arXiv subjects

D. S. Judson

Publications and source records attributed to D. S. Judson.

At least 19 recordsLinked to original sources

arXiv2026

Beta delayed neutron emission of $N=84$ $^{132}$Cd

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)], 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 $N\geq82$ 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.

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arXiv2026

Direct transfer to $^{46,48}$K as a survey of the $π(s_{1/2})$$-ν(sdpf)$ interaction

The collapse of the canonical $N=28$ magic number in nuclei with $Z<20$ has drawn significant interest as it relates to the emergence of an island of inversion centered on $^{42}$Si and $^{44}$S. In particular, interactions between the $πs_{1/2}$ orbital -- empty in $^{42}$Si and full in $^{44}$S -- and the neutron orbitals just above and below the $N=28$ gap are expected to be critical in this region, but remain relatively unexplored. In this paper, we expand upon the results of our previous study of the direct transfer reaction $^{47}$K(d,p$γ$)$^{48}$K [C.\,J.~Paxman \textit{et al.}, Phys. Rev. Lett. 134, 162504 (2025)] with the results of the complementary $^{47}$K(d,t$γ$)$^{46}$K reaction. Through this study, we present a comprehensive scan of the interaction between the critical $πs_{1/2}$ orbital and a broad range of neutron orbitals spanning nearly two full shells. We identify several discrepancies between the experimental results and state-of-the-art shell model calculations, which suggest a deficiency of the shell model to fully capture the complex proton configuration mixing in this region, highlighting a significant challenge for single-particle descriptions of the island of inversion.

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arXiv2025

The 76Cu conundrum remains unsolved

Near the doubly-magic nucleus \nuc{Ni}{78} ($Z=28$, $N=50$), there has been a decades-long debate on the existence of a long-lived isomer in \nuc{Cu}{76}. A recent mass measurement claimed to have settled the debate, by measuring the energy of the isomer and shedding light on the structure of the nucleus. In this work, we present new, more accurate, and precise values of the half-lives of the isomeric and ground states in \nuc{Cu}{76}. Our findings suggest that both states have very similar half-lives, in the 600-700 ms range, in disagreement with the literature values, implying that they cannot be differentiated by their decay curves. These results raise more questions than they answer, reopening the debate and showing that the structures in \nuc{Cu}{76} are still not fully understood.

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arXiv2025

Probing exotic cross-shell interactions at N=28 with single-neutron transfer on 47K

We present the first measurement of the $^{47}$K($d,pγ$)$^{48}$K transfer reaction, performed in inverse kinematics using a reaccelerated beam of $^{47}$K. The level scheme of $^{48}$K has been greatly extended with nine new bound excited states identified and spectroscopic factors deduced. Detailed comparisons with SDPF-U and SDPF-MU shell-model calculations reveal a number of discrepancies with these results, and a preference for SDPF-MU is found. Intriguingly, an apparent systematic overestimation of spectroscopic factors and a poor reproduction of the energies for 1$^-$ states suggests that the mixing between the $πs^{\,\,\,1}_{1/2} d^{\,\,\,4}_{3/2}$ and $πs^{\,\,\,2}_{1/2} d^{\,\,\,3}_{3/2}$ proton configurations in $^{48}$K is not correctly described using current interactions, challenging our descriptions of light $N=28$ nuclei.

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arXiv2024

Revealing the nature of yrast states in neutron-rich polonium isotopes

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 one available in 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 $B(E2;8_1^+ \to 6_1^+)$ 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 towards the heavier isotopes.

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arXiv2024

Shape evolution in even-mass $^{98-104}$Zr isotopes via lifetime measurements using the $γγ$-coincidence technique

The Zirconium (Z = 40) isotopic chain has attracted interest for more than four decades. The abrupt lowering of the energy of the first $2^+$ state and the increase in the transition strength B(E2; $2_1^\rightarrow 0_1^+$ going from $^{98}$Zr to $^{100}$Zr has been the first example of "quantum phase transition" in nuclear shapes, which has few equivalents in the nuclear chart. Although a multitude of experiments have been performed to measure nuclear properties related to nuclear shapes and collectivity in the region, none of the measured lifetimes were obtained using the Recoil Distance Doppler Shift method in the $γγ$-coincidence mode where a gate on the direct feeding transition of the state of interest allows a strict control of systematical errors. This work reports the results of lifetime measurements for the first yrast excited states in $^{98-104}$Zr carried out to extract reduced transition probabilities. The new lifetime values in $γγ$-coincidence and $γ$-single mode are compared with the results of former experiments. Recent predictions of the Interacting Boson Model with Configuration Mixing, the Symmetry Conserving Configuration Mixing model based on the Hartree-Fock-Bogoliubov approach and the Monte Carlo Shell Model are presented and compared with the experimental data.

