Boron abundance

Cunha K. and Smith V. V. (1999) A determination of the solar photospheric boron abundance. Astrophys. J. 512, 1006-1013. 

Boron-isotopic data also show the strong decrease in slab-derived boron across the width of the arc. Figure 5(a) documents the decline in 5 B across the Kurile and Izu-Bonin arcs, which follow cross-arc declines in boron abundances (Ishikawa and Nakamura, 1994 Ryan et al, 1995 Ishikawa and Tera, 1997). Ishikawa and Tera (1997) interpreted the cross-arc decline of boron isotopes in the Kuriles as a simple mixture of AOB-dominated slab boron with the mantle, which should be both boron depleted. 

Ryan J. G. and Langmuir C. H. (1992) The systematics of boron abundances in young volcanic rocks. Geochim. Cosmochim. Acta 57, 1489-1498. 

In contrast to helium and CNO, the light elements are destroyed relatively close to the stellar surface. For both stable boron isotopes, 10B and nB, the life time against proton capture, the dominant destruction mechanism, is equal to the main sequence life time of a 10 M0 star (107yr) at a temperature of roughly 7106K. This temperature occurs sufficiently deep inside the stellar envelope (i.e. roughly 1 M0 below the surface cf. Fig. 10) that its surface abundance can not be altered due to mass loss alone on the main sequence in the B star regime. Thus, the boron abundance in B stars is a critical... 

Due to the degeneracy of the HRD positions during the main sequence evolution (see Fig. 8), a comparison of the observed stellar boron abundances and effective temperatures... 

Timmes, Woosley Weaver (1995) developed a chemical evolution model of the solar neighbourhood in an attempt to account for the observed abundances of elements from H to Zn in metal-rich and metal-poor stars. The (/-process contributions were included. With their predicted yields of nB and excluding 10B and nB from cosmic ray driven spallation, they were able to reproduce the then fragmentary data on the run of the boron abundance with metallicity (see their Fig. 9) from [Fe/H] —2.5 to [Fe/H] cz 0 and including a fit to the meteoritic abundance. Newer data on the B abundances is equally... 

Of the five Group III elements, only boron and aluminium are reasonably familiar elements. Aluminium is in fact the most abundant metal, the third most abundant element in nature, but the other elements are rare and boron is the only one so far found In concentrated deposits. 

One of the first applications of this technique was to the enrichment of and "B isotopes, present as 18.7 and 81.3 per cent, respectively, in natural abundance. Boron trichloride, BCI3, dissociates when irradiated with a pulsed CO2 laser in the 3g vibrational band at 958 cm (vj is an e vibration of the planar, D j, molecule). One of the products of dissociation was detected by reaction with O2 to form BO which then produced chemiluminescence (emission of radiation as a result of energy gained by chemical reaction) in the visible region due to A U — fluorescence. Irradiation in the 3g band of BCls or "BCI3 resulted in °BO or BO chemiluminescence. The fluorescence of °BO is easily resolved from that of "BO. 

Boron-10 has a natural abundance of 19.61 atomic % and a thermal neutron cross section of 3.837 x 10 m (3837 bams) as compared to the cross section of 5 x 10 m (0.005 bams). Boron-10 is used at 40—95 atomic % in safety devices and control rods of nuclear reactors. Its use is also intended for breeder-reactor control rods. 

Boron [7440-42-8] B, is unique in that it is the only nonmetal in Group 13 (IIIA) of the Periodic Table. Boron, at wt 10.81, at no. 5, has more similarity to carbon and siUcon than to the other elements in Group 13. There are two stable boron isotopes, B and B, which are naturally present at 19.10—20.31% and 79.69—80.90%, respectively. The range of the isotopic abundancies reflects a variabiUty in naturally occurring deposits such as high B ore from Turkey and low °B ore from California. Other boron isotopes, B, B, and B, have half-Hves of less than a second. The B isotope has a very high cross-section for absorption of thermal neutrons, 3.835 x 10 (3835 bams). This neutron absorption produces alpha particles. 

There is a very low cosmic abundance of boron, but its occurrence at all is surprising for two reasons. First, boron s isotopes are not involved in a star s normal chain of thermonuclear reactions, and second, boron should not survive a star s extreme thermal condition. The formation of boron has been proposed to arise predominantly from cosmic ray bombardment of interstellar gas in a process called spallation (1). 

