Previous Seminars

Gemma L. Wilson Studying beta-delayed neutron emission with recoil-ion spectroscopy
Sean Collins Primary standardisation of Th-227 – developing traceability and nuclear data for a novel alpha-emitting radiopharmaceutical
Steven W. Yates Probing the structure of the Ge nuclei with fast neutrons: Neutrinoless Double-Beta Decay and Shape Coexistence
Konstantin Mashtakov Study of the Pygmy Dipole Resonance in 96Zr following the beta decay of 96Y
Skyler Degenkolb Searching for permanent electric dipole moments
Jack Wilson Space-Based Measurement of the Neutron Lifetime using Data from the Neutron Spectrometers on NASA's MESSENGER and Lunar Prospector Missions
Antonio Márquez Romero Proton-neutron pairing description using symmetry-restored mean-field methods
David O'Donnell Measurements of the low-energy dipole strength in actinide nuclei
Ragnar Stroberg Can we do all of nuclear physics ab initio?
Pieter Van Isacker The Structure of Octupole Phonons in Nuclei
Mark Spieker Isospin symmetry around 56Ni
Ruben Pieter De Groote New frontiers in optical spectroscopy of radioactive nuclei
Kaitlin Cook Halo structure of the neutron-dripline nucleus 19B
Manuela Cavallaro Nuclear Reactions for neutrinoless double beta decay
Ruth Newton Quantum Entanglement in PET imaging
Sergio Cristallo The cosmic nucleosynthesis competition between low mass stars and neutron stars mergers
Carlo Barbieri Ab Initio Computations of Ground State Correlations and Optical Potentials in Nuclei
Robin Smith Nuclear structure and astrophysics with TPC detectors and gamma beams
Ryo Taniuchi In-beam gamma-ray spectroscopy of 78Ni revealed its double magicity and shape-coexistence
Daniel Doherty Shape Evolution and Triaxiality in Hitherto Inaccessible Regions of the Nuclear Chart
Lindsay Michelle Donaldson Resolving discrepancies between (p,p') and (γ,xn) reactions
Kyle Leach The BeEST Experiment: A Search for keV-Scale Neutrinos in the EC Decay of 7Be with Superconducting Quantum Sensors
David Sharp Probing single-particle structure near the Island of Inversion with the ISOLDE Solenoidal Spectrometer
Michael Bowry The Search for Nuclear Pear Shapes
Gregory Christian Particle-Gated Transfer Reactions to Understand Stellar Nucleosynthesis
Kelly Chipps Experimental Approaches for Constraining Nuclear Contributions to R-Process Uncertainties
Jack Henderson Testing modern microscopic calculations: Coulomb excitation of mirror pairs in the sd-shell
Benjamin Kay Solenoidal spectrometer techniques: HELIOS, ISS, and SOLARIS
Alessandro Pastore Neurons, Trees and Forests: A different approach to simple nuclear structure problems

Gemma L. Wilson

Louisiana State University/Argonne National Laboratory

Studying beta-delayed neutron emission with recoil-ion spectroscopy
In nuclear β decay, β-delayed neutron (βn) emission is a viable process if the Qβ value of the parent (precursor) nucleus is greater than the neutron separation energy Sn in the daughter (emitter) nucleus, making it a common decay mode in neutron-rich nuclei. The lack of experimental βn data is being addressed with experimental efforts at radioactive ion facilities worldwide, including recoil-ion time-of-flight spectroscopy.
The use of trapped ions for βn spectroscopy is a relatively new and powerful technique. By design this technique avoids any difficulties inherent in neutron detection, but instead infers all neutron information from a distinct signature of the recoiling emitter nucleus. The Beta-decay Paul Trap (BPT) at Argonne National Laboratory (ANL) is used to confine ions to a small volume (~1 mm3) and decay products are detected by a simple detector system. From the detection of the β, the recoiling nucleus and any γ rays, β decay can be distinguished from βn decay, and a neutron energy spectrum can be inferred. The measurements are relatively low in background and can potentially be made with beam intensities as low as ~0.1 ions/s, which opens up a wide range of exotic nuclei for study.
Following the success of this technique with the BPT, the next generation of trap and detector array for recoil-ion time-of-flight spectroscopy has been designed for use with beams from the CAlifornium Rare Isotope Breeder Upgrade (CARIBU) at ANL, and has been fully funded by the US DOE Office of Nuclear Physics. The BEtARecoil ion trap, or BEARtrap, is a dedicated setup, which incorporates improvements on the BPT that have been investigated using simulations with GEANT4 and SimIon.
This talk will discuss details of this technique and present the various physical phenomena that influence the reconstruction of the βn energy inferred from the trapped ion technique. The finalized design of BEARtrap will be presented, including results from simulations, and details of approved upcoming experiments and future prospects.
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Sean Collins

