The neutron-deuteron (nd) breakup reaction serves as a fertile testing ground for theories of thr... more The neutron-deuteron (nd) breakup reaction serves as a fertile testing ground for theories of three nucleon dynamics and meson exchange descriptions of nuclear systems. The three-body kinematics of the nd breakup reaction allow observables to be studied in a variety of exit-channel configurations to test nucleon-nucleon potential models as well as three-nucleon force models. Over the last two decades there have been significant advances in modeling three-nucleon dynamics using empirical nucleon-nucleon potential models. These calculations have shown excellent agreement with most experimental data. However, there remain some exceptions where serious discrepancies arise. We have undertaken new cross-section measurements to provide further insight into one of these discrepancies, the space-star anomaly. The space-star configuration is a special case of the symmetric constant relative energy (SCRE) configuration in nd breakup. The SCRE configuration occurs when the three outgoing nucleo...
Creative Commons Attribution-Noncommercial License Two separate experimental searches for second-... more Creative Commons Attribution-Noncommercial License Two separate experimental searches for second-order weak nuclear decays to excited final states were conducted. Both experiments were carried out at the Kimballton Underground Research Facility to provide shielding from cosmic rays. The first search is for the 2νββ decay of 96Zr to excited final states of the daughter nucleus, 96Mo. As a byproduct of this experiment, the β decay of 96Zr was also investigated. Two coaxial high-purity germanium detectors were used in coincidence to detect γ rays produced by the daughter nucleus as it de-excited to the ground state. After collecting 1.92 years of data with 17.91 g of enriched 96Zr, half-life limits at the level of 1020 yr were produced. Measurements of this decay are important to test 0νββ-decay nuclear matrix element calculations, which are necessary to extract the neutrino mass from a measurement of the 0νββ decay half-life. The second experiment is a search for the resonantly-enhanc...
The Bohr hypothesis, one of the most fundamental assumptions in nuclear fission theory, states th... more The Bohr hypothesis, one of the most fundamental assumptions in nuclear fission theory, states that the decay of a compound nucleus with a given excitation energy, spin and parity is independent of its formation. Using fission product yields (FPYs) as a sensitive probe, we have performed new high precision test of the combined effects of the entrance channel, spin and parity on the fission process. Two different reactions were used in a self-consistent manner to produce a compound 240Pu nucleus with the same excitation energy: neutron induced fission of 239Pu at En = 4.6 MeV and photon-induced fission of 240Pu at Eγ = 11.2 MeV. The FPYs from these two reactions were measured using quasimonoenergetic neutron beams from the TUNL's FN tandem Van de Graaff accelerator and quasimonenergetic photon beams from the High Intensity γ-ray Source (HlγS) facility. The first results comparing the FPYs from these two reactions will be presented. Implications for validating the Bohr hypothesis ...
I am pleased to say that we have had a very active and productive year in terms of both research ... more I am pleased to say that we have had a very active and productive year in terms of both research and education here at Duke Physics. This is my first year as Chair, as many of you know, and it was a year of challenges and learning for me personally. Certainly the most interesting things I learned came from finding out what my colleagues in other subfields are doing; this broad view – from biophysics to particle physics, from optics to gamma rays, from teaching introductory physics to advising graduate students – has deepened my appreciation for our department. Six of the more significant research achievements are highlighted in this newsletter. News about undergraduate and graduate education are covered in their respective sections. Here I want to highlight some general news about the department and faculty:
A joint TUNL-LLNL-LANL collaboration was formed to measure the absolute fission product yields fr... more A joint TUNL-LLNL-LANL collaboration was formed to measure the absolute fission product yields from the 235 U, 238 U, and 239 Pu isotopes. Our goal is to study the energy evolution of fission products using monoenergetic beams. In order to extend our successful fission product-yield studies to include products with shorter half-lives, a RApid Belt-driven Irradiated Target Transfer System, named RABITTS, was constructed. This system allows us to perform cyclic activation and quantify fission products with γ-ray spectroscopy using HPGe detectors. Both a 1 meter and 10 meter transfer system have been developed, with transit times of 0.4 and 1.1 seconds, respectively. Using these systems, we have measured sub-second half-lives. Our goal is to measure fission product yields from neutron-induced fission with En = 0.5 − 14.8 MeV and photofission with Eγ = 8 − 15 MeV. A detailed characterization of the system’s performance is presented, including preliminary fission product measurements, an...
