Decay of a microsecond seniority 3 isomeric state in Hf155

Excited states in the neutron-deficient nuclide <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:mmultiscripts><a:mi>Hf</a:mi><a:mprescripts/><a:none/><a:mn>155</a:mn></a:mmultiscripts></a:math> have been investigated in experiments performed at the Accelerator Laboratory of the University of Jyväskylä. The <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"><b:mmultiscripts><b:mi>Hf</b:mi><b:mprescripts/><b:none/><b:mn>155</b:mn></b:mmultiscripts></b:math> nuclei were produced in fusion-evaporation reactions induced by beams of 295 and 315 MeV <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"><c:mmultiscripts><c:mi>Ni</c:mi><c:mprescripts/><c:none/><c:mn>58</c:mn></c:mmultiscripts></c:math> ions bombarding an isotopically enriched <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"><d:mmultiscripts><d:mi>Pd</d:mi><d:mprescripts/><d:none/><d:mn>102</d:mn></d:mmultiscripts></d:math> target and separated using the recoil mass separator MARA. An isomeric state having a half-life of 510(30) ns was discovered and is interpreted as a seniority <e:math xmlns:e="http://www.w3.org/1998/Math/MathML"><e:mrow><e:mi>υ</e:mi><e:mo>=</e:mo><e:mn>3</e:mn></e:mrow><e:mo>,</e:mo><e:mo> </e:mo><e:mrow><e:mrow><e:mo>(</e:mo><e:mi>π</e:mi><e:msubsup><e:mi>h</e:mi><e:mrow><e:mn>11</e:mn><e:mo>/</e:mo><e:mn>2</e:mn></e:mrow><e:mn>2</e:mn></e:msubsup><e:mo>⊗</e:mo><e:mi>ν</e:mi><e:msub><e:mi>f</e:mi><e:mrow><e:mn>7</e:mn><e:mo>/</e:mo><e:mn>2</e:mn></e:mrow></e:msub><e:mo>)</e:mo></e:mrow><e:mn>27</e:mn><e:mo>/</e:mo><e:msup><e:mn>2</e:mn><e:mo>−</e:mo></e:msup></e:mrow></e:math> configuration. The <f:math xmlns:f="http://www.w3.org/1998/Math/MathML"><f:mi>γ</f:mi></f:math>-ray transitions emitted in the deexcitation of the isomeric state to the ground state were identified and a level scheme was constructed, from which the excitation energy of the isomer was determined to be 2581.5(10) keV. A <g:math xmlns:g="http://www.w3.org/1998/Math/MathML"><g:mrow><g:mi>B</g:mi><g:mo>(</g:mo><g:mi>E</g:mi><g:mn>2</g:mn><g:mo>)</g:mo></g:mrow></g:math> value of 0.45(3) W.u. was deduced for the 105.4 keV transition depopulating the isomeric state. The deduced level scheme and <h:math xmlns:h="http://www.w3.org/1998/Math/MathML"><h:mrow><h:mi>B</h:mi><h:mo>(</h:mo><h:mi>E</h:mi><h:mn>2</h:mn><h:mo>)</h:mo></h:mrow></h:math> value are compared with systematics and shell-model calculations. Published by the American Physical Society 2024