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| 2. |
- DiJulio, Douglas, et al.
(author)
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Coulomb excitation of In-107
- 2013
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In: Physical Review C (Nuclear Physics). - 0556-2813. ; 87:1
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Journal article (peer-reviewed)abstract
- The radioactive isotope In-107 was studied using sub-barrier Coulomb excitation at the REX-ISOLDE facility at CERN. Two gamma rays were observed during the experiment, corresponding to the low-lying 11/2(+) and 3/2(-)states. The reduced transition probability of the 11/2(+) state was determined with the semiclassical Coulomb excitation code GOSIA2. The result is discussed in comparison to large-scale shell-model calculations, previous unified-model calculations, and earlier Coulomb excitation measurements in the odd-mass In isotopes. DOI: 10.1103/PhysRevC.87.017301
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| 3. |
- DiJulio, Douglas, et al.
(author)
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Coulomb excitation of Sn-107
- 2012
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In: European Physical Journal A. Hadrons and Nuclei. - : Springer Science and Business Media LLC. - 1434-6001. ; 48:7
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Journal article (peer-reviewed)abstract
- The radioactive isotope Sn-107 was studied using Coulomb excitation at the REX-ISOLDE facility at CERN. This is the lightest odd-Sn nucleus examined using this technique. The reduced transition probability of the lowest-lying 3/2(+) state was measured and is compared to shell-model predictions based on several sets of single-neutron energies relative to Sn-100. Similar to the transition probabilities for the 2(+) states in the neutron-deficient even-even Sn nuclei, the measured value is underestimated by shell-model calculations. Part of the strength may be recovered by considering the ordering of the d(5/2) and g(7/2) single-neutron states.
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| 4. |
- DiJulio, Douglas, et al.
(author)
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Electromagnetic properties of vibrational bands in Er-170
- 2011
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In: European Physical Journal A. - : Springer Science and Business Media LLC. - 1434-6001 .- 1434-601X. ; 47:2, s. 25-
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Journal article (peer-reviewed)abstract
- Excited states of the nucleus Er-170 have been studied by Coulomb excitation using the GASP gamma-ray detector system at the Laboratori Nazionali di Legnaro. The ground-state band along with a low-lying K-pi = 0(+) band and gamma-vibrational band were populated during the experiment. Based on the measured gamma-ray yields, a set of interband and intraband matrix elements has been extracted using the Coulomb excitation code GOSIA. The resulting E2 matrix elements are compared to collective model predictions.
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| 5. |
- DiJulio, Douglas, et al.
(author)
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Excitation strengths in Sn-109: Single-neutron and collective excitations near Sn-100
- 2012
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In: Physical Review C (Nuclear Physics). - 0556-2813. ; 86:3
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Journal article (peer-reviewed)abstract
- A set of B(E2) values for the low-lying excited states in the radioactive isotope Sn-109 were deduced from a Coulomb excitation experiment. The 2.87-MeV/u radioactive beam was produced at the REX-ISOLDE facility at CERN and was incident on a secondary Ni-58 target. The B(E2) values were determined using the known 2(+) -> 0(+) reduced transition probability in Ni-58 as normalization with the semiclassical Coulomb excitation code GOSIA2. The transition probabilities are compared to shell-model calculations based on a realistic nucleon-nucleon interaction and the predictions of a simple core-excitation model. This measurement represents the first determination of multiple B(E2) values in a light Sn nucleus using the Coulomb excitation technique with low-energy radioactive beams. The results provide constraints for the single-neutron states relative to Sn-100 and also indicate the importance of both single-neutron and collective excitations in the light Sn isotopes.
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| 6. |
- DiJulio, Douglas, et al.
(author)
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Optimization of multi-channel neutron focusing guides for extreme sample environments
- 2014
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In: International Workshop on Neutron Optics and Detectors (NOP&D 2013) 2–5 July 2013, Munich, Germany. - : IOP Publishing. - 1742-6596 .- 1742-6588. ; 528, s. 012006-012006
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Conference paper (peer-reviewed)abstract
- In this work, we present and discuss simulation results for the design of multi-channel neutron focusing guides for extreme sample environments. A single focusing guide consists of any number of supermirror-coated curved outer channels surrounding a central channel. Furthermore, a guide is separated into two sections in order to allow for extension into a sample environment. The performance of a guide is evaluated through a Monte-Carlo ray tracing simulation which is further coupled to an optimization algorithm in order to find the best possible guide for a given situation. A number of population-based algorithms have been investigated for this purpose. These include particle-swarm optimization, artificial bee colony, and differential evolution. The performance of each algorithm and preliminary results of the design of a multi-channel neutron focusing guide using these methods are described. We found that a three-channel focusing guide offered the best performance, with a gain factor of 2.4 compared to no focusing guide, for the design scenario investigated in this work.