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arXiv2024

Detailed study of the decay of $^{21}$Mg

Beta-delayed proton and gamma emission in the decay of $^{21}$Mg has been measured at ISOLDE, CERN with the ISOLDE Decay Station (IDS) set-up. The existing decay scheme is updated, in particular what concerns proton transitions to excited states in $^{20}$Ne. Signatures of interference in several parts of the spectrum are used to settle spin and parity assignments to highly excited states in $^{21}$Na. The previously reported $β$p$α$ branch is confirmed. A half-life of 120.5(4) ms is extracted for $^{21}$Mg. The revised decay scheme is employed to test mirror symmetry in the decay and to extract the beta strength distribution of $^{21}$Mg that is compared with theory.

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arXiv2023

Simultaneous $γ$-ray and electron spectroscopy of $^{182,184,186}$Hg isotopes

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 $ρ^2(E0)$, however, currently the experimental information is scarce and lacks precision, especially for the $I^π\rightarrow I^π$ ($I \neq 0$) 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 $β$ decay of $^{182,184,186}$Tl, produced at ISOLDE and purified by laser ionization and mass separation. The $γ$-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 $β$-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 $ρ^2(E0;0^+_2\rightarrow 0^+_1)$ 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.

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arXiv2023

133In: A Rosetta Stone for decays of r-process nuclei

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.

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arXiv2023

Beta-delayed neutron spectroscopy of $^{133}$In

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 $β$-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 $9/2^+\rightarrow7/2^+$ 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 $β$-decay selection rules, the logft values, and systematics.

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arXiv2020

Decay studies of the long-lived states in $^{186}$Tl

Decay spectroscopy of the long-lived states in $^{186}$Tl has been performed at the ISOLDE Decay Station at ISOLDE, CERN. The $α$ decay from the low-spin $(2^-)$ state in $^{186}$Tl was observed for the first time and a half-life of $3.4^{+0.5}_{-0.4}$ s was determined. Based on the $α$-decay energy, the relative positions of the long-lived states were fixed, with the $(2^-)$ state as the ground state, the $7^{(+)}$ state at 77(56)~keV and the $10^{(-)}$ state at 451(56) keV. The level scheme of the internal decay of the $^{186}$Tl($10^{(-)}$) state ($T_{1/2} = 3.40(9)$ s), which was known to decay solely through emission of 374 keV $γ$-ray transition, was extended and a lower-limit for the $β$-decay branching $b_β> 5.9(3)\%$ was determined. The extracted retardation factors for the $γ$ decay of the $10^{(-)}$ state were compared to the available data in neighboring odd-odd thallium isotopes indicating the importance of the $πd_{3/2}$ shell in the isomeric decay and significant structure differences between $^{184}$Tl and $^{186}$Tl.

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arXiv2020

Detailed spectroscopy of doubly magic $^{132}$Sn

The structure of the doubly magic $^{132}_{50}$Sn$_{82}$ has been investigated at the ISOLDE facility at CERN, populated both by the $β^-$decay of $^{132}$In and $β^-$-delayed neutron emission of $^{133}$In. The level scheme of $^{132}$Sn is greatly expanded with the addition of 68 $γ$-transitions and 17 levels observed for the first time in the $β$ decay. The information on the excited structure is completed by new $γ$-transitions and states populated in the $β$-n decay of $^{133}$In. Improved delayed neutron emission probabilities are obtained both for $^{132}$In and $^{133}$In. Level lifetimes are measured via the Advanced Time-Delayed $βγγ$(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 \textit{N} = 82 and \textit{Z} = 50 shells, leading to positive and negative parity particle-hole multiplets. The experimental information provides new data to challenge the theoretical description of $^{132}$Sn.

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arXiv2020

Testing ab initio nuclear structure in neutron-rich nuclei: lifetime measurements of second 2+ states in 16C and 20O

To test the predictive power of ab initio nuclear structure theory, the lifetime of the second 2+ state in neutron-rich 20O, tau(2+_2 ) = 150(+80-30) fs, and an estimate for the lifetime of the second 2+ state in 16C have been obtained, for the first time. The results were achieved via a novel Monte Carlo technique that allowed us to measure nuclear state lifetimes in the tens-to-hundreds femtoseconds range, by analyzing the Doppler-shifted gamma-transition line shapes of products of low-energy transfer and deep-inelastic processes in the reaction 18O (7.0 MeV/u) + 181Ta. The requested sensitivity could only be reached owing to the excellent performances of the AGATA gamma-tracking array, coupled to the PARIS scintillator array and to the VAMOS++ magnetic spectrometer. The experimental lifetimes agree with predictions of ab initio calculations using two- and three-nucleon interactions, obtained with the valence-space in-medium similarity renormalization group for 20O, and with the no-core shell model for 16C. The present measurement shows the power of electromagnetic observables, determined with high-precision gamma spectroscopy, to assess the quality of first-principles nuclear structure calculations, complementing common benchmarks based on nuclear energies. The proposed experimental approach will be essential for short lifetimes measurements in unexplored regions of the nuclear chart, including r-process nuclei, when intense ISOL-type beams become available.

