Lithium, Beryllium and Boron

Present theoretical ideas about LiBeB encompass sites as diverse as the Big Bang, 

The Big Bang. In what is generally known as the standard family of Big Bang (Friedmann) models, 7Li is the only LiBeB nuclide synthesised in observable amounts. This Li in full or in part is seen in warm very metal-poor stars, as the Spite plateau. Nonstandard Big Bang models in a wide variety of forms have been proposed. Often, the consequences for the primordial nucleosynthesis are a focus of these proposals. 

Stars - SN II. The neutrino torrent created at core-collapse of a massive star is so intense that, despite their very small cross-sections, interactions between neutrinos and nuclei in the outer layers of a supernova synthesise several trace species from abundant targets at levels that suggest Type II SN ejecta may be a major influence on the Galactic chemical evolution of these trace species. Notably, nB is synthesised from 12C in the C-shell uC(i/,i/ n)uC(e+i/e)nB and 12C(i/,i/ p)nB. Also, 7Li may be made in the He-shell via 4He( u, u n)3He followed by 3He(a, 7)7Be(e, z/e)7Li. No other LiBeB nuclide is predicted to be synthesised in interesting amounts. In particular, 9Be, the sole stable Be isotope, is not synthesized. 

The 3He reservoir of a main sequence star may also be tapped during a nova outburst. The 3He is in the gas accreted by the white dwarf from its main sequence companion. Although the reaction chain known as the 7Be-transport mechanism is important, other reactions influence the predicted 7Li yields from the explosions on C-O and O-Ne white dwarfs. Jose (2002) estimates that the contribution from novae to the Galactic 7Li abundance is rather small (i.e., less than 15%), even if the 7Li yield from the most favorable case, a massive CO nova, is considered.  

Interstellar Gas. LiBeB synthesis in interstellar (or circumstellar) gas occurs as cosmic rays collide wth ambient nuclei. Spallation reactions of the type (C, N, and O) + (p or a) result in LiBeB production. Fusion reactions a + a contribute to the synthesis of 6Li and 7Li. 

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The chemical formulas for the oxides of lithium, beryllium, and boron are Li20, BeO, and B2O3. Write the formulas for the oxides of sodium, potassium, magnesium, calcium, aluminum, and gallium. Explain how you determined their formulas. 

Launched like missiles, atomic nuclei can smash head-on into other atomic nuclei, fragmenting both projectile and target. Rare and precious species can emerge intact from amongst the debris. Examples are lithium, beryllium and boron, for which nature has found no other means of manufacture. 

The precipitous chasm inhabited by lithium, beryllium and boron reflects the extreme fragility of the nuclei of these species. Note that fluorine, located just above the favoured number of eight protons, is as expected rather scarce. 

In addition to all these fusion and neutron capture processes, there is a further type of nuclear reaction, called spallation. Rather than fusing together, nuclei are smashed up or chipped to produce smaller species. This process is thought to be the origin of most of the lithium, beryllium and boron in the Universe. 

At low temperatures (15 million K), reactions between helium nuclei are inhibited by electrical repulsion. On the other hand, the nuclear properties of lithium, beryllium and boron nuclei (Z = 3,4, 5), and in particular their stability, are such that they are extremely fragile, decaying at temperatures of only 1 million K. For this reason, they are not formed in appreciable quantities in stars and cannot serve to bridge the gap between helium and carbon, species noted for their nuclear stability but which, it should be recalled, occur only in minute amounts in nature. 

Stellar nucleosynthesis thereby leap-frogs over three fragile elements, lithium, beryllium and boron, moving more or less directly from helium to... 

It is not therefore to the planets that we should associate the elements iron with Mars, lead with Saturn, mercury with Mercury. It is indeed the stars that have nurtured them. Some stars make carbon, others gold. Thermonuclear combustion modifies the composition of the hottest regions within stars. Each star is responsible for the confection and distribution of a particular batch of atoms, apart from hydrogen and a large part of the helium in the Universe which were synthesised in the Big Bang, and the lightweight trio lithium, beryllium and boron. 

A large increase in the O/Fe ratio in stars at low metallicity was reported by Israelian et al. in 1998 and by Boesgaard et al. in 1999, contradicting earlier data which suggested an approximately constant O/Fe ratio. Now oxygen is particularly relevant to the astrophysics of cosmic rays. This is because spallation products under collision include the light nuclei lithium, beryllium and boron. 

Well, not quite everything. The hght elements lithium, beryllium, and boron are formed mostly by the break-up of heavier nuclei when hit by cosmic rays and other high-energy particles in interstellar space. This process, which whittles the nuclei down to hghter elements, is called spallation. Nucleosynthesis in stars produces very httle of these three elements. 

In this chapter, we reviewed the broad outlines of the Big Bang model for the origin of the universe and discussed some of the supporting observations. We showed that the Big Bang gave rise to hydrogen, helium, and some lithium, beryllium, and boron, but that other elements were produced primarily in stars. The rest of the elements were synthesized in stars via the nuclear reactions that cause the stars to shine. To understand stellar nucleosynthesis, it is necessary to understand the characteristics of stars. Astronomers use... 

Second, lithium, beryllium, and boron have very low abundances. These elements are, for the most part, not made in stars and were not made efficiently in the Big Bang. They are produced via cosmic ray interactions. Nuclei of heavier atoms, when hit by fast moving protons or other nuclei, can break into pieces, including protons, neutrons, alpha particles, and heavier fragments. Some of these fragments are lithium, beryllium, and boron nuclei. 

The observed abundance of light elements can be used to deduce some of the properties of cosmic rays, which are fast-moving particles such as electrons and protons. The abundances of elements such as lithium, beryllium, and boron suggest that each proton has to... 

It is appropriate to begin this lecture with a diagram from the review of Shapiro Silberberg, 1970, which compares the abundances of elements in the cosmic radiation with solar system abundances. This classic measurement is one of the foundations of cosmic-ray physics. The elements lithium, beryllium and boron are quite abundant among cosmic rays even though they constitute only a tiny fraction of the material in the solar system and the interstellar medium. This fact is understood largely as the result of spallation of the... 

And in starspots, where the magnetic field may be many times greater than in sunspots, we expect particles of very high energy. These naturally accelerated particles can produce elements like lithium, beryllium, and boron which are very rare in the stars but which have been detected by analyzing starlight with a spectroscope. 

The light and fragile elements lithium, beryllium, and boron (LiBeB) are not primarily produced in primordial or stellar nucleosynthesis. In fact, the abundance curve in O Fig. 12.13 shows a huge dip (almost a gap, actually) for the mass numbers 8-11, reflecting the scarcity of LiBeB-nuclei in the solar system. Only the nuclide Li can be produced both in primordial (see Sect. 12.3) and in stellar nucleosynthesis (see Sect. 12.4.2), whereas the nuclides Li, Be, B, and B are almost pure spallation products of heavier elements. 

Leroy G (1983) Stability of chemical species. Int J Quantum Chem 23 271-308 Leroy G, SanaM, WUante C, van Zieleghem M-J (1991) Revaluation of the bond energy terms for bonds between atoms of the first rows of the Periodic Table, including lithium, beryllium and boron. J Molec Struct 247 199-215... 

The SINDO 1 technique is claimed to give more reliable calculated ionization potentials than MINDO/3, MNDO, and STO-3G calculations for molecules containing lithium, beryllium, and boron atoms. A Urey-Bradley forcefield... 

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