National Physical Laboratory/University of Surrey

Primary standardisation of Th-227 – developing traceability and nuclear data for a novel alpha-emitting radiopharmaceutical
The National Physical Laboratory (NPL) is the National Metrology Institute (NMI) for the UK. As an NMI it has a key role to provide traceability for pre-clinical and clinical administrations of radiopharmaceuticals through primary standardisation of radioactivity. These primary standardisations are typically performed through coincidence counting techniques, which negate the need for any prior knowledge of the detection efficiency or of nuclear data. Thorium-227 (T1/2 = 18.697 d) is one such radionuclide with potential as a therapeutic radionuclide for applications in targeted alpha-radioimmunotherapy. Through binding of Th-227 to a monoclonal antibody this radiopharmaceutical has been shown as a having proficient tumour killing capabilities for a range of lymphoma, leukaemia, breast, and ovarian tumour cells. To provide nuclear medicine departments involved in Phase I clinical trials traceability the NPL has developed a primary standard for Th-227. To manufacture this radiopharmaceutical before administration to patients, the decay progeny must be removed initially to create a radiochemically pure starting material. This poses complications for accurate activity measurements, since transient equilibrium is not reached until well after 200 days, as the ingrowth and decay of the decay progeny must be corrected for as well as determining the effective time zero of the radiochemical separation. As a consequence of the temporal relationship of Th-227 with its decay progeny accurate and precise nuclear data are required for accurate activity measurements, which at the start of this project were not available. In this presentation, we will discuss the realisation of the Th-227 primary standardisation along with determinations of the half-lives and absolute gamma-ray emission intensities of Th-227 and its decay progeny.
Missing first 5 minutes, please see attached slides.
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Steven W. Yates

University of Kentucky

Probing the structure of the Ge nuclei with fast neutrons: Neutrinoless Double-Beta Decay and Shape Coexistence
At the University of Kentucky Accelerator Laboratory, we observed γ rays following inelastic scattering of fast neutrons from several candidates for neutrinoless double-beta decay (0νββ), with our recent measurements focusing on 76Ge [1], 136Xe [2], and other nuclei in these regions. From these measurements, low-lying excited states were characterized, 0+ states and their decays were identified, level lifetimes were measured with the Doppler-shift attenuation method, multipole mixing ratios were established, and transition probabilities were determined.
The rate of 0νββ is approximately the product of three factors: the known phase- space factor for the emission of the two electrons, the effective Majorana mass of the electron neutrino, and a nuclear matrix element (NME) squared. The NMEs cannot be determined experimentally and, therefore, must be calculated from nuclear structure models. A focus of our recent measurements has been on providing detailed nuclear structure data to guide these model calculations in the Ge region, and a procedure for future work, which will lead to meaningful data for constraining calculations of NMEs, is suggested.
This material is based upon work supported by the U.S. National Science Foundation under grant no. PHY-1913028.
[1] S. Mukhopadhyay, et al., Phys. Rev. C 95, 014327 (2017).
[2] E.E. Peters, et al., Phys. Rev. C 98, 034302 (2018).
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Konstantin Mashtakov

University of the West of Scotland

Study of the Pygmy Dipole Resonance in 96Zr following the beta decay of 96Y
The pygmy dipole resonance (PDR) is a nuclear phenomenon which is associated with the movement of the ‘neutron skin’ of a nucleus against an isospin saturated proton-neutron core. The nature of the PDR is of particular interest due to its importance in many areas of nuclear and astrophysics.
Current experimental techniques used to study this phenomenon produce inconsistent results. This is mostly due to the unknown branching behaviour of the Jπ =1 levels, which form the PDR. The nuclear resonance fluorescence (NRF) technique, which is widely used to study low-lying E1 strength in stable nuclei, loses decay branches to lower-lying excited states to the atomic background. The latter effect leads to underestimated values of E1 strength of the PDR. Recently it was realised that electric dipole levels associated with the PDR could also be excited following the β decay of certain nuclei. The novel approach of using β decay to populate high-lying 1 states allows the extraction of branching transitions previously not resolved in NRF, which will recover missing E1 strength associated with the PDR.
In this work, the nature of the high-lying final levels of the 96Ygs beta decay, one of the three most important contributors to the high-energy reactor antineutrino spectrum, has been investigated in high-resolution gamma-ray spectroscopy following the beta decay as well as in a campaign of inelastic photon scattering experiments. The combined data represents a comprehensive approach to the wavefunction of the 1 levels below the Qbeta value (7.1 MeV), which are also studied in the Quasiparticle Phonon Model. The calculations reveal that the components populated in beta decay contribute only with small amplitudes to the complex wavefunction of these 1 levels. A comparison of the beta decay results to data from total absorption gamma-ray spectroscopy demonstrates that high-resolution spectroscopy using modern detector arrays is capable to resolve the pandemonium effect.
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Skyler Degenkolb

