Zenon Janas

The structure of the doubly magic ${}_{50}{}^{132}\mathrm{Sn}_{82}$ has been investigated at the ISOLDE facility at CERN, populated both by the ${\beta }^{-}\mathrm{decay}$ of ${}^{132}\mathrm{In}$ and ${\beta }^{-}$-delayed neutron emission of ${}^{133}\mathrm{In}$. The level scheme of ${}^{132}\mathrm{Sn}$ is greatly expanded with the addition of 68 $\gamma$ transitions and 17 levels observed for the first time in the $\beta$ decay. The information on the excited structure is completed by new $\gamma$ transitions and states populated in the $\beta \text{−}n$ decay of ${}^{133}\mathrm{In}$. Improved delayed neutron emission probabilities are obtained both for ${}^{132}\mathrm{In}$ and ${}^{133}\mathrm{In}$. Level lifetimes are measured via the advanced time-delayed $\beta \gamma \gamma$(t) fast-timing method. An interpretation of the level structure is given based on the experimental findings and the particle-hole configurations arising from core excitations both from the $N$ = 82 and $Z$ = 50 shells, leading to positive- and negative-parity particle-hole multiplets. The experimental information provides new data to challenge the theoretical description of ${}^{132}\mathrm{Sn}$.

The $\beta$ decay of ${}^{57}\mathrm{Zn}$ and ${}^{58}\mathrm{Zn}$ was investigated in an experiment at the National Superconducting Cyclotron Laboratory of Michigan State University. For the first time $\beta$-delayed proton emission from ${}^{58}\mathrm{Zn}$ was observed with a branching ratio of 0.7(1)%. The proton-energy spectrum allowed for probing the Gamow-Teller strength distribution above the proton-separation energy in the daughter nucleus. Moreover, the absolute branching ration for delayed-proton emission from ${}^{57}\mathrm{Zn}$ was found to be compatible with 100%.

The most remote isotope from the proton dripline (by 4 atomic mass units) has been observed: ${}^{31}\mathrm{K}$. It is unbound with respect to three-proton ($3p$) emission, and its decays have been detected in flight by measuring the trajectories of all decay products using microstrip detectors. The $3p$ emission processes have been studied by the means of angular correlations of ${}^{28}\mathrm{S}+3p$ and the respective decay vertices. The energies of the previously unknown ground and excited states of ${}^{31}\mathrm{K}$ have been determined. This provides its $3p$ separation energy value $S_{3p}$ of $-4.6(2)\mathrm{MeV}$. Upper half-life limits of 10 ps of the observed ${}^{31}\mathrm{K}$ states have been derived from distributions of the measured decay vertices.

Excited states in ${}^{133}\mathrm{Sn}$ were investigated through the $\beta$ decay of ${}^{133}\mathrm{In}$ at the ISOLDE facility. The ISOLDE Resonance Ionization Laser Ion Source (RILIS) provided isomer-selective ionization for ${}^{133}\mathrm{In}$, allowing us to study separately, and in detail, the $\beta$-decay branch of ${}^{133}\mathrm{In}{\mathrm{J}}^{\pi }=(9/2^{+}$) ground state and its ${\mathrm{J}}^{\pi }=(1/2^{-}$) isomer. Thanks to the large spin difference of the two $\beta$-decaying states of ${}^{133}\mathrm{In}$, it is possible to investigate separately the lower and higher spin states in the daughter, ${}^{133}\mathrm{Sn}$, and thus to probe independently different single-particle and single-hole levels. We report here new $\gamma$ transitions observed in the decay of ${}^{133}\mathrm{In}$, including those assigned to the deexcitation of the neutron-unbound states.

Prospects of experimental studies of argon and chlorine isotopes located far beyond the proton dripline are studied by using systematics and cluster models. The deviations from the widespread systematics observed in ${}^{28,29}\mathrm{Cl}$ and ${}^{29,30}\mathrm{Ar}$ have been theoretically substantiated, and analogous deviations have been predicted for the lighter chlorine and argon isotopes. The limits of nuclear structure existence are predicted for Ar and Cl isotopic chains, with ${}^{26}\mathrm{Ar}$ and ${}^{25}\mathrm{Cl}$ found to be the lightest sufficiently long-living nuclear systems. By simultaneous measurements of protons and $\gamma$ rays following decays of such systems as well as their $\beta$-delayed emission, an interesting synergy effect may be achieved, which is demonstrated by the example of ${}^{30}\mathrm{Cl}$ and ${}^{31}\mathrm{Ar}$ ground-state studies. Such a synergy effect may be provided by the new EXPERT setup (EXotic Particle Emission and Radioactivity by Tracking) being operated inside the fragment separator and spectrometer facility at GSI, Darmstadt.

The proton-unbound argon and chlorine isotopes have been studied by measuring trajectories of their decay-in-flight products by using a tracking technique with microstrip detectors. The proton ($1p$) and two-proton ($2p$) emission processes have been detected in the measured angular correlations “heavy-fragment”+$p$ and “heavy-fragment”+$p+p$, respectively. The ground states of the previously unknown isotopes ${}^{30}\mathrm{Cl}$ and ${}^{28}\mathrm{Cl}$ have been observed for the first time, providing the $1p$-separation energies $S_p$ of $-0.48\left(2\right)$ and $-1.60\left(8\right)$, MeV, respectively. The relevant systematics of $1p$- and $2p$-separation energies have been studied theoretically in the $\mathrm{core}+p$ and $\mathrm{core}+p+p$ cluster models. The first-time observed excited states of ${}^{31}\mathrm{Ar}$ allow one to infer the $2p$-separation energy $S_{2p}$ of 6(34) keV for its ground state. The first-time observed state in ${}^{29}\mathrm{Ar}$ with $S_{2p}=-5.50\left(18\right)$ MeV can be identified as either a ground state or an excited state according to different systematics.