

Geiger counter

A Geiger counter, also called a Geiger–Müller counter, is a type of particle detector that measures ionizing radiation. They detect the emission of nuclear radiation: alpha particles, beta particles or gamma rays. A Geiger counter detects radiation by ionization produced in a low-pressure gas in a...

, but uses a lower operating voltage

Voltage

Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...

. All X-ray proportional counters consist of a windowed gas cell. Often this cell is subdivided into a number of low- and high-electric field regions by some arrangement of electrodes.

An individual medium energy proportional counter on EXOSAT

EXOSAT

The European X-ray Observatory Satellite , originally named HELOS, was operational from May 1983 until April 1986 and in that time made 1780 observations in the X-ray band of most classes of astronomical object including active galactic nuclei, stellar coronae, cataclysmic variables, white dwarfs,...

had a front window of beryllium

Beryllium

Beryllium is the chemical element with the symbol Be and atomic number 4. It is a divalent element which occurs naturally only in combination with other elements in minerals. Notable gemstones which contain beryllium include beryl and chrysoberyl...

with aluminized kapton

Kapton

Kapton is a polyimide film developed by DuPont which can remain stable in a wide range of temperatures, from -273 to +400 °C...

foil for thermal protection, a front chamber filled with an argon/CO₂ mixture, a rear chamber with xenon/CO₂, and a beryllium

Beryllium

window separating the two chambers. The argon portion of the detector was optimized for 2-6 keV and the total energy ranges for both detectors was 1.5-15 keV and 5-50 keV, respectively.

The US portion of the Apollo-Soyuz mission (July 1975) carried a proportional counter system sensitive to 0.18-0.28 and 0.6-10.0 keV X-rays. The total effective area was 0.1 m², and there was a 4.5° FWHM circular FOV.

The French TOURNESOL instrument consisted of four proportional counters and two optical detector

Photodetector

Photosensors or photodetectors are sensors of light or other electromagnetic energy. There are several varieties:*Active pixel sensors are image sensors consisting of an integrated circuit that contains an array of pixel sensors, each pixel containing a both a light sensor and an active amplifier...

s. The proportional counters detected photons between 2 keV and 20 MeV in a 6° × 6° FOV. The visible detectors had a field of view of 5° × 5°. The instrument was designed to look for optical counterparts of high-energy burst sources, as well as performing spectral analysis

Spectroscopy

Spectroscopy is the study of the interaction between matter and radiated energy. Historically, spectroscopy originated through the study of visible light dispersed according to its wavelength, e.g., by a prism. Later the concept was expanded greatly to comprise any interaction with radiative...

of the high-energy events.

X-ray monitor

Monitoring

System Monitoring

A system monitor in systems engineering is a process within a distributed system for collecting and storing state data.- Overview :The configuration for the system monitor takes two forms:# configuration data for the monitor application itself, and...

generally means to be aware of the state of a system. A device that displays or sends a signal for displaying X-ray output from an X-ray generating source so as to be aware of the state of the source is referred to as an X-ray monitor in space applications. On Apollo 15

Apollo 15

Apollo 15 was the ninth manned mission in the American Apollo space program, the fourth to land on the Moon and the eighth successful manned mission. It was the first of what were termed "J missions", long duration stays on the Moon with a greater focus on science than had been possible on previous...

in orbit above the Moon

Moon

The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...

, for example, an X-ray monitor was used to follow the possible variation in solar X-ray intensity and spectral shape while mapping the lunar surface with respect to its chemical composition due to the production of secondary X-rays

X-ray fluorescence

X-ray fluorescence is the emission of characteristic "secondary" X-rays from a material that has been excited by bombarding with high-energy X-rays or gamma rays...

.

The X-ray monitor of Solwind

P78-1

P78-1 or Solwind was a United States satellite launched aboard an Atlas F rocket from Vandenberg Air Force Base in California on February 24, 1979. The satellite operated until September 13, 1985, when it was shot down in orbit by an F-15 Eagle fighter aircraft during an US Air Force ASM-135 ASAT...

, designated NRL-608 or XMON, was a collaboration between the Naval Research Laboratory and Los Alamos National Laboratory

Los Alamos National Laboratory

Los Alamos National Laboratory is a United States Department of Energy national laboratory, managed and operated by Los Alamos National Security , located in Los Alamos, New Mexico...

