Bulletin of the American Physical Society
APS April Meeting 2016
Volume 61, Number 6
Saturday–Tuesday, April 16–19, 2016; Salt Lake City, Utah
Session H9: Nuclear Structure I |
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Sponsoring Units: DNP Chair: Christopher Chiara, U.S. Army Research Laboratory Room: 250A |
Sunday, April 17, 2016 8:30AM - 8:42AM |
H9.00001: Investigating 3-body Decays of Cluster States with the PAT-TPC Lisa Carpenter, Y. Ayyad Limonge, D. Bazin, S. Beceiro-Novo, J. Bradt, M. Cortesi, W. Mittig, T. Ahn, J.J. Kolata, Z. Meisel, F.D. Bechetti, A. Fritsch, A. Howard Recent model calculations with most advanced methods for cluster states have shown the need of experimental data to probe the structure of light exotic nuclei, including those with $\alpha$-clustering, such as $^{14}$C. The Prototype Active Target Time Projection Chamber (PAT-TPC) allows us to investigate these types of structures, giving access to the full excitation function with a single beam energy. This type of experiment measures resonances in $^{14}$C that can be compared to the models. With an improved Micromegas pad plane with a circular backgammon design we are able to investigate 3-body decays in addition to 2-body scattering. The measurements were carried out by resonant alpha-scattering on $^{10}$Be beam delivered by the {\textit{TwinSol}} facility at the University of Notre Dame. We also observed the 3-body decay of the Hoyle State in $^{12}$C from a $^{12}$N or $^{12}$B beam with the same device. Preliminary results will be presented. [Preview Abstract] |
Sunday, April 17, 2016 8:42AM - 8:54AM |
H9.00002: Search for $\alpha$-Cluster Structure in Exotic Nuclei with the Prototype Active-Target Time-Projection Chamber A. Fritsch, Y. Ayyad, D. Bazin, S. Beceiro-Novo, J. Bradt, L. Carpenter, M. Cortesi, W. Mittig, D. Suzuki, T. Ahn, J.J. Kolata, F.D. Becchetti, A.M. Howard Some exotic nuclei appear to exhibit $\alpha$-cluster structure. While various theoretical models currently describe such clustering, more experimental data are needed to constrain model predictions. The Prototype Active-Target Time-Projection Chamber (PAT-TPC) has low-energy thresholds for charged-particle decay and a high luminosity due to its thick gaseous active target volume, making it well-suited to search for low-energy $\alpha$-cluster reactions. Radioactive-ion beams produced by the {\textit{TwinSol}} facility at the University of Notre Dame were delivered to the PAT-TPC to study nuclei including $^{14}$C and $^{14}$O via $\alpha$-resonant scattering. Differential cross sections and excitation functions were measured. Preliminary results from our recent experiments will be presented. [Preview Abstract] |
Sunday, April 17, 2016 8:54AM - 9:06AM |
H9.00003: $\beta$-delayed $\gamma$-decay of $^{26}\mathrm{P}$ David Perez-Loureiro, C. Wrede, M. B. Bennett, S. N. Liddick The $\beta$-decay of proton-rich nuclei is a powerful tool in nuclear science; it can be used to probe quenching of the Gamow-Teller strength, isospin asymmetries, and nuclear astrophysics. $^{26}$P $\beta$-delayed $\gamma$-decay has been recently measured at the National Superconducting Cyclotron Laboratory at MSU with much higher sensitivity than the previous experiment. A fast $^{26}$P beam produced using nuclear fragmentation was implanted into a planar germaninum detector. This detector was surrounded by the SeGA germanium array in order to detect the $\gamma$ rays emitted in coincidence with $\beta$-decays with high resolution. Absolute $\gamma$-ray intensities were measured and a complete decay scheme was built for the allowed transitions to bound excited states of $^{26}$Si. ${\mathrm{Log}}\,ft$ values and Gamow-Teller strengths were determined for each transition and compared to shell model calculations and the $\beta$-decay of its mirror nucleus $^{26}$Na. Results of this study, including a larger Gamow-Teller quenching than the $sd$ shell average and a substantial mirror asymmetry between the $\beta^+$ and $\beta^-$ transitions to the first excited states of $^{26}$Si and $^{26}$Mg, respectively, will be presented and interpreted. [Preview Abstract] |
Sunday, April 17, 2016 9:06AM - 9:18AM |
