Isospin mixing in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mi>Ga</mml:mi> <mml:mprescripts/> <mml:none/> <mml:mrow> <mml:mn>64</mml:mn> <mml:mo>,</mml:mo> <mml:mn>66</mml:mn> </mml:mrow> </mml:mmultiscripts>

New measurements of the β decay of <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:mmultiscripts> <a:mi>Ga</a:mi> <a:mprescripts/> <a:none/> <a:mn>64</a:mn> </a:mmultiscripts> </a:math> and <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"> <b:mmultiscripts> <b:mi>Ga</b:mi> <b:mprescripts/> <b:none/> <b:mn>66</b:mn> </b:mmultiscripts> </b:math> have been carried out using total absorption spectroscopy at CERN-ISOLDE. The purpose of the study was to determine whether systemic effects such as have affected previous measurements and also determine the degree of isospin mixing in these proton-rich nuclei. Our results show that the β strength distribution of <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"> <c:mmultiscripts> <c:mi>Ga</c:mi> <c:mprescripts/> <c:none/> <c:mn>64</c:mn> </c:mmultiscripts> </c:math> was previously underestimated, while that of <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"> <d:mmultiscripts> <d:mi>Ga</d:mi> <d:mprescripts/> <d:none/> <d:mn>66</d:mn> </d:mmultiscripts> </d:math> agrees well with previous high-resolution measurements. The results allowed us to determine the amount of isospin mixing in the <e:math xmlns:e="http://www.w3.org/1998/Math/MathML"> <e:mrow> <e:msup> <e:mn>0</e:mn> <e:mo>+</e:mo> </e:msup> <e:mo>→</e:mo> <e:msup> <e:mn>0</e:mn> <e:mo>+</e:mo> </e:msup> </e:mrow> </e:math> transitions to the ground states of the daughter nuclei. From the extracted <f:math xmlns:f="http://www.w3.org/1998/Math/MathML"> <f:mrow> <f:mo form="prefix">log</f:mo> <f:mi>f</f:mi> <f:mi>t</f:mi> </f:mrow> </f:math> values, we determined the isospin mixing parameter <h:math xmlns:h="http://www.w3.org/1998/Math/MathML"> <h:mi>α</h:mi> </h:math> for the two cases. They were found to be consistent with values for similar transitions in other nuclei. <i:math xmlns:i="http://www.w3.org/1998/Math/MathML"> <i:mmultiscripts> <i:mi>Ga</i:mi> <i:mprescripts/> <i:none/> <i:mn>64</i:mn> </i:mmultiscripts> </i:math> exhibits the largest amount of isospin mixing in such nuclei. These findings improve our understanding of beta decay and have implications for nuclear structure models and medical applications of <j:math xmlns:j="http://www.w3.org/1998/Math/MathML"> <j:mmultiscripts> <j:mi>Ga</j:mi> <j:mprescripts/> <j:none/> <j:mn>66</j:mn> </j:mmultiscripts> </j:math> in PET imaging.