. The monitor consisted of 2 collimated argon proportional counters. The instrument bandwidth of 3-10 keV was defined by the detector window absorption (the window was 0.254 mm beryllium) and the upper level discriminator. The active gas volume (P-10 mixture) was 2.54 cm deep, providing good efficiency up to 10 keV. Counts were recorded in 2 energy channels. Slat collimators defined a FOV of 3° × 30° (FWHM) for each detector; the long axes of the FOVs were perpendicular to each other. The long axes were inclined 45° to the scan direction, allowing localization of transient events to about 1°. The centers of the FOVs coincided, and were pointed 40° below the scan equator of the wheel in order to avoid scanning across the Sun. The spacecraft wheel rotated once every 6 seconds. This scan rate corresponds to 1° every 16 milliseconds (ms); counts were telemetered in 64 or 32 ms bins to minimize smearing the collimator response.

The instrument parameters and data yield implied a 3 σ point source sensitivity of 30 UFU in one day's operation (1 UFU = 2.66⁻¹² erg/cm²-s-keV). Each detector was about 0.1 of the area of the Uhuru

Uhuru (satellite)

Uhuru was the first satellite launched specifically for the purpose of X-ray astronomy. It was also known as the X-ray Explorer Satellite, SAS-A , SAS 1, or Explorer 42.The observatory was launched on 12 December 1970 into an initial orbit of about 560 km apogee, 520 km...

instrument. The instrument background at low geomagnetic latitudes was ~16 counts/s. Of this background, ~6 counts/s comes from the diffuse cosmic X-ray background, with the rest being instrumental. Assuming a conservative 10% data return, the net source duty cycle in scanning mode was 1.4 × 10⁻³, implying a source exposure of 120 seconds per day. For a background of 16 counts/s, the 3 σ error in determining the flux from a given sky bin was then 4.5 counts/s, or about 45 UFU, after 1 day. A limiting sensitivity of 30 UFU was obtained by combining both detectors. A comparable error existed in the flux determination for moderately bright galactic sources. Source confusion due to the 5° FOV projected along the scan direction complicated the observation of sources in the galactic bulge region (approximately 30° > l > -30°, |b| < 10°).

Scintillation detector

A scintillator is a material which exhibits the property of luminescence

Luminescence

Luminescence is emission of light by a substance not resulting from heat; it is thus a form of cold body radiation. It can be caused by chemical reactions, electrical energy, subatomic motions, or stress on a crystal. This distinguishes luminescence from incandescence, which is light emitted by a...

when excited by ionizing radiation

Ionizing radiation

. Luminescent materials, when struck by an incoming particle, such as an X-ray photon, absorb its energy and scintillate, i.e. reemit the absorbed energy in the form of a small flash of light, typically in the visible range.

The scintillation X-ray detector (XC) aboard Vela 5A

Vela (satellite)

Vela was the name of a group of satellites developed as the Vela Hotel element of Project Vela by the United States to monitor compliance with the 1963 Partial Test Ban Treaty by the Soviet Union, and other nuclear-capable states. It means vigil or "watch" in Spanish.Vela started out as a small...

and its twin Vela 5B

Vela (satellite)

consisted of two 1 mm thick NaI(Tl) crystals mounted on photomultiplier tubes and covered by a 0.13 mm thick beryllium

Beryllium

window. Electronic thresholds provided two energy channels, 3-12 keV and 6-12 keV. In front of each crystal was a slat collimator providing a full width at half maximum (FWHM) aperture of ~6.1 × 6.1°. The effective detector area was ~26 cm². Sensitivity to celestial sources was severely limited by the high intrinsic detector background.

The X-ray telescope onboard OSO 4 consisted of a single thin NaI(Tl) scintillation crystal plus phototube assembly enclosed in a CsI(Tl) anti-coincidence shield. The energy resolution was 45% at 30 keV. The instrument operated from ~8 to 200 keV with 6 channel resolution.

OSO 5 carried a CsI crystal scintillator

Scintillator

A scintillator is a special material, which exhibits scintillation—the property of luminescence when excited by ionizing radiation. Luminescent materials, when struck by an incoming particle, absorb its energy and scintillate, i.e., reemit the absorbed energy in the form of light...

. The central crystal was 0.635 cm thick, had a sensitive area of 70 cm², and was viewed from behind by a pair of photomultiplier tubes. The shield crystal had a wall thickness of 4.4 cm and was viewed by 4 photomultipliers. The field of view was ~40°. The energy range covered was 14-254 keV. There were 9 energy channels: the first covering 14-28 keV and the others equally spaced from 28 to 254 keV. In-flight calibration was done with an ²⁴¹Am source.

The PHEBUS experiment recorded high energy transient events in the range 100 keV to 100 MeV. It consisted of two independent detectors and their associated electronics

Electronics

Electronics is the branch of science, engineering and technology that deals with electrical circuits involving active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies...

