Accurate Excitation Energies ofB11States Below 7 MeV

A recent precision measurement of gamma-ray energy made with a lithium-drifted germanium detector disagrees with an earlier value of an excitation energy obtained by measurement of charged-particle energies. To investigate this discrepancy and to confirm the level assignment of the gamma-ray transition, excitation energies of ${\mathrm{B}}^{11}$ states were measured using both the ${\mathrm{B}}^{10}(d, p){\mathrm{B}}^{11}$ and ${\mathrm{Be}}^9({\mathrm{He}}^3, p){\mathrm{B}}^{11}$ reactions. Particle energies were measured with a broad-range spectrograph calibrated with a ${\mathrm{Po}}^{210}$ alpha source (5304.5 keV). Excitation energies determined with the data from the two reactions agree within 2.9 keV in all cases. The mean values are (in keV) 2124.4±0.7, 4444.4±1.4, 5018.9±1.7, 6742.9±1.8, and 6792.8±1.8. The uncertainties are combinations of an uncertainty in the shape of the calibration curve with the standard deviation of the mean or the assumed internal error, whichever is greater. These uncertainties may be considered as standard deviations. The energy difference between the last two levels was found to be 49.8±0.3 keV. The value 6792.8 agrees exactly with the gamma-ray energy, whereas this and the other excitation energies disagree by as much as 22 keV with earlier values from charged-particle measurement.