User:Marshallsumter/Radiation astronomy1/Materials

"Space is considered an environment — an extreme environment, filled with entities that can be harmful to spacecraft."

"In space, there are several environmental threats that can harm materials used to create spacecraft. These threats include ultraviolet rays and x-rays from the sun; solar wind particle radiation; thermal cycling (hot and cold cycles); space particles (micrometeoroids and debris); and atomic oxygen."

"Since 2001, NASA and its partners have operated a series of flight experiments called Materials International Space Station Experiment, or MISSE. The objective of MISSE is to test the stability and durability of materials and devices in the space environment."

"PECs [Passive Experiment Containers], which are attached to the exterior of the International Space Station, are about 2-feet by 2-feet and hold a variety of materials samples and devices whose reactions in space are of interest."

"The PECs are positioned in either a ram/wake orientation or in a zenith/nadir orientation. The ram orientation is the direction in which the space station is traveling, and the wake orientation faces the direction traveled. The zenith orientation faces away from Earth into space, while the nadir orientation faces straight down to Earth. Each orientation exposes the samples to different space environmental factors."

Bismuth germinates
has a cubic crystal structure (a = 1.0513 nm, z = 4, Pearson symbol cI76, space group I$\overline{4}$3d No. 220) and a density of 7.12 g/cm3. When irradiated by X-rays or gamma rays it emits photons of wavelengths between 375 and 650 nm, with peak at 480 nm, produces about 8500 photons per megaelectronvolt of the high energy radiation absorbed, has good nuclear hardness (radiation hardness) (parameters remaining stable up to 5.104 grays (Gys)), high scintillation efficiency, good energy resolution between 5 and 20 MeV, is mechanically strong, and is not hygroscopic, melting point is 1050 °C, the most common oxide-based scintillator.

Cadmium tellurides
Cadmium telluride (CdTe) doped with chlorine is used as a radiation detector for [X-rays], gamma rays, beta particles and alpha particles. CdTe can operate at room temperature allowing the construction of compact detectors for a wide variety of applications in nuclear spectroscopy. The properties that make CdTe superior for the realization of high performance gamma- and x-ray detectors are high atomic number, large bandgap and high electron mobility ~1100 cm2/V·s, which result in high intrinsic μτ (mobility-lifetime) product and therefore high degree of charge collection and excellent spectral resolution.

The intrinsic carrier concentration for HgCdTe is given by

$$n_{i}(t,x) = (5.585 - 3.82x + (1.753\cdot 10^{-3})t - 1.364\cdot 10^{-3}t\cdot x)\cdot 10^{14}\cdot E_{g}(t,x)^{0.75}\cdot t^{1.5} \cdot e^{\frac{-E_{g}(t,x)\cdot q}{2\cdot k\cdot t}}$$

where k is Boltzmann's constant, q is the elementary electric charge, t is the material temperature, x is the percentage of cadmium concentration, and Eg is the bandgap given by

$$E_{g}(t,x) = -0.302 + 1.93\cdot x+(5.35\cdot 10^{-4})\cdot t\cdot (1-2\cdot x)-0.81\cdot x^{2}+0.832\cdot x^{3}$$

Using the relationship $$\lambda _{p} = \frac{1.24}{E_{g}}$$, where λ is in µm and Eg. is in electron volts, one can also obtain the cutoff wavelength as a function of x and t:

$$\lambda _{p} = (-0.244 + 1.556\cdot x + (4.31\cdot 10^{-4})\cdot t\cdot (1-2\cdot x) - 0.65\cdot x^{2} + 0.671\cdot x^{3})^{-1}$$

The Auger 1 minority carrier lifetime for intrinsic (undoped) HgCdTe is given by

$$\tau _{Auger1}(t,x) = \frac{2.12\cdot 10^{-14}\cdot \sqrt{E_{g}(t,x)}\cdot e^{\frac{q\cdot E_{g}(t,x)}{k\cdot t}}}{FF^{2}\cdot (\frac{k\cdot t}{q})^{1.5}}$$

where FF is the overlap integral (approximately 0.221).

The Auger 1 minority carrier lifetime for doped HgCdTe is given by

$$\tau _{Auger1_{doped}}(t,x,n) = \frac{2\cdot \tau _{Auger1(t,x)}}{1+(\frac{n}{n_{i}(t,x)})^{2}}$$

where n is the equilibrium electron concentration.

Cadmium zinc tellurides
Cadmium zinc telluride, (CdZnTe) or CZT, is an alloy of cadmium telluride and zinc Telluride, a direct bandgap semiconductor, used in a variety of applications, including semiconductor radiation detectors, photorefractive gratings, electro-optic modulators, solar cells, and terahertz generation and detection, with a band gap that varies from approximately 1.4 to 2.2 eV, depending on composition.

CZT radiation detectors advantages include high sensitivity for x-rays and gamma-rays, due to the high atomic numbers of Cd and Te, and better energy resolution than [scintillator detectors.

