Rigidity of the Doubly-Magic 100Sn Core
Research output: Thesis › Doctoral Thesis (compilation)
The doubly magic nucleus <sup>100</sup>Sn represents a crucial test for the nuclear shell model, which is a widely used model for a quantitative description of nuclei. Excited states in <sup>100</sup>Sn are experimentally not accessible with present day techniques, but it is possible to gain insight into its structure by studying the properties of excited states of neighboring nuclei. These nuclei are by themselves very interesting since they enable the determination of single-particle energies and two-body matrix elements, which are the basic parameters of the shell model. Excited states of nuclei in the vicinity of <sup>100</sup>Sn have been studied in a series of experiments using three different experimental setups. The first experiment utilized the NORDBALL detector array where for the first time excited states in the T<sub>z</sub>=-3/2 nuclei <sup>99</sup>Cd and <sup>101</sup>In were identified. In addition, the level schemes of several nuclei with previously known excited states were significantly extended. The nuclei <sup>103</sup>In, <sup>105</sup>In, <sup>107</sup>In and <sup>109</sup>In are described in this thesis. The following experiments used a recoil catcher setup in combination with two EUROBALL cluster detectors, where for the first time excited states in the T<sub>z</sub>=-1 nuclei <sup>98</sup>Cd and <sup>102</sup>Sn were identified. These two nuclei are now the nearest neighbors of <sup>100</sup>Sn with known excited states. The last three experiments used the Fragment Mass Analyzer at Argonne National Laboratory to study <sup>102</sup>Sn in more detail. In all experiments a beam of <sup>58</sup>Ni ions was used to bombard targets of <sup>46</sup>Ti and <sup>50</sup>Cr. The experimental level schemes of <sup>98</sup>Cd, <sup>99</sup>Cd, <sup>102</sup>Sn and <sup>103</sup>In are well reproduced by the shell model calculations. Isomeric states were found in <sup>98</sup>Cd, <sup>99</sup>Cd and <sup>102</sup>Sn and their half-lives were measured. The isomeric states in all three nuclei decay via low energy E2 transitions. The deduced E2 transition rates lead to controversial results for the proton and neutron effective charges, which are also basic shell model parameters. In <sup>102</sup>Sn the measured B(E2;6<sup>+</sup>-4<sup>+</sup>) value leads to a neutron effective charge of 2.0<sup>+0.5</sup><sub>-0.3</sub>e, which is a fairly large value. The analysis of the isomeric 17/2<sup>+</sup> state in <sup>99</sup>Cd suggests a proton effective charge of 1.4(1) e, whereas the measured B(E2;8<sup>+</sup>-6<sup>+</sup>) value in <sup>98</sup>Cd requires a proton effective charge of only 0.93<sup>+0.14</sup><sub>-0.10</sub>e. The small proton effective charge in <sup>98</sup>Cd is very surprising, since it is even smaller than the bare proton charge. In all other nuclei studied so far, the effective charges are larger than the bare nucleon charges, and usually the neutron effective charge is lower than the proton effective charge. The large neutron effective charge points to a softness of the <sup>100</sup>Sn core with respect to quadrupole shape changes, whereas the two proton holes weakly polarize the core in <sup>99</sup>Cd and not at all in <sup>98</sup>Cd.
|Research areas and keywords||
Subject classification (UKÄ) – MANDATORY
|Award date||1998 May 29|
|Publication status||Published - 1998|
Defence details Date: 1998-05-29 Time: 13:15 Place: Hall B, Department of Physics External reviewer(s) Name: Fogelberg, Birger Title: Dr Affiliation: Uppsala University ---