Nuclear Energy – The Better Energy?

Date – Sep 29, 2020
Event – Michiana Science Cafe organized by the Science Policy Initiative at Notre Dame
Presenter – N. Sensharma
Facebook Live (Invited)

Abstract: The United States depends on nuclear power to meet about one-fifth of its demand for electricity. This equals the combined total of the generation capacity of two leading nuclear power producing countries, France and Japan. However, we have been standing still for the last 30 years with absolutely no progress in this sector. Is the halt a result of economic, political or scientific reasons and how is this affecting the ever-escalating climate crises? Do we have an alternative?

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Convolutional Autoencoders for Anomaly Detection in the L1 Trigger 

Date – Aug 21, 2020
Event – Internal CMS Presentation (CERN)
Presenter – S. Weyhmiller
Oral Presentation

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Chiral Wobbling in ¹³⁵Pr

Date – Oct 16, 2019
Event – Fall meeting of the Department of Nuclear Physics (DNP) of the American Physical Society, Arlington, Virginia
Presenter – N. Sensharma
Oral Presentation

Abstract: Chirality and wobbling are the two unique signatures that help in the identification of the rare triaxial shape in nuclei. While both these modes have been separately established in a few limited regions of the nuclear chart, the coexistence of chirality and wobbling in a nucleus, a Chiral Wobbler, has never been observed so far. Using a high statistics Gammasphere experiment with the ¹²³Sb(¹⁶O,4n)¹³⁵Pr reaction, the very first observation of a Chiral Wobbler in ¹³⁵Pr has been made. In addition to the previously established n_w = 1 and n_w = 2 wobbling bands, two chiral-partner bands with the configuration πh_11/2 × νh_11/2^-2 have been observed in this nucleus. Angular distribution analyses of the ∆I = 1 connecting transitions between the two chiral partners have revealed their characteristic M1/E2 nature. Tilted axis cranking (TAC) calculations are found to be in good agreement with the experiment.
This work has been supported by the U.S. National Science Foundation [Grant No. PHY-1713857]

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A Method to Account for Hydroxide Contamination in Characterizing the Giant Monopole Resonance to Determine an Accurate K_τ

Date – Oct 15, 2019
Event – Fall meeting of the Department of Nuclear Physics (DNP) of the American Physical Society, Arlington, Virginia
Presenter – S. Weyhmiller
Poster Presentation

Abstract: Measurements on the isoscalar giant monopole resonance (ISGMR) in finite nuclei over a range of isotopes permit the extraction of K_τ, the nuclear incompressibility asymmetry term. K_τ is critical to understanding proton/neutron asymmetric systems. A recent study has claimed that the energy of the ISGMR is higher in heavier calcium isotopes than lighter ones, indicating a positive K_τ. This is surprising when compared to most research on extracting finite nuclear incompressibilities from giant resonances. To independently verify the claim, a simultaneous study of the GMR of ^40,42,44,48Ca was conducted. However, contributions from hydroxide contamination were found in the ⁴⁸Ca foil used in the experiment. The methodology for accounting for the contribution of ¹⁶O to the experimental spectra will be presented, and the implications will be discussed.
Supported by NSF Grant No. PHY-1559848 and the Glynn Family.

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Exotic Triaxial Shape and Wobbling Motion in ¹⁸⁹Au

Date – Oct 15, 2019
Event – Fall meeting of the Department of Nuclear Physics (DNP) of the American Physical Society, Arlington, Virginia
Presenter – J. L. Cozzi
Poster Presentation

Abstract: While most nuclei are symmetrically shaped, exotic asymmetric shapes have been observed in the excited nuclear states of heavy mass nuclei. One such asymmetric shape, the triaxial shape, is characterized by three different lengths for each of the three primary axes. Due to the asymmetry in its shape, an excited triaxial nucleus spins irregularly. This non-uniform rotational motion is known as ‘wobble’ and results in the emission of highly mixed electric and magnetic gamma rays as the nucleus transitions from higher to lower rotational energy states. Excited ¹⁸⁹Au nuclei were created through a dehydration fusion reaction performed at Argonne National Laboratory. Gammashpere, an array of 110 high purity germanium detectors housed at Argonne, was used to capture the gamma ray decay spectrum from the excited ¹⁸⁹Au. This spectrum is being analyzed in order to confirm and expand upon previously published level schemes of ¹⁸⁹Au. Directed coefficients of orientated nuclei and angular distributions will be calculated and used to identify the polarity and electromagnetic characteristics of key transitions in the ¹⁸⁹Au gamma ray decay spectrum. The level scheme and analysis results from this study on the nuclear shape and rotational motion of ¹⁸⁹Au will be presented.

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Are the Molybdenums Fluffy Too?

