Bulletin of the American Physical Society
2020 Fall Meeting of the APS Division of Nuclear Physics
Volume 65, Number 12
Thursday–Sunday, October 29–November 1 2020; Time Zone: Central Time, USA
Session RP: Nuclear Structure: A=70-100 |
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Chair: Peter Bender, UMASS, Lowell |
Sunday, November 1, 2020 8:30AM - 8:42AM |
RP.00001: Isospin symmetry breaking in the $T=3/2$ mirror pair $^{73}$Sr - $^{73}$Br Augusto Macchiavelli, Alfredo Poves, Silvia Lenzi Recently, Hoff {\it et al.} reported the results of a measurement carried out at MSU-NSCL [1], in which the decay of the proton-rich, $T=3/2$, $T_{z}$=-3/2, isotope $^{73}$Sr was studied. The experimental data is consistent with a $I^{\pi}$= 5/2$^{-}$ ground state, which inverts relative to its mirror $T_{z}$=3/2 partner $^{73}$Br which has $I^{\pi}$= 1/2$^{-}$. In this work, we propose an explanation within the framework of the shell model for the nuclear part of the problem, plus a detailed treatment of the Coulomb and other isospin-symmetry breaking effects in line with the findings of Refs.~[2,3]. In the present calculation we use the ${0f_{7/2}}$, ${1p_{3/2}}$, ${0f_{5/2}}$, ${1p_{1/2}}$, ${0g_{9/2}}$ and ${1d_{5/2}}$ valence space with the single particle energies taken directly from the experimental spectra of $^{41}$Ca. We show that the large scale shell-model results reproduce well the observed inversion, with the Coulomb interaction playing a dominant role in breaking the isospin symmetry in the $^{73}$Sr - $^{73}$Br mirror pair.\\ [1] E. M. Hoff, {\it et al.}, Nature {\bf 580} 52 (2020).\\ [2] A.P.Zuker, {\it et al.}, Phys. Rev. Lett {\bf 89} 142502 (2002). \\ [3] M. Bentley and S. M. Lenzi, PPNP {\bf 59} 497 (2007). [Preview Abstract] |
Sunday, November 1, 2020 8:42AM - 8:54AM |
RP.00002: Beta-delayed neutron and two-neutron emission in the 78Ni region Rin Yokoyama, Robert Grzywacz, Bertis Rasco, Nathan Brewer, Krzysztof Rykaczewski, Iris Dillmann, Jose-Louis Tain, Shuniji Nishimura Beta-delayed neutron emission is found in neutron-rich nuclei where the decay energy window is high enough to populate states above the neutron separation energy in the daughter nucleus. Understanding of the neutron emission process is important since one, or even multiple neutron emissions are the dominant decay modes for the neutron-rich nuclei along the r-process path and the branching ratios change the final abundance. However, experimental data of multi-neutron emission properties for the r-process nuclei are almost non-existent. One-neutron and two-neutron branching ratios ($P_{1n}$ and $P_{2n}$) have been measured in the decay of neutron-rich $^{84-87}$Ga at the RI-beam Factory (RIBF) at the RIKEN Nishina Center using a high-efficiency array of $^{3}$He neutron counters (BRIKEN). The experimental $P_{xn}$ values agree with theoretical calculations only when Hauser Feshbach statistical model is included [1]. The $P_{xn}$ results demonstrated the necessity of the statistical model as a two-stage model that can take one-neutron emissions from two-neutron unbound states into account. Gamma-ray spectroscopy results provide additional information for confirming the statistical model in beta-delayed neutron emission. [1] R. Yokoyama et al., Phys. Rev. C 100, 031302(R) (2019) [Preview Abstract] |
Sunday, November 1, 2020 8:54AM - 9:06AM |
RP.00003: Spectroscopy of Beta-delayed Neutron Emitters in the \textsuperscript{78}Ni Region using VANDLE M. Singh, R. Yokoyama, T. King, R. Grzywacz, M. Madurga, I. Cox, A. Keeler, S. Neupane, S. Neupane, N. Brewer, K. Rykaczewski, A. Fijalkowska, S. Nishimura, S. Go, M. Rajabali Beta-delayed neutron emission is a prevalent decay process for neutron-rich isotopes involved in the r-process, affecting the abundance patterns of the isotopes involved. An experiment was performed at the RIKEN Nishina Center aiming at the spectroscopy of the delayed neutron precursors around (27 $\geq$ Z $\geq$ 34) the doubly-magic \textsuperscript{78}Ni using VANDLE digital neutron array, and a segmented YSO based implant detector. The YSO detector has high beta-detection ($\sim$ 80 $\%$) efficiency, and good position and time resolution needed for the reliable time of flight measurements. The presentation will highlight the first results from the ongoing analysis process for the data about the decays of (N$>$50) Ga and Cu isotopes. The results will be compared to the predictions of neutron-emission probabilities (Pn) using a shell model for the strength distribution combined with the neutron-emission model as was done previously to explain the neutron-emission branching ratios for \textsuperscript{86, 87}Ga by Yokoyama et al., 2019. [Preview Abstract] |
Sunday, November 1, 2020 9:06AM - 9:18AM |
RP.00004: Reducing uncertainties in spectroscopic factors of N$\approx$50 nuclei through a combined analysis of neutron transfer reactions at two energies H. Sims, D. Walter, J. A. Cizewski, A. Lepailleur, S. D. Pain, A. Ratkiewicz, S. Ahn Neutron-transfer reactions with radioactive-ion beams (RIBs) probe the single-neutron components of the nuclear wave function. Through (d,p) reactions, spectroscopic factors can be deduced by comparing experimental differential cross sections to those calculated using nuclear reaction theory. Deduced spectroscopic factors are, however, sensitive to the parameters chosen to model the final bound-state potential. A combined method with low- and high-energy RIBs constrains the single-particle asymptotic normalization coefficient (spANC) - reducing the uncertainties on the extracted spectroscopic factors. The ground- and first-excited states in $^{85}$Se were investigated through the $^{84}$Se(d,p) reaction, measured at 4.5- (Thomas \emph{et al.}) and 45~MeV/u (This work) - where silicon detector arrays measured reaction protons in coincidence with recoils. Constrained spANCs and spectroscopic factors will be presented. Continuing investigations of N$\approx$50 nuclei, a measurement of $^{80}$Ge(d,p$\gamma$) at 45~MeV/u is scheduled at the NSCL using the GRETINA - ORRUBA Dual Detector for Experimental Structure Studies (GODDESS) to detect protons and gamma-rays in coincidence. This will be compared to the 3.875~MeV/u measurement by Ahn et al. Preliminary results will be presented. [Preview Abstract] |