H9.00004: Revalidation of the Isobaric Multiplet Mass Equation for the A$=$20 quintet Brent Glassman, D. Perez-Loureiro, C. Wrede, J. Allen, D. Bardyan, M. Bennett, A. Brown, K. Chipps, M. Febbraro, Cathleen Fry, O. Hall, M. Hall, S. Liddick, P. O'Malley, W. Ong, S. Pain, S. Schwartz, P. Shidling, H. Sims, P. Thompson, E. Zhang An unexpected breakdown of the Isobaric Multiplet Mass Equation (IMME) for the A$=$20, T$=$2 quintet was recently reported based on a precise measurement of the $^{20}$Mg mass and adopted data on the other members. The adopted value for 20Na presented the greatest deviation from the IMME fit and was based on relatively imprecise beta delayed proton decay measurements. We used the superallowed 0$^{+}$ to 0$^{+}$ beta decay of $^{20}$Mg to feed the lowest T$=$2 state in $^{20}$Na, and the high purity germanium detector array SeGA to detect its gamma-ray de-excitation for the first time. Using the gamma-ray energies, we were able to precisely measure the excitation energy to be 6498.4 \textpm 0$.$2$_{stat\, }$\textpm 0.4$_{syst}$ keV. By incorporating this newly measured value we find that the IMME is revalidated. [Preview Abstract] |
Sunday, April 17, 2016 9:18AM - 9:30AM |
H9.00005: Rotational Band Structure in $^{32}$Mg Heather Crawford There is significant evidence supporting the existence of deformed ground states within the neutron-rich N =20 neon, sodium, and magnesium isotopes that make up what is commonly called the "Island of Inversion". However, rotational band structures, a characteristic fingerprint of a rigid non-spherical shape, have yet to be observed. We report on a measurement and analysis of the yrast (lowest lying) rotational band in $^{32}$Mg up to spin $I$ = 6+, produced in a two-step projectile fragmentation reaction and observed using the state-of-the-art $\gamma$-ray tracking detector array, GRETINA. Large-scale shell model calculations using the SDPF-U-MIX effective interaction show excellent agreement with the new data. Moreover, a theoretical analysis of the spectrum of rotational states as a function of the pairing gap, together with cranked shell model calculations, provides intriguing evidence for a reduction in pairing correlations with increased angular momentum, also in line with the shell-model results. [Preview Abstract] |
Sunday, April 17, 2016 9:30AM - 9:42AM |
H9.00006: Structure of T$_z=3/2$, $^{33}$P Nucleus Rebeka Sultana Lubna, Vandana Tripathi, Samuel Tabor, Pei-Laun Tai, Peter Bender The excited states of the nucleus $^{33}$P were populated by the $^{18}$O($^{18}$O, p-2n$\gamma$)$^{33}$P fusion evaporation reaction at $E_{lab}=25$ MeV.Gammasphere was used along with the particle detector Microball to detect the $\gamma$ emissions in coincidence with the emitted charged particles from the compound nucleus $^{36}$S. The auxiliary detector Microball was used to select the charged particle channel and to determine the exact position and the energy of the emitted proton. The purpose of finding the position and energy of proton was to determine a more precise angle between the recoil nucleus and the emitted $\gamma$ which was later employed to get a better Doppler correction. Along with the selection of the proton channel, the $\gamma$-$\gamma$ coincidence technique helped to isolate $^{33}$P from the other phosphorus isotopes and also reduced the contaminations from the dominant pure neutron channels. A number of transitions and states was identified that were not observed before. The 4$\pi$ arrangement of Gammasphere offered an excellent opportunity to measure the angular distribution of the electromagnetic emissions leading to the assignment of the spins for most of the new states. The experimental observations were compared to the shell model calculation using [Preview Abstract] |
Sunday, April 17, 2016 9:42AM - 9:54AM |
H9.00007: Study of the Nuclear Structure of $^{39}$P Using Beta-Delayed Gamma Spectroscopy Brittany Abromeit Investigation of nuclei with neutron and proton imbalance is at the forefront of nuclear physics research today. This is driven by the fact that the structure in these regimes may vary with that seen near the valley of stability. With eight neutrons more than the stable isotope of phosphorous, $^{39}$P is a neutron-rich exotic nucleus that has very limited information on it: previous studies of $^{39}$P produce only three known energy levels and gamma rays. The fragmentation of a $^{48}$Ca primary beam on a 564mg/cm$^2$ thick Be target at the National Superconducting Cyclotron Laboratory (NSCL) was used to produce exotic $^{39}$Si. Using the NSCL Beta Counting System (BCS), consisting of a thick planner germanium double-sided strip detector (GeDSSD) and 16 High-purity germanium detectors in an array, SeGA, the beta-gamma coincidences from the decay of $^{39}$Si to $^{39}$P were analyzed. The resulting level scheme of $^{39}$P, including over 12 new gamma rays and energy states, confirmation of the previously measured half-life, and first-time log\textit{ft} values will be presented. [Preview Abstract] |
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