Bulletin of the American Physical Society
2017 Fall Meeting of the APS Division of Nuclear Physics
Volume 62, Number 11
Wednesday–Saturday, October 25–28, 2017; Pittsburgh, Pennsylvania
Session CD: Nuclear Structure I |
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Chair: Anthony Kuchera, Davidson College Room: Salon 4 |
Thursday, October 26, 2017 8:30AM - 8:42AM |
CD.00001: Elastic and Inelastic Scattering of $^8$He Using a Solid Hydrogen Target Matthias Holl, Ritu Kanungo, Martin Alcorta, Devin Connolly, Barry Davids, Alejandra Diaz Varela, Greg Hackman, Jack Henderson, Shigeru Ishimoto, Ali Ihsan Kilic, Reiner Krücken, Annika Lennarz, Johnson Liang, James Measures, Wolfgang Mittig, Owen Paetkau, Athanasios Psaltus, Jaspreet Singh Randhawa, James Smallcombe, Matt Williams The nucleus $^8$He is the most neutron-rich nucleus known. Its structure, consisting of a $^4$He core surrounded by four neutrons makes it an ideal case to study phenomena in highly neutron-proton asymmetric systems. An experiment studying elastic and inelastic scattering of $^8$He has been carried out at the IRIS setup at ISAC-II at TRIUMF. It utilized the novel IRIS solid H$_2$ target in combination with a low pressure ionization chamber for the identification of the incoming beam and two $\Delta E-E$ telescopes to measure the reaction products. The current status of the analysis will be shown, including the optical model analysis of the elastic scattering compared to global potentials and the analysis of excited states in $^8$He from inelastic scattering. [Preview Abstract] |
Thursday, October 26, 2017 8:42AM - 8:54AM |
CD.00002: Precision excited-state lifetime measurements of 7,8Li C Morse, CJ Lister, GL Wilson, EA McCutchan, G Hackman, M Bowry, R Caballero-Folch, LJ Evitts, AB Garnsworthy, J Henderson, A Kurkjian, JP Measures, M Moukaddam, P Ruotsalainen, J Smallcombe, JK Smith, D Southall, M Williams, AJ Mitchell, CY Wu Advancing computational capabilities are providing increasingly detailed insights into light nuclear systems through \textit{ab initio} models such as Green's Function Monte Carlo and No-Core Shell Model calculations. Recently, efforts have been directed towards investigating charge currents in these systems, which give rise to magnetic moments and $M1$ transition rates. In order to help guide such investigations, precise experimental data are required in order to differentiate between different theoretical predictions. We have performed a new measurement to precisely determine the excited-state lifetimes of $^{7,8}$Li in order to constrain the $B(M1)$ transition rates in these nuclei. The experiment was performed at TRIUMF using TIGRESS, populating excited states through $(d,p)$ reactions in inverse kinematics. The lifetimes were determined using the Doppler Shift Attenuation Method. Preliminary results will be presented. [Preview Abstract] |
Thursday, October 26, 2017 8:54AM - 9:06AM |
CD.00003: Study of 11Be on 9Be one neutron transfer reactions at TRIUMF ISAC-II Ryan Braid, Fred Sarazin The structure of neutron-rich Beryllium isotopes displays interesting properties arising from the interplay of alpha clustering and valence neutrons, leading in some cases to halo states. In this presentation, we will present the results of the $^{11}$Be on $^{9}$Be reaction at 55 MeV and 30.14 MeV, leading to two interesting exit channels. The first channel allows for the study of $^{12}$Be, while the second enables the study of $^{10}$Be. The emphasis of this paper will be on the latter, namely the analysis of the $^{9}$Be( $^{11}$Be, $^{10}$Be) $^{10}$Be channel. This transfer reaction using a heavier-than-usual target has advantages over the traditional $(d,p)$ methods, since the reactants are both equal in mass, they both scatter in the Printed Circuit Board-Based Charged Particle (PCB$^2$) detector setup. The addition of TIGRESS allows precise tagging of the $^{10}$Be excited states. Some challenges in analysis include the $^{10}$Be degeneracy, $^{11}$Be breakup, and multiple particle excitation. The data and ongoing analysis will be presented. This work is partially supported by the US Department of Energy through Grant/Contract No. DE-FG03-93ER40789 (Colorado School of Mines). [Preview Abstract] |