. Each detector consisted of a bismuth germinate (BGO) crystal 78 mm in diameter

Diameter

In geometry, a diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints are on the circle. The diameters are the longest chords of the circle...

by 120 mm thick, surrounded by a plastic anti-coincidence jacket. The two detectors were arranged on the spacecraft so as to observe 4π

' is a mathematical constant that is the ratio of any circle's circumference to its diameter. is approximately equal to 3.14. Many formulae in mathematics, science, and engineering involve , which makes it one of the most important mathematical constants...

steradian

Steradian

The steradian is the SI unit of solid angle. It is used to describe two-dimensional angular spans in three-dimensional space, analogous to the way in which the radian describes angles in a plane...

s. The burst mode was triggered when the count rate in the 0.1 to 1.5 MeV energy range exceeded the background level by 8 σ (standard deviations) in either 0.25 or 1.0 seconds. There were 116 channels over the energy range.

The KONUS-B instrument consisted of seven detectors distributed around the spacecraft that responded to photon

Photon

s of 10 keV to 8 MeV energy. They consisted of NaI

Sodium iodide

Sodium iodide is a white, crystalline salt with chemical formula NaI used in radiation detection, treatment of iodine deficiency, and as a reactant in the Finkelstein reaction.-Uses:Sodium iodide is commonly used to treat and prevent iodine deficiency....

(Tl) scintillator crystals 200 mm in diameter by 50 mm thick behind a Be

Beryllium

entrance window. The side surfaces were protected by a 5 mm thick lead layer. The burst detection threshold was 5 × 10 to 5 × 10 ergs/cm², depending on the burst spectrum and rise time

Rise time

In electronics, when describing a voltage or current step function, rise time refers to the time required for a signal to change from a specified low value to a specified high value...

. Spectra

Spectrum

A spectrum is a condition that is not limited to a specific set of values but can vary infinitely within a continuum. The word saw its first scientific use within the field of optics to describe the rainbow of colors in visible light when separated using a prism; it has since been applied by...

were taken in two 31-channel pulse height analyzer

Pulse height analyzer

A Pulse Height Analyzer is an instrument used in nuclear and elementary particle physics research which accepts electronic pulses of varying heights from particle and event detectors, digitizes the pulse heights, and saves the number of pulses of each height in registers or channels for later...

s (PHAs), of which the first eight were measured with 1/16 s time resolution and the remaining with variable time resolutions depending on the count rate. The range of resolutions covered 0.25 to 8 s.

Kvant-1

Kvant-1

Kvant-1 was the second module of the Soviet space station Mir. It was the first addition to the Mir base block and contained scientific instruments for astrophysical observations and materials science experiments....

carried the HEXE, or High Energy X-ray Experiment, which employed a phoswich

Phoswich Detector

Originally, "Phoswich detectors were developed to detect low-intensity, low-energy gamma rays, X-rays, as well as alpha and beta particles efficiently in a higher-energy ambient background...

of sodium iodide and caesium iodide. It covered the energy range 15-200 keV with a 1.6° × 1.6° FOV FWHM. Each of the 4 identical detectors had a geometric area of 200 cm². The maximum time resolution was 0.3-25 ms.

Modulation collimator

In electronics

Electronics

, Modulation

Modulation

In electronics and telecommunications, modulation is the process of varying one or more properties of a high-frequency periodic waveform, called the carrier signal, with a modulating signal which typically contains information to be transmitted...

is the process of varying one waveform in relation to another waveform. With a 'modulation collimator' the amplitude (intensity) of the incoming X-rays is reduced by the presence of two or more 'diffraction gratings' of parallel wires that block or greatly reduce that portion of the signal incident upon the wires.

An X-ray collimator is a device that filters a stream of X-rays so that only those traveling parallel to a specified direction are allowed through.

Minoru Oda, President of Tokyo University of Information Sciences, invented the modulation collimator, first used to identify the counterpart of Sco X-1 in 1966, which led to the most accurate positions for X-ray sources available, prior to the launch of X-ray imaging telescopes.

SAS 3 carried modulation collimators (2-11 keV) and Slat and Tube collimators (1 up to 60keV).

On board the Granat

Granat

The International Astrophysical Observatory "GRANAT" , was a Soviet space observatory developed in collaboration with France, Denmark and Bulgaria. It was launched on 1 December 1989 aboard a Proton rocket and placed in a highly eccentric four-day orbit, of which three were devoted to observations...

