Atomic masses of ${}^6\mathrm{Li},{}^{23}\mathrm{Na},{}^{39,41}\mathrm{K},{}^{85,87}\mathrm{Rb}$, and ${}^{133}\mathrm{Cs}$

The atomic masses of the alkali-metal isotopes ${}^6\mathrm{Li},{}^{23}\mathrm{Na},{}^{39,41}\mathrm{K},{}^{85,87}\mathrm{Rb}$, and ${}^{133}\mathrm{Cs}$ have been obtained from measurements of cyclotron frequency ratios of pairs of ions simultaneously trapped in a Penning trap. The results, with one standard deviation uncertainty, are: $M({}^6\mathrm{Li})=6.015\hspace{0.5em}122\hspace{0.5em}887\hspace{0.5em}4(16)\mathrm{u},M({}^{23}\mathrm{Na})=22.989769\hspace{0.5em}282\hspace{0.5em}8(26)\mathrm{u},M({}^{39}\mathrm{K})=38.963\hspace{0.5em}706\hspace{0.5em}485\hspace{0.5em}6(52)\mathrm{u},M({}^{41}\mathrm{K})=40.961\hspace{0.5em}825\hspace{0.5em}257\hspace{0.5em}4(48)\mathrm{u},M({}^{85}\mathrm{Rb})=84.911\hspace{0.5em}789739(9)\mathrm{u},M({}^{87}\mathrm{Rb})=86.909\hspace{0.5em}180\hspace{0.5em}535(10)\mathrm{u}$, and $M({}^{133}\mathrm{Cs})=132.905\hspace{0.5em}451\hspace{0.5em}963(13)\mathrm{u}$. Our mass of ${}^6\mathrm{Li}$ yields an improved neutron separation energy for ${}^7\mathrm{Li}$ of 7251.1014(45) keV.

Figure 1

An example of cyclotron frequency ratio data. The cyclotron frequency of one ion at the center of the trap is measured three times, while the other ion remains in a large cyclotron orbit. The ions are then interchanged, and the process is repeated. The vertical scales give the cyclotron frequencies of the two ions in hertz, and the horizontal scale is the time during the day. The cyclotron frequency ratio is obtained from a simultaneous fit of similar polynomials to both ions’ cyclotron frequencies. The ratio obtained from this particular run had a statistical uncertainty of $7\times {10}^{-11}$.