Using the time-of-flight technique, we measured the beta-delayed neutron emission of ^{132}Cd. From our large-scale shell model (LSSM) calculation using the N^{3}LO interaction [Z. Y. Xu et al., Phys. Rev. Lett. 131, 022501 (2023)PRLTAO0031-900710.1103/PhysRevLett.131.022501], we suggest the decay is dominated by the transformation of a neutron in the g_{7/2} orbital, deep below the Fermi surface, into a proton in the g_{9/2} orbital. We compare the beta-decay half-lives and neutron branching ratios of nuclei with Z<50 and N≥82 obtained with our LSSM with those of leading "global" models such as finite-range droplet model (FRDM). Our calculations match known half-lives and neutron branching ratios well and suggest that current leading models overestimate the yet-to-be-measured half-lives. Our model, backed by the ^{132}Cd decay data presented here, offers robust predictive power for nuclei of astrophysical interest such as r-process waiting points.

Polonium isotopes having two protons above the shell closure at Z=82 show a wide variety of low-lying, high-spin isomeric states across the whole chain. The structure of neutron-deficient isotopes up to ^{210}Po  (N=126) is well established as they are easily produced through various methods. However, there is not much information available for the neutron-rich counterparts for which only selective techniques can be used for their production. We report on the first fast-timing measurements of yrast states up to the 8^{+} level in ^{214,216,218}Po isotopes produced in the β^{-} decay of ^{214,216,218}Bi at ISOLDE, CERN. In particular, our new half-life value of 607(14) ps for the 8_{1}^{+} state in ^{214}Po is nearly 20 times shorter than the value available in the literature and comparable with the newly measured half-lives of 409(16) and 628(25) ps for the corresponding 8_{1}^{+} states in ^{216,218}Po, respectively. The measured B(E2;8_{1}^{+}→6_{1}^{+}) transition probability values follow an increasing trend relative to isotope mass, reaching a maximum for ^{216}Po. The increase contradicts the previous claims of isomerism for the 8^{+} yrast states in neutron-rich ^{214}Po and beyond. Together with the other measured yrast transitions, the B(E2) values provide a crucial test of the different theoretical approaches describing the underlying configurations of the yrast band. The new experimental results are compared to shell-model calculations using the KHPE and H208 effective interactions and their pairing-modified versions, showing an increase in configuration mixing when moving toward the heavier isotopes.

A detailed level scheme of 213Fr126 following the EC/beta+ decay of the 1/2- 213 Ra parent ground state was built in an experiment performed at the ISOLDE Decay Station, CERN. The fragmented total beta decay strength favours the direct population of several low-spin (J 7/2) excited states. The analysis of the gamma-singles spectrum and gamma-gamma coincidences allowed us to identify many new gamma-ray transitions and excited states in 213 Fr up to about 3.6 MeV excitation energy. The spins and parities of the newly established levels, on top of the (7/2-1 ) state, were mainly assigned based on the systematics of the N = 126 isotones and further compared with shell-model calculations. The level scheme displays a structural pattern, with several groups of states with negative parity, emerging from the well-defined, simple, pi ( h 59 / 2 ), pi ( h 4 9 / 2 f 17 / 2 ) configurations or from their configuration mixing. The strength of the E 2 transitions within the multiplets is compared with shell-model theoretical calculations performed with the KHPE and H 208 effective interactions. A new (3/2-) isomer with a half-life of 26(3) ns has been identified. An upper limit of 35 ps was determined for the half-life of the first excited state, 7/2-. The possibility of a mixed M 1 + E 2 character is discussed for the 7/2-1 -> 9/2-gs decay in 213 Fr, which leads to an l-forbidden nature of the pi f 7 / 2 -> pi h 9 / 2 transition.

We investigated decays of ^{51,52,53}K at the ISOLDE Decay Station at CERN in order to understand the mechanism of the β-delayed neutron-emission (βn) process. The experiment quantified neutron and γ-ray emission paths for each precursor. We used this information to test the hypothesis, first formulated by Bohr in 1939, that neutrons in the βn process originate from the structureless "compound nucleus." The data are consistent with this postulate for most of the observed decay paths. The agreement, however, is surprising because the compound-nucleus stage should not be achieved in the studied β decay due to insufficient excitation energy and level densities in the neutron emitter. In the ^{53}K βn decay, we found a preferential population of the first excited state in ^{52}Ca that contradicted Bohr's hypothesis. The latter was interpreted as evidence for direct neutron emission sensitive to the structure of the neutron-unbound state. We propose that the observed nonstatistical neutron emission proceeds through the coupling with nearby doorway states that have large neutron-emission probabilities. The appearance of "compound-nucleus" decay is caused by the aggregated small contributions of multiple doorway states at higher excitation energy.

