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Title: Recoil Distance Method lifetime measurements via gamma-ray and charged-particle spectroscopy at NSCL
Creator: Voss, Philip Jonathan
Date: 2011
Collection: Electronic Theses & Dissertations
Description: The Recoil Distance Method (RDM) is a well-established technique for measuring lifetimes of electromagnetic transitions. Transition matrix elements derived from the lifetimes provide valuable insight into nuclear structure. Recent RDM investigations at NSCL present a powerful new model-independent tool for the spectroscopy of nuclei with extreme proton-to-neutron ratios that exhibit surprising behavior. Neutron-rich 18C is one such example, where a small B(E2; 2+...
Show moreThe Recoil Distance Method (RDM) is a well-established technique for measuring lifetimes of electromagnetic transitions. Transition matrix elements derived from the lifetimes provide valuable insight into nuclear structure. Recent RDM investigations at NSCL present a powerful new model-independent tool for the spectroscopy of nuclei with extreme proton-to-neutron ratios that exhibit surprising behavior. Neutron-rich 18C is one such example, where a small B(E2; 2+₁ &rarr 0+_gs) represented a dramatic shift from the expected inverse relationship between the B(E2) and 2+₁ excitation energy. To shed light on the nature of this quadrupole excitation, the RDM lifetime technique was applied with the Köln/NSCL plunger. States in 18C were populated by the one-proton knockout reaction of a 19N secondary beam. De-excitation gamma rays were detected with the Segmented Germanium Array in coincidence with reaction residues at the focal plane of the S800 Magnetic Spectrometer. The deduced B(E2) and excitation energy were both well described by ab initio no-core shell model calculations.In addition, a novel extension of RDM lifetime measurements via charged-particle spectroscopy of exotic proton emitters has been investigated. Substituting the reaction residue degrader of the Köln/NSCL plunger with a thin silicon detector permits the study of short-lived nuclei beyond the proton dripline. A proof of concept measurement of the mean lifetime of the two-proton emitter 19Mg was conducted. The results indicated a sub-picosecond lifetime, one order of magnitude smaller than the published results, and validate this new technique for lifetime measurements of charged-particle emitters.
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Title: Fission in exotic nuclei using density functional theory
Creator: Matheson, Zachary
Date: 2019
Collection: Electronic Theses & Dissertations
Description: Historically, most experimental and theoretical studies of fission have centered around the region of actinides near 235U, which includes isotopes of uranium, plutonium, and thorium relevant for reactor physics and stockpile stewardship. Isotopes in this region tend to fission asymmetrically, with the larger prefragment influenced by the doubly-magic shell structure of 132Sn and resulting in a heavy fragment distribution centered around 140Te. However, fission is a common decay mode of nuclei...
Show moreHistorically, most experimental and theoretical studies of fission have centered around the region of actinides near 235U, which includes isotopes of uranium, plutonium, and thorium relevant for reactor physics and stockpile stewardship. Isotopes in this region tend to fission asymmetrically, with the larger prefragment influenced by the doubly-magic shell structure of 132Sn and resulting in a heavy fragment distribution centered around 140Te. However, fission is a common decay mode of nuclei, both lighter and heavier than the actinides. Given the nuclear physics community's interest in rare and exotic nuclei, we have applied nuclear density functional theory to study spontaneous fission primary fragment yields in exotic systems found in other regions of the nuclear chart, including neutron-deficient 178Pt, superheavy 294Og, and neutron-rich nuclei with relevance to the r-process such as 254Pu.
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Title: Transition rates beyond ⁴⁸Ca : effective charge in the pf shell
Creator: Cook, Jonathan Michael
Date: 2009
Collection: Electronic Theses & Dissertations

Title: Structure studies of ¹¹Li and ¹⁰Li
Creator: Young, Brian Matthew
Date: 1993
Collection: Electronic Theses & Dissertations

