Chemicals/Borons

Boron is synthesized entirely by cosmic ray spallation and supernovae and not by stellar nucleosynthesis, so it is a low-abundance element in the Solar System and in the Earth's crust. It constitutes about 0.001 percent by weight of Earth's crust. It is concentrated on Earth by the water-solubility of its more common naturally occurring compounds, the borate mineral such as borax and kernite.

Elemental boron is a metalloid that is found in small amounts in meteoroids but chemically uncombined boron is not otherwise found naturally on Earth.

The "presence in ... cosmic radiation [is] of a much greater proportion of "secondary" nuclei, such as lithium, beryllium and boron, than is found generally in the universe."

Emissions and absorptions
Boron (B I) line is at 249.67 nm.

Above is a light spectrum of the emission and absorption lines of neutral, atomic boron.

Important for violet astronomy is the two strong lines well within the violet range and one weaker line on the fringe of the violet and blue portions of the visual spectrum.

The emission and absorption spectra for boron contain lines on the border between violet and blue.

Boron has a line in the cyan.

Similar to beryllium, the visual spectrum of boron is missing lines in the yellow, but unlike it is also missing lines in the green and has a line in the orange.

Boron has a red line near the orange portion of the visual spectrum.

There are B I lines at 1624.0371 and 1624.4670 nm.

"[T]he solar system meteoritic NB/NBe ratio 28 ± 4 (Anders & Grevesse 1989) is within our limits of uncertainty, implying that the same process could in principle be responsible for the production of B and Be throughout the history of the Galaxy."

Cosmic rays
Def. "an energetic particle originating outside our solar system" is called a cosmic ray.

"Cosmic rays arise from galactic source accelerators."

Cosmic rays may be upwards of a ZeV (1021 eV).

About 89% of cosmic rays are simple protons or hydrogen nuclei, 10% are helium nuclei of alpha particles, and 1% are the nuclei of heavier elements. Solitary electrons constitute much of the remaining 1%.

Def. cosmic rays that originate from astrophysical sources are called primary cosmic rays.

Def. cosmic rays that are created when primary cosmic rays interact with interstellar matter are called secondary cosmic rays.

Def. low energy cosmic rays associated with solar flares are called solar cosmic rays.

Cosmic rays are not charge balanced; that is, positive ions heavily outnumber electrons. The positive ions are
 * 1) free protons,
 * 2) alpha particles (helium nuclei),
 * 3) lithium nuclei,
 * 4) beryllium nuclei, and
 * 5) boron nuclei.

Def. a nuclear reaction in which a nucleus fragments into many nucleons is called spallation.

Cosmic rays cause spallation when a ray particle (e.g. a proton) impacts with matter, including other cosmic rays. The result of the collision is the expulsion of large numbers of nucleons (protons and neutrons) from the object hit.

Carbon and oxygen nuclei collide with interstellar matter to form lithium, beryllium and boron in a process termed cosmic ray spallation.

Subatomics
"In cosmic rays, both the isotopes 10B and 11B are present in comparable quantities."

In the figure on the right are absolute boron and carbon fluxes multiplied by E2.7 as measured by PAMELA, together with results from other experiments (AMS02 Oliva et al. (2013), CREAM Ahn et al. (2008), TRACER Obermeier et al. (2011), ATIC-2 Panov et al. (2007), HEAO Engelmann et al. (1990), AMS01 Aguilar et al. (2010), CRN Swordy et al. (1990)) and a theoretical calculation based on GALPROP, as functions of kinetic energy per nucleon.

Neutrons
Absorptive reactions with prompt reactions - Low energy neutrons are typically detected indirectly through absorption reactions. Typical absorber materials used have high cross sections for absorption of neutrons and include Helium-3, Lithium-6, Boron-10, and Uranium-235 Each of these reacts by emission of high energy ionized particles, the ionization track of which can be detected by a number of means. Commonly used reactions include 3He(n,p) 3H, 6Li(n,α) 3H, 10B(n,α) 7Li and the fission of uranium.

Positrons
"If the proton and neutron are part of an atomic nucleus, these decay processes transmute one chemical element into another. For example:



A_ZN \rightarrow ~ ^{A}_{Z-1}N' + e^+ + \nu_e, $$

where A = 22, Z = 11, N = Na, Z-1 = 10, and N' = Ne.