The excited structure of the single-hole nucleus 131 Sn populated by the beta - decay of 131 In was investigated in detail at the ISOLDE facility at CERN. This new experiment took advantage of isomeric purification capabilities provided by resonant ionization, making it possible to independently study the decay of each isomer for the first time. The position of the first-excited nu h 11 / 2 neutron-hole state was confirmed via an independent mass spectroscopy experiment performed at the Ion Guide Isotope Separator On-Line facility at the University of Jyv & auml;skyl & auml;. The level scheme of 131 Sn was notably expanded with the addition of 31 new gamma-ray transitions and 22 new excited levels. The gamma-emitting excited levels above the neutron separation energy in 131 Sn were investigated, revealing a large number of states, which in some cases decay by transitions to other neutron-unbound states. Our analysis showed the dependence between the population of these states in 131 Sn and the beta-decaying 131 In state feeding them. Profiting from the isomer selectivity, it was possible to estimate the direct beta feeding to the 3/2+ / 2 + ground and 11/2- / 2 - isomeric states, disentangling the contributions from the three indium parent states. This made possible to resolve the discrepancies in log ft for first-forbidden transitions observed in previous studies, and to determine the beta-delayed neutron decay probability (Pn) P n ) values of each indium isomers independently. The first measurement of subnanosecond lifetimes in 131 Sn was performed in this work. A short T 1 / 2 = 18(4)-ps value was measured for the 1/2+ / 2 + neutron single-hole 332-keV state, which indicates an enhanced l-forbidden M 1 behavior for the nu 3 s - 1 1/2 / 2 -> nu 3 d - 13 / 2 transition. The measured half-lives of high-energy states populated in the beta decay of the (21/2+) / 2 + ) second isomeric state ( 131 m 2 In) provided valuable information on transition rates, supporting the interpretation of these levels as core-excited states analogous to those observed in the doubly-magic 132 Sn.

High-precision lifetime measurements in 28Mg were performed to study neutron shell evolution in Mg isotopes and the onset of the =20 island of inversion. Using both the recoil distance and Doppler shift attenuation methods, five lifetimes were measured in addition to six upper limits. The observation of two long-lived, negative-parity states demonstrate the importance of studying Mg isotopes for the contribution of intruder configurations to -shell nuclei. Lifetimes of the 2+1 and 4+1 states of 1.81(5) ps and 172(+11-10)stat.(4)stop.(8)feed.(4)targ.fs, respectively, demonstrate a loss of collectivity with increasing spin in the yrast band, permitting for distinguishing between current theoretical models. These measurements also highlight the progression of yrast structure across the Mg isotopic chain from rotational at =12 to large shape mixing at =16 and back to collective behavior at =20 but with dominating intruder configurations.

The excited structure of the single-hole nucleus Sn131 populated by the β− decay of In131 was investigated in detail at the ISOLDE facility at CERN. This new experiment took advantage of isomeric purification capabilities provided by resonant ionization, making it possible to independently study the decay of each isomer for the first time. The position of the first-excited νh11/2 neutron-hole state was confirmed via an independent mass spectroscopy experiment performed at the Ion Guide Isotope Separator On-Line facility at the University of Jyväskylä. The level scheme of Sn131 was notably expanded with the addition of 31 new γ-ray transitions and 22 new excited levels. The γ-emitting excited levels above the neutron separation energy in Sn131 were investigated, revealing a large number of states, which in some cases decay by transitions to other neutron-unbound states. Our analysis showed the dependence between the population of these states in Sn131 and the β-decaying In131 state feeding them. Profiting from the isomer selectivity, it was possible to estimate the direct β feeding to the 3/2+ ground and 11/2− isomeric states, disentangling the contributions from the three indium parent states. This made possible to resolve the discrepancies in logft for first-forbidden transitions observed in previous studies, and to determine the β-delayed neutron decay probability (Pn) values of each indium isomers independently. The first measurement of subnanosecond lifetimes in Sn131 was performed in this work. A short T1/2=18(4)−ps value was measured for the 1/2+ neutron single-hole 332-keV state, which indicates an enhanced l-forbidden M1 behavior for the ν3s1/2−1→ν3d3/2−1 transition. The measured half-lives of high-energy states populated in the β decay of the (21/2+) second isomeric state (In131m2) provided valuable information on transition rates, supporting the interpretation of these levels as core-excited states analogous to those observed in the doubly-magic Sn132. Published by the American Physical Society 2024

