Nuclear Excitation by Single-Quantum Annihilation of Positrons

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9505886 Palathingal When the electromagnetic energy released as a positron gets annihilated in flight with a bound atomic electron in the Coulomb field of the nucleus, meets the energy criterion for resonance absorption, the excitation of the nucleus could be a possible result. There are major discrepancies between the results of calculations of this phenomenon and the available experimental data. The various experiments conducted so far have all suffered from common disadvantages. They utilized whole spectra of positrons derived from radioactive sources and thick targets. Metastable states of the nucleus were studied for periods of a few life times. The results were not accurate, and were prone to ambiguities for interpretation. In view of this, experiments have been called for that would use monoenergetic positrons and thin targets. Such studies will be undertaken utilizing the Dynamitron at Brookhaven and at ORELA at Oak Ridge National Lab. Short-lived states will be studied, that would make a continuous- running beam experiment possible. Thin targets of varied thickness will be used. Secondary effects that might contribute to the nuclear excitation alongside the single-quantum annihilation, proposed by differing theoretical models, would be explored. It is expected that data could be derived that would be accessible for unambiguous interpretation, and would lead to a clear understanding of the physical processes underlying the phenomenon. ***