CZT can be formed into different shapes for different radiation-detecting applications, and a variety of electrode geometries, such as coplanar grids and HEXITEC, small pixel detectors, have been developed to provide unipolar (electron-only) operation, thereby improving energy resolution. A 1 cm³ CZT crystal has a sensitivity range of 30 keV to 3 MeV with a 2.5% full width at half maximum (FWHM) energy resolution at 662 keV.

Gadolinium oxysulfides
Gadolinium oxysulfide (: Pr, Ce, F powder complex) based ceramics exhibit final densities of 99.7% to 99.99% of the theoretical density (7.32 g/cm3) and an average grain size ranging from 5 micrometers to 50 micrometers in dependence with the fabrication procedure. There are two main disadvantages to this scintillator; one being the hexagonal crystal structure, which emits only optical translucency and low external light collection at the photodiode and the other is the high X-ray damage to the sample.

The structure is a sulfur layer with double layers of gadolinium and oxygen in between.

Terbium-activated gadolinium oxysulfide is frequently used as a scintillator for x-ray imaging that emits wavelengths between 382-622 nm, though the primary emission peak is at 545 nm and is used as a green phosphor in projection cathode ray tubes, though its drawback is marked lowering of efficiency at higher temperatures.

When Gadolinium oxysulfide comes in contact with mineral acids, hydrogen sulfide can be produced.

Lead(II) iodides
Lead(II) iodide with the formula has a few specialized applications, such as the manufacture of X-ray and gamma ray detectors.

is used as a high-energy photon detector for gamma-rays and X-rays, due to its wide band gap which ensures low noise operation.

"The µ𝛕 product of [a lead iodide ] crystal is estimated to be about 1 x 10-6 cm2/V for electrons and about 6 x 10-7 cm2/V for holes. The resistivity of the crystal is estimated to be about 1012 𝛺/cm. The FWHM energy resolution of the detector for a photoelectric peak for the 59.5 keV 𝛾-rays is found to be about 5 keV."

Lead(II)) sulfides
Like the related materials lead selenide (PbSe) and lead telluride (PbTe), PbS is a semiconductor. In fact, lead sulfide was one of the earliest materials to be used as a semiconductor.

Lead sulfide-containing nanoparticle and quantum dots have been well studied. Traditionally, such materials are produced by combining lead salts with a variety of sulfide sources. PbS nanoparticles have been recently examined for use in solar cells.

Although of little commercial value, PbS is one of the oldest and most common detection element materials in various infrared detectors.

Crystals of PbS were grown aboard the LDEF Mission I Experiments.

Long Duration Exposure Facility
Although is usually assumed to have been produced by the Big Bang nuclear fusion, excesses (100x) of the isotope on the leading edge of the Long Duration Exposure Facility (LDEF) relative to the trailing edge suggest that fusion near the surface of the Sun is the most likely source. The particular reaction (α,γ) and the associated reaction chains (e-,νe)(p,α)α and (p,γ) => 2α + e+ + νe generate 14% and 0.1% of the α-particles, respectively, and 10.7% of the present-epoch luminosity of the Sun. Usually, the produced is assumed to be deep within the core of the Sun; however, such  would not escape to reach the leading edge of the LDEF.

Lunar materials
Based on the -flare flux from the Sun's surface and Surveyor 3 samples (implanted and  in lunar material) from the surface of the Moon, the level of nuclear fusion occurring in the solar atmosphere is approximately at least two to three orders of magnitude greater than that estimated from solar flares such as those of August 1972.

Lutetium aluminum garnets
Lutetium aluminum garnet (LuAG, molecular formula ) is an inorganic compound useful in the synthesis of transparent ceramics.

LuAG is a dopable scintillating crystal that demonstrates luminescence after excitation selected for high structural perfection, high density and high effective atomic number. LuAG is particularly favored over other crystals for its high density and thermal conductivity, a relatively small lattice constant in comparison to the other rare-earth element garnets, which results in a higher density producing a crystal field with narrower linewidths and greater energy level splitting in absorption and emission.

These properties make it an excellent host for active ions such as Yb, Tm, Er, and Ho employed in diode-pumped solid-state lasers, where the density of the lutetium crystal is greater than that of other metals, such as yttrium, meaning that the crystal properties do not change with the addition of dopant ions. It can be especially useful for high energy particle detection and quantification on account of its density and thermal stability. This high melting temperature, in addition to the lack of availability of lutetium has made this crystal less commonly used than its fellow garnets, despite its favorable physical properties.

Mercury tellurides
Coloradoite (HgTe), or mercury telluride, usually has gold within as a high-finess native metal.

Coloradoite, a member of the coordination subclass of tellurides, is a covalent compound that is isostructural with sphalerite (ZnS).