A detailed β-decay study of the low- and high-spin states in Bi216 has been performed at the ISOLDE Decay Station at the CERN-ISOLDE facility. In total, 48 new levels and 83 new transitions in the β-decay daughter Po216 were identified. Shell-model calculations for excited states in Bi216 and Po216 were performed using the H208 and the modified Kuo-Herling particle effective interactions. Based on the experimental observations and the shell-model calculations, the most likely spin and parity assignments for the β-decaying states in Bi216 are (3−) and (8−), respectively. Published by the American Physical Society 2024

The cross-shell excited states of 34Si have been investigated via beta decays of the 4- ground state and the 1+ isomeric state of 34Al. Since the valence protons and valence neutrons occupy different major shells in the ground state as well as the intruder 1+ isomeric state of 34Al, intruder levels of 34Si are populated via allowed beta decays. Spin assignments to such intruder levels of 34Si were established through gamma -gamma angular correlation analysis for the negative-parity states with dominant configurations (nu d3/2)-1 (R) (nu f7/2)1 as well as the positive-parity states with dominant configurations (nu sd )-2 (R) (nu f7/2p3/2)2. The configurations of such intruder states play crucial roles in our understanding of the N = 20 shell gap evolution. A configuration interaction model derived from the FSU Hamiltonian was utilized in order to interpret the intruder states in 34Si. Shell model interaction derived from a more fundamental theory with the valence space in medium similarity renormalization group method was also employed to interpret the structure of 34Si.

Background: Detailed spectroscopy of neutron-rich, heavy, deformed nuclei is of broad interest for nuclear astrophysics and nuclear structure. Nuclei in the r-process path and following freeze-out region impact the resulting r-process abundance distribution, and the structure of nuclei midshell in both proton and neutron number helps to understand the evolution of subshell gaps and large deformation in these nuclei. Purpose: We aim to improve the understanding of the nuclear structure of 160Gd, specifically the K & pi; = 4+ bands, as well as study the & beta; decay of 160Eu into 160Gd. Methods: High-statistics decay spectroscopy of 160Gd resulting from the & beta;-decay of 160Eu was collected using the GRIFFIN spectrometer at the TRIUMF-ISAC facility. Results: Two new excited states and ten new transitions were observed in 160Gd. The & beta;-decaying half-lives of the low-and high-spin isomers in 160Eu were determined, and the low-spin state's half-life was measured to be t1/2 = 26.0(8) s, & AP;16% shorter than previous measurements. Lifetimes of the two K & pi; = 4+ bandheads in 160Gd were measured for the first time, as well as & gamma; -& gamma; angular correlations and mixing ratios of intense transitions out of those bandheads. Conclusions: Lifetimes and mixing ratios suggest that the hexadecapole phonon model of the K & pi; = 4+ bandheads in 160Gd is preferred over a simple two-state strong mixing scenario, although further theoretical calculations are needed to fully understand these states. Additionally, the 1999.0-keV state in 160Gd heavily populated in & beta; decay is shown to have positive parity, which raises questions regarding the structure of the high-spin & beta;-decaying state in 160Eu.

The detailed study of the β + /EC decay of the very neutron-deficient and alpha-unbound nucleus 115 Cs is presented.The measurement was performed at the ISOLDE, CERN where delayed charged particles and γ rays were detected.The observed delayed γ rays are in agreement with the previously reported characteristics γ rays of 115 Xe.Based on the experimental observations, the tentative ground-state spin of 115 Cs is suggested to be 7/2 + or 9/2 + .Furthermore, the measured decay branching ratio of delayed protons exceeds the previously reported value.Additionally, new delayed α-branching ratio and several reconstructed proton and α-unbound excited states of 115 Xe are being reported for the first time.The properties of proton-unbound states at excitation energies from 3.9-7.9MeV have been obtained by fitting the delayed proton spectrum via the Bayesian method.The measured lifetimes of these proton-unbound states are in the order of zeptoseconds.