Beta decay does not change the number of nucleons, A, in the nucleus but changes only its charge, Z. Thus the set of all nuclides with the same A can be introduced; these isobaric nuclides may turn into each other via beta decay. Among them, several nuclides (at least one) are beta stable, because they present local minima of the mass excess: if such a nucleus has (A, Z) numbers, the neighbour nuclei (A, Z&minus;1) and (A, Z+1) have higher mass excess and can beta decay into (A, Z), but not vice versa. For all odd mass numbers A the global minimum is also the unique local minimum. For even A, there are up to three different beta-stable isobars experimentally known. There are about 355 known beta-decay stable nuclides total.

In decay, or "positron emission", the weak interaction converts a nucleus into its next-lower neighbor on the periodic table while emitting an positron  and an electron neutrino :



^A_ZN \rightarrow ~ ^{A}_{Z-1}N' + e^+ + \nu_e. $$

decay cannot occur in an isolated proton because it requires energy due to the mass of the neutron being greater than the mass of the proton. decay can only happen inside nuclei when the value of the binding energy of the mother nucleus is less than that of the daughter nucleus. The difference between these energies goes into the reaction of converting a proton into a neutron, a positron and a neutrino and into the kinetic energy of these particles.

Positron emission or beta plus decay' (β+ decay) is a type of beta decay in which a proton is converted, via the weak force, to a neutron, releasing a positron and a neutrino.

Isotopes which undergo this decay and thereby emit positrons include carbon-11, potassium-40, nitrogen-13, oxygen-15, fluorine-18, and iodine-121. As an example, the following equation describes the beta plus decay of carbon-11 to boron-11, emitting a positron and a neutrino:



^{11}_{6}C \rightarrow ~ ^{11}_{5}B + e^+ + \nu_e + \gamma {(0.96 MeV)}. $$

The figure at right shows a positron (e+) emitted from an atomic nucleus together with a neutrino (v). Subsequently, the positron moves randomly through the surrounding matter where it hits several different electrons (e-) until it finally loses enough energy that it interacts with a single electron. This process is called an "annihilation" and results in two diametrically emitted photons with a typical energy of 511 keV each. Under normal circumstances the photons are not emitted exactly diametrically (180 degrees). This is due to the remaining energy of the positron having conservation of momentum.

At energies near and beyond the mass of the carriers of the weak force, the W and Z bosons, the strength of the weak force becomes comparable with electromagnetism. It becomes much easier to produce particles such as neutrinos that interact only weakly.

"The proton-proton chain, or hydrogen burning, is postulated by standard stellar theory as the principal mechanism of energy generation in the sun during the current stage of its evolution. The net result of this chain of nuclear reactions is conversion of four protons into helium-4, and the energy released is carried off by photons, positrons, and neutrinos."

"The nuclear reaction chains postulated by the standard model as the mechanism of solar energy generation [...] include a number of weak interactions (electron captures and beta decays [such as the beta decay of boron-8]) that produce neutrinos."

Neutrinos
"A star is considered to be at zero age (protostellar) when it is assumed to have a homogeneous composition and to be just beginning to derive most of its luminosity from nuclear reactions (so neglecting the period of contraction from a cloud of gas and dust). To obtain the SSM, a one solar mass stellar model at zero age is evolved numerically to the age of the Sun. The abundance of elements in the zero age solar model is estimated from primordial meteorites. Along with this abundance information, a reasonable guess at the zero-age luminosity (such as the present-day Sun's luminosity) is then converted by an iterative procedure into the correct value for the model, and the temperature, pressure and density throughout the model calculated by solving the equations of stellar structure numerically assuming the star to be in a steady state. The model is then evolved numerically up to the age of the Sun. Any discrepancy from the measured values of the Sun's luminosity, surface abundances, etc. can then be used to refine the model. For example, since the Sun formed, the helium and heavy elements have settled out of the photosphere by diffusion. As a result, the Solar photosphere now contains about 87% as much helium and heavy elements as the protostellar photosphere had; the protostellar Solar photosphere was 71.1% hydrogen, 27.4% helium, and 1.5% metals. A measure of heavy-element settling by diffusion is required for a more accurate model."

