High-accuracy mass measurements of neutron-rich Kr isotopes

The atomic masses of the neutron-rich krypton isotopes ${}^{84,86-95}\mathrm{Kr}$ have been determined with the tandem Penning trap mass spectrometer ISOLTRAP with uncertainties ranging from 20 to 220 ppb. The masses of the short-lived isotopes ${}^{94}\mathrm{Kr}$ and ${}^{95}\mathrm{Kr}$ were measured for the first time. The masses of the radioactive nuclides ${}^{89}\mathrm{Kr}$ and ${}^{91}\mathrm{Kr}$ disagree by 4 and 6 standard deviations, respectively, from the present Atomic-Mass Evaluation database. The resulting modification of the mass surface with respect to the two-neutron separation energies as well as implications for mass models and stellar nucleosynthesis are discussed.

Figure 1

The layout of the tandem Penning trap mass spectrometer ISOLTRAP. Micro-channel-plate detectors (MCP) are used to monitor the ion transfer and to record the time-of-flight resonance. The inset shows a time-of-flight resonance for ${}^{86}\mathrm{Kr}$${}^{+}$ with 900 ms excitation duration. The solid line is a fit of the expected line shape to the data points.

Figure 2

Comparison of the results of the ISOLTRAP mass measurements with the literature values taken from the AME2003 database [9]. The AME2003 mass values of the ${}^{94,95}\mathrm{Kr}$ nuclides are estimated from systematic trends.

Figure 3

An example of experimental time-of-flight resonance and associated fit, obtained for ${}^{95}\mathrm{Kr}$. See text for details.

Figure 4

(a) Comparison of the results of the latest ${}^{84}\mathrm{Kr}$ Penning trap mass measurements (open symbols) with the previous measurements (full symbols) used in the AME2003 [9]. The gray area corresponds to the AME2003 uncertainty. (b) Comparison of the results of the measurements used in the revised evaluation of the mass of ${}^{84}\mathrm{Kr}$ from the AMDC. The line corresponds to the new mass evaluation. For further explanation see text.

Figure 5

Distribution of the $Q_{{\beta }^{-}}$ values for the decay of ${}^{89}\mathrm{Br}$ as in Table 3a of Ref. [29].

Figure 6

Comparison of the masses of krypton isotopes predicted by the models FRDM [34], DZ95 [35], and HFB2 [36] with the reported measurements as a function of the neutron number $N$. See text for more details.

Figure 7

Two-neutron separation energies as a function of the neutron number for krypton and neighboring elements. The values deduced from the new measurements reported here are shown in dashed lines. (Right) The reduced two-neutron separation energies of the Krypton isotopes as deduced from the ISOLTRAP measurements. For further explanation see text.

Figure 8

The nuclear chart around $A=70\text{−}130$ with stable nuclides shown as black squares. The nucleus ${}^{95}\mathrm{Kr}$ is marked by $⊠$. Also shown are two possible paths for a rapid neutron-capture process. The temperatures $T_9$ are expressed in 10${}^9$ K, the neutron density $N_n$ unit is cm${}^{-3}$. For further explanation see text.