Date – Oct 29, 2018
Event – 6th Conference on Collective Motion of Nuclei under Extreme Conditions (COMEX6), Cape Town, ZA
Presenter – K. B. Howard
Oral Presentation

Abstract : Why are the tin isotopes fluffy? has remained, for nearly a decade, a fundamental open problem in nuclear structure physics: models which reproduce the ISGMR in the standard doubly-closed shell nuclei, ⁹⁰Zr, ²⁰⁸Pb, overestimate, by as much as 1 MeV, the ISGMR energies of the open-shell tin and cadmium nuclei . To further elucidate this question as also to examine when this fluffiness appears in moving away from the doubly-closed nucleus ⁹⁰Zr, and how this effect develops, we have carried out measurements of the isoscalar giant resonance strength distributions in a series of molybdenum nuclei. The measurements were performed for ^{94,96,97,98,100}Mo, using inelastic scattering of 100 MeV/u ⁴He particles at the Research Center for Nuclear Physics, Osaka University. The targets, with approximate thicknesses 5 mg/cm², were enriched to an isotopic purity of approximately 95%. The measurements on all nuclei were performed within the same experiment so as to minimize any systematic effects in the final results. The versatile, high-precision mass spectrometer, Grand Raiden, provided small angle (0−10 degrees) spectra virtually free of all instrumental background. The resulting double-differential cross sections can be used to reliably extract ISGMR strength distributions using a multipole decomposition analysis; this procedure is currently in progress. The extracted ISGMR strengths will be presented. It is hoped that these results, in combination with previously published results for the ISGMR strength in ^90,92Zr and ⁹²Mo, will provide important information for possible refinements of theoretical models in describing this mode in open- and closed-shell nuclei alike. This work has been supported in part by the National Science Foundation (Grant Nos. PHY-1713857 and PHY-1419765), and by the Liu Institute for Asia and Asian Studies, University of Notre Dame.

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Wobbling motion in A ~ 190 region

Date – Oct 24, 2018
Event – Fifth Joint Meeting of the Nuclear Physics Divisions of the American Physical Society and the Japan Physical Society, Hawaii Island, USA
Presenter – N. Sensharma
Oral Presentation

Abstract: The rare phenomenon of nuclear wobbling motion has already been established in the A ∼ 160 and the A ∼ 130 regions. Based on observations of significant triaxiality at low spins in the A ∼ 190 region, we have extended our investigation of wobbling motion to the ¹⁸⁷Au nucleus. The experiment was performed using the Gammasphere array at the Argonne National Laboratory and the ¹⁷⁴Yb(¹⁹F,6n)¹⁸⁷Au reaction was used to populate the levels of interest. A longitudinal wobbling band has been identified by establishing the characteristic ∆I = 1, E2 nature of the n_w+1 → n_w linking transitions. Calculations in the framework of the Particle Rotor Model (PRM) are found to be in good agreement with the experiment. This observation opens a new mass region where nuclear wobbling motion may be found.
This work has been supported by the U.S. National Science Foundation [Grant No. PHY-1713857]

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Two-phonon wobbling in ¹³⁵Pr

Date – Aug 7, 2018
Event – Nuclear Structure Conference 2018, East Lansing, MI
Presenter – N. Sensharma
Poster Presentation

Abstract: Triaxial nuclear shapes are a very rare phenomenon that are manifested experimentally via their unique signatures – chirality and wobbling. The recent discovery of wobbling in ¹³⁵Pr exhibited the first such case in A ∼ 130 region at low spin and deformation. Following this measurement, a second experiment was performed with the ¹²³Sb(¹⁶O,4n)¹³⁵Pr reaction using the Gammasphere array at the Argonne National Laboratory to identify the expected two-phonon wobbling band in this nucleus. The n_w = 2 band was, indeed, observed and its nature confirmed by the characteristic predominantly E2 nature of the n_w+1 → n_w linking transitions based on angular distribution measurements. These results further establish the presence of wobbling motion in A ∼ 130 region, independent of any particular spin or deformation.
This work was supported by NSL grant no. PHY-1713857

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Isoscalar Giant Resonances in Molybdenum Isotopes

Date – Apr 14, 2018
Event – American Physical Society April Meeting, Columbus, Ohio
Presenter – K. B. Howard
Oral Presentation

Abstract: It is a well-established question in nuclear structure as to why the incompressibility of nuclear matter calculated from the giant resonance strength distributions of open-shell nuclei, such as tin and cadmium isotopes, is lower than that determined by using data on closed-shell nuclei such as ²⁰⁸Pb. To investigate this, giant resonance strength distributions have been extracted for the isotopic chain ^{94,96,97,98,100}Mo. Angular distributions for 100 MeV/u ⁴He were obtained using the spectrometer Grand Raiden. Multipole decompositions were carried out on the distributions to isolate the monopole, dipole, and quadrupole strength over the excitation energy range of the spectra. Results of the analysis and implications for the nuclear incompressibility will be discussed.

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