arXiv subjects

C. J. Griffin

Publications and source records attributed to C. J. Griffin.

16 recordsLinked to original sources

arXiv2026

First observation of the fine structure of the Pygmy Dipole Resonance in a nucleus away from stability via the $β^-$ decay of $^{92}$Rb to $^{92}$Sr

A comprehensive $γ$-ray spectroscopy study of excited states in $^{92}$Sr populated via $β^-$ decay of $^{92}$Rb ($J^π=0^-$, $Q_β=8095(6)$~keV) was performed with the GRIFFIN spectrometer at the Isotope Separator and Accelerator (ISAC) radioactive ion beam facility at TRIUMF. The high $γ$-ray efficiency of the GRIFFIN spectrometer combined with the intense rubidium beams produced allowed for 864 $γ$-ray transitions to be placed in the level scheme with 190 excited levels populated, most of them identified for the first time. The excitation energies of low-spin states in $^{92}$Sr are well reproduced by large-scale Shell Model calculations up to 5~MeV. The $β$-feeding intensities are in very good agreement with results from a recent study employing Modular Total Absorption Spectroscopy, indicating a significant suppression of the Pandemonium effect. The experimental picture reveals the energy level dependence of log~$ft$ values in unprecedented detail. These log~$ft$ values are well reproduced by Multiple-Commutator Model calculations that identify the features in the excited levels' wavefunctions that enable the population of high-lying levels with a low effective Q-value that belong to the Pygmy Dipole Resonance.

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arXiv2025

First Proton-Induced Cross Sections on a Stored Rare Ion Beam: Measurement of 118Te(p,γ) for Explosive Nucleosynthesis

We present the first nuclear cross-section measurements of (p,γ) and (p,n) reactions on 118Te at energies relevant for the γ-process nucleosynthesis. Absolute cross-section values for center-of-mass energies of 6, 7 and 10 MeV are provided, together with a theoretical extrapolation to the Gamow window. This experiment marks the first time that direct proton-induced reactions have been measured on a radioactive ion beam at the Experimental Storage Ring (ESR) at GSI, Darmstadt. This paves the way for a large variety of measurements, delivering new constraints for explosive nucleosynthesis and for physics beyond nuclear stability.

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arXiv2025

Bayesian and Monte Carlo approaches to estimating uncertainty for the measurement of the bound-state $β$ decay of $^{205}\mathrm{Tl}^{81+}$

The measurement of the bound-state $β$ decay of $^{205}\mathrm{Tl}^{81+}$ at the Experimental Storage Ring at GSI, Darmstadt, has recently been reported with substantial impact on the use of $^{205}\mathrm{Pb}$ as an early Solar System chronometer and the low-energy measurement of the solar neutrino spectrum via the LOREX project. Due to the technical challenges in producing a high-purity $^{205}\mathrm{Tl}^{81+}$ secondary beam, a robust statistical method needed to be developed to estimate the variation in the contaminant $^{205}\mathrm{Pb}^{81+}$ produced in the fragmentation reaction, which was subsequently transmitted and stored in the ESR. Here we show that Bayesian and Monte Carlo methods produced comparable estimates for the contaminant variation, each with unique advantages and challenges given the complex statistical problems for this experiment. We recommend the adoption of such methods in future experiments that exhibit unknown statistical fluctuations.

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arXiv2025

Investigation of the Excited States of $^{114}\mathrm{Sn}$ Using the GRIFFIN Spectrometer at TRIUMF

The semi-magic $^{110-122}\mathrm{Sn}$ isotopes display signs of shape coexistence in their excited $0^+$ states, which, in contrast to the spherical $0^+$ ground states, are deformed. This paper investigates the nuclear structure of $^{114}\mathrm{Sn}$ using the competing $β^+$ decay and electron capture of a radioactive beam of $^{114}\mathrm{Sb}$ produced at the TRIUMF-ISAC facility using the GRIFFIN spectrometer. This study will allow for an in-depth understanding of the excited $0^+$ states in $^{114}\mathrm{Sn}$, by focusing on their decay patterns. In the present experiment, transitions at 856.2-keV and 1405.0-keV, which were observed in an earlier $β^+$ decay study but not placed in the $^{114}\mathrm{Sn}$ level scheme, have been assigned to the level scheme in connection to the $0^+_3$ level at 2156.0-keV. Properly assigning these transitions refines the level scheme and enhances our understanding of the nuclear structure in $^{114}\mathrm{Sn}$.

