Resonant laser ionization and spectroscopy are widely used techniques at radioactive ion beam facilities to produce pure beams of exotic nuclei and measure the shape, size, spin and electromagnetic multipole moments of these nuclei. However, in such measurements it is difficult to combine a high efficiency with a high spectral resolution. Here we demonstrate the on-line application of atomic laser ionization spectroscopy in a supersonic gas jet, a technique suited for high-precision studies of the ground- and isomeric-state properties of nuclei located at the extremes of stability. The technique is characterized in a measurement on actinium isotopes around theN=126 neutron shell closure. A significant improvement in the spectral resolution by more than one order of magnitude is achieved in these experiments without loss in efficiency.

Atomic masses of the neutron-rich isotopes Cd121\char21{}128, In129,131, Sn130\char21{}135, Sb131\char21{}136, and Te132\char21{}140 have been measured with high precision (10~ppb) using the Penning-trap mass spectrometer JYFLTRAP. Among these, the masses of four r-process nuclei Sn135, Sb136, and Te139,140 were measured for the first time. An empirical neutron pairing gap expressed as the odd-even staggering of isotopic masses shows a strong quenching across N=82 for Sn, with a Z dependence that is unexplainable by the current theoretical models.

The double Penning trap mass spectrometer JYFLTRAP has been employed to measure masses and excitation energies for $11/{2}^{$-${}}$ isomers in ${}^{121}$Cd, ${}^{123}$Cd, ${}^{125}$Cd, and ${}^{133}$Te, for $1/{2}^{$-${}}$ isomers in ${}^{129}$In and ${}^{131}$In, and for ${7}^{$-${}}$ isomers in ${}^{130}$Sn and ${}^{134}$Sb. These first direct mass measurements of the Cd and In isomers reveal deviations to the excitation energies based on results from $$\beta${}$-decay experiments and yield new information on neutron- and proton-hole states close to ${}^{132}$Sn. A new excitation energy of $144(4)$ keV has been determined for ${}^{123}$Cd${}^{m}$. A good agreement with the precisely known excitation energies of ${}^{121}$Cd${}^{m}$, ${}^{130}$Sn${}^{m}$, and ${}^{134}$Sb${}^{m}$ has been found.

We investigate the decay of ${}^{87,88}\mathrm{Br}$ and ${}^{94}\mathrm{Rb}$ using total absorption $\gamma$-ray spectroscopy. These important fission products are $\beta$-delayed neutron emitters. Our data show considerable $\beta \gamma$ intensity, so far unobserved in high-resolution $\gamma$-ray spectroscopy, from states at high excitation energy. We also find significant differences with the $\beta$ intensity that can be deduced from existing measurements of the $\beta$ spectrum. We evaluate the impact of the present data on reactor decay heat using summation calculations. Although the effect is relatively small it helps to reduce the discrepancy between calculations and integral measurements of the photon component for ${}^{235}\mathrm{U}$ fission at cooling times in the range $1\text{–}100$ s. We also use summation calculations to evaluate the impact of present data on reactor antineutrino spectra. We find a significant effect at antineutrino energies in the range of 5 to 9 MeV. In addition, we observe an unexpected strong probability for $\gamma$ emission from neutron unbound states populated in the daughter nucleus. The $\gamma$ branching is compared to Hauser-Feshbach calculations, which allow one to explain the large value for bromine isotopes as due to nuclear structure. However the branching for ${}^{94}\mathrm{Rb}$, although much smaller, hints of the need to increase the radiative width ${\mathrm{\Gamma }}_{\gamma }$ by one order of magnitude. This increase in ${\mathrm{\Gamma }}_{\gamma }$ would lead to a similar increase in the calculated $(\mathrm{n},\gamma )$ cross section for this very neutron-rich nucleus with a potential impact on $r$ process abundance calculations.

The mass of S31 has been measured with the JYFLTRAP double Penning trap mass spectrometer. The new mass excess value of -19$\hskip0.3em${}042.55(24)$\hskip0.3em${}keV deviates from the adopted value of -19$\hskip0.3em${}044.6(15)$\hskip0.3em${}keV by 1.4$\sigma${}. The mass value of Cl32 has been revised with the new S31 result and the latest data from $\beta${}-delayed proton decay of Cl32. The new mass excess value for Cl32 is -13$\hskip0.3em${}334.88(65)$\hskip0.3em${}keV, which is the most precise value for Cl32 so far and in agreement with the recent (He3,t) data. The isobaric multiplet mass equation has been tested in the T=2 quintet at A=32, and the cubic form of the equation has been found to agree with the experimental data. The QEC value for the $\beta${} decay of T=1/2 mirror nucleus S31 has been determined as QEC=5397.99(24)$\hskip0.3em${}keV, which slightly deviates from the previously adopted value.