Measurement of the Isolated Nuclear Two-Photon Decay in Ge72

The nuclear two-photon or double-gamma (<a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mn>2</a:mn><a:mi>γ</a:mi></a:math>) decay is a second-order electromagnetic process whereby a nucleus in an excited state emits two gamma rays simultaneously. To be able to directly measure the <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:mn>2</c:mn><c:mi>γ</c:mi></c:math> decay rate in the low-energy regime below the electron-positron pair-creation threshold, we combined the isochronous mode of a storage ring with Schottky resonant cavities. The newly developed technique can be applied to isomers with excitation energies down to <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:mo>∼</e:mo><e:mn>100</e:mn><e:mtext> </e:mtext><e:mtext> </e:mtext><e:mi>keV</e:mi></e:math> and half-lives as short as <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"><g:mo>∼</g:mo><g:mn>10</g:mn><g:mtext> </g:mtext><g:mtext> </g:mtext><g:mi>ms</g:mi></g:math>. The half-life for the <i:math xmlns:i="http://www.w3.org/1998/Math/MathML" display="inline"><i:mn>2</i:mn><i:mi>γ</i:mi></i:math> decay of the first-excited <k:math xmlns:k="http://www.w3.org/1998/Math/MathML" display="inline"><k:msup><k:mn>0</k:mn><k:mo>+</k:mo></k:msup></k:math> state in bare <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" display="inline"><m:mrow><m:mmultiscripts><m:mrow><m:mi>Ge</m:mi></m:mrow><m:mprescripts/><m:none/><m:mrow><m:mn>72</m:mn></m:mrow></m:mmultiscripts></m:mrow></m:math> ions was determined to be 23.9(6) ms, which strongly deviates from expectations. Published by the American Physical Society 2024