Bismuth nuclei

Write a nuclear equation for each of the following transformations (a) 25 Rf produced by the bombardment of califomium-245 with carbon-12 nuclei (b) the first synthesis of 266Mt by the bombardment of bismuth-209 with iron-58 nuclei. Given that the first decay of meitnerium is by a emission, what is the daughter nucleus ... 

These fissioning nuclei (such as 8tP°i2-211> formed by reaction of Bi209 and a deuteron) have a nearly spherical normal-state structure, resembling that of the doubly magic nucleus seP m208, with an outer core of 16 spherons and an inner core of 4 spherons, shown in Fig. 6. The nucleus is excited, with vibrational energy about 25 Mev (for bismuth bombard-... 

When Z gets big enough, no number of neutrons is enough to stabilize the nucleus. Notice in Figure 2-20 that there are no stable nuclei above bismuth, Z — 83. Some elements with higher Z are found on Earth, notably radium (Z = 88), thorium (Z = 90), and uranium (Z = 92), but all such elements are unstable and eventually disintegrate into nuclei with Z < 83. Consequently, the set of stable nuclei, those that make up the world of normal chemistry and provide the material for all terrestrial chemical reactions, is a small subset of all possible nuclei. 

All elements, by definition, have a unique proton number, but some also have a unique number of neutrons (at least, in naturally occurring forms) and therefore a unique atomic weight - examples are gold (Au Z = 79, N = 118, giving A =197), bismuth (Bi Z = 83, N = 126, A = 209), and at the lighter end of the scale, fluorine (F Z = 9, N = 10, A = 19) and sodium (Na Z = 11, N= 12, A = 23). Such behavior is, however, rare in the periodic table, where the vast majority of natural stable elements can exist with two or more different neutron numbers in their nucleus. These are termed isotopes. Isotopes of the same element have the same number of protons in their nucleus (and hence orbital electrons, and hence chemical properties), but... 

Fig. 5.6. Path of s and r processes across the Z, N) plane. Everything begins with iron. The s process follows roughly along the valley of statrility, flowing like a river along the banks it defines. It ends with the a decay of bismuth-209. The r process takes matter far out of the valley on the neutron-rich side, whilst the weak interaction brings it back to the fold. In this case neutron capture continues until the nucleus undergoes fission. The climb to neutron-rich summits is indeed vertiginous.

Once a star s core temperature has reached about three billion degrees, fusion processes generate iron. And here they stop, because iron is the most stable nucleus of all. There is no energy to be gained by fusing iron nuclei. Yet heavier elements clearly do exist. They are created in the outer regions of the star, where neutrons emitted by fusion reactions are captured by nuclei to build all the elements up to bismuth (atomic number 73). 

The last member of the quadrupolar Group V nuclei, ° Bi, represents another potentially useful nucleus although, surprisingly, the literature seems to be devoid of any chemical applications of its resonance. ° Bi is the only stable bismuth isotope. It has a spin off, a magnetic moment of 4 039 jUn, and is only six times less sensitive than the proton. Its quadrupolar moment of —0-38 barn definitely confines applications to symmetric moieties. 

Bismuth is the heaviest element to have a stable, nonradioactive nucleus polonium and all heavier elements are radioactive. 

Bismuth(lll) salts such as BiCls, BiBrj, Bi(OCOR)3, and Bi (OTf), [166] have been widely used as Lewis acid catalysts to mediate C-C bond formation. Bi (OTf) 3, Bi2O3, and BiCl, catalyze Friedel-Crafts acylation with acyl chlorides or acid anhydrides [167]. Both electron-rich and electron-deficient arenes are acylated in high yields under catalysis by Bi(OTf)3 (Scheme 14.82). Under microwave irradiation the catalytic activity of BiX3 (X = C1, OTf) in the acylation of aromatic ethers is enhanced [168]. The N-acyl group of p-substituted anilides migrates to the ortho position of the aromatic nucleus under BiCls catalysis [169]. Treatment of 2,3-dichloroanisole with the ethyl glyoxylate polymer in the presence of a catalytic amount of Bi(OTf)3 affords an a,a-diarylacetic acid ester quantitatively (Scheme 14.83) [170]. 

The release of so many neutrons all at once provides another mechanism for the production of new elements. Now the density of neutrons is so great that n,y reactions of the type seen for the s process can occur with isotopes having very short half-lives. Suppose, for example, that a nucleus of the only stable isotope of bismuth, bismuth-209, is projected from the center of a star during a supernova explosion. Then, an s-like n,y reaction can occur, as follows ... 

Astatine could not have been made using the small cyclotron of 1936. But as soon as a bigger one became available it was possible to bombard bismuth with alpha particles of sufficient energy to penetrate the nucleus. 

An alpha particle contains 2 protons and 2 neutrons. If the 2 protons could be put into the nucleus of a bismuth atom—which has 83 protons—then we make the astatine with 85 protons. The way to do this is as follows. Electrons are stripped from atoms of helium, leaving the helium nuclei, or alpha particles. The alpha particles are accelerated in the cyclotron, which starts them going around, faster and faster, until they ultimately strike the bismuth atoms in the target. When an alpha particle enters the nucleus of a bismuth atom, two neutrons are shot out and you are left with an atom of astatine. 

The body burden of bismuth is very low the daily oral intake of Bi, combined with inhalational intake, is estimated at 5-20 jg (Tsalev and Zaprianov 1983). Bismuth is one of the trace elements present in tissues, with relatively high levels being found in the nucleus ruber (Leonov 1956). Following its absorption, bismuth is found in all tissues, though no relationship between tissue concentration and therapeutic effect has yet been established. It is... 

Indeed, around 1980, first experimental results on atomic parity violation have been reported, in particular measurements of the optical activity of bismuth, thallium and lead vapours as well as measurements of an induced electric dipole (El) amplitude to a highly forbidden magnetic dipole transition (Ml) in caesium. These experiments have nowadays reached very high resolution so that even effects from the nuclear anapole moment, which results from weak interactions within the nucleus, have been observed in caesium. The electronic structure calculations for caesium are progressing to a sub-percent accuracy for atomic parity violating effects and the reader is referred to chapter 9 of the first part of this book [12]. 

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