Simultaneous <math><mi>γ</mi></math>-ray and electron spectroscopy of <math><mmultiscripts><mi>Hg</mi><mprescripts/><none/><mrow><mn>182</mn><mo>,</mo><mn>184</mn><mo>,</mo><mn>186</mn></mrow></mmultiscripts></math> isotopes

Background: The mercury isotopes around <math><mrow><mi>N</mi><mo>=</mo><mn>104</mn></mrow></math> are a well-known example of nuclei exhibiting shape coexistence. Mixing of configurations can be studied by measuring the monopole strength <math><mrow><msup><mi>ρ</mi><mn>2</mn></msup><mrow><mo>(</mo><mi>E</mi><mn>0</mn><mo>)</mo></mrow></mrow></math>, however, currently the experimental information is scarce and lacks precision, especially for the <math><mrow><msup><mi>I</mi><mi>π</mi></msup><mo>→</mo><msup><mi>I</mi><mi>π</mi></msup></mrow></math> (<math><mrow><mi>I</mi><mo>≠</mo><mn>0</mn></mrow></math>) transitions. Purpose: The goals of this study were to increase the precision of the known branching ratios and internal conversion coefficients, to increase the amount of available information regarding excited states in <math><mmultiscripts><mi>Hg</mi><mprescripts/><none/><mrow><mn>182</mn><mo>,</mo><mn>184</mn><mo>,</mo><mn>186</mn></mrow></mmultiscripts></math>, and to interpret the results in the framework of shape coexistence using different models. Method: The low-energy structures in <math><mmultiscripts><mi>Hg</mi><mprescripts/><none/><mrow><mn>182</mn><mo>,</mo><mn>184</mn><mo>,</mo><mn>186</mn></mrow></mmultiscripts></math> were populated in the <math><mi>β</mi></math> decay of <math><mmultiscripts><mi>Tl</mi><mprescripts/><none/><mrow><mn>182</mn><mo>,</mo><mn>184</mn><mo>,</mo><mn>186</mn></mrow></mmultiscripts></math>, produced at ISOLDE, CERN and purified by laser ionization and mass separation. The <math><mi>γ</mi></math>-ray and internal conversion electron events were detected by five germanium clover detectors and a segmented silicon detector, respectively, and correlated in time to build decay schemes. Results: In total, 193, 178, and 156 transitions, including 144, 140, and 108 observed for the first time in a <math><mi>β</mi></math>-decay experiment, were assigned to <math><mmultiscripts><mi>Hg</mi><mprescripts/><none/><mrow><mn>182</mn><mo>,</mo><mn>184</mn><mo>,</mo><mn>186</mn></mrow></mmultiscripts></math>, respectively. Internal conversion coefficients were determined for 23 transitions, out of which 12 had an <math><mrow><mi>E</mi><mn>0</mn></mrow></math> component. Extracted branching ratios allowed the sign of the interference term in <math><mmultiscripts><mi>Hg</mi><mprescripts/><none/><mn>182</mn></mmultiscripts></math> as well as <math><mrow><msup><mi>ρ</mi><mn>2</mn></msup><mrow><mo>(</mo><mi>E</mi><mn>0</mn><mo>;</mo><msubsup><mn>0</mn><mn>2</mn><mo>+</mo></msubsup><mo>→</mo><msubsup><mn>0</mn><mn>1</mn><mo>+</mo></msubsup><mo>)</mo></mrow></mrow></math> and <math><mrow><mi>B</mi><mo>(</mo><mi>E</mi><mn>2</mn><mo>;</mo><msubsup><mn>0</mn><mn>2</mn><mo>+</mo></msubsup><mo>→</mo><msubsup><mn>2</mn><mn>1</mn><mo>+</mo></msubsup><mo>)</mo></mrow></math> in <math><mmultiscripts><mi>Hg</mi><mprescripts/><none/><mn>184</mn></mmultiscripts></math> to be determined. By means of electron-electron coincidences, the <math><msubsup><mn>0</mn><mn>3</mn><mo>+</mo></msubsup></math> state was identified in <math><mmultiscripts><mi>Hg</mi><mprescripts/><none/><mn>184</mn></mmultiscripts></math>. The experimental results were qualitatively reproduced by five theoretical approaches, the interacting boson model with configuration mixing with two different parametrizations, the general Bohr Hamiltonian, the beyond mean-field model, and the symmetry-conserving configuration-mixing model. However, a quantitative description is lacking. Conclusions: The presence of shape coexistence in neutron-deficient mercury isotopes was confirmed and evidence for the phenomenon existing at higher energies was found. The new experimental results provide important spectroscopic input for future Coulomb excitation studies.