"Nuclear reactions in the core of the Sun change its composition, by converting hydrogen nuclei into helium nuclei by the proton-proton chain and (to a lesser extent in the Sun than in more massive stars) the CNO cycle. This decreases the mean molecular weight in the core of the Sun, which should lead to a decrease in pressure. This does not happen as instead the core contracts. By the Virial Theorem half of the gravitational potential energy released by this contraction goes towards raising the temperature of the core, and the other half is radiated away. By the ideal gas law this increase in temperature also increases the pressure and restores the balance of hydrostatic equilibrium. The luminosity of the Sun is increased by the temperature rise, increasing the rate of nuclear reactions. The outer layers expand to compensate for the increased temperature and pressure gradients, so the radius also increases. "

"Most of the neutrinos produced in the sun come from the first step of the pp chain but their energy is so low (<0.425 MeV) they are very difficult to detect. A rare side branch of the pp chain produces the "boron-8" neutrinos with a maximum energy of roughly 15 MeV, and these are the easiest neutrinos to detect. A very rare interaction in the pp chain produces the "hep" neutrinos, the highest energy neutrinos predicted to be produced by our sun. They are predicted to have a maximum energy of about 18 MeV."

"All of the interactions described above produce neutrinos with a spectrum of energies. The electron capture of 7Be produces neutrinos at either roughly 0.862 MeV (~90%) or 0.384 MeV (~10%). "

"Also of importance in this emerging field [of observational neutrino astrophysics] are the observation of solar boron-8 neutrinos and the detection of high-energy point sources."


 * $$\nu + ^{97}Mo \rightarrow e^- + ^{97}Tc,$$ and


 * $$\nu + ^{98}Mo \rightarrow e^- + ^{98}Tc.$$

These "reactions probe precisely the time scale and neutrino-flux component of most interest: the boron-8 neutrino luminosity, which is the most sensitive monitor of variations in the solar core temperature, during and before the Pleistocene epoch. (The half-lives of technetium-97 and -98 are, respectively, 2.6 and 4.2 million years; the reaction on molybdenum-98 is induced only by the high-energy boron-8 neutrinos; and the reaction on molybdenum-97 may sample in addition the flux of beryllium-7 neutrinos, which are second only to boron-8 neutrinos in sensitivity to the core temperature.)"

A "quantitative test can be made of nonstandard solar models that suggest a connection between the solar neutrino puzzle, the proximity of the Pleistocene glacial epoch, and the fundamental thermal and nuclear times of the solar core."

Solar "mixing about four million years ago [may have] initiated the Pleistocene epoch and a persisting depression of the high-energy solar neutrino flux. Clear memory of the steady-state solar phase that preceded mixing should be retained in technetium-98 with its half-life of 4.2 million years. Recovery of this isotope in a quantity lower than that predicted by the standard solar model but significantly higher than that detected by the Davis experiment would support suggestions of solar variability and solar influence on terrestrial climate."

Petrochemistry
Many rocky objects are composed of oxide minerals. Oxygen has three known stable isotopes: 16O, 17O, and 18O.

"The stable isotopic compositions of low-mass (light) elements such as oxygen, hydrogen, [helium, lithium, beryllium, boron,] carbon, nitrogen, [fluorine, neon, sodium, magnesium, aluminum, silicon, phosphorus,] and sulfur are normally reported as "delta" ([δ]) values in parts per thousand (denoted as ‰ [per mille]) enrichments or depletions relative to a standard of known composition."

For 18O to 16O:


 * $$\delta ^{18}O = \Biggl( \frac{\bigl( \frac{^{18}O}{^{16}O} \bigr)_{sample}}{\bigl( \frac{^{18}O}{^{16}O} \bigr)_{standard}} -1 \Biggr) * 1000\ ^{o}\!/\!_{oo}$$

The "ratio [by convention is] of the heavy to light isotope in the sample or standard."

"Various isotope standards are used for reporting isotopic compositions; the compositions of each of the standards have been defined as 0‰. Stable oxygen and hydrogen isotopic ratios are normally reported relative to the SMOW standard ("Standard Mean Ocean Water" (Craig, 1961b)) or the virtually equivalent VSMOW (Vienna-SMOW) standard. Carbon stable isotope ratios are reported relative to the PDB (for Pee Dee Belemnite) or the equivalent VPDB (Vienna PDB) standard. The oxygen stable isotope ratios of carbonates are commonly reported relative to PDB or VPDB, also. Sulfur and nitrogen isotopes are reported relative to CDT (for Cañon Diablo Troilite) and AIR (for atmospheric air), respectively."

