Resonances in ${}^7\mathrm{Be}$ which decay into the ${}^3\mathrm{He}+\alpha$ exit channel have been measured with improved precision using preexisting data sets. The energy and width of the $J^{\pi }=7/2^{-}$ state have been extracted from an invariant-mass study of projectile-breakup products originating from interactions of an $E/A=10.7-\mathrm{MeV}{}^{10}\mathrm{C}$ beam on Be and C targets. The excitation energy of this state (from the pole of the $S$ matrix) is determined to be $E^{*}=4.545\left(6\right)$ MeV, a factor of 8 improvement in precision as compared to the ENSDF value. This improvement is enabled by fine tuning the detector calibrations using calibration resonances in ${}^6\mathrm{Li}, {}^7\mathrm{Li}, {}^6\mathrm{Be}, {}^9\mathrm{B}$, and ${}^{12}\mathrm{C}$ whose decay energies are known to high precision. The $J^{\pi }=7/2^{-}$ resonance in ${}^7\mathrm{Be}$ can now itself be used as a calibration resonance in invariant-mass experiments. This utility is particularly helpful for ${}^3\mathrm{He}$ energy calibrations of CsI(Tl) detectors which are often used in detector arrays employed for measurements with fast beams. This utility is demonstrated with a data set associated with $E/A=70$-MeV ${}^7\mathrm{Be}$ beams which are inelastically excited to the $7/2^{-}$ and $5/2_1^{-}$ resonances. Again using the pole of the $S$ matrix as the definition of the resonance parameters, the fitted excitation energy of the $5/2_1^{-}$ resonance is 6.376(17) MeV, approximately 300 keV lower than the ENSDF value. Its width of 565(4) keV is roughly half of the ENSDF value.

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• Energy levels
• Heavy-particle decays
• Lifetimes & widths
• Nuclear structure & decays
• 6 ≤ A ≤ 19
• Radioactive beams