New Mass Value for ${}^7\mathrm{Li}$

A high-accuracy mass measurement of ${}^7\mathrm{Li}$ was performed with the SMILETRAP Penning-trap mass spectrometer via a cyclotron frequency comparison of ${}^7\mathrm{Li}^{3+}$ and $\mathrm{H}_2{}^{+}$. A new atomic-mass value of ${}^7\mathrm{Li}$ has been determined to be $7.0160034256(45)\mathrm{u}$ with a relative uncertainty of 0.63 ppb. It has uncovered a discrepancy as large as $14\sigma$ ($1.1\mu \mathrm{u}$) deviation relative to the literature value given in the Atomic-Mass Evaluation AME 2003. The importance of the improved and revised ${}^7\mathrm{Li}$ mass value, for calibration purposes in nuclear-charge radii and atomic-mass measurements of the neutron halos ${}^9\mathrm{Li}$ and ${}^{11}\mathrm{Li}$, is discussed.

Figure 1

The time-of-flight cyclotron frequency resonance of ${}^7\mathrm{Li}^{3+}$ from 100 scans, representing only $<10\%$ of the overall data. The central part of the resonance is approximated with a Gaussian (solid line) in the data evaluation resulting in a FWHM of less than 1 Hz. The absence of well-pronounced sidebands is explained in the text.

Figure 2

Comparison of the atomic mass value of ${}^7\mathrm{Li}$ from the measurement reported here with previous results published in the Atomic-Mass Evaluations AME83 [24], AME93 [25], and AME2003 [13]. The recent AME2003 value deviates by 160 ppb from our measurement.

Figure 3

The $Q$ value of the ${}^6\mathrm{Li}(n,\gamma ){}^7\mathrm{Li}$ reaction in chronological order. The values are 1968 from Ref. 26, 1972 from Ref. 27, 1985 from Ref. 16. The first point at 2003 is from Ref. 28 and the second from Ref. 13. The 2005 data are the values derived from our direct mass measurements using ${}^6\mathrm{Li}$ and ${}^7\mathrm{Li}$.