The decay properties of ^133In were studied in detail at the ISOLDE Decay Station (IDS). The implementation of the Resonance Ionization Laser Ion Source (RILIS) allowed separate measurements of its 9/2^+ ground state (^133gIn) and 1/2^- isomer (^133mIn). With the use of β-delayed neutron and γ spectroscopy, the decay strengths above the neutron separation energy were quantified in this neutron-rich nucleus for the first time. The allowed Gamow-Teller transition 9/2^+→7/2^+ was located at 5.92 MeV in the ^133gIn decay with a logft = 4.7(1). In addition, several neutron-unbound states were populated at lower excitation energies by the First-Forbidden decays of ^133g,mIn. We assigned spins and parities to those neutron-unbound states based on the β-decay selection rules, the logft values, and systematics.

Background: Detailed spectroscopy of neutron-rich, heavy, deformed nuclei is of broad interest for nuclear astrophysics and nuclear structure. Nuclei in the $r$-process path and following freeze-out region impact the resulting $r$-process abundance distribution, and the structure of nuclei midshell in both proton and neutron number helps to understand the evolution of subshell gaps and large deformation in these nuclei.Purpose: We aim to improve the understanding of the nuclear structure of $^{160}\mathrm{Gd}$, specifically the ${K}^{\ensuremath{\pi}}={4}^{+}$ bands, as well as study the $\ensuremath{\beta}$ decay of $^{160}\mathrm{Eu}$ into $^{160}\mathrm{Gd}$.Methods: High-statistics decay spectroscopy of $^{160}\mathrm{Gd}$ resulting from the $\ensuremath{\beta}$-decay of $^{160}\mathrm{Eu}$ was collected using the GRIFFIN spectrometer at the TRIUMF-ISAC facility.Results: Two new excited states and ten new transitions were observed in $^{160}\mathrm{Gd}$. The $\ensuremath{\beta}$-decaying half-lives of the low- and high-spin isomers in $^{160}\mathrm{Eu}$ were determined, and the low-spin state's half-life was measured to be ${t}_{1/2}=26.0(8)$ s, $\ensuremath{\approx}16%$ shorter than previous measurements. Lifetimes of the two ${K}^{\ensuremath{\pi}}={4}^{+}$ bandheads in $^{160}\mathrm{Gd}$ were measured for the first time, as well as $\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma}$ angular correlations and mixing ratios of intense transitions out of those bandheads.Conclusions: Lifetimes and mixing ratios suggest that the hexadecapole phonon model of the ${K}^{\ensuremath{\pi}}={4}^{+}$ bandheads in $^{160}\mathrm{Gd}$ is preferred over a simple two-state strong mixing scenario, although further theoretical calculations are needed to fully understand these states. Additionally, the 1999.0-keV state in $^{160}\mathrm{Gd}$ heavily populated in $\ensuremath{\beta}$ decay is shown to have positive parity, which raises questions regarding the structure of the high-spin $\ensuremath{\beta}$-decaying state in $^{160}\mathrm{Eu}$.

The decay properties of $^{133}$In were studied in detail at the ISOLDE Decay Station (IDS). The implementation of the Resonance Ionization Laser Ion Source (RILIS) allowed separate measurements of its $9/2^+$ ground state ($^{133g}$In) and $1/2^-$ isomer ($^{133m}$In). With the use of $\beta$-delayed neutron and $\gamma$ spectroscopy, the decay strengths above the neutron separation energy were quantified in this neutron-rich nucleus for the first time. The allowed Gamow-Teller transition $9/2^+\rightarrow7/2^+$ was located at 5.92 MeV in the $^{133g}$In decay with a logft = 4.7(1). In addition, several neutron-unbound states were populated at lower excitation energies by the First-Forbidden decays of $^{133g,m}$In. We assigned spins and parities to those neutron-unbound states based on the $\beta$-decay selection rules, the logft values, and systematics.

