Extraction of neutron-capture cross sections on ${}^{92}$Zr using the charge-exchange Oslo method

Abstract

The ${}^{93}$Nb($t$,${}^3$He) reaction at 115 MeV/u was studied to demonstrate that nuclear level densities and $\gamma$-ray strength functions can be extracted from charge-exchange reactions at intermediate energies using the Oslo technique. The matrix of excitation energy in ${}^{93}$Zr, reconstructed from the ($t$,${}^3$He) reaction, versus the energy of $\gamma$ rays emitted by the excited ${}^{93}$Zr nuclei, was obtained in an experiment with the S800 Spectrograph operated in coincidence with the GRETINA $\gamma$-ray detector. The extracted level density and $\gamma$-ray strength function obtained by applying the Oslo method to this matrix were used to estimate the ${}^{92}$Zr($n$,$\gamma$)${}^{93}$Zr cross section by combining the new results with other experimental data and theoretical calculations for $E$1 and $M$1 strength functions at higher energies. Good agreement with direct measurements of the ${}^{92}$Zr($n$,$\gamma$)${}^{93}$Zr cross section was found. The contribution from the upbend in the extracted $\gamma$-ray strength function was important to achieve the consistency as the neutron-capture cross section without this contribution is significantly below the direct measurements otherwise. Since charge-exchange reactions at intermediate energies have long been used for extracting Gamow-Teller strengths, the successful demonstration of the charge-exchange Oslo method enables experiments in which ($n$,$\gamma$) cross sections and Gamow-Teller strengths can be measured simultaneously, which is of benefit for astrophysical studies.

References in corpus (10)

• The r-process of stellar nucleosynthesis: Astrophysics and nuclear physics achievements and mysteries
• Analysis of possible systematic errors in the Oslo method
• Novel technique for constraining r-process (n,$\gamma$) reaction rates
• Large low-energy $M1$ strength for ${}^{56,57}$Fe within the nuclear shell model
• Novel Techniques for Constraining Neutron-Capture Rates Relevant for r-Process Heavy-Element Nucleosynthesis
• Radiogenic p-isotopes from SNIa, nuclear physics uncertainties and Galactic chemical evolution compared with values in primitive meteorites
• Low energy magnetic radiation enhancement in the f${}_{7/2}$ shell
• Quasicontinuum $\gamma$-decay of ${}^{91,92}$Zr: benchmarking indirect ($n,\gamma$) cross section measurements for the $s$-process
• UCGretina GEANT4 Simulation of the GRETINA Gamma-Ray Energy Tracking Array
• Nuclear Level Density and $\gamma$-ray Strength Function of ${}^{67}\mathrm{Ni}$ and the impact on the i-process