Abundances of lUPAC (the International Union of Pure and Applied Chemistry). Their most recent recommendations are tabulated on the inside front fly sheet. From this it is clear that there is still a wide variation in the reliability of the data. The most accurately quoted value is that for fluorine which is known to better than I part in 38 million the least accurate is for boron (1 part in 1500, i.e. 7 parts in [O ). Apart from boron all values are reliable to better than 5 parts in [O and the majority arc reliable to better than I part in 10. For some elements (such as boron) the rather large uncertainty arises not because of experimental error, since the use of mass-spcctrometric measurements has yielded results of very high precision, but because the natural variation in the relative abundance of the 2 isotopes °B and "B results in a range of values of at least 0.003 about the quoted value of 10.811. By contrast, there is no known variation in isotopic abundances for elements such as selenium and osmium, but calibrated mass-spcctrometric data are not available, and the existence of 6 and 7 stable isotopes respectively for these elements makes high precision difficult to obtain they are thus prime candidates for improvement. 

Boron is comparatively unabundant in the universe (p. 14) it occurs to the extent of about 9 ppm in crustal rocks and is therefore rather less abundant than lithium (18 ppm) or lead (13 ppm) but is similar to praseodymium (9.1 ppm) and thorium (8.1 ppm). It occurs almost invariably as borate minerals or as borosilicates. Commercially valuable deposits are rare, but where they do occur, as in California or Turkey, they can be vast (see Panel). Isolated deposits are also worked in the former Soviet Union, Tibet and Argentina. 

A photovoltaic cell (often called a solar cell) consists of layers of semiconductor materials with different electronic properties. In most of today s solar cells the semiconductor is silicon, an abundant element in the earth s crust. By doping (i.e., chemically introducing impurity elements) most of the silicon with boron to give it a positive or p-type electrical character, and doping a thin layer on the front of the cell with phosphorus to give it a negative or n-type character, a transition region between the two types... 

E.ll The molar mass of boron atoms in a natural sample is 10.81 g-mol-1. The sample is known to consist of 10B (molar mass 10.013 g-mol ) and UB (molar mass 1 1.093 g-mol 1). What are the percentage abundances of the two isotopes ... 

The boron atom in natural abundance is approximately 80% nB and 26% 10B. Identify all of die possible symmetry groups for LaBg with these isotopic species, e.g. LanB t L Bj B, La,1B410B2, LanB3,0B3 etc. A model is especially useful in this case. 

Boron has two isotopes, both of which have spin 10B has a natural abundance of 18.8%, and a spin of 1 = 3 (allowed spin states -3, -2, -1, 0, +1, +2, +3 i.e., one signal will he split into seven lines of equal intensity), whilst nB has a natural abundance of 81.2%, and a spin of 1 = 3/2 (allowed spin states -3/2, -1/2, +1/2, and +3/2 i.e., one signal will be split into four lines of equal intensity). 

Recent Hubble observations of boron in a sample of Li-rich K giants (de la Reza, Smith Cunha in preparation) have apparently not detected any signal of a substantial presence of this element. In some cases, the large rotation and the presence of strong UV emission lines at the 2497 A region difficult the measure of the real B abundances. In conclusion, it appears that there is no indication of the presence of other than 7Li light elements in the Li rich K giants. 

This spurious contribution could be attributed to the presence of boron nuclei in the metallized wafer. Boron is present in nature with two stable isotopes (10B, nB), one having nuclear spin 3/2 and abundance of 80.3%, and the other nuclear spin 3 and abundance of 19.7%. The nuclei have non-zero electric quadrupole moments. 

Although boron ranks 48th among the elements in abundance, it is not found uncombined. The most common minerals containing boron are the tetraborates of sodium or calcium. Borax, Na2B407 10H2O, is the most important source of boron, and large deposits of borax are found in southern California, from which about three-fourths of the world demand is obtained. 

A The average atomic mass of boron is 10.811, which is closer to 11.009305 than to 10.012937. Thus, boron-11 is the isotope present in greater abundance. 

In a high-temperature atmosphere created by the combustion of a host hydrocarbon fuel, there will be an abundance of hydroxyl radicals. Thus, boron monoxide reacts with hydroxyl radicals to form gaseous metaboric oxide HOBO. 

The elements lithium ( T.i, Li), boron ( °B, and vanadium ( °V, come together with a lighter isotope of lower abundance than the heavier one and thus, they can be grouped together as X-1 elements (cf. Chap. 3.1.4). 

ORIGIN OF NAME It is named after the Arabic word bawraq, which means "white borax." ISOTOPES There are a total of 13 isotopes of boron, two of which are stable. The stable isotope B-10 provides 19.85% of the element s abundance as found in the Earth s crust, and the isotope B-11 provides 80.2% of boron s abundance on Earth. 

Boron is the 38th most abundant element on Earth. It makes up about 0.001% of the Earths crust, or 10 parts per mdhon, which is about the same abundance as lead. It is not found as a free element in nature but rather in the mineral borax, which is a compound of hydrated sodium, hydrogen, and water. Borax is found in salty lakes, dry lake-beds, or alkali soils. Other naturally occurring compounds are either red crystalline or less dense, dark-brown or black powder. 

Boron has two stable isotopes with the following abundances (Rosman and Taylor 1998). 

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