"Ordinary water consists of slightly different kinds of so-called isotopic water molecules of equal chemical properties but different masses: a light one (H2O16), which occurs most frequently by far in natural waters, and quite a few heavier ones, of which the H2O18 and the [deuterium, D) HDO16 components occur in concentrations of approximately 2000 and 320 ppm (parts per million) water molecules, respectively. Due to slightly different vapour pressures and rates of reaction, the concentrations of the isotopic components change somewhat during phase-shifts in the natural water cycle".

Ice "cores contain a wealth of information on past climates in the form of a great number of parameters, of which some are listed below:"
 * 1) Concentrations of the oxygen-18 and deuterium components of water in the ice give information about the cloud temperature and precipitation at the time of deposition,
 * 2) the content of air in bubbles reveals the altitude of the then ice surface,
 * 3) the concentrations of carbon dioxide and methane in the air bubbles tell about the greenhouse effect in past atmospheres,
 * 4) the chemical composition of the ice itself gives information about other aspects of the chemistry in past atmospheres,
 * 5) dust and calcium concentration tell about the violence and frequency of the storms that carried dust from ice free areas to the inland ice, and
 * 6) the acidity of the ice indicates the fall-out of volcanic acids and thereby past volcanic activity.

Oceans
The "pH change for deep Pacific Ocean water associated with both the 3% increase in salinity resulting from the growth of the ice caps and the 700-m deepening of the lysocline9 are so small that they would lie within the uncertainty of pH reconstruction based on boron isotopes. If the glacial to Holocene drop in pH (0.3 units) suggested by the boron isotope measurements on benthic foraminifera was mainly accomplished by excess CaCO2 accumulation, then the alkalinity of deep Pacific water must have been ~10% higher during glacial time. As a result, the carbonate ion concentration of deep Pacific water during glacial time would have been ~100 µmol kg-1 higher than the present-day value, deepening the calcite saturation horizon by several kilometres."

Reedmergnerites
For the "reedmergnerite unit, BSi4O10 ... The spectra showed small amounts of it, and we saw no evidence of fragmentation (i.e., no corresponding smaller fragments that would appear to be constituents). Thus, it does not appear to be the dominant group in the glass network. ... The borate association remains dominant, however, even as we increase the soda content."

Flame emission spectroscopy
In flame emission spectroscopy, as shown in the image on the right, a small mineral sample is put into the flame as either a gas, sprayed solution, or on a small loop of wire, usually platinum. The flame evaporates the mineral and breaks chemical bonds to create free atoms. Each element emits light at a characteristic wavelength. These emissions are dispersed by a grating or prism and detected in the spectrometer. Boron emits a bright green.

If a Bunsen burner is available where you are trying to chemically analyze a mineral sample, inserting a small piece safely in the flame could prove helpful as the image on the right shows.

Isotope geochemistry
{{legend|#feff41|alpha decay}} {{legend|#000000|stable nuclide}} {{legend|#e78cc7|beta+/EC decay}} {{legend|#63c5de|beta- decay}} {{legend|#ff9472|proton decay}} {{legend|#53b552|spontaneous fission}} {{legend|#9b7bbc|neutron emission}} A table of nuclides or chart of nuclides is a two-dimensional graph in which one axis represents the number of neutrons and the other represents the number of protons in an atomic nucleus. Each point plotted on the graph thus represents the nuclide of a real or hypothetical chemical element. Hydrogen is at the lower left.

Isotope geochemistry involves the determination of the relative and absolute concentrations of the [chemical] elements and their isotopes in the earth and on earth's surface.

For most stable isotopes, the magnitude of fractionation from kinetic and equilibrium fractionation is very small; for this reason, enrichments are typically reported in "per mil" (‰, parts per thousand).

Enrichments ($$\delta$$) represent the ratio of heavy isotope to light isotope in the sample over the ratio of a standard.


 * $$\delta ^{A}isotope = \Biggl( \frac{\bigl( \frac{^{A}isotope}{^{B}isotope} \bigr)_{sample}}{\bigl( \frac{^{A}isotope}{^{B}isotope} \bigr)_{standard}} -1 \Biggr) * 1000\ ^{o}\!/\!_{oo}$$

"The depletion of total [boron] B [in the Victorian volcanic-crater lakes of southeastern Australia] and the high positive δ 11B values relative to seawater (B/Cl ratio = 7.9 x 10-4; δ 11B = 39%.) are attributed to a marine (cyclic) salt origin together with adsorption processes in closed systems with low water/sediment (W/R) ratios."

"Although the δ [11B] value of borate minerals may be a discriminant of marine or non-marine origin, boron isotopes are less distinctive in evaporative environments where boron is not an abundant component and where water/sediment interaction occurs."

