Nucleus splitting

Nuclear fission Splitting nuclei such as 238U to produce daughter nuclei and an excess energy. This process can occur for nuclei heavier than Fe. 

The energy is locked up within a body or species in three principal ways (or modes ). First, energy is locked within the atomic nuclei. The only way to release it is to split the nucleus, as happens in atomic weapons and nuclear power stations to yield nuclear energy. The changes in energy caused by splitting nuclei are massive. We will briefly mention nuclear energy in Chapter 8, but the topic will not be discussed otherwise. It is too rare for most physical chemists to consider further. 

Combining and splitting nuclei with fusion and fission... 

Which type of nuclear process splits nuclei to release energy ... 

Hydrogen is a very special case also when it is a part of other molecules. We saw that in the lithium row and in the sodium row of the periodic table both a valence s state and a valence p state are present. We will see that when these atoms form molecules, the bond orbitals are mixtures of both s and p orbitals. There is no valence p state in hydrogen, and its behavior is quite different. In many ways the hydrogen proton may be regarded as a loose positive charge that keeps a molecule neutral rather than as an atom that forms a bond in the same sense that heavier atoms do. Thus we can think of methane, CH4, as neon with four protons split off from the nucleus, just as we can think of H2 as helium with a split nucleus. 

The molecular ion (the analog of HJ) is composed of three objects the proton, the split nucleus of charge +1 and the electron. 

The split nucleus is also composed of three objects d,t,/x (a mini-model of Hj). 

Franck-Condon rule (p. 266) funnel effect (p. 266) non-radiative transitions (p. 266) photochemical reaction (p. 266) muon catalyzed nuclear fusion (p. 268) split nucleus effect (p. 270)... 

A perturbation calculation for the model of an atom with a split nucleus leads to the same result. 

The effect of a slow or "thermar neutron on a nucleus of is to split it into one or more neutrons and into large fragments of approximately equal mass. There is a liberation of energy equal to the loss in total mass, If the neutrons produced effect further fissions, a chain-reaction of successive fissions may be set up. Am and... 

In principle, every nucleus in a molecule, with spm quantum number /, splits every other resonance in the molecule into 2/ -t 1 equal peaks, i.e. one for each of its allowed values of m. This could make the NMR spectra of most molecules very complex indeed. Fortunately, many simplifications exist. 

You may have noticed another characteristic of NMR spectra—all of the peaks are singlets With a spin of a nucleus is subject to the same splitting rules that apply to H and we might expect to see splittings due to and — H couplings... 

Figure 5.12 shows the J= — 0 transition of the linear molecule cyanodiacetylene (H—C=C—C=C—C=N) observed in emission in Sagittarius B2 (Figure 5.4 shows part of the absorption spectrum in the laboratory). The three hyperfine components into which the transition is split are due to interaction between the rotational angular momentum and the nuclear spin of the nucleus for which 1= 1 (see Table 1.3). The vertical scale is a measure of the change of the temperature of the antenna due to the received signal. 

If the nucleus possesses a spin angular momentum, these states are further split and therefore, perhaps, should not have been called states in the first place However, the splitting due to nuclear spin is small and it is normal to refer to nuclear spin components of states. 

The " N nucleus (/ = 1, 99%) has a moderately large magnetic moment and hyperfine splittings from this nucleus are a distinctive feature of the EPR spectra of chalcogen-nitrogen radicals. A-Arylthio-2,4,6-triphenylanilino radicals (3.16) are exceptionally persistent and oxygen-insensitive m solution. They exhibit a characteristic 1 1 1... 

Figure 4-3. Energy level splitting for a nucleus with / = 5 in applied field Hn. The energy separation is proportional to Ho-...

All have zero nuclear spin except (33.8% abundance) which has a nuclear spin quantum number this isotope finds much use in nmr spectroscopy both via direct observation of the Pt resonance and even more by the observation of Pt satellites . Thus, a given nucleus coupled to Pt will be split into a doublet symmetrically placed about the central unsplit resonance arising from those species containing any of the other 5 isotopes of Pt. The relative intensity of the three resonances will be (i X 33.8) 66.2 ( x 33.8), i.e. 1 4 1. 

In 1938 Niels Bohr had brought the astounding news from Europe that the radiochemists Otto Hahn and Fritz Strassmann in Berlin had conclusively demonstrated that one of the products of the bom-bardmeiit of uranium by neutrons was barium, with atomic number 56, in the middle of the periodic table of elements. He also announced that in Stockholm Lise Meitner and her nephew Otto Frisch had proposed a theory to explain what they called nuclear fission, the splitting of a uranium nucleus under neutron bombardment into two pieces, each with a mass roughly equal to half the mass of the uranium nucleus. The products of Fermi s neutron bombardment of uranium back in Rome had therefore not been transuranic elements, but radioactive isotopes of known elements from the middle of the periodic table. 

Doublet (Section 13.11) A two-line NMR absorption caused by spin-spin splitting when the spin of the nucleus under observation couples with the spin of a neighboring magnetic nucleus. 

Fission, nuclear The splitting of a heavy nucleus by a neutron into two lighter nuclei, accompanied by the release of energy, 523 discovery, 523-524 process, 524-525 reactors, 525-526... 

Instead of producing new kinds of substances by combination of atoms, the element uranium has combined with a neutron and as a result has split into two other elements—barium and krypton—plus three more neutrons. Atoms of a given element are characterized by their atomic number, the number of units of positive charge on the nucleus. For one element to change into another element the nucleus must be altered. In our example the uranium nucleus, as a result of reacting with a neutron, splits or fissions into two other nuclei and releases, in addition, neutrons. ... 

Figure 4.54 The effect of an electric field gradient (EFG) creating asymmetry in the electron distribution round a gold nucleus, leading to a quadrupole splitting in the Mossbauer spectrum. (Reproduced with permission from Gold Bull., 1982,15, 53, published by World Gold Council.)...

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