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arXiv2025

Impact of newly measured $β$\nobreakdash-delayed neutron emitters around \myisoSimp{78}{Ni} on light element nucleosynthesis in the neutrino-wind following a neutron star merger

Neutron emission probabilities and half-lives of 37 beta-delayed neutron emitters from 75Ni to 92Br were measured at the RIKEN Nishina Center in Japan, including 11 one-neutron and 13 two-neutron emission probabilities and 6 half-lives measured for the first time, which supersede theoretical estimates. These nuclei lie in the path of the weak r-process occurring in neutrino-driven winds from the accretion disk formed after the merger of two neutron stars, synthesizing elements in the A~80 abundance peak. The presence of such elements dominates the accompanying kilonova emission over the first few days and has been identified in the AT2017gfo event, associated with the gravitational wave detection GW170817. Abundance calculations based on over 17000 simulated trajectories describing the evolution of matter properties in the merger outflows show that the new data lead to an increase of 50-70 percent in the abundance of Y, Zr, Nb, and Mo. This enhancement is large compared to the scatter of relative abundances observed in old very metal-poor stars and is therefore significant in the comparison with other possible astrophysical processes contributing to light-element production. These results underline the importance of including experimental decay data for very neutron-rich beta-delayed neutron emitters into r-process models.

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arXiv2024

First simultaneous measurement of the gamma-ray and neutron emission probabilities in inverse kinematics at a heavy-ion storage ring

The probabilities for gamma-ray and particle emission as a function of the excitation energy of a decaying nucleus are valuable observables for constraining the ingredients of the models that describe the de-excitation of nuclei near the particle emission threshold. These models are essential in nuclear astrophysics and applications. In this work, we have for the first time simultaneously measured the gamma-ray and neutron emission probabilities of 208Pb. The measurement was performed in inverse kinematics at the Experimental Storage Ring (ESR) of the GSI/FAIR facility, where a 208Pb beam interacted through the 208Pb(p,p') reaction with a hydrogen gas jet target. Instead of detecting the gamma-rays and neutrons emitted by 208Pb, we detected the heavy beam-like residues produced after gamma and neutron emission. These heavy residues were fully separated by a dipole magnet of the ESR and were detected with outstanding efficiencies. The comparison of the measured probabilities with model calculations has allowed us to test and select different descriptions of the gamma-ray strength function and the nuclear level density available in the literature.

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arXiv2024

First measurement of the neutron-emission probability with a surrogate reaction in inverse kinematics at a heavy-ion storage ring

Neutron-induced reaction cross sections of short-lived nuclei are imperative to understand the origin of heavy elements in stellar nucleosynthesis and for societal applications, but their measurement is extremely complicated due to the radioactivity of the targets involved. One way of overcoming this issue is to combine surrogate reactions with the unique possibilities offered by heavy-ion storage rings. In this work, we describe the first surrogate-reaction experiment in inverse kinematics, which we successfully conducted at the Experimental Storage Ring (ESR) of the GSI/FAIR facility, using the 208Pb(p,p') reaction as a surrogate for neutron capture on 207Pb. Thanks to the outstanding detection efficiencies possible at the ESR, we were able to measure for the first time the neutron-emission probability as a function of the excitation energy of 208Pb. We have used this probability to select different descriptions of the gamma-ray strength function and nuclear level density, and provide reliable results for the neutron-induced radiative capture cross section of 207Pb at energies for which no experimental data exist.