The chemical formula for coloradoite is HgTe. Theoretically the composition (%) of HgTe is Hg 61.14, Te 38.86; The table shows results from a chemical analyses on samples collected from two different locations. Because it is found with other telluride ores, it carries some other metals like gold and silver. In its pure form, it has the composition mentioned above. A little hard to identify, petzite which is hazardous could be mistaken for coloradoite, on the other hand, petzite is anisotropic as opposed to coloradoite being an isotropic mineral. It is a binary compound with the general formula AX.

Coloradoite has a sphalerite structure also known as the "diamond" or "blende" structure; a face centered cubic array in which Hg2+ are in tetrahedral coordination with Te2−, with a stacking sequence of ABCABC. The tetrahedra in the sphalerite group are joined together through their apices and rotated through 60° with respect to each other. Figure 1 shows the atomic structure of coloradoite. The structure is a unit cube with the Te2− ions at the corners and face centers. The four mercury atoms are coordinated so that each mercury atom lies at the center of a regular tetrahedron of tellurium atoms and each tellurium lies at the center of a regular tetrahedron of mercury atoms. Its crystal point group of $\overline{4}$3m and space group is F$\overline{4}$3m. It is a covalent compound with a high proportion of metallic bonding, due to its low valencies and even lower interatomic distances. It is also isotropic, meaning it has just one refractive index.

Common Impurities: Pb.

HgTe bonds are weak leading to low hardness values: 2.7×107 kg/m2.

HgTe is naturally p-type due to mercury vacancies. P-type doping is also achieved by introducing zinc, copper, silver, or gold.

Mercury-telluride quantum well shows a unique new state of matter—the "topological insulator": while the bulk is an insulator, current can be carried by electronic states confined close to the sample edges, unlike the quantum hall effect, here no magnetic field is required to create this unique behavior.

Oppositely directed edge states carry opposite spin projections.

Micrometeoroids
"At the Kennedy Space Center [...], engineers are assessing options for fixing a radiator panel mounted on the inside of the shuttle Atlantis' right-side payload bay door. The panel apparently was damaged when a piece of space debris or a micrometeoroid slammed into the radiator, presumably during the shuttle's flight last month [September 2006], blasting .108-inch-wide hole in the upper surface and destroying the aluminum honeycomb material below before exiting the other side."

"The impact did not threaten the crew and the damage can be repaired. But it illustrates the danger posed by micrometeoroid/orbital debris (MMOD) and the reason why NASA considers such strikes a high risk. The odds of a catastrophic impact-related entry failure range between 1-in-210 to 1-in-350, depending on whether the astronauts inspect the ship in orbit prior to re-entry."

"A preliminary engineering analysis shows the impact in question was one of the most significant instances of MMOD damage in shuttle history, second only to a cargo bay door impact during shuttle mission STS-72 in 1996."

"The shuttle's 60-foot-long payload bay doors each feature four radiator panels that are exposed to space once the doors are opened in orbit. The forward two radiator panels measure about one inch thick, feature Freon coolant tubes positioned about 1.9 inches apart and can pivot to radiate from both sides. The aft panels are fixed and only radiate from one side. They measure a half inch thick and feature coolant tubes separated by about 5 inches. The interior of the panels is made up of an aluminum honeycomb material."

"The impact on Atlantis's right-side, or starboard, radiator was found roughly midway between two coolant lines on panel No. 4. The object blasted a .108-inch-wide hole and presumably broke apart on impact. The resulting spray of debris created a cone-shaped damage cavity immediately below the face plate, destroying the honeycomb interior to the full half-inch depth of the panel. The lower face sheet was pushed out in two places. A .26-inch crack and a .03-inch-wide exit hole were found."

"At orbital velocities, even tiny pieces of debris pose a serious threat. An aluminum sphere just .4 inches across moving at 10 kilometers per second, or 22,370 mph, carries the same impact energy as a bowling ball moving at 300 mph."

Thallium bromides
"Thallium bromide (TlBr) is a compound semiconductor characterized by wide band-gap energy (2.68 eV), high atomic numbers (Tl: 81, Br: 35) and high density (7.56 g/cm3). Mobility-lifetime products for electrons and holes in TlBr crystals are 1 x 103 cm2/V and 3 x 10-4 cm2/V, respectively, which are comparable to for carriers in CdTe crystals. Therefore, TlBr is a suitable material for fabrication of X- and gamma-ray detectors."

Hypotheses

 * 1) The use of satellites should provide ten times the information as sounding rockets or balloons.

A control group for a radiation satellite would contain
 * 1) a radiation astronomy telescope,
 * 2) a two-way communication system,
 * 3) a positional locator,
 * 4) an orientation propulsion system, and
 * 5) power supplies and energy sources for all components.

A control group for radiation astronomy satellites may include an ideal or rigorously stable orbit so that the satellite observes the radiation at or to a much higher resolution than an Earth-based ground-level observatory is capable of.