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| 7. |
- DiJulio, Douglas
(author)
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Probing single-particle and collective states in atomic nuclei with Coulomb excitation
- 2013
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Doctoral thesis (other academic/artistic)abstract
- A series of experiments and developments, related to stable and radioactive isotopes, have been carried out. These studies have focused on measuring the low-lying excitations of spherical and deformed nuclei using electromagnetic (Coulomb) excitation and also on developments in detector technology for upcoming radioactive ion beams facilities. The low-lying excitations in the nuclei 107,109Sn and 107In have been investigated using low-energy Coulomb excitation at the REX-ISOLDE facility at CERN. The measured reduced transition probabilities were compared to predictions of nuclear structure models. In addition, a relativistic Coulomb excitation experiment was carried out using the FRS at GSI with the nucleus 104Sn. These radioactive ion beam experiments provide important constraints for large-scale-shell-model calculations in the region of the doubly magic nucleus 100Sn. A stable Coulomb excitation experiment was also carried out in order to explore the properties of low-lying structures in the nucleus 170Er. These measurements resulted in new data for the reduced transition matrix elements in this nucleus. The results were compared to predictions of models of deformed nuclei. The last study contained in this work is related to the design of a new detector system, to be deployed at the upcoming radioactive ion beam facility FAIR. A prototype of the detector was tested with a 180 MeV proton beam and the results were compared to Geant4 simulations. The results highlight important constraints for the design of the full detector system.
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| 8. |
- DiJulio, Douglas, et al.
(author)
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Shell model based Coulomb excitation gamma-ray intensity calculations in Sn-107
- 2012
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In: Physica Scripta. - 0031-8949. ; T150
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Journal article (peer-reviewed)abstract
- In this work, we present recent shell model calculations, based on a realistic nucleon-nucleon interaction, for the light Sn-107,Sn-109 nuclei. By combining the calculations with the semi-classical Coulomb excitation code GOSIA, a set of gamma-ray intensities has been generated. The calculated intensities are compared with the data from recent Coulomb excitation studies in inverse kinematics at the REX-ISOLDE facility with the nucleus Sn-107. The results are discussed in the context of the ordering of the single-particle orbits relative to Sn-100.
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| 9. |
- DiJulio, Douglas, et al.
(author)
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Sub-barrier Coulomb excitation of Sn-107
- 2012
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In: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 381, s. 012073-012073
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Conference paper (peer-reviewed)abstract
- A Coulomb excitation experiment in inverse kinematics has been carried out at the REX-ISOLDE facility in order to study the properties of low-lying excited states in Sn-107. The measured gamma ray spectrum has been compared with predicted gamma ray spectra from a combined shell-model and GOSIA analysis. In this approach, a set of matrix elements, generated within the shell-model framework, based on a realistic nucleon-nucleon interaction and a set of single-particle energies relative to Sn-100, is used as input. Comparison between the calculated and predicted spectra can be used to help identify the placement of the single-neutron states in Sn-101. In particular, the results can potentially provide clues on the ordering of the two lowest-lying orbits; the g(7/2) and d(5/2) states.
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| 10. |
- Ekström, Andreas, et al.
(author)
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Determination of the isomeric fraction in a postaccelerated radioactive ion beam using the coupled decay-chain equations
- 2010
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In: Nuclear Instruments & Methods in Physics Research. Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment. - : Elsevier BV. - 0167-5087 .- 0168-9002. ; 614:2, s. 303-307
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Journal article (peer-reviewed)abstract
- A method based on the coupled decay-chain equations for extracting the isotopic and the isomeric composition of a postaccelerated radioactive ion beam is presented and demonstrated on a data set from a Coulomb excitation experiment. This is the first attempt of analyzing the content of a postaccelerated radioactive ion beam using this technique. The beam composition is required for an absolute normalization of the measurement. The strength of the method, as compared to present online-based methods, lies in the determination of the isomeric fraction of a partially isomeric beam using all data accumulated during the experiment. We discuss the limitations and sensitivity of the method with respect to the gamma-ray detection efficiency and the accumulated flux. (C) 2010 Elsevier B.V. All rights reserved.
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