Beryllium abundance

Fig. 9.6. Beryllium abundance as a function of oxygen abundance, according to models (curves) and observations (open circles) by Gilmore et al. (1992). (a in the key is actually the quantity called a in the text.) After Pagel (1994). With kind permission from Kluwer Academic Publishers.

Fig. 9.8. Trend of beryllium abundance with metallicity compared to predictions from two models (a) CRS denotes cosmic-ray acceleration in superbubbles rich in iron and oxygen as predicted from theoretical supernova yields (in this case those of Tsujimoto and Shigeyama 1998) and (b) CRI denoting cosmic rays accelerated from the general interstellar medium. The density dependence comes from its influence on the delay in the deposition of the synthesized Be. Virtually identical results were obtained using the yields from Woosley and Weaver (1995). After Ramaty et al. (2000).

The Op mechanism leads to proportionality between oxygen and beryllium abundances, for example, because these two elements arise from the same source, namely, type 11 supernovas, oxygen directly and beryllium indirectly (via collisional disintegration of oxygen into beryllium). A constant Be/0 ratio, independent of O/H, would be the hallmark of the Op mechanism. 

Boesgaard, A.M., Deliyannis, C.P., King, J.R., Ryan, S.G., Vogt, S.S. Beers, T.C. 1999 Beryllium abundances in halo stars from Keck/HIRES observations. A J 117, 1549. 

Primas, F., Asplund, M., Nissen, P.E. Hill, V. 2000 The beryllium abundance in the very metal-poor halo star G64-12 from VLT/UVES observations. A A 364, L42. 

One of the most obvious features of Figs. 1.1 and 1.5 is the very low cosmic abundance of the stable isotopes of lithium, beryllium and... 

Uranium is not a very rare element. It is widely disseminated in nature with estimates of its average abundance in the Earth s crust varying from 2 to 4 ppm, close to that of molybdenum, tungsten, arsenic, and beryllium, but richer than such metals as bismuth, cadmium, mercury, and silver its crustal abundance is 2.7 ppm. The economically usable tenor of uranium ore deposits is about 0.2%, and hence the concentration factor needed to form economic ore deposits is about 750. In contrast, the enrichment factors needed to form usable ore deposits of common metals such as lead and chromium are as high as 3125 and 1750, respectively. 

Another view, equally consistent with the source abundances and better suited to account for the abundance of light elements like beryllium in stars of the Galactic halo (see below), is that dust particles in the supernova ejecta are the source of ions that are preferentially accelerated within the hot, tenuous gas of superbubbles surrounding regions of star formation (Lingenfelter, Ramaty Kozlovsky 1998). 

The predictions of this model (normalized to meteoritic abundance for solar metallicity) are illustrated in Fig. 9.6 and compared with observational data for beryllium in stars, based on ground-based measurements of the near-UV Be II doublet A 3130. Assuming that surface Be can suffer some destruction in some of the metal-rich disk stars, there is fair agreement down to about 0.1 of solar abundance, but the secondary trend predicted at still lower metallicities is too steep. 

The above models are all rather unsatisfactory, because they involve somewhat arbitrary assumptions about the time-dependence of the cosmic-ray flux and spectrum and because they predict a secondary-like behaviour for Be and B abundances, whereas the overall trend indicated by the data is more like a primary one and there are the energetic difficulties pointed out above. In the case of nB, there is a possible primary mechanism for stellar production in supemovae by neutrino spallation processes (Woosley et al. 1990 Woosley Weaver 1995), but the primary-like behaviour of beryllium in metal-poor stars, combined with a constant B/Be ratio of about 20 fully consistent with cosmic-ray spallation (Garcia Lopez et al. 1998) in the absence of any known similar process for Be, indicates that this does not solve the problem unless a primary process can be found for Be as well. Indeed,... 

Assuming a cosmic-ray confinement time of 106 7 years and an interstellar hydrogen density of 1 atom cm-3, with present-day CNO abundances, use Eq. (9.10) to deduce Q/W for beryllium. 

Pegmatite deposits are the most abundant. They contain a variety of minerals including tantalum, niobium, lithium and beryllium, as well as REE and zircon. 

Fig. 8.3. Lithium, beryllium and iron. The symbol [Fe/H] denotes the logarithm of the ratio of Fe/H for the star and Fe/H for the Sun. The evolution of lithium and beryUium in the halo [Fe/H] < — 1 is a classic example. The lithium content remains independent of the iron content in halo stars. This is known as the Spite plateau, named after the two French astronomers Monica and Fran ois Spite. It indicates a primordial origin (i.e. in the Big Bang). An upturn occurs just when the disk stars begin to take over. Berylhumis an archetypal example of elements created by spallation. Its abundance increases monotonicaUy by accumulation as time goes by.

SNII events alone explain the observed solar abundance distribution between oxygen and chromium. This can be taken as a major theoretical achievement. Complementary sources of hydrogen, helium, lithium, beryllium, boron, carbon and nitrogen are required, and these have been identified. They are the Big Bang, cosmic rays and intermediate-mass stars. Around iron and a little beyond, we must invoke a contribution from type la supernovas (Pig. 8.5). These must be included to reproduce the evolution of iron abundances, a fact which suggests... 

It is known that the oxygen abundance in the interstellar medium increases all the time this nucleus is produced by type 11 supernovas which, one after the other, also contribute their iron production to the Galaxy (Fig. 8.7). The pO mechanism is thus likely to grow in importance as the Galaxy evolves. In other words, clues to the Op mechanism should be sought in the early phases of galactic evolution, that is, in halo stars. The fact remains that the two mechanisms induce different evolution in beryllium and boron as a function of oxygen. 

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. 

Strontium has four naturally occurring isotopes (Table 4.2). It is a member of the alkaline earths (Group 2A) along with beryllium, magnesium, calcium, barium, and radium (Fig. 2.4). Strontium substitutes for calcium and is abundant in minerals such as plagioclase, apatite, and calcium carbonate. 

Beryllium-10 P-decays to 10B with a half-life of 1.5 Myr. Beryllium and boron (along with lithium) are several orders of magnitude less abundant than the other light elements in the solar system because, except for 7Li, they are not produced in stars. They are produced when high-energy cosmic rays, mostly protons, fragment atomic nuclei into small pieces in a process called spallation. Beryllium-10 is constantly being produced at low levels by spallation in the solar system, and its abundance in bulk meteorites is used to estimate the amount of time that they were exposed to cosmic rays as small bodies (their cosmic-ray... 

An important feature of beryllium amide studies since 1980 has been the acquisition of Be NMR data. NMR signals for this nucleus, which has 100% abundance, 1= 3/2 and a receptivity almost two orders of magnitude greater than the nucleus,can be obtained without major difficulties. Some chemical shift data gathered from Refs. 17,18 and 20 are... 

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... 

Rice, D.L. (1986) Early diagenesis in bioadvective sediments relationships between the diagenesis of beryllium-7, sediment reworking rates, and the abundance of conveyor-belt deposit-feeders. J. Mar. Res. 44, 149-184. 

The moderately abundant heavier elements are found principally as sulphates SrS04 and BaS04, whereas beryllium is rather rare and occurs in beryl Be3Al2Si6018. Radium is radioactive, its longest-lived... 

Natural isotopes of beryllium and their solar abundances... 

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