Fission product yields (FPYs) are a uniquely sensitive probe of the fission process, with well es... more Fission product yields (FPYs) are a uniquely sensitive probe of the fission process, with well established dependence on the species of nucleus undergoing fission, its excitation energy and spin. Thus FPYs are well suited for testing Bohr’s hypothesis in the context of nuclear fission, which states that the decay of a compound nucleus with a given excitation energy, spin and parity is independent of its formation. Using FPYs, we have performed a new highprecision test of the combined effects of the entrance channel, spin and parity on the fission process from two of the most commonly used particles to induce fission neutrons and photons. The 239 Pu(n,f) reaction at En = 4.6 MeV and the 240 Pu(γ,f) reaction at Eγ = 11.2 MeV were used to produce a 240 Pu∗ compound nucleus with the same excitation energy. The FPYs from these two reactions were measured using quasimonoenergetic neutron beams from the TUNL’s FN tandem Van de Graaff accelerator and quasimonenergetic photon beams from the ...
Proceedings of The 9th International workshop on Chiral Dynamics — PoS(CD2018), 2020
The main goal of few-nucleon research at the Triangle Universities Nuclear Laboratory (TUNL) is t... more The main goal of few-nucleon research at the Triangle Universities Nuclear Laboratory (TUNL) is to perform high-precision measurements that contribute to advancing ab-initio calculations and testing nucleon-interaction models. The current focus is on the three-nucleon system, which has highly developed theory and has sufficient complexity to exhibit influences of threenucleon forces.The few-nucleon measurements performed at the High Intensity Gamma-ray Source (HIγS) and in the tandem lab provide complementary information. We have performed the first exclusive differential cross-section measurements for photodisintegration of 3 He at low energy. The measurements were carried out at an incident beam energy of 15 MeV. A difference in the 1 S 0 neutron-proton scattering length determined in this reaction from the value established by two-nucleon scattering data would be potential evidence for three-nucleon interactions that are not included in current calculations. The strength of the neutron-neutron (nn) 1 S 0 interaction is directly evaluated using nn quasi-free scattering in neutron-deuteron breakup. We are performing measurements of this process at two incident neutron beam energies, 10 and 16 MeV, using substantially different detector setups. The experiment methods and preliminary results of these experiments will be presented. The 9th International workshop on Chiral Dynamics 17
Despite their potential for treating type 1 diabetes (T1D), induced pluripotent stem cells (iPSCs... more Despite their potential for treating type 1 diabetes (T1D), induced pluripotent stem cells (iPSCs) have not yet been used successfully in the clinic. In this article, advances in iPSC therapies are reviewed and compared with current methods of treating T1D. Encapsulation of iPSCs is being pursued to address such safety concerns as the possibility of immune rejection or teratoma formation, and provide for retrievability. Issues of material selection, cell differentiation, size of islet aggregates, sites of implantation, animal models, and vascularization are also being addressed. Clinical trials are being conducted to test a variety of new devices with the hope of providing additional therapies for T1D.
The Jefferson Laboratory E93-038 collaboration conducted measurements of the ratio of the electri... more The Jefferson Laboratory E93-038 collaboration conducted measurements of the ratio of the electric form factor to the magnetic form factor of the neutron, G{sup n}E/G{sup n}M, via recoil polarimetry from the quasielastic {sup 2}H({rvec e},e/{rvec n}){sup 1}H reaction at three ...
The most complete set of differential cross sections σ(θ) and vector analyzing power Ay(θ) for ne... more The most complete set of differential cross sections σ(θ) and vector analyzing power Ay(θ) for neutron scattering from 28Si and 32S over the 8 to 40 MeV energy range has been collected and evaluated. These data have been successfully described with the spherical optical model (SOM) and with phenomenological coupled-channels (CC) calculations. For the case of 28Si, various calculations were performed to determine the sensitivity of the data and calculations to the sign of the potential deformation parameters β2 and β4. Comparisons of the present analyses to the corresponding analyses of proton-scattering data have yielded interesting results concerning the magnitudes of the Coulomb corrections to the OM potentials for 28Si and 32S.
The neutron-deuteron (nd) breakup reaction serves as a fertile testing ground for theories of thr... more The neutron-deuteron (nd) breakup reaction serves as a fertile testing ground for theories of three nucleon dynamics and meson exchange descriptions of nuclear systems. The three-body kinematics of the nd breakup reaction allow observables to be studied in a variety of exit-channel configurations to test nucleon-nucleon potential models as well as three-nucleon force models. Over the last two decades there have been significant advances in modeling three-nucleon dynamics using empirical nucleon-nucleon potential models. These calculations have shown excellent agreement with most experimental data. However, there remain some exceptions where serious discrepancies arise. We have undertaken new cross-section measurements to provide further insight into one of these discrepancies, the space-star anomaly. The space-star configuration is a special case of the symmetric constant relative energy (SCRE) configuration in nd breakup. The SCRE configuration occurs when the three outgoing nucleo...