The incidence of 18O (the heavy isotope of oxygen) can be used as an indicator of polar ice sheet extent, and boron isotopes are key indicators of the pH and CO2 content of oceans in the geologic past.

Although rubidium is monoisotopic, naturally occurring rubidium is composed of two isotopes: the stable 85Rb (72.2%) and the radioactive 87Rb (27.8%). Natural rubidium is radioactive with specific activity of about 670 (Becquerel) Bq/g, enough to significantly expose a photographic film in 110 days.

Hardness
Unlike other silica polymorphs, the crystal structure of stishovite resembles that of rutile. The silicon in stishovite adopts an octahedral coordination geometry, being bound to six oxides. Similarly, the oxides are three-connected, unlike low-pressure forms of SiO2. In most silicates, silicon is tetrahedral, being bound to four oxides. It was long considered the hardest known oxide (~30 GPa Vickers ); however, boron suboxide has been discovered in 2002 to be much harder.

Meteorites
Boron has been found in Martian meteorites that included MIZ 09030 in 2013, MIL 09030, the Nakhla meteorite, the Lafayette meteorite, and the Chassigny meteorite.

Serpentines
Chromite present in the protolith will be altered to chromium-rich magnetite at lower serpentinization temperatures. At higher temperatures, it will be altered to iron-rich chromite (ferrit-chromite). During serpentinization, the rock is enriched in chlorine, boron, fluorine, and sulfur. Sulfur will be reduce to hydrogen sulfide and sulfide minerals, though significant quantities are incorporated into serpentine minerals, and some may later be reoxidized to sulfate minerals such as anhydrite. The sulfides produced include nickel-rich sulfides, such as mackinawite.

Lavas
"Boron contents [have been] measured in representative Quaternary lavas from the Central American Volcanic Arc to evaluate along-strike variations in subduction processes."

"Despite the significant range in B concentrations (~2–37 ppm) in the mafic lavas, B/La ratios vary in a systematic fashion along the arc; higher values (> 1) are typical between Guatemala and northern Costa Rica, whereas low values (most <0.5) typify central Costa Rica and western Panama."

Granulites
"Boron contents are uniformly low in more than 100 granulites from exposed terranes in India, Norway, and Scotland and from xenolith suites in the western USA."

"Boron is apparently depleted in all granulite protoliths during prograde metamorphism and dehydration."

Mars
The element boron has been found on Mars in mineral veins, where there must have been a temperature between 0-60 degrees Celsius, a neutral-to-alkaline pH, and dissolved minerals of the groundwater to support a habitable environment.

The boron was identified by the rover's laser-shooting Chemistry and Camera (ChemCam) instrument, which was developed at Los Alamos National Laboratory. Hematite, clay minerals and boron are found to be more abundant in layers farther uphill in Gale Crater, compared with lower, older layers.

Stars
"Stars with an initial mass less than the solar mass have a large deficiency of light elements — lithium, beryllium, and boron — which burn up almost completely both in the interior and in the convective envelope."

"The light elements deuterium, lithium, beryllium, and boron pose a special problem for any theory of the origin of the elements which proposes that all the elements are built up from hydrogen in the stars. ... The difficulty arises because the lifetimes of these elements against proton capture, at the temperatures and pressures at which most stellar matter exists, are short compared to the stable lifetimes of stars. These elements then cannot be produced in stellar interiors unless they are transported rapidly to the surface, and if they are produced at the surface, non-equilibrium processes must be involved. Further, they can exist in significant quantities at the surface only in the absence of rapid mixing to the interior."

Boron is detected in the Population II star HD 140283 by observing the "wavelength region around the resonance lines of B I at 2497 Å ... with the Goddard High Resolution Spectrograph (GHRS) of the Hubble Space Telescope on September 5, 1992, ... and continued on February 15, and 21, 1993" "The resulting B/Be ratio is in the range 9-34 with 17 being the most probable value. This is in very good agreement with predictions for cosmic ray spallation."

A "sample of 23 stars contained objects with (1) strong Be and strong B, (2) weak Be and strong B, (3) strong Be and weak B, as well as (4) weak Be and B."

"Boron is estimated to be overabundant by at least 2.0 dex in these three stars [κ Cnc, HR 7361, and 20 Tau] ... Three [additional] stars (HR 2676, γ Crv, and HR 7143) show strong B II lines as in the case of κ Cnc".