Thursday, October 26, 2017 9:06AM - 9:18AM |
CD.00004: Studying $^{10}$Be and $^{11}$Be Halo States through the (p,d) Single-Neutron Transfer Reaction Keri Kuhn, Fred Sarazin One-neutron transfer reactions are being used to study single-particle neutron states in nuclei. For one-neutron halo nuclei, such as $^{11}$Be, the (p,d) reaction enables the removal of the halo neutron or of one of the core neutrons. This way, it is possible to simultaneously study the halo wavefunction of the $^{11}$Be ground-state but also a possible excited halo state in $^{10}$Be. The $^{11}$Be(p, d)$^{10}$Be transfer reaction at 10 MeV/nucleon is being investigated at the TRIUMF-ISAC II facility with the Printed Circuit Board Based Charged Particle ((PCB)$^2$) array inside the TRIUMF ISAC Gamma-Ray Escape-Suppressed Spectrometer (TIGRESS). The ground state and first excited state of $^{10}$Be can be directly identified using deuteron identification and kinematics from the charged particle array, while the four excited states in$^{10}$Be around 6 MeV, including the suspected halo state ( 2$^-$ state), are identified using coincident gamma rays from TIGRESS with the identified deuterons. Angular distributions for the $^{10}$Be populated states will be shown along with their FRESCO fits. [Preview Abstract] |
Thursday, October 26, 2017 9:18AM - 9:30AM |
CD.00005: Vertex Reconstruction for the $^{10}$C($\alpha$,$\alpha$)$^{10}$C scattering reaction using the Prototype Active-Target Time-Projection Chamber T. Ahn, J. Lai, D. W. Bardayan, M. Brodeur, M. Hall, O. Hall, J. Hu, J. J. Kolata, J. Long, P. O'Malley, Y. Ayyad, D. Bazin, S. Beceiro Novo, J. Bradt, M. Cortesi, L. Carpenter, W. Mittig The investigation of the importance of $\alpha$-cluster structure on the proton-rich side of stability in the light nucleus $^{14}$O has been investigated using a $^{10}$C($\alpha$,$\alpha$)$^{10}$C scattering reaction. The Prototype Active-Target Time-Projection Chamber was used to provide a He gas target and image charged-particle tracks. The key experimental observables that are needed are the vertex position, which determines the energy at which the reaction occurred. The precision of this vertex position gives the reaction energy uncertainty, which needs to be determined to a few mm. The performance of various algorithms for vertex reconstruction will be presented including their advantages and disadvantages. The impact of the energy resolution on particle identification and determining cross sections for the $\alpha$-resonant scattering experiment will be presented. [Preview Abstract] |
Thursday, October 26, 2017 9:30AM - 9:42AM |
CD.00006: Structure of $^{10}$N Joshua Hooker, Grigory Rogachev, Vladilen Goldberg, Evgeny Koshchiy, Brian Roeder, Heshani Jayatissa, Curtis Hunt, Cordero Magana, Sriteja Upadhyayula, Ethan Uberseder, Antti Saastamoinen We report on the first observation of the ground and first excited states in $^{10}$N via $^{9}$C+p resonance scattering. The experiment was carried out at the Cyclotron Institute at Texas A\&M University. Both states were determined to be $\ell=0$. We can now reliably place the location of the $2$s$_{1/2}$ shell in $^{10}$N at $2.3 \pm 0.2$ MeV above the proton decay threshold. Using mirror symmetry and correcting for Thomas-Ehrman shift we argue that the ground state of $^{10}$Li is an $\ell=0$ states that should be very close to the neutron threshold. [Preview Abstract] |