The accurate determination of reactor antineutrino spectra remains a very hot research topic, where new questions have emerged in recent years. Indeed, after the “reactor anomaly” – a deficit of measured antineutrinos at short baseline reactor experiments with respect to spectral predictions – the three international reactor neutrino experiments Double Chooz, Daya Bay and Reno have evidenced spectral distortions in their measurements with respect to the same spectral predictions. This puzzle is called the “shape anomaly”. Recently summation calculations of reactor antineutrino spectra based on the use of nuclear data have obtained the best agreement to date with the reactor neutrino flux measurements at the level of 2% thanks to a decade of Total Absorption Gamma-ray Spectroscopy (TAGS) measurements at the radioactive beam facility of the University of Jyväskylä in two experimental campaigns. A selection of the results obtained so far is presented.

The β decays from both the ground state and a long-lived isomer of ^{133}In were studied at the ISOLDE Decay Station (IDS). With a hybrid detection system sensitive to β, γ, and neutron spectroscopy, the comparative partial half-lives (logft) have been measured for all their dominant β-decay channels for the first time, including a low-energy Gamow-Teller transition and several first-forbidden (FF) transitions. Uniquely for such a heavy neutron-rich nucleus, their β decays selectively populate only a few isolated neutron unbound states in ^{133}Sn. Precise energy and branching-ratio measurements of those resonances allow us to benchmark β-decay theories at an unprecedented level in this region of the nuclear chart. The results show good agreement with the newly developed large-scale shell model (LSSM) calculations. The experimental findings establish an archetype for the β decay of neutron-rich nuclei southeast of ^{132}Sn and will serve as a guide for future theoretical development aiming to describe accurately the key β decays in the rapid-neutron capture (r-) process.

Models of the beta-delayed neutron emission (beta n) assume that neutrons are emitted statistically via an intermediate compound nucleus post beta decay. Evidence to the contrary was found in an In-134 beta-decay experiment carried out at ISOLDE CERN. Neutron emission probabilities from the unbound states in Sn-134 to known low-lying, single-particle states in Sn-133 were measured. The neutron energies were determined using the time-of-flight technique, and the subsequent decay of excited states in Sn-133 was studied using gamma-ray detectors. Individual beta n probabilities were determined by correlating the relative intensities and energies of neutrons and gamma rays. The experimental data disagree with the predictions of representative statistical models which are based upon the compound nucleus postulate. Our results suggest that violation of the compound nucleus assumption may occur in beta-delayed neutron emission. This impacts the neutron-emission probabilities and other properties of nuclei participating in the r-process. A model of neutron emission, which links the observed neutron emission probabilities to nuclear shell effects, is proposed.

A beta-decay experiment aiming at investigation of the low-spin structure of 100Zr was performed using the GRIFFIN spectrometer at TRIUMF-ISAC. Based on the obtained data, a new 2+ state is postulated which is degenerate in energy with the established (5+) level at 2209 keV.

Background: The mercury isotopes around $N=104$ are a well-known example of nuclei exhibiting shape coexistence. Mixing of configurations can be studied by measuring the monopole strength $\rho^2(E0)$, however, currently the experimental information is scarce and lacks precision, especially for the $I^\pi \rightarrow I^\pi$ ($I \neq 0$) transitions. Purpose: The goals of this study were to increase the precision of the known branching ratios and internal conversion coefficients, to increase the amount of available information regarding excited states in $^{182,184,186}$Hg and to interpret the results in the framework of shape coexistence using different models. Method: The low-energy structures in $^{182,184,186}$Hg were populated in the $\beta$ decay of $^{182,184,186}$Tl, produced at ISOLDE and purified by laser ionization and mass separation. The $\gamma$-ray and internal conversion electron events were detected by five germanium clover detectors and a segmented silicon detector, respectively, and correlated in time to build decay schemes. Results: In total, 193, 178 and 156 transitions, including 144, 140 and 108 observed for the first time in a $\beta$-decay experiment, were assigned to $^{182,184,186}$Hg, respectively. Internal conversion coefficients were determined for 23 transitions, out of which 12 had an $E0$ component. Extracted branching ratios allowed the sign of the interference term in $^{182}$Hg as well as $\rho^2(E0;0^+_2\rightarrow 0^+_1)$ and $B(E2;0^+_2\rightarrow 2^+_1)$ in $^{184}$Hg to be determined. By means of electron-electron coincidences, the $0^+_3$ state was identified in $^{184}$Hg. The experimental results were qualitatively reproduced by five theoretical approaches, the IBM with configuration mixing with two different parametrizations, the General Bohr Hamiltonian, the BMF model and the SCCM model. However, a quantitative description is lacking.