Institut Laue–Langevin (ILL)

Searching for permanent electric dipole moments
Discrete symmetries provide a powerful means of classifying and constraining models in nuclear and particle physics, including the Standard Model. Although the Standard Model predicts finite values for CP-violating electromagnetic moments (both for fundamental particles and for composite systems), today's experiments are insufficiently sensitive -- by several orders of magnitude -- to test these predictions. Nevertheless, experimental limits consistent with zero have played an important role in constraining Standard Model parameters and extended models with new sources of CP violation. In particular, searches for permanent electric dipole moments (EDMs) test the Standard Model at high precision, provide diagnostic power for new sources of CP violation, and connect deeply to the symmetry-breaking mechanisms required for baryogenesis. I will survey the main target systems and experimental techniques that are employed in modern EDM measurements, with some emphasis on neutrons and the nuclei of diamagnetic atoms. I will also discuss the phenomenological interpretation of EDM limits, and in particular the "global analysis", or joint constraints, that are enabled by multiple experiments in complementary systems.
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Jack Wilson

Johns Hopkins University Applied Physics Laboratory

Space-Based Measurement of the Neutron Lifetime using Data from the Neutron Spectrometers on NASA's MESSENGER and Lunar Prospector Missions
Precise knowledge of the free neutron lifetime, τn, is required to test the consistency of the standard model and uncertainties in τn dominate those in predicted primordial 4He abundance from Big Bang nucleosynthesis. Presently, there exist two classes of experiments that have successfully made measurements of τn. The `Beam' class involves measuring the activation of cold neutron beams and the `Bottle' class uses storage (material, magnetic and/or gravitational) to trap neutrons and measure the rate of decay during storage. However, there currently exists a 4σ disagreement between the `beam' and `bottle' measurements. We have developed a new technique for using space-based neutron spectroscopy measurements to determine τn. Under this technique the change in planet-originating neutron flux with planet-to-spacecraft distance yields a measure of τn. Here, we will present an analysis of data from the neutron spectrometer on NASA's MESSENGER and Lunar Prospector missions as a proof-of-principle demonstration of a space-based τn measurement. Here I discuss the basis of the technique, statistical and systematic errors of the measurement, and presented the results that we have so far.
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IoP Early Career Prize Winner

Antonio Márquez Romero

University of North Carolina at Chapel Hill

Proton-neutron pairing description using symmetry-restored mean-field methods
By means of a full restoration of particle-number (A), spin (S), and isospin (T) broken symmetries of paired mean-field quasiparticle states, we show that proton-neutron (pn) and like-nucleon pair condensates coexist. We use the Thouless representation for these states, parametrised by the normalised isovector (T=1) and isoscalar (T=0) pair amplitudes. Using a simple and well-known SO(8) pairing Hamiltonian, whose exact solutions are known, we minimize the energy calculated with the symmetry-restored paired states, that is, we use the so-called variation after projection (VAP) approach. The results obtained using this method are strikingly accurate in comparison with the exact results, and for all interaction strengths the isovector and isoscalar pairs coexist, in opposition of the pure mean-field approach. This study suggests that further work on properties of proton-neutron pairing should be carried out within the VAP approach to mean-field pairing methods.

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David O'Donnell

University of the West of Scotland

Measurements of the low-energy dipole strength in actinide nuclei
Atomic nuclei with certain combinations of proton and neutron numbers can adopt reflection-asymmetric or octupole-deformed shapes at low excitation energy. These nuclei present a promising avenue in the search for a permanent atomic electric dipole moment — the existence of which has implications for physics beyond the Standard Model of particle physics. Theoretical studies have suggested that certain thorium isotopes may have large octupole deformation. However, due to experimental challenges, the extent of the octupole collectivity in the low-energy states in these thorium nuclei has not yet been demonstrated. Here, we report measurements of the lifetimes of low-energy states in the actinide nuclei 228Th (Z = 90) and 234U (Z = 92) with a direct electronic fast-timing technique, the mirror symmetric centroid difference method. From lifetime measurements of the low-lying Jπ = 1- and Jπ = 3- states, the E1 transition probability rates and the intrinsic dipole moments are extracted. Through comparisons with theoretical calculations, we have been able to estimate the extent of the octupole deformation of these nuclei. This study indicates that the nuclei 229Th and 229Pa (Z = 91) may be good candidates for the search for a permanent atomic electric dipole moment.
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