International Astrophysical Observatory were four WATCH instruments that could localize bright sources in the 6 to 180 keV range to within 0.5° using a Rotation Modulation Collimator. Taken together, the instruments' three fields of view covered approximately 75% of the sky. The energy resolution was 30% FWHM

Full width at half maximum

Full width at half maximum is an expression of the extent of a function, given by the difference between the two extreme values of the independent variable at which the dependent variable is equal to half of its maximum value....

at 60 keV. During quiet periods, count rates in two energy bands (6 to 15 and 15 to 180 keV) were accumulated for 4, 8, or 16 seconds, depending on onboard computer memory availability. During a burst or transient event, count rates were accumulated with a time resolution

Temporal resolution

Temporal resolution refers to the precision of a measurement with respect to time. Often there is a tradeoff between temporal resolution of a measurement and its spatial resolution. This trade-off can be attributed to the finite speed of light and the fact that it takes a certain period of time...

of 1 s per 36 s.

The Reuven Ramaty High Energy Solar Spectroscopic Imager

Reuven Ramaty High Energy Solar Spectroscopic Imager

Reuven Ramaty High Energy Solar Spectroscopic Imager is the sixth mission in the line of NASA Small Explorer missions...

(RHESSI), Explorer 81, images solar flares from soft X-rays to gamma rays (~3 keV to ~20 MeV). Its imaging capability is based on a Fourier-transform technique using a set of 9 rotational modulation collimators

Rotational Modulation Collimator

Rotational Modulation Collimators are a specialization of the modulation collimator, an imaging device invented by Minoru Oda. Devices of this type create images of high energy X-rays . Since high energy X-rays are not easily focused, such optics have found applications in various instruments...

X-ray spectrometer

OSO 8 had on board a Graphite Crystal X-ray Spectrometer, with energy range of 2-8 keV, FOV 3°.

The Granat

Granat

ART-S X-ray spectrometer covered the energy range 3 to 100 keV, FOV 2° × 2°. The instrument consisted of four detectors based on spectroscopic

Spectroscopy

MWPCs, making an effective area of 2,400 cm² at 10 keV and 800 cm² at 100 keV. The time resolution was 200 microsecond

Microsecond

A microsecond is an SI unit of time equal to one millionth of a second. Its symbol is µs.A microsecond is equal to 1000 nanoseconds or 1/1000 millisecond...

s.

The X-ray spectrometer aboard ISEE-3 was designed to study both solar flares and cosmic gamma-ray bursts over the energy range 5-228 keV. The detector provided full-time coverage, 3π FOV for E > 130 keV, time resolution of 0.25 ms, and absolute timing to within 1 ms. It was intended to be a part of a long baseline interferometry network of widely separated spacecraft. The efforts were aimed primarily at determining the origin of the bursts through precise directional information established by such a network. The experiment consisted of 2 cylindrical X-ray detectors: a Xenon filled proportional counter covering 5-14 keV, and a NaI(Tl) scintillator covering 12-1250 keV. The proportional counter was 1.27 cm in diameter and was filled with a mixture of 97% Xenon and 3% carbon dioxide. The central part of the counter body was made of 0.51 mm thick beryllium and served as the X-ray entrance window. The scintillator consisted of a 1.0 cm thick cylindrical shell of NaI(Tl) crystal surrounded on all sides by 0.3 cm thick plastic scintillator. The central region, 4.1 cm in diameter, was filled by a quartz light pipe. The whole assembly was enclosed (except for one end) in a 0.1 cm thick beryllium container. The energy channel resolution and timing resolution could be selected by commands sent to the spacecraft. The proportional counter could have up to 9 channels with 0.5 s resolution; the NaI scintillator could have up to 16 channels and 0.00025 s resolution.

CCDs

Most existing X-ray telescopes use CCD

Charge-coupled device

A charge-coupled device is a device for the movement of electrical charge, usually from within the device to an area where the charge can be manipulated, for example conversion into a digital value. This is achieved by "shifting" the signals between stages within the device one at a time...

detectors, similar to those in visible-light cameras. In visible-light, a single photon can produce a single electron of charge in a pixel, and an image is built up by accumulating many such charges from many photons during the exposure time. When an X-ray photon hits a CCD, it produces enough charge (hundreds to thousands of electrons, proportional to its energy) that the individual X-rays have their energies measured on read-out.

Microcalorimeters

Microcalorimeters can only detect X-rays one photon at a time (but can measure the energy of each).

Transition edge sensors

TES devices are the next step in microcalorimetry. In essence they are super-conducting metals kept as close as possible to their transition temperature. This is the temperature at which these metals become super-conductors and their resistance drops to zero. These transition temperatures are usually just a few degrees above absolute zero (usually less than 10 K

Kelvin

The kelvin is a unit of measurement for temperature. It is one of the seven base units in the International System of Units and is assigned the unit symbol K. The Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all...

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