Title: Nuclear structure of proton-rich intermediate mass nuclei studied with advanced lifetime measurement techniques
Creator: Morse, Christopher Scott
Date: 2015
Collection: Electronic Theses & Dissertations
Description: The transition matrix elements between excited nuclear states provide valuable information about the structure of exotic nuclei. Lifetime measurements area model-independent way to deduce these matrix elements from experimental data.Two studies of proton-rich nuclei near mass 70 are presented herein usingadvanced lifetime measurement techniques.The first study is a measurement of the $8^+_1$ and $9^+_1$ states in the odd-$N$, odd-$Z$ nucleus $^{70}$As.The lifetimes of these states were...
Show moreThe transition matrix elements between excited nuclear states provide valuable information about the structure of exotic nuclei. Lifetime measurements area model-independent way to deduce these matrix elements from experimental data.Two studies of proton-rich nuclei near mass 70 are presented herein usingadvanced lifetime measurement techniques.The first study is a measurement of the $8^+_1$ and $9^+_1$ states in the odd-$N$, odd-$Z$ nucleus $^{70}$As.The lifetimes of these states were determined by the application of the $\gamma$-ray lineshape method to $\gamma$-$\gamma$ coincidence data.The states were populated using with the $^9$Be($^{78}$Rb,$^{70}$As) reaction and$\gamma$ rays were detected with the Segmented Germanium Array in coincidencewith reaction products detected in the focal plane of the S800 Spectrograph.The $B(E1;8^+\rightarrow7^-)$ and $B(M1;9^+\rightarrow8^+)$ transition strengthswere deduced and were found to support the assignment of these states to a coupling of the odd proton and neutron in the $g_{9/2}$ orbital.The second study is a measurement of the $2_1^+$ state lifetime in the $N=Z$nucleus $^{74}$Rb. A novel technique called the Differential Recoil DistanceMethod was used to extract the lifetime from the $\gamma$-ray spectra. The next-generation $\gamma$-ray detector array GRETINA was used in theexperiment, again coupled to the S800 Spectrograph to detect residues from $^9$Be($^{74}$Kr,$^{74}$Rb) charge exchange reactions. The $B(E2;2^+_1\rightarrow0^+_1)$ strength was calculated and is consistent with the measured strength of the transition between the isobaric analogue states in $^{74}$Kr, which may be a signature of shape coexistence in $^{74}$Rb.
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Title: The (p, n) charge-exchange reaction in inverse kinematics as a probe for isovector giant resonances in exotic nuclei
Creator: Lipschutz, Samuel Israel
Date: 2018
Collection: Electronic Theses & Dissertations
Description: "Charge-exchange experiments at intermediate (223C100 MeV/u) beam energies have long been a tool to study isovector giant resonances in nuclei. Since the 1970s, many probes and techniques have been developed to study and isolate different isovector giant resonances, which have illuminated the spin-isospin response of nuclei. However, these experiments have almost solely been restricted to stable nuclei. The advent of rare-isotope beam facilities has created increased interest in studying...
Show more"Charge-exchange experiments at intermediate (223C100 MeV/u) beam energies have long been a tool to study isovector giant resonances in nuclei. Since the 1970s, many probes and techniques have been developed to study and isolate different isovector giant resonances, which have illuminated the spin-isospin response of nuclei. However, these experiments have almost solely been restricted to stable nuclei. The advent of rare-isotope beam facilities has created increased interest in studying these resonances in radioactive nuclei. Such experiments are important for better constraining models that aim to describe the properties of nuclei and nuclear matter, with important applications in astro and neutrino physics. To take advantage of these rare-isotope facilities, new techniques in inverse kinematics need to be developed and validated. This thesis presents a new technique for studying isovector giant resonances on unstable nuclei in the delta-Tz = -1 direction, through the (p,n) reaction in inverse kinematics. The technique was validated through the measurement of the absolute differential cross section in the neutron-rich 16C(p,n)16N* reaction at 100 MeV/u up to 223C20 MeV of excitation energy. From the data, the Gamow-Teller (GT) strength distribution [B(GT)] and the spin-dipole (SD) differential cross section were extracted. The extracted B(GT) was compared with shell-model calculations in order to test their reliability in the neutron-rich, high-excitation energy regime. A total GT strength up to 20 MeV was extracted and compared to the model-independent sum rule, giving a quenching factor of 73.5 ±2.8(st) ± 15.5(sys)%. This experiment provided one of the first measurements of isovector strength in a neutron-rich nucleus and has paved the way for future exploration of isovector giant resonances in exotic nuclei."--Pages ii-iii.
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Title: Unbound states in the lightest island of inversion : neutron decay measurements of 11Li, 10Li, and 12Be
Creator: Smith, Jenna Kathleen
Date: 2014
Collection: Electronic Theses & Dissertations
Description: The light nuclei in the N∼8 region provide easily accessible systems for studying the structure of exotic nuclei. The nuclide 11Li is a two-neutron halo system, a Borromean nucleus, and located in the N∼8 island of inversion. The next lightest lithium isotope, 10Li is neutron unbound, located on the western edge of the island of inversion, and important for the understanding of the 11Li system. 12Be is the heaviest N=8...
Show moreThe light nuclei in the N∼8 region provide easily accessible systems for studying the structure of exotic nuclei. The nuclide 11Li is a two-neutron halo system, a Borromean nucleus, and located in the N∼8 island of inversion. The next lightest lithium isotope, 10Li is neutron unbound, located on the western edge of the island of inversion, and important for the understanding of the 11Li system. 12Be is the heaviest N=8 isotone in the island of inversion. Neutron unbound states from all three systems have been measured and analyzed in this work.The experiment was conducted at the National Superconducting Cyclotron Laboratory. Beams of exotic boron isotopes (12B and 13B) were provided by the Coupled Cyclotron Facility and delivered to the MoNA-LISA-Sweeper setup, each at 71 MeV/u. The neutron-unbound isotopes were created in a secondary beryllium target where they immediately decayed into a charged daughter fragment and one or two neutrons. The charged daughter fragment was measured by a suite of charged particle detectors and the neutrons were detected by MoNA-LISA.Measurement of the 11Li unbound system showed a state at 1210±80 keV excitation energy with a width greater than 1200 keV, consistent with previous measurements. Correlations between the three decay products were examined with use of Jacobi spectra and Dalitz plots, which revealed a correlation between the two neutrons stronger than that expected from the decay of two neutrons uncorrelated in the nucleus. This is the first correlation measurement attributable to a specific unbound state in 11Li. Unbound states in 10Li were populated with a two-proton knockout from a 12B beam, a reaction expected to populate primarily positive-parity states. The decay energy spectra of 10Li was fit with three peaks at 110±40 keV, 500±100 keV, and 1100±100 keV. The lowest two of these peaks are expected to be a 1+<\super>/2+ doublet. Calculation of the 0p__1/2 single particle energy in the 10Li system and comparison with Faddeev calculations suggests that both states of the 1+<\super>/2+ doublet are below 50 keV, consistent with previous measurements of one l=0 state at 50 keV or below. In the 12Be system, a measured decay energy of 1243±20 keV corresponds to an excitation energy between 4400 and 4800 keV, depending on the combination of final states populated in 11Be. A lack of decays to 10Be placed an upper limit of 5% on the branching ratio to the ground state of 10Be via 2n emission. This low branching ratio, as well as spin and parity selectivity from the 1p-knockout production mechanism, suggests that the spin and parity of this state is 1-<\super> or 2-<\super>.
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Title: Ground state of ¹⁰Li and ¹³Be
Creator: Yokoyama, Shigeru Kennedy
Date: 1996
Collection: Electronic Theses & Dissertations

