Radiative decay of the Th 229 m nuclear clock isomer in different host materials

A comparative vacuum ultraviolet spectroscopy study conducted at ISOLDE-CERN of the radiative decay of the <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:mmultiscripts> <a:mi>Th</a:mi> <a:mprescripts/> <a:none/> <a:mrow> <a:mn>229</a:mn> <a:mi>m</a:mi> </a:mrow> </a:mmultiscripts> </a:math> nuclear clock isomer embedded in different host materials is reported. The ratio of the number of radiative decay photons and the number of <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"> <b:mmultiscripts> <b:mi>Th</b:mi> <b:mprescripts/> <b:none/> <b:mrow> <b:mn>229</b:mn> <b:mi>m</b:mi> </b:mrow> </b:mmultiscripts> </b:math> embedded are determined for single crystalline <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"> <c:msub> <c:mi>CaF</c:mi> <c:mn>2</c:mn> </c:msub> <c:mo>,</c:mo> <c:mo> </c:mo> <c:msub> <c:mi>MgF</c:mi> <c:mn>2</c:mn> </c:msub> <c:mo>,</c:mo> <c:mo> </c:mo> <c:msub> <c:mi>LiSrAlF</c:mi> <c:mn>6</c:mn> </c:msub> </c:math> , AlN, and amorphous <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"> <d:msub> <d:mi>SiO</d:mi> <d:mn>2</d:mn> </d:msub> </d:math> . For the latter two materials, no radiative decay signal was observed and an upper limit of the ratio is reported. The radiative decay wavelength was determined in <e:math xmlns:e="http://www.w3.org/1998/Math/MathML"> <e:msub> <e:mi>LiSrAlF</e:mi> <e:mn>6</e:mn> </e:msub> </e:math> and <f:math xmlns:f="http://www.w3.org/1998/Math/MathML"> <f:msub> <f:mi>CaF</f:mi> <f:mn>2</f:mn> </f:msub> </f:math> , reducing its uncertainty by a factor of 2.5 relative to our previous measurement. This value is in agreement with the recently reported improved values from laser excitation.