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arXiv2019

Pairing-quadrupole interplay in the neutron-deficient tin nuclei: first lifetime measurements of low-lying states in $^{106,108}$Sn

The lifetimes of the low-lying excited states $2^+$ and $4^+$ have been directly measured in the neutron-deficient $^{106,108}$Sn isotopes. The nuclei were populated via a deep-inelastic reaction and the lifetime measurement was performed employing a differential plunger device. The emitted $γ$ rays were detected by the AGATA array, while the reaction products were uniquely identified by the VAMOS++ magnetic spectrometer. Large-Scale Shell-Model calculations with realistic forces indicate that, independently of the pairing content of the interaction, the quadrupole force is dominant in the $B(E2; 2_1^+ \to 0_{g.s.}^+)$ values and it describes well the experimental pattern for $^{104-114}$Sn; the $B(E2; 4_1^+ \to 2_1^+)$ values, measured here for the first time, depend critically on a delicate pairing-quadrupole balance, disclosed by the very precise results in $^{108}$Sn. This result provides insight in the hitherto unexplained $B(E2; 4_1^+ \to 2_1^+)/B(E2; 2_1^+ \to 0_{g.s.}^+) < 1$ anomaly.

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arXiv2018

First Accurate Normalization of the $β$-delayed $α$ Decay of $^{16}$N and Implications for the $^{12}$C$(α,γ)^{16}$O Astrophysical Reaction Rate

The $^{12}\text{C}(α,γ){}^{16}\text{O}$ reaction plays a central role in astrophysics, but its cross section at energies relevant for astrophysical applications is only poorly constrained by laboratory data. The reduced $α$ width, $γ_{11}$, of the bound $1^-$ level in $^{16}$O is particularly important to determine the cross section. The magnitude of $γ_{11}$ is determined via sub-Coulomb $α$-transfer reactions or the $β$-delayed $α$ decay of $^{16}$N, but the latter approach is presently hampered by the lack of sufficiently precise data on the $β$-decay branching ratios. Here we report improved branching ratios for the bound $1^-$ level [$b_{β,11} = (5.02\pm 0.10)\times 10^{-2}$] and for $β$-delayed $α$ emission [$b_{βα} = (1.59\pm 0.06)\times 10^{-5}$]. Our value for $b_{βα}$ is 33% larger than previously held, leading to a substantial increase in $γ_{11}$. Our revised value for $γ_{11}$ is in good agreement with the value obtained in $α$-transfer studies and the weighted average of the two gives a robust and precise determination of $γ_{11}$, which provides significantly improved constraints on the $^{12}$C$(α,γ)$ cross section in the energy range relevant to hydrostatic He burning.

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arXiv2016

A new technique for elucidating $β$-decay schemes which involve daughter nuclei with very low energy excited states

A new technique of elucidating $β$-decay schemes of isotopes with large density of states at low excitation energies has been developed, in which a Broad Energy Germanium (BEGe) detector is used in conjunction with coaxial hyper-pure germanium detectors. The power of this technique has been demonstrated on the example of 183Hg decay. Mass-separated samples of 183Hg were produced by a deposition of the low-energy radioactive-ion beam delivered by the ISOLDE facility at CERN. The excellent energy resolution of the BEGe detector allowed $γ$ rays energies to be determined with a precision of a few tens of electronvolts, which was sufficient for the analysis of the Rydberg-Ritz combinations in the level scheme. The timestamped structure of the data was used for unambiguous separation of $γ$ rays arising from the decay of 183Hg from those due to the daughter decays.

physics.ins-det↗

arXiv2012

High-spin structure in $^{40}$K

High-spin states of $^{40}$K have been populated in the fusion-evaporation reaction $^{12}$C($^{30}$Si,np)$^{40}$K and studied by means of $γ$-ray spectroscopy techniques using one AGATA triple cluster detector, at INFN - Laboratori Nazionali di Legnaro. Several new states with excitation energy up to 8 MeV and spin up to $10^-$ have been discovered. These new states are discussed in terms of J=3 and T=0 neutron-proton hole pairs. Shell-model calculations in a large model space have shown a good agreement with the experimental data for most of the energy levels. The evolution of the structure of this nucleus is here studied as a function of excitation energy and angular momentum.

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arXiv2011

Quadrupole Moments of Collective Structures up to Spin $\sim$ $65\hbar$ in $^{157}$Er and $^{158}$Er: A Challenge for Understanding Triaxiality in Nuclei

The transition quadrupole moments, $Q_{\rm t}$, of four weakly populated collective bands up to spin $\sim$ $65\hbar$ in $^{157,158}$Er have been measured to be ${\sim}11 {\rm eb}$ demonstrating that these sequences are associated with large deformations. However, the data are inconsistent with calculated values from cranked Nilsson-Strutinsky calculations that predict the lowest energy triaxial shape to be associated with rotation about the short principal axis. The data appear to favor either a stable triaxial shape rotating about the intermediate axis or, alternatively, a triaxial shape with larger deformation rotating about the short axis. These new results challenge the present understanding of triaxiality in nuclei.

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