Measurement of the ${}^{90,92}$Zr($p$,$\gamma$)${}^{91,93}$Nb reactions for the nucleosynthesis of elements near $A=90$

Cross section measurements of the reactions ${}^{90,92}$Zr($p$,$\gamma$)${}^{91,93}$Nb were performed using the National Superconducting Cyclotron Laboratory Summing NaI(Tl) detector at the University of Notre Dame. These reactions are part of the nuclear reaction flow for the synthesis of the light $p$ nuclei. For the ${}^{90}$Zr($p$,$\gamma$)${}^{91}$Nb reaction the new measurement resolves the disagreement between previous results. For the ${}^{92}$Zr($p$,$\gamma$)${}^{93}$Nb reaction the present work reports the first measurement of this reaction cross section. Both reaction cross sections are compared to theoretical calculations and a very good agreement with the standard non-smoker model is observed.

Figure 1

Spectra taken with the SuN detector for (a) the ${}^{90}$Zr($p$,$\gamma$)${}^{91}$Nb reaction at proton beam energy of 4 MeV and (b) the ${}^{92}$Zr($p$,$\gamma$)${}^{93}$Nb reaction at 2.8 MeV. In both figures the black-solid line represents the beam-on-target spectrum while the red-dashed line shows the normalized room background.

Figure 2

Sensitivity of the reaction ${}^{90}$Zr($p$,$\gamma$)${}^{91}$Nb (a) and ${}^{92}$Zr($p$,$\gamma$)${}^{93}$Nb (b) to the various widths in the Hauser-Feshbach model. The solid (red) line corresponds to the sensitivity to the $\gamma$ width, the dashed (blue) line shows the sensitivity to the proton width and the dot-dashed (black) line shows the sensitivity to the neutron width.

Figure 3

Main figure: cross section of the reaction ${}^{90}$Zr($p$,$\gamma$)${}^{91}$Nb from the present work (black dots) and from Laird et al. [17] (open circles). Standard non-smoker theoretical calculations [25] are shown in the solid (black) line and two talys calculations [26] using different nuclear level densities (NLD) are shown in the dashed (blue) and dotted (red) lines. See text for details. The inset shows a comparison of the reaction rate extracted by Roughton et al. [16] (open squares) compared to the standard non-smoker calculation.

Figure 4

Cross section of the reaction ${}^{92}$Zr($p$,$\gamma$)${}^{93}$Nb from the present work (black dots) compared to three theoretical calculations. Standard non-smoker calculations [25] are shown in the solid (black) line and two talys calculations [26] using different NLD are shown in the dashed (blue) and dotted (red) lines. See text for details.