Title: Production of proton-rich nuclei between nickel and zirconium
Creator: Mohar, Michael Florian
Date: 1991
Collection: Electronic Theses & Dissertations

Title: Production of nuclei near the neutron drip-line by projectile fragmentation
Creator: Kwan, Elaine
Date: 2006
Collection: Electronic Theses & Dissertations

Title: Spectroscopy of exotic nuclei with the S800 spectrograph
Creator: Caggiano, Joseph Arthur
Date: 1999
Collection: Electronic Theses & Dissertations

Title: Production of nuclei in neutron unbound states via primary fragmentation of ⁴⁸CA
Creator: Christian, Gregory Arthur
Date: 2008
Collection: Electronic Theses & Dissertations

Title: Investigation of ion capture in an electron beam ion trap charge-breeder for rare isotopes
Creator: Kittimanapun, Kritsada
Date: 2014
Collection: Electronic Theses & Dissertations
Description: Charge breeding of rare isotope ions has become an important ingredient for providing reaccelerated rare isotope beams for science. At the National Superconducting Cyclotron Laboratory (NSCL), a reaccelerator, ReA, has been built that employs an advanced Electron Beam Ion Trap (EBIT) as a charge breeder. ReA will provide rare-isotope beams with energies of a few hundred keV/u up to tens of MeV/u to enable the study of properties of rare isotopes via low energy Coulomb excitation and transfer...
Show moreCharge breeding of rare isotope ions has become an important ingredient for providing reaccelerated rare isotope beams for science. At the National Superconducting Cyclotron Laboratory (NSCL), a reaccelerator, ReA, has been built that employs an advanced Electron Beam Ion Trap (EBIT) as a charge breeder. ReA will provide rare-isotope beams with energies of a few hundred keV/u up to tens of MeV/u to enable the study of properties of rare isotopes via low energy Coulomb excitation and transfer reactions, and to investigate nuclear reactions important for nuclear astrophysics. ReA consists of an EBIT charge breeder, a charge-over-mass selector, a room temperature radio-frequency quadrupole accelerator, and a superconducting radio-frequency linear accelerator. The EBIT charge breeder features a high-current electron gun, a long trap structure, and a hybrid superconducting magnet to reach both high acceptance for injected low-charge ions as well as high-electron beam current densities for fast charge breeding.In this work, continuous ion injection and capture in the EBIT have been investigated with a dedicated Monte-Carlo simulation code and in experimental studies. The Monte-Carlo code NEBIT considers the electron-impact ionization cross sections, space charge due to the electron beam current, ion dynamics, electric field from electrodes, and magnetic field from the superconducting magnet. Experiments were performed to study the capture efficiency as a function of injected ion beam current, electron beam current, trap size, and trap potential depth. The charge state evolution of trapped ions was studied, providing information about the effective current density of the electron beam inside the EBIT. An attempt was made to measure the effective space-charge potential of the electron beam by studying the dynamics of a beam injected and reflected inside the trap.
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