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arXiv2024

Cross-shell excited configurations in the structure of 34Si

The cross-shell excited states of $^{34}$Si have been investigated via $β$-decays of the $4^-$ ground state and the $1^+$ isomeric state of $^{34}$Al. Since the valence protons and valence neutrons occupy different major shells in the ground state as well as the intruder $1^+$ isomeric state of $^{34}$Al, intruder levels of $^{34}$Si are populated via allowed $β$ decays. Spin assignments to such intruder levels of $^{34}$Si were established through $γ$-$γ$ angular correlation analysis for the negative parity states with dominant configurations $(νd_{3/2})^{-1} \otimes (νf_{7/2})^{1}$ as well as the positive parity states with dominant configurations $(νsd)^{-2} \otimes (νf_{7/2}p_{3/2})^2$. 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 $^{34}$Si. Shell model interaction derived from a more fundamental theory with the Valence Space In Medium Similarity Renormalization Group (VS-IMSRG) method was also employed to interpret the structure of $^{34}$Si.

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arXiv2023

Measurement of the Isolated Nuclear Two-Photon Decay in $^{72}\mathrm{Ge}$

The nuclear two-photon or double-gamma ($2γ$) decay is a second-order electromagnetic process whereby a nucleus in an excited state emits two gamma rays simultaneously. To be able to directly measure the $2γ$ decay rate in the low-energy regime below the electron-positron pair-creation threshold, we combined the isochronous mode of a storage ring with Schottky resonant cavities. The newly developed technique can be applied to isomers with excitation energies down to $\sim100$\,keV and half-lives as short as $\sim10$\,ms. The half-life for the $2γ$ decay of the first-excited $0^+$ state in bare $^{72}\mathrm{Ge}$ ions was determined to be $23.9\left(6\right)$\,ms, which strongly deviates from expectations.

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arXiv2023

Storage, Accumulation and Deceleration of Secondary Beams for Nuclear Astrophysics

Low-energy investigations on rare ion beams are often limited by the available intensity and purity of the ion species in focus. Here, we present the first application of a technique that combines in-flight production at relativistic energies with subsequent secondary beam storage, accumulation and finally deceleration to the energy of interest. Using the FRS and ESR facilities at GSI, this scheme was pioneered to provide a secondary beam of $^{118}$Te$^{52+}$ for the measurement of nuclear proton-capture at energies of 6 and 7 MeV/u. The technique provided stored beam intensities of about $10^6$ ions at high purity and brilliance, representing a major step towards low-energy nuclear physics studies using rare ion beams.

physics.ins-det↗

arXiv2023

First Evidence of Axial Shape Asymmetry and Configuration Coexistence in $^{74}$Zn: Suggestion for a Northern Extension of the $N=40$ Island of Inversion

The excited states of $N=44$ $^{74}$Zn were investigated via $γ$-ray spectroscopy following $^{74}$Cu $β$ decay. By exploiting $γ$-$γ$ angular correlation analysis, the $2_2^+$, $3_1^+$, $0_2^+$ and $2_3^+$ states in $^{74}$Zn were firmly established. The $γ$-ray branching and $E2/M1$ mixing ratios for transitions de-exciting the $2_2^+$, $3_1^+$ and $2_3^+$ states were measured, allowing for the extraction of relative $B(E2)$ values. In particular, the $2_3^+ \to 0_2^+$ and $2_3^+ \to 4_1^+$ transitions were observed for the first time. The results show excellent agreement with new microscopic large-scale shell-model calculations, and are discussed in terms of underlying shapes, as well as the role of neutron excitations across the $N=40$ gap. Enhanced axial shape asymmetry (triaxiality) is suggested to characterize $^{74}$Zn in its ground state. Furthermore, an excited $K=0$ band with a significantly larger softness in its shape is identified. A shore of the $N=40$ ``island of inversion'' appears to manifest above $Z=26$, previously thought as its northern limit in the chart of the nuclides.

