Nuclei with Atomic Number Greater Than

22-8 Nuclei with Atomic Number Greater Than 83 

The decay of radium-22 6 was originally reported in 1902 by Rutherford and Soddy. It was the first transmutation of an element ever observed. A few heavy nuclides also decay by beta emission, positron emission, and electron capture. 

Some isotopes of uranium (Z = 92) and elements of higher atomic number, the transuianium elements, also decay by spontaneous nuclear fission. In this process, a heavy nuclide splits to form nuclides of intermediate mass and emits neutrons. 

Write the balanced equation for each of the following radioactive decay processes. 

For each process, write the nuclide symbols for the reactant species and for the particle that is captured (as a reactant) or that is emitted (as a product). Then use mass balance and charge balance to write the super- and subscripts for the product nuclide. Determine the atomic symbol for the product nuclide from its atomic number (the subscript). 

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Nuclei with Atomic Number Greater Than 83 Detection of Radiation Rates of Decay and Half-Life Disintegration Series Uses of Radionuclides Artificial Transmutations of Elements Nuclear Fission Nuclear Fission Reactors Nuclear Fusion... 

NUCLEI WITH ATOMIC NUMBER GREATER THAN 83... 

Nuclei with atomic numbers greater than 83 are all radioactive. 

Badioactivity. Natural nonradioactive (stable) nuclei, plotted in Fig. 25.4, fall within a narrow region of stability. In the light elements the ratio N/Z is close to 1. However, in the heavier elements the ratio of neutrons to protons increases to about 1,5. Apparently, relatively more neutrons are needed in the heavier nuclei to balance the electrostatic repulsion between the protons. All nuclei with atomic numbers greater than 83 are radioactive of these, only ind Th occur on the... 

The stability of the atomic nucleus depends upon a critical balance between the repulsive and attractive forces involving the protons and neutrons. For the lighter elements, a neutron to proton ratio (N P) of about 1 1 is required for the nucleus to be stable but with increasing atomic mass, the N P ratio for a stable nucleus rises to a value of approximately 1.5 1. A nucleus whose N P ratio differs significantly from these values will undergo a nuclear reaction in order to restore the ratio and the element is said to be radioactive. There is, however, a maximum size above which any nucleus is unstable and most elements with atomic numbers greater than 82 are radioactive. 

NUCLEAR TRANSMUTATIONS (SECTION 21.3) Nuclear transmutations, induced conversions of one nucleus into another, can be brought about by bombarding nuclei with either charged particles or neutrons. Particle accelerators increase the kinetic energies of positively charged particles, allowing these particles to overcome their electrostatic repulsion by the nucleus. Nuclear transmutations are used to produce the transuranium elements, those elements with atomic numbers greater than that of uranium. 

All nuclides with atomic number greater than Z = 83 are radioactive, as we have noted. Many of these nuclides decay by alpha emission. Alpha particles, or He nuclei, are especially stable and are formed in the radioactive nucleus at the moment of decay. By emitting an alpha particle, the nncleus reduces its atomic number, becoming more stable. HowevCT, if the nncleus has a very large atomic number, the product nucleus is also radioactive. Natural radioactive elements, snch as uranium-238, give a radioactive decay series, a sequence in which one radioactive nucleus decays to a second, which then decays to a third, and so forth. Eventually, a stable nucleus, which is an isotope of lead, is reached. 

The transuranium elements are elements with atomic numbers greater than that of uranium (Z = 92), the naturally occurring element of greatest Z. In 1940, E. M. McMillan and P. H. Abelson, at the University of CaUfomia at Beikeley, discovaed the first transuranium element They produced an isotope of element 93, which they named neptunium, by bombarding uranium-238 with neutrons. This gave uranium-239, by the capture of a neutron, and this nucleus decayed in a few days by beta emission to neptunium-239. 

It is relatively easy to summarize how nuclear stability (and hence the attractive nuclear forces) depends upon the numbers of protons and neutrons in the nucleus. For atoms with atomic number less than 20, the most stable nuclei are those in which there are equal numbers of protons and neutrons. For atoms with atomic numbers between 20 and 83, the most stable nuclei have more neutrons than protons. For atoms of atomic number greater than 83, no nucleus can be considered stable by our definition. These... 

The final model that accounts for nuclear stabilities must, of course, be the strong force, or rather the residual component of the strong force that works outside of quark confinement. Natural or artificial radioactive nuclei can exhibit several decay modes a decay (N1 = N — 4, Z = Z — 2, A = A — 4, with emission of a 2He4 nucleus), which is dominant for elements of atomic number greater than Pb / -decay or electron emission (N1 = N — 1, Z = Z + 1, A = A this involves the weak force and the extra emission of a neutrino) positron or / + decay (N = N + 1, Z =Z — 1, A = A, emission of a positron and an antineutrino this also involves the weak force) y decay no changes in N or Z, and electron capture (N1 =... 

Because the daughter nucleus is left with an additional proton, its atomic number is greater by 1 than the parent nucleus. The mass number is unchanged, because the total number of nucleons in the nucleus is unchanged. For example, when sodium-24 undergoes (3 decay, the daughter nucleus is an atom of the element with atomic number 12 (magnesium), but with the same mass number as the parent nucleus ... 

If the nucleus of the acceptor atom M has a nuclear spin quantum number greater than -j, the nucleus has an electric quadrupole moment as well as a magnetic dipole moment. The quadrupole interacts with any electric field gradient at the nucleus and, in combination with the molecular motion of the complex, this can provide an important mechanism of relaxation of the M nucleus. At relaxation rates that are slow compared with Jp M, spin multiplets are observable in the spectra of M and P. As the relaxation rate increases, the multiplets broaden, but the line separations may still be used to derive 7p Mwith good accuracy. At faster relaxation rates the multiplet components of M and P coalesce into a single broadened line, and at high relaxation rates, the phosphorus resonance becomes sharp and the M resonance may become so broad as to be unobservable. 

For an atom to be neutral, the number of electrons that it contains must equal the total positive charge on its nucleus. Because each element has a characteristic positive charge associated with its nucleus, ranging from +1 for hydrogen to greater than +100 for the heaviest elements, atoms of different elements have different numbers of electrons. 

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