Mass and $Q_{\mathrm{EC}}$ value of ${}^{26}\mathrm{Si}$

The $Q_{\mathrm{EC}}$ value of the superallowed $\beta$ emitter ${}^{26}\mathrm{Si}$ has been measured with the JYFLTRAP Penning trap facility to be 4840.85(10) keV which is ten times more precise than any previous measurement. This leaves only the branching ratio to be improved before the $\mathcal{F}t$ value of ${}^{26}\mathrm{Si}$ can be used to test the conserved vector current hypothesis. As a consequence, the ${}^{25}\mathrm{Al}(p,\gamma ){}^{26}\mathrm{Si}$ reaction $Q$-value ($Q_{p\gamma }$) was improved to be 5513.7(5) keV, limited now by the mass excess of ${}^{25}\mathrm{Al}$. The new $Q_{p\gamma }$ value changes the stellar production rate of ${}^{26}\mathrm{Si}$ in nova ignition temperatures by about 10%.

Figure 1

Part of a $\beta$-decay scheme for the $A=26$ isobar. The given marked nuclear states were simultaneously available in the radioactive beam from the IGISOL separator. The resolving power employed in the purification trap was sufficient to separate the ground and isomeric states of ${}^{26}\mathrm{Al}$. The mass differences indicated with A, B and C were measured.

Figure 2

Time-of-flight cyclotron resonance obtained for ${}^{26}\mathrm{Si}$. Here, a quadrupolar RF-excitation time of 300 ms was used.

Figure 3

Example of one set of $Q_{\mathrm{EC}}$ values that were recorded for ${}^{26}\mathrm{Si}—{}^{26}\mathrm{Al}{}^m$. The weighted average of the set, 4840.94(19) keV agrees well with the final result 4840.85(10) keV, which comprises all collected data.

Figure 4

Comparison of different mass excess values obtained for ${}^{26}\mathrm{Si}$. (a) Hardy et al. [9] (calibrated with modern standards), (b) Parikh et al. [10] and (c) this work. The horizontal line denotes the AME2003 value [19] with one standard deviation (shaded).

Figure 5

Different contributions to the total reaction rates. The dashed lines are contributions from the resonances and the grey line is contribution from the direct capture (DC).The solid line with full boxes depict the total rate. The grey band around the total rate is its approximated uncertainty.

Figure 6

The $\mathcal{F}t$-value of ${}^{26}\mathrm{Si}$ among the most precisely known $\mathcal{F}t$-values. The new value for ${}^{26}\mathrm{Si}$ (filled blue circle) has still rather large uncertainty due to limited precision of the branching ratio. The horizontal grey bar denotes one standard deviation around the average $\mathcal{F}t$-value.