Thursday, October 26, 2017 9:42AM - 9:54AM |
CD.00007: Strongly Coupled Rotational Band in $^{33}$Mg Andrea L. Richard, Heather L. Crawford The "Island of Inversion" at $N\sim$ 20 for the neon, sodium, and magnesium isotopes has long been an area of interest both experimentally and theoretically due to the subtle competition between 0p-0h and $n$p-$n$h configurations leading to deformed shapes. However, the presence of rotational band structures, which are fingerprints of deformed shapes, have only recently been observed in this region. A measurement of the low-lying level structure of $^{33}$Mg populated by a two-stage projectile fragmentation reaction and studied with GRETINA was performed at the NSCL. The newly identified rotational band level energies and $\gamma$-ray intensities, as well as other available experimental data on the ground state magnetic moment and intrinsic quadrupole moment show good agreement with the strong-coupling limit of a rotational model. We present here the analysis and interpretation of the available experimental observables for $^{33}$Mg within a rotational framework. [Preview Abstract] |
Thursday, October 26, 2017 9:54AM - 10:06AM |
CD.00008: Kerman's Problem in the Continuum A. O. Macchiavelli, R. F. Casten, R. M. Clark, C. M. Campbell, H. L. Crawford, M. Cromaz, P. Fallon, M. D. Jones, M. Salathe In 1956 Kerman published a seminal paper on rotational perturbations in nuclei [1]. Since then, Coriolis and rotational alignment effects have been extensively studied and are rather well understood [2,3]. With the development of exotic beam facilities and advanced instrumentation it is becoming possible to access regions of deformation in the nuclear chart, near the neutron drip-line. Here, the effects of weak binding are expected to play an important role, affecting the dynamics of the nuclear motion. In this work we study Kerman's problem when the single-particle levels involved are resonant states. We will present results showing the behavior of the kinematic and dynamic moments of inertia as a function of the state widths. Connection to possible experiments will be discussed. \\ \\ 1. A. K. Kerman, Mat. Fys. Medd. 30. No.16 (1956). \\ 2. F. S. Stephens, Rev. Mod. Phys. 47 43 (1975).\\ 3. R. Bengtsson and S. Frauendorf, Nucl. Phys. A137 129 (1979). [Preview Abstract] |
Thursday, October 26, 2017 10:06AM - 10:18AM |
CD.00009: Nuclear shell evolution in the "Island of Inversion" D. Muecher, E. E. Peters, B. A. Brown, N. Pietralla, B. Tokiwa, S. W. Yates Recent publications suggest a re-interpretation for the "Island of Inversion" (IOI) around Mg-32 at N=20. In contrast to earlier beliefs, significant amounts of intruder configurations might be present in the ground states of Mg-28 and Mg-30, already [N. Tsunoda et al. PRC 95, 021304(R)]. Also, the excited 0+ state in Mg-32 seems to be dominated by 2p2h and 4p4h contributions [A. O. Macchiavelli et al., PRC 94, 051303(R)]. We here confirm this picture for the region of the IOI around Ni-68, based on large-scale shell model calculations in the fpg shell using the new JJ44C effective interaction. We show that the nature of shell evolution in the IOI is not unique to neutron-rich, exotic nuclei. Instead, the tensor force is essential understanding the transition into the IOI, also affecting the interpretation of R4/2 values. We show that the mixing of np-nh configurations results in characteristic low-lying strong M1 transitions, which we confirm based on new lifetime measurements in 70Zn at N=40. The M1 strength systematics around N=20 and N=40 is found to be correlated with the behaviour of the presumed shape-coexisting 0+ states, offering a re-interpreation of low-lying M1 transitions in medium-light nuclei. [Preview Abstract] |
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