Precision measurement of the half-lifes of the excited nuclear states in Fe-57

Abstract The half-lifes of the nuclear isomeric states in 57 Fe at 14.4 keV and 136.5 keV above the ground state are measured with unprecedented precision using hybrid pixel detectors based on Timepix3 technology. These detectors enable dead-time-free single-photon detection and provide simultaneous measurements of photon energy and arrival time, allowing for nanosecond-scale determination of time differences between characteristic X-rays and $$\gamma $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>γ</mml:mi> </mml:math> -rays emitted during the electron-capture decay of 57 Co. Employing the delayed coincidence technique, the half-life of the 14.4-keV state is determined as $$t^{14.4 \text { keV}}_{1/2} = 97.82(5)$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msubsup> <mml:mi>t</mml:mi> <mml:mrow> <mml:mn>1</mml:mn> <mml:mo>/</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>14.4</mml:mn> <mml:mspace/> <mml:mtext>keV</mml:mtext> </mml:mrow> </mml:msubsup> <mml:mo>=</mml:mo> <mml:mn>97.82</mml:mn> <mml:mrow> <mml:mo>(</mml:mo> <mml:mn>5</mml:mn> <mml:mo>)</mml:mo> </mml:mrow> </mml:mrow> </mml:math> ns, achieving a fourfold improvement in precision over previous measurements. The half-life of the 136.5-keV state is measured as $$t^{136 \text { keV}}_{1/2}= 8.730(17)$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msubsup> <mml:mi>t</mml:mi> <mml:mrow> <mml:mn>1</mml:mn> <mml:mo>/</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>136</mml:mn> <mml:mspace/> <mml:mtext>keV</mml:mtext> </mml:mrow> </mml:msubsup> <mml:mo>=</mml:mo> <mml:mn>8.730</mml:mn> <mml:mrow> <mml:mo>(</mml:mo> <mml:mn>17</mml:mn> <mml:mo>)</mml:mo> </mml:mrow> </mml:mrow> </mml:math> ns, reducing the uncertainty by a factor of two. These results are discussed in the context of previous works.