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 ME: Mini-Symposium: Gamma-Particle Coincidence Studies with Radioactive Ion Beams |
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Chair: Artemis Spyrou, MSU-NSCL/FRIB |
Saturday, October 31, 2020 2:00PM - 2:36PM |
ME.00001: Gamma-Particle Coincidence Studies with Radioactive Beams Invited Speaker: Andrew Ratkiewicz Reactions in normal kinematics, in which a light ion is impinged on a heavier stable or long-lived target, have long been used to probe the internal structure of nuclei and to constrain the properties of the astrophysical processes that synthesized the nuclei from which our universe is composed. The advent of radioactive ion beams (RIBs) brought these studies to radioactive nuclei in inverse kinematics, with a stable light-ion target and a radioactive heavy beam, greatly expanding the reach of the technique. While these reactions offer powerful and well-understood tools for determining nuclear properties, the systems typically used to detect these particles have limited resolution, thus are not capable of discriminating between the population of closely spaced nuclear levels. There are also a number of experimental challenges inherent in these techniques: for instance, many studies employ targets with a carbon matrix, leading to fusion-evaporation backgrounds that can be significant. Additionally, RIB studies are often limited by the beam rate, necessitating thicker targets to maintain luminosity, which leads to kinematic broadening in the target, decreasing the achievable energy resolution. These effects can be mitigated by measuring $\gamma $ rays in coincidence with particles. Gamma-ray detectors, especially those made of High-Purity Germanium (HPGe) offer dramatically better energy resolution -- often more than an order of magnitude -- than is achievable with the popularly-used silicon particle detectors. Additionally, measurements of $\gamma $ rays can provide information about states not directly populated in the reaction studied and can be used to determine the lifetimes of excited states and the character of transitions between them. With the availability of large HPGe detector arrays, a number of particle-$\gamma $ spectrometers have been built. I will discuss recent measurements with some of these detectors and provide an outlook for future work in the FRIB era. [Preview Abstract] |
Saturday, October 31, 2020 2:36PM - 2:48PM |
ME.00002: Constraining the $^{30}$P(p,$\gamma$)$^{31}$S reaction using $^{30}$P(d,p$\gamma$)$^{31}$P with GODDESS Rajesh Ghimire, Steven Pain, Kate Jones, Joshua Hooker, Andrew Ratkiewicz, Jolie Cizewski, Harrison Sims, Gwenaelle Seymour, Chad Ummel, Gemma Wilson The $^{30}$P(p,$\gamma$)$^{31}$S reaction rate critically affects the mass flow into the A=30-40 range, impacting abundances of isotopes of P, S and Si during classical nova nucleosynthesis. This reaction rate depends on undetermined spectroscopic strengths of low-lying resonances in $^{31}$S, lying between 6 and 7 MeV in excitation. But, direct measurement of (p,$\gamma$) reaction is not possible due to low intensities of currently available $^{30}$P beam and proton spectroscopic factors on unstable nuclei are difficult to measure experimentally. We performed a $^{30}$P(d,p$\gamma$)$^{31}$P reaction measurement using the newly commissioned GODDESS (Gretina-ORRUBA: Dual Detectors for Experimental Structure Studies) system-with an 8 MeV/u $^{30}$P beam, from RAISOR at ATLAS, to provide constraints on the proton spectroscopic strengths for $^{31}$S levels via mirror symmetry. Experimental details and data analysis status will be presented. [Preview Abstract] |
Saturday, October 31, 2020 2:48PM - 3:00PM |
ME.00003: Cross-shell Excitations in $^{46}$Ca studied with Fusion Reactions induced by Re-accelerated Rare Isotope Beams John Ash, Hironori Iwasaki, Tea Mijatovic, Tamas Budner, Robert Elder, Brandon Elman, Moshe Friedman, Alexandra Gade, Mara Grinder, Jack Henderson, Brenden Longfellow, Aldric Revel, Daniel Rhodes, Mark Spieker, Yutaka Utsuno, Dirk Weisshaar, Ching-Yen Wu The evolution of shell structure has been investigated by tracking the nuclear structure information of low-lying states from stability toward the neutron dripline. Discovering unexplored high-spin states can open up a new direction to study band structure and the associated shell structure in the neutron-rich regime. However, experimental reach has so far been limited to neutron-deficient or stable nuclei due to the nature of fusion reactions used in such studies. We report the first gamma ray spectroscopy with fusion reactions using reaccelerated rare isotope beams at the ReA3 facility of the National Superconducting Cyclotron Laboratory. Using particle and gamma coincidence techniques, three new higher-lying states around 6 MeV and five new gamma transitions were identified for $^{46}$Ca, suggesting three independent band structures. New results are compared to large-scale shell model calculations. [Preview Abstract] |
Saturday, October 31, 2020 3:00PM - 3:12PM |
