Session GG: Nuclear Structure III

High spin states of 29Si populated by two particle trasfer reactions

Recent work studying high spin, high excitation states in ²⁹Si done at FSU Fox Lab with the Super Enge Split-pole Spectrograph has shown sharp states well above the neutron and proton separation energies. Using fusion evaporation with HPGe detectors our group has previously observed high spin states that gamma decay above S(n) and S(p) in other sd shell nuclei. The findings of sharp states in ²⁹Si is not unique, but it still surprising at almost twice the energy of S(n) in ²⁹Si. I will show how using basic spectroscopic arguments and the FSU shell model interaction constraints on the spin and parity for these high lying states can be made.

    

From ENSDF to NuDat: Disseminating Digestible Data Using Modern Web-based Technologies to Search, Filter, and Visualize Nuclear Data

       The National Nuclear Data Center (NNDC) at Brookhaven National Laboratory (BNL) has developed and maintained NuDat, a web application where users can explore several databases containing nuclear structure, nuclear decay, and neutron-induced nuclear reaction information. NuDat is the primary web application used to query and visualize meticulously evaluated recommended values derived from all published experimental nuclear structure and decay data contained within the Evaluated Nuclear Structure Data File (ENSDF). NuDat was first developed over 15 years ago and now there are over 4 million queries to NuDat each year for research, education, and a wide range of applications.

      The modernized NuDat 3.0 contains responsive nuclear data visualizations to support user needs and uniquely visualize the dense and complex multi-dimensional scientific data available in ENSDF. Users can seamlessly interact with over 3,300 nuclides with intuitive pan and zoom gestures. NuDat 3.0 has a full range of features to support exploring nuclear data such as supplementary plots that can automatically sync to the current view of the interactive chart of nuclides.

      Beyond the interactive chart of nuclides, NuDat offers a full suite of web applications to search and visualize nuclear data.The Advanced Cross-Variable Plot provides users with an interface to create various plots by selecting axis variables from a multitude of observable properties.Fully interactive level and decay schemes for relevant nuclei have been implemented.

      The NNDC aims to improve NuDat based on community feedback with a focus on disseminating digestible data to a broad spectrum of users. NuDat's novel visualization tools provide users with an intuitive interface to the nuclear data within ENSDF. The ubiquitous demand for authoritative evaluated nuclear data emphasizes the need for modernizing NuDat using the latest computing technologies, in order to provide an enhanced user experience.      

Population of 33Mg* Neutron-Unbound States from Reactions on 36Si and 34Al

Population of excited states often depend on the reaction that produces them. An experiment performed at the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University produced secondary beams of ³⁶Si and ³⁴Al from a ⁴⁸Ca primary beam by fragmentation on a beryllium production target. Neutron-unbound states in ³³Mg* were populated when the secondary beams impinged on a segmented target consisting of alternating layers of four Si-PIN detectors (140 micrometers thick each) and three beryllium targets (199 mg/cm² thick each). The charged fragment of ³²Mg was deflected by a superconducting sweeper magnet into charged particle detectors and the neutron was detected in the MoNA-LISA scintillator array, which were detected in coincidence. Neutron unbound state energies were reconstructed using the invariant mass technique and compared to simulation. Deduced resonant energies of ³³Mg* produced by 1p-knockout from ³⁴Al or multiple particle knockout from ³⁶Si yielded different decay energy spectra, which will be presented.   

