Abstract
Usingα-particles in the energy range 42–51 MeV, the209Bi(α, 4n)209At reaction was studied with the intention of investigating the properties of excited high spin states in209At. In-beam prompt and delayed gamma-ray and conversion electron spectroscopy reveal two isomeric states at 2429 and 1428 keV having the half-lives of 875±100 ns and 25±1 ns, respectively. The spins and parities of these states are found to be 29/2+ and 21/2−, respectively. Theg-factors of the isomeric states are 1.06±0.02 and 0.88±0.06, which, within the experimental errors, are the same as theg-factors of the corresponding states in211At. This suggests that the isomeric states are due to the\(\pi \left( {h_{{9 \mathord{\left/ {\vphantom {9 2}} \right. \kern-\nulldelimiterspace} 2}}^2 } \right)_{8^ + } i_{1 {3 \mathord{\left/ {\vphantom {3 2}} \right. \kern-\nulldelimiterspace} 2}} v\left( {j^{ - 2} } \right)_{0^ + } \) and\(\pi \left( {h_{{9 \mathord{\left/ {\vphantom {9 2}} \right. \kern-\nulldelimiterspace} 2}}^3 } \right)v\left( {j^{ - 2} } \right)_{0^ + } \) configurations, respectively. The deviation between the calculated and experimentally found excitation energies of the isomeric levels are −146±26 and +72 ±26 keV. This deviation which in cases of a208Pb-core usually is smaller than 15 keV, is likely to be due to the neglect of the interaction between two particles via the exchange of virtual 2+ phonons in the206Pb core. This two-particle polarization interaction is found to be approximately described by aP 2-force.
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The idea of possible two-particle polarization is due to Dr. Jan Blomqvist. We are very much indebted to him for the stimulation and inspiration he has given us in our experimental work. We also appreciate the possibility which we have had to discuss the theoretical aspects of this work with Dr. Torbjörn Eriksson.
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Bergström, I., Herrlander, C.J., Lindblad, T. et al. Evidence for two-particle core polarization in the isomeric 29/2+ and 21/2− states of the\(\pi \left( {h_{{9 \mathord{\left/ {\vphantom {9 2}} \right. \kern-\nulldelimiterspace} 2}}^2 } \right)_{8^ + } i_{1 {3 \mathord{\left/ {\vphantom {3 2}} \right. \kern-\nulldelimiterspace} 2}} v\left( {j^{ - 2} } \right)_{0^ + } \) and\(\pi \left( {h_{{9 \mathord{\left/ {\vphantom {9 2}} \right. \kern-\nulldelimiterspace} 2}}^3 } \right)v\left( {j^{ - 2} } \right)_{0^ + } \) configurations in209At. Z Physik A 273, 291–304 (1975). https://doi.org/10.1007/BF01410012
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DOI: https://doi.org/10.1007/BF01410012