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arXiv2021

Isomeric states in neutron-rich nuclei around $N = 40$

Neutron-rich nuclei in the vicinity of the $N=40$ island of inversion are characterized by shell evolution and exhibit deformed ground states. In several nuclei isomeric states have been observed and attributed to excitations to the intruder neutron $1g_{9/2}$ orbital. In the present study we searched for isomeric states in nuclei around $N=40$, $Z=22$ produced by projectile fragmentation at RIBF. Delayed $γ$ rays were detected by the EURICA germanium detector array. High statistics data allowed for an updated decay scheme of $^{60}$V. The lifetime of an isomeric state in $^{64}$V was measured for the first time in the present experiment. A previously unobserved isomeric state was discovered in $^{58}$Sc. The measured lifetime suggests a parity changing transition, originating from an odd number of neutrons in the $1g_{9/2}$ orbital. The nature of the isomeric state in $^{58}$Sc is thus different from isomers in the less exotic V and Sc nuclei.

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arXiv2020

High-Precision Branching Ratio Measurement and Spin Assignment Implications for $^{62}$Ga Superallowed $β$ Decay

A high-precision branching ratio measurement for the superallowed Fermi $β^{+}$ emitter $^{62}$Ga was performed with the Gamma-Ray Infrastructure for Fundamental Investigations of Nuclei (GRIFFIN) spectrometer at the Isotope Separator and Accelerator (ISAC) radioactive ion beam facility at TRIUMF. The high efficiency of the GRIFFIN spectrometer allowed 63 $γ$-ray transitions, with intensities down to $\approx$1 part per million (ppm) per $^{62}$Ga $β^{+}$ decay, to be placed in the level scheme of the daughter nucleus $^{62}$Zn, establishing the superallowed $β$ branching ratio for $^{62}$Ga decay to be 99.8577$^{+0.0023}_{-0.0029}\%$, a factor of 4 more precise than the previous world average. For several cascades, $γ-γ$ angular correlation measurements were performed to assign spins and/or determine the mixing ratios of transitions. In particular, the spin of the 2.342 MeV excited state in the daughter nucleus $^{62}$Zn was definitively assigned as $J = 0$. This assignment resolves a discrepancy between previous measurements and has important implications for the isospin symmetry breaking correction, $δ_{C1}$, in $^{62}$Ga superallowed Fermi $β$ decay.

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arXiv2019

First spectroscopy of 61Ti and the transition to the Island of Inversion at N = 40

Isomeric states in 59,61Ti have been populated in the projectile fragmentation of a 345 AMeV 238U beam at the Radioactive Isotope Beam Factory. The decay lifetimes and delayed gamma-ray transitions were measured with the EURICA array. Besides the known isomeric state in 59Ti, two isomeric states in 61Ti are observed for the first time. Based on the measured lifetimes, transition multipolarities as well as tentative spins and parities are assigned. Large-scale shell model calculations based on the modified LNPS interaction show that both 59Ti and 61Ti belong to the Island of Inversion at N=40 with ground state configurations dominated by particle-hole excitations to the g_9/2 and d_5/2 orbits.

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arXiv2018

Commissioning of the BRIKEN detector for the measurement of very exotic beta-delayed neutron emitters

A new detection system has been installed at the RIKEN Nishina Center (Japan) to investigate decay properties of very neutron-rich nuclei. The setup consists of three main parts: a moderated neutron counter, a detection system sensitive to the implantation and decay of radioactive ions, and gamma-ray detectors. We describe here the setup, the commissioning experiment and some selected results demonstrating its performance for the measurement of half-lives and beta-delayed neutron emission probabilities. The methodology followed in the analysis of the data is described in detail. Particular emphasis is placed on the correction of the accidental neutron background.

physics.ins-det↗

arXiv1993

Fermionic Field Theory and Gauge Interactions on Random Lattices

Random-lattice fermions have been shown to be free of the doubling problem if there are no interactions or interactions of a non-gauge nature. However, gauge interactions impose stringent constraints as expressed by the Ward-Takahashi identities which could revive the free-field suppressed doubler modes in loop diagrams. After introducing a formulation for fermions on a new kind of random lattice, we compare random, naive and Wilson fermions in two dimensional Abelian background gauge theory. We show that the doublers are revived for random lattices in the continuum limit, while demonstrating that gauge invariance plays the critical role in this revival. Some implications of the persistent doubling phenomenon on random lattices are also discussed.

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