Search for microsecond isomers at the dripline of the island of inversion

The island of inversion around 32Mg, characterized by tensor-force-driven deformation, has

been well characterized in its north and west “shores.” The south-eastern “beaches” offer

intriguing physics where deformation and neutron dripline effects overlap, yet they remain

poorly known due to the difficulty in producing them in experimental facilities. In particular, if

standard ordering is restored at the dripline, it will suppress low-energy opposite-parity

intruders. Furthermore, inverting the parity order could result in microsecond isomers

between the same parity states. In this talk, I will present experimental work done at the

National Superconducting Laboratory as a part of the E19044 collaboration. A 48Ca beam

was fragmented to produce a cocktail beam of isotopes around Z=9, N=20 29F and

separated by mass using the A1900 spectrometer. The cocktail beam was implanted in a

YSO crystal, and the decay products were detected using 3 HPGe clovers for gamma rays

and 48 VANDLE bars for beta delayed neutrons. A comprehensive search for microsecond

isomers was performed on all Z>8 nuclei in the cocktail beam, using the delayed-gamma

beta-correlation technique. We propose a new state in 36Mg at 883 keV from observing a

168 keV isomeric transition. The isomer’s half-life, [120-400] ns at three standard

deviations, indicates it corresponds to an E2 transition feeding the first 2+ state. We

conclude it corresponds to a deformed second 0+ state, confirming shape coexistence

between the N=20 and N=28 islands of inversion.   

From the core of nuclei to the matter of neutron stars with two-photon emission

The nuclear equation of state requires rigorous bench-marking of experimentally observable properties which can be accurately calculated. One such observable is the electric polarizability of nuclear matter and its difference for an excited nuclear state. One possible way of extracting this quantity is through the second order electromagnetic process of nuclear two-photon emission occurring between low-lying $0^+$ states where a single photon transition is forbidden. The first excited state of $^{90}$Zr satisfies these conditions and has been previously observed to undergo two-photon emission. The GRIFFIN spectrometer at TRIUMF-ISAC is a powerful set-up for decay studies that has the angular sensitivity, energy resolution, and data acquisition system required to make a precision measurement of $^{90}$Zr decay using a high-activity $^{90}$Sr source. In this talk I will discuss the development of this technique with GRIFFIN using source data, and how we can extend this to radioactive beam experiments for two-photon decay.   

Complete β-decay study of deformed, odd-odd 104,104mNb*

Properties of deformed, neutron-rich nuclei in the A~110 mass region are essential ingredients in

the interpretation of r-process nucleosynthesis and fission-like applications where little is known

owing to difficulties in the production of these nuclei at existence RIB facilities.

Predicated on these ideas, we have initiated a dedicated decay spectroscopy experimental program

at Argonne National Laboratory, by combining the CARIBU facility with the newly developed

Gammasphere Decay Station. The initial focus was to study β- decays of ground state and excited

isomeric state of several deformed odd-odd nuclei that selectively populate a variety of structures

in the daughter nucleus.

In this work, we will present new results from time-correlated β-decay spectroscopy studies of the

ground state (6.1 (1) s) and isomer (0.89 (1) s) in the deformed ¹⁰⁴Nb nucleus. The new data will

be compared with predictions from multi-quasiparticle blocking calculations. Significant

differences in terms of beta-decay feeding pattern and the structure of the observed isomers with

recent measurements utilizing the Total Absorption Gamma-ray Spectroscopy technique will also

be discussed.   

Towards the total absorption spectroscopy of doubly magic 78Ni

78Ni is a unique doubly magic nucleus far from beta stability line, the only one decaying with β-delayed neutron emission channel. Its decay properties influence the early r-process nucleosynthesis and the beta decays of exotic nuclei north-east of Z=28 and N=50.

BRIKEN collaboration at RIKEN has operated the world largest beta-delayed neutron detection system with nearly 150 3He tubes, having 87% of 3He neutron detection volume and two Ge clovers contributed from ORNL.  Few versions of the ion implantation-beta decay array have been used inside BRIKEN, from highly pixelated AIDA array to WASABI Si-stack complemented by the YSO scintillator developed at the UTK.  Experiments performed at the BigRIPS including the study of 78Ni were profiting from high intensities of 238U primary beam at 345 MeV/u separator at RIKEN.

The status of data evaluation and further plans to study 78Ni decay with the ORNL’s Modular Total Absorption Spectrometer at the Facility for Rare Isotopes Beams will be presented.