Sunday, November 1, 2020 9:18AM - 9:30AM |
RP.00005: Determination of Ground State Feeding in Beta-decay using Modular Total Absorption Spectrometer Peng Shuai Determination of the branching ratio of ground state feeding in $\beta$-decay of fission products is of high importance in the investigations of reactor antineutrino anomaly and decay heat calculations. Ground state branches are important or even dominant in a number of such decays. However, the determination of ground state feeding probabilities encounters large systematic uncertainties due to the difficulty to precisely simulate the response function to low-energy electrons. Modular Total Absorption Spectrometer (MTAS), which is approximately one ton of NaI(Tl) hexagonal modules covering almost 4$\pi$ solid angle, is a versatile spectrometer to detect the $\beta$-decay particles including gammas, electrons and beta-delayed neutrons with high efficiency. MTAS has capability to determine not only the $\beta$-decay branching ratios to the exited states free from Pandemonium effect, but also the ground state feeding which is not followed by coincidence gammas. In this talk, we use $^{88}$Rb and $^{88}$Kr decay as examples to demonstrate the ability of MTAS to determine the absolute ground state feeding branching with improved precision. We also discuss various possible sources that contribute to the systematic uncertainties in MTAS experiments. [Preview Abstract] |
Sunday, November 1, 2020 9:30AM - 9:42AM |
RP.00006: A Study of the Two-Photon Emission of $^{90}$Zr Using the GRIFFIN Spectrometer C. R. Natzke, A. B. Garnsworthy, K. G. Leach Theoretical models predicting neutron star properties require rigorous bench-marking of calculated properties which are experimentally observable; for example the electric polarizability of nuclear matter and the difference in electric polarizability for excited nuclear matter. One possible way of extracting this quantity is through the Compton polarimetry of the second order electromagnetic process of nuclear two-photon decay between low-lying $0^+$ states where single photon emission is forbidden. The first excited state of $^{90}$Zr satisfies these conditions and has been 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. Source data has been collected using a $^{90}$Sr source to test GRIFFIN's sensitivity to $2\gamma$ emission and the progress on these investigations will be discussed. [Preview Abstract] |
Sunday, November 1, 2020 9:42AM - 9:54AM |
RP.00007: Electron Population Manipulation of Transition Metal Isotopes in an RFQ Ion Trap Jeremy Lantis, K. Minamisono, D. Garand, C. Kalman, N. Kasaraneni, K. Koenig, Y. Liu, A. Miller, S. Pineda, R. Powel, J. Zuzelski Collinear laser spectroscopy(CLS) is commonly used for determination of the charge radii and electromagnetic moments of rare isotopes. However, the first and second-row transition metal elements have proven difficult to study with CLS due to low production rates and inaccessible electronic transitions. An electronic population manipulation technique using optical pumping in an RFQ ion trap has been developed at the BECOLA facility at the NSCL/MSU to enable the study of transition metal isotopes. The optical pumping technique was demonstrated using stable \textsuperscript{90}Zr ions captured in an RFQ ion trap. Pulsed laser light irradiated the ions for population manipulation followed by laser-resonant fluorescence (CLS) measurements. Details of the technique and performance characteristics will be discussed. [Preview Abstract] |
Sunday, November 1, 2020 9:54AM - 10:06AM |
RP.00008: Nuclear 2$\gamma$ decay of $^{98}$Mo and $^{98}$Zr at the TITAN-EBIT Zachary Hockenbery, Erich Leistenschneider, Jon Ringuette, Corina Andreoiu, Thomas Brunner, Iris Dillmann, Ania Kwiatkowski, Kyle Leach Nuclear 2$\gamma$ decay is a second-order electromagnetic interaction wherein two photons are simultaneously emitted during a nuclear de-excitation. This transition is uniquely sensitive to the electromagnetic polarizability of the nucleus and has been studied in non-competitive cases for $0_2^+ \longrightarrow 0_1^+$ transitions between the first excited and ground states of even-even nuclei. So far, observations have been limited to the closed-shell nuclei $^{16}$O, $^{40}$Ca, and $^{90}$Zr. An important constraint to the theory can be provided through experimental observations of 2$\gamma$ transitions in nuclei that exist away from shell closures. However, such cases have eluded experimental observation, among other reasons, because of a strongly competing internal conversion (IC) branch. We propose to use the TITAN Electron Beam Ion Trap (EBIT) at TRIUMF to selectively block the IC branch by stripping the atom of all electrons which will allow the observation of 2$\gamma$ transitions in $^{98}$Mo and $^{98}$Zr. The experimental concept, status of development, and simulated results will be reported. [Preview Abstract] |
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