Unconventional <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mi>Cu</mml:mi> <mml:mprescripts/> <mml:none/> <mml:mn>67</mml:mn> </mml:mmultiscripts> </mml:math> production using high-energy bremsstrahlung and cross

The use of theranostic isotope pairs is an emerging field in contemporary medicine, yet their clinical availability is often constrained by production and supply chain challenges. Among them, <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:mmultiscripts> <a:mi>Cu</a:mi> <a:mprescripts/> <a:none/> <a:mn>67</a:mn> </a:mmultiscripts> </a:math> has gained significant interest as the therapeutic counterpart in the <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"> <b:mrow> <b:mmultiscripts> <b:mi>Cu</b:mi> <b:mprescripts/> <b:none/> <b:mn>67</b:mn> </b:mmultiscripts> <b:mtext>/</b:mtext> <b:mmultiscripts> <b:mi>Cu</b:mi> <b:mprescripts/> <b:none/> <b:mn>64</b:mn> </b:mmultiscripts> </b:mrow> </b:math> theranostic pair. Traditional production methods rely on reactor-based or charged-particle accelerator routes, both of which face limitations in scalability and isotopic purity. This work investigates the photonuclear production of <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"> <c:mmultiscripts> <c:mi>Cu</c:mi> <c:mprescripts/> <c:none/> <c:mn>67</c:mn> </c:mmultiscripts> </c:math> via the <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"> <d:mrow> <d:mmultiscripts> <d:mi>Zn</d:mi> <d:mprescripts/> <d:none/> <d:mn>68</d:mn> </d:mmultiscripts> <d:mo>(</d:mo> <d:mi>γ</d:mi> <d:mo>,</d:mo> <d:mi>p</d:mi> <d:mo>)</d:mo> <d:mmultiscripts> <d:mi>Cu</d:mi> <d:mprescripts/> <d:none/> <d:mn>67</d:mn> </d:mmultiscripts> </d:mrow> </d:math> reaction, using high-energy bremsstrahlung photons from an electron accelerator. In addition to quantifying production yields and radionuclidic purity, the work provides spectrum-weighted average cross sections for multiple emission channels, serving as a test of reaction modeling under broad excitation conditions. The results inform both the optimization of <e:math xmlns:e="http://www.w3.org/1998/Math/MathML"> <e:mmultiscripts> <e:mi>Cu</e:mi> <e:mprescripts/> <e:none/> <e:mn>67</e:mn> </e:mmultiscripts> </e:math> production for theranostic applications and the improvement of nuclear reaction theory in an underexplored energy regime. Natural zinc targets were irradiated using bremsstrahlung photons from an 855 MeV electron beam at the Mainzer Mikrotron (MAMI). The photon energy spectrum was measured via tagging and extended beyond the tagged range using simulations. Reaction products were identified via gamma-ray spectroscopy, and spectrum-weighted average cross sections were derived. Theoretical cross sections were calculated using , incorporating giant dipole resonance and quasideuteron components of the photon absorption cross section. A model sensitivity analysis was performed to assess the influence of level density and photon strength function variations on the predicted cross sections. A production yield of 0.410(16) MBq <f:math xmlns:f="http://www.w3.org/1998/Math/MathML"> <f:mrow> <f:mi>µ</f:mi> <f:msup> <f:mrow> <f:mi mathvariant="normal">A</f:mi> </f:mrow> <f:mrow> <f:mo>−</f:mo> <f:mn>1</f:mn> </f:mrow> </f:msup> <f:msup> <f:mrow> <f:mi mathvariant="normal">h</f:mi> </f:mrow> <f:mrow> <f:mo>−</f:mo> <f:mn>1</f:mn> </f:mrow> </f:msup> <f:msup> <f:mrow> <f:mi mathvariant="normal">g</f:mi> </f:mrow> <f:mrow> <f:mo>−</f:mo> <f:mn>1</f:mn> </f:mrow> </f:msup> </f:mrow> </f:math> was measured for <j:math xmlns:j="http://www.w3.org/1998/Math/MathML"> <j:mmultiscripts> <j:mi>Cu</j:mi> <j:mprescripts/> <j:none/> <j:mn>67</j:mn> </j:mmultiscripts> </j:math> , with corresponding average cross sections determined from the bremsstrahlung spectrum. Yields and average cross sections were also measured for coproduced isotopes including <k:math xmlns:k="http://www.w3.org/1998/Math/MathML"> <k:mmultiscripts> <k:mi>Cu</k:mi> <k:mprescripts/> <k:none/> <k:mn>64</k:mn> </k:mmultiscripts> <k:mo>,</k:mo> <k:mo> </k:mo> <k:mmultiscripts> <k:mi>Cu</k:mi> <k:mprescripts/> <k:none/> <k:mn>61</k:mn> </k:mmultiscripts> <k:mo>,</k:mo> <k:mo> </k:mo> <k:mmultiscripts> <k:mi>Cu</k:mi> <k:mprescripts/> <k:none/> <k:mn>60</k:mn> </k:mmultiscripts> <k:mo>,</k:mo> <k:mo> </k:mo> <k:mmultiscripts> <k:mi>Zn</k:mi> <k:mprescripts/> <k:none/> <k:mrow> <k:mn>69</k:mn> <k:mi>m</k:mi> </k:mrow> </k:mmultiscripts> <k:mo>,</k:mo> <k:mo> </k:mo> <k:mmultiscripts> <k:mi>Zn</k:mi> <k:mprescripts/> <k:none/> <k:mn>65</k:mn> </k:mmultiscripts> <k:mo>,</k:mo> <k:mo> </k:mo> <k:mmultiscripts> <k:mi>Zn</k:mi> <k:mprescripts/> <k:none/> <k:mn>63</k:mn> </k:mmultiscripts> </k:math> , and <l:math xmlns:l="http://www.w3.org/1998/Math/MathML"> <l:mmultiscripts> <l:mi>Zn</l:mi> <l:mprescripts/> <l:none/> <l:mn>62</l:mn> </l:mmultiscripts> </l:math> . The relatively low production of nontarget isotopes indicates that the <m:math xmlns:m="http://www.w3.org/1998/Math/MathML"> <m:mrow> <m:mmultiscripts> <m:mi>Zn</m:mi> <m:mprescripts/> <m:none/> <m:mn>68</m:mn> </m:mmultiscripts> <m:mo>(</m:mo> <m:mi>γ</m:mi> <m:mo>,</m:mo> <m:mi>p</m:mi> <m:mo>)</m:mo> <m:mmultiscripts> <m:mi>Cu</m:mi> <m:mprescripts/> <m:none/> <m:mn>67</m:mn> </m:mmultiscripts> </m:mrow> </m:math> reaction proceeds with favorable radionuclidic selectivity under the applied irradiation conditions. calculations showed good agreement with the ( <n:math xmlns:n="http://www.w3.org/1998/Mat