METHOD FOR PRODUCING EXCITED STATES OF ATOMIC NUCLEI

摘要

1432301 Nuclear excitation INTERNATIONAL NUCLEAR FUEL CO Ltd 7 Jan 1974 [9 Jan 1973 11 July 1973] 00591/74 Heading G6P Excited states of atomic nuclei are produced by transfer of energy, during electron transitions, to the nuclei. Atoms whose nuclei are to be so excited have to satisfy the following conditions: (i) the difference between the binding energies of two selected electron orbits must be substantially equal to the excitation energy of the nuclear excited state to be produced; and (ii) spin and parity conservation laws must be satisfied. Such atoms are bombarded by X-rays or electrons whose energies are larger than the binding energy of electrons in that one of the selected orbits which is the nearer to the nucleus to be excited. Such bombardment causes an electron to be ejected from that orbit to create a vacancy which is filled by electron transition from the other, more distant orbit. Surplus energy resulting from the transition may be transferred to the nucleus, raising it to an excited state. The nucleus will subsequently return to its ground state by emitting -rays or internal conversion electrons. Thus, substances whose nuclei are raised, by the method described, to excited states are useful as radioactive sources. In an example, the first excited state of osmium 189 is produced. A particular application is to the separation of isotopes from mixtures thereof. In an example, nuclei of U-235 in a mixture of uranium isotopes are selectively raised to their second excited state by the method described. This state decays immediately to the first excited state which has a 26-minute half-life. Ionization of atoms whose nuclei are in the first excited state enables these to be separated out using chemical or electrochemical techniques, following the Szilard-Chalmers process. Other nuclides to which this application is relevant are: osmium 189, neptunium 237, gold 197, iridium 193, tantalum 181, dyspessium 161 and tin 119.