ME.00004: $\beta$-Delayed Proton Emission of $^{71}$Kr Sanjanee Waniganeththi, D.E.M. Hoff, A.M. Rogers, P.C. Bender, K. Brandenburg, K. Childers, J.A. Clark, A.C. Dombos, E.R. Doucet, S. Jin, R. Lewis, S.N. Liddick, C.J. Lister, Z. Meisel, C.M. Morse, H. Schatz, K. Schmidt, D. Soltesz, S.K. Subedi Mirror nuclei and their decay properties are key in understanding the role of isospin in nuclear structure. The character of ground state and low-lying states in the Kr/Br mirror pair has been under debate. Properties of this mirror system were investigated in an implant-decay experiment at the NSCL using a beam containing $^{71}$Kr, produced by projectile fragmentation of a $^{92}$Mo beam on a Be target and purified with the RF Fragment Separator. The purified beam was implanted into the Beta-Counting Station surrounded by SeGA. A previously unobserved $\beta$-decay branch to the 407-keV state of $^{71}$Br, delayed proton decay to the 944-keV state of $^{70}$Se, as well as a precise measurement of the $^{71}$Kr half-life, will be presented. The intensity of observed 944-keV $\gamma$-ray transitions provides evidence that the spin of $^{71}$Kr must be greater than $J^{\pi}$ = 3/2- [Preview Abstract] |
Saturday, October 31, 2020 3:12PM - 3:24PM |
ME.00005: Informing the level scheme of $^{\mathrm{95}}$Mo through $^{\mathrm{95}}$Mo(d,p$\gamma )^{\mathrm{96}}$Mo with GODDESS Heather Garland, J.A. Cizewski, A. Lepailleur, G. Seymour, H. Sims, S.D. Pain, A. Ratkiewicz Nearly half of the heavy elements are created through the rapid neutron capture process. The Surrogate Reaction Method (SRM), in which (e.g.) a (d,p) reaction is measured, was designed to constrain important (n,$\gamma )$ cross sections on short-lived isotopes, many of which are important to the r process. The use of SRM with deuteron-induced reactions requires a modern reaction model, which includes deuteron break-up, to account for the discrepancy in spins and parities populated via the surrogate reaction versus those populated via the neutron capture reaction. Last year, (d,p) reactions have been validated as a surrogate for (n, $\gamma )$ reactions in normal kinematics [1]. To extend the benchmarking of the SRM to inverse kinematics, a (d,p$\gamma )$ measurement with a $^{\mathrm{95}}$Mo beam was performed using GODDESS (Gammasphere ORRUBA: Dual Detectors for Experimental Structure Studies) at ATLAS. This is the first measurement of a (d,p) reaction to states below 4 MeV in $^{\mathrm{96}}$Mo. By combining the (d,p) measurement with coincident gamma-rays, additions to the level scheme of $^{\mathrm{96}}$Mo can be made. Preliminary results of particle-gamma coincidences from protons populating states below and above the neutron separation energy in $^{\mathrm{96}}$Mo will be presented. [1] A. Ratkiewicz et al. Phys. Rev. Let., \textbf{122} 052502 (2019). [Preview Abstract] |
Saturday, October 31, 2020 3:24PM - 3:36PM |
ME.00006: Measuring the $^{134}\mathrm{Te}(d,p\gamma)^{135}\mathrm{Te}$ Reaction with GODDESS to Probe the Single-Particle Structure of $^{135}\mathrm{Te}$ C.C. Ummel, J.A. Cizewski, S.D. Pain, K.L. Jones, A. Ratkiewicz, G.L. Wilson The single-particle energy spectra of nuclei near shell closures provide important inputs for the nuclear shell model. $^{135}$Te ($Z=52$, $N=83$) is of particular interest due to its proximity to the $Z=50$ and $N=82$ closed shells. Additionally, neutron capture on $^{134}$Te has been identified as a key reaction in attempts to explain an overabundance of $^{134,136}$Xe observed in some pre-solar grains. The $^{134}$Te$(n,\gamma)^{135}$Te direct capture cross section can be constrained via the measurement of excitation energies, spin-parities, and spectroscopic factors of single-neutron states in $^{135}$Te using neutron transfer reactions such as $(d,p)$. The $^{135}$Te level scheme is highly fragmented, with many closely-spaced levels that are difficult to separate by charged particle measurement alone. However, enhanced resolution can be achieved by coincident measurement of gamma rays emitted by excited $^{135}$Te states. The $^{134}$Te$(d,p\gamma)^{135}$Te reaction was accordingly measured with GODDESS (GRETINA-ORRUBA: Dual Detectors for Experimental Structure Studies) at ATLAS with a 9 MeV/u $^{134}$Te beam provided by CARIBU with 60\% purity and an approximate intensity of 1200 pps incident upon a CD$_2$ target. Preliminary results will be presented. [Preview Abstract] |
Saturday, October 31, 2020 3:36PM - 3:48PM |
ME.00007: What can we learn about deformation with Coulomb excitation of radioactive ions? Jack Henderson The emergent phenomenon of collectivity in atomic nuclei provides a sensitive diagnostic of underlying microscopic behaviours. For example, the breaking down of traditional magic numbers typically comes hand-in-hand with an enhancement of deformation. Coulomb excitation provides the most straightforward route towards experimentally establishing this deformation in unstable nuclei, especially with regards to the nature of the quadrupole deformation. I will discuss recent results, using particle-gamma coincidence spectroscopy to establish the deformation of mid-mass nuclei, as well as potential limitations, in particular when it comes to establishing the softness of the nuclear shape. [Preview Abstract] |
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