[PDF] Pion Double Charge Exchange On Medium Mass Nuclei eBook

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File Size : 48,34 MB
Release : 1987
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Pion double charge exchange to both the double-analog state and the ground state is studied for medium weight nuclei. The relative cross section of these two transitions and the importance of nuclear structure as a function of pion kinetic energy is examined. 16 figs., 5 tabs.

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File Size : 19,27 MB
Release : 1988
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Recent measurements of pion double-charge exchange (DCX) at energies 20 to 70 MeV are providing a new means for studying nucleon-nucleon correlations in nuclei. At these energies the nucleus is relatively transparent, allowing simpler theoretical models to be used in interpreting the data and leading to a clearer picture. Also the contribution to DCX of sequential charge-exchange scattering through the intermediate analog state is suppressed near 50 MeV and transitions through non-analog intermediate states become very important. Recent theoretical studies by several groups have shown that while transitions through the analog route involve relatively long nucleon-nucleon distances, those through non-analog intermediate states obtain nearly half their strength from nucleon pairs with less than 1 fermi separation. Thus DCX near 50 MeV is an excellent way to study short-range nucleon-nucleon correlations. Data has been obtained for double-isobaric analog state (DIAS) transitions on 14C, 18O, 26Mg, and a number of nuclei in the f-7/2 shell including /sup 42,44,48/Ca, primarily at 35 and 50 MeV. Additional data for non-analog (ground state) transitions has also been obtained for 12C. These data are consistent with the two-amplitude theoretical models where the two amplitudes represent scattering through analog and through non-analog intermediate states. Calculations based on shell-model correlations explain the general trends of the data. Preliminary new data on the forward-angle energy dependence of the DIAS and g.s. transitions for /sup 42,44,48/Ca from 25 to 70 MeV is presented here and the current theoretical picture based upon this data is reviewed. 26 refs., 31 figs., 4 tabs.

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File Size : 24,24 MB
Release : 1988
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In this paper we have calculated the lowest order pion double charge reaction mechanism using shell model wavefunctions of medium weight nuclei. We have the sequential reaction mechanism in which the pion undergoes two single-charge exchange scatterings on the valence neutrons. The distortion of the incoming, intermediate, and outgoing pion are included. The closure approximation is made for the intermediate states with an average excitation energy used in the pion propagator. The double-charge exchange is assumed to take place on the valence nucleons which are assumed to be in one spherical shell model orbital. 34 refs., 5 figs., 3 tabs.

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Page : 13 pages
File Size : 31,84 MB
Release : 1991
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This paper will review theoretical results to show how pion double charge exchange is contributing to our understanding of hadron dynamics in nuclei. The exploitation of the nucleus as a filter is shown to be essential in facilitating the comparison between theory and experiment. 23 refs., 3 figs., 2 tabs.

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File Size : 11,26 MB
Release : 1985
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Cross sections for the /sup 13,14/C, 26Mg, 56Fe(.pi., .pi.−)/sup 13,14/O, 26Si, 56Ni reactions were measured with the Energetic Pion Channel and Spectrometer at the Clinton P. Anderson Meson Physics Facility for 120 less than or equal to T/sub .pi./ less than or equal to 292 MeV and 0 less than or equal to theta less than or equal to 50. The double isobaric analog states (DIAS) are of primary interest. In addition, cross sections for transitions to 14O(0, 5.92 MeV), 14O(2+, 7.77 MeV), 56Ni(gs), 13O(gs), and 13O(4.21 MeV) are presented. The 13O(4.21 MeV) state is postulated to have J/sup .pi./ = 1/2−. The data are compared to previously measured double-charge-exchange cross sections on other nuclei, and the systematics of double charge exchange on T greater than or equal to 1 target nuclei leading to the DIAS are studied. Near the .delta.33 resonance, cross sections for the DIAS transitions are in disagreement with calculations in which the reaction is treated as sequential charge exchange through the free pion-nucleon amplitude, while for T/sub .pi./> 200 MeV the anomalous features of the 164 MeV data are not apparent. This is evidence for significant higher order contributions to the double-charge-exchange amplitude near the reasonable energy. Two theoretical approaches that include two nucleon processes are applied to the DIAS data. 64 references.