Creative Commons Attribution-Noncommercial License Two separate experimental searches for second-... more Creative Commons Attribution-Noncommercial License Two separate experimental searches for second-order weak nuclear decays to excited final states were conducted. Both experiments were carried out at the Kimballton Underground Research Facility to provide shielding from cosmic rays. The first search is for the 2νββ decay of 96Zr to excited final states of the daughter nucleus, 96Mo. As a byproduct of this experiment, the β decay of 96Zr was also investigated. Two coaxial high-purity germanium detectors were used in coincidence to detect γ rays produced by the daughter nucleus as it de-excited to the ground state. After collecting 1.92 years of data with 17.91 g of enriched 96Zr, half-life limits at the level of 1020 yr were produced. Measurements of this decay are important to test 0νββ-decay nuclear matrix element calculations, which are necessary to extract the neutrino mass from a measurement of the 0νββ decay half-life. The second experiment is a search for the resonantly-enhanc...
The Bohr hypothesis, one of the most fundamental assumptions in nuclear fission theory, states th... more The Bohr hypothesis, one of the most fundamental assumptions in nuclear fission theory, states that the decay of a compound nucleus with a given excitation energy, spin and parity is independent of its formation. Using fission product yields (FPYs) as a sensitive probe, we have performed new high precision test of the combined effects of the entrance channel, spin and parity on the fission process. Two different reactions were used in a self-consistent manner to produce a compound 240Pu nucleus with the same excitation energy: neutron induced fission of 239Pu at En = 4.6 MeV and photon-induced fission of 240Pu at Eγ = 11.2 MeV. The FPYs from these two reactions were measured using quasimonoenergetic neutron beams from the TUNL's FN tandem Van de Graaff accelerator and quasimonenergetic photon beams from the High Intensity γ-ray Source (HlγS) facility. The first results comparing the FPYs from these two reactions will be presented. Implications for validating the Bohr hypothesis ...
I am pleased to say that we have had a very active and productive year in terms of both research ... more I am pleased to say that we have had a very active and productive year in terms of both research and education here at Duke Physics. This is my first year as Chair, as many of you know, and it was a year of challenges and learning for me personally. Certainly the most interesting things I learned came from finding out what my colleagues in other subfields are doing; this broad view – from biophysics to particle physics, from optics to gamma rays, from teaching introductory physics to advising graduate students – has deepened my appreciation for our department. Six of the more significant research achievements are highlighted in this newsletter. News about undergraduate and graduate education are covered in their respective sections. Here I want to highlight some general news about the department and faculty:
A joint TUNL-LLNL-LANL collaboration was formed to measure the absolute fission product yields fr... more A joint TUNL-LLNL-LANL collaboration was formed to measure the absolute fission product yields from the 235 U, 238 U, and 239 Pu isotopes. Our goal is to study the energy evolution of fission products using monoenergetic beams. In order to extend our successful fission product-yield studies to include products with shorter half-lives, a RApid Belt-driven Irradiated Target Transfer System, named RABITTS, was constructed. This system allows us to perform cyclic activation and quantify fission products with γ-ray spectroscopy using HPGe detectors. Both a 1 meter and 10 meter transfer system have been developed, with transit times of 0.4 and 1.1 seconds, respectively. Using these systems, we have measured sub-second half-lives. Our goal is to measure fission product yields from neutron-induced fission with En = 0.5 − 14.8 MeV and photofission with Eγ = 8 − 15 MeV. A detailed characterization of the system’s performance is presented, including preliminary fission product measurements, an...
Fission product yields (FPYs) are a uniquely sensitive probe of the fission process, with well es... more Fission product yields (FPYs) are a uniquely sensitive probe of the fission process, with well established dependence on the species of nucleus undergoing fission, its excitation energy and spin. Thus FPYs are well suited for testing Bohr’s hypothesis in the context of nuclear fission, which states that the decay of a compound nucleus with a given excitation energy, spin and parity is independent of its formation. Using FPYs, we have performed a new highprecision test of the combined effects of the entrance channel, spin and parity on the fission process from two of the most commonly used particles to induce fission neutrons and photons. The 239 Pu(n,f) reaction at En = 4.6 MeV and the 240 Pu(γ,f) reaction at Eγ = 11.2 MeV were used to produce a 240 Pu∗ compound nucleus with the same excitation energy. The FPYs from these two reactions were measured using quasimonoenergetic neutron beams from the TUNL’s FN tandem Van de Graaff accelerator and quasimonenergetic photon beams from the ...
Proceedings of The 9th International workshop on Chiral Dynamics — PoS(CD2018), 2020
The main goal of few-nucleon research at the Triangle Universities Nuclear Laboratory (TUNL) is t... more The main goal of few-nucleon research at the Triangle Universities Nuclear Laboratory (TUNL) is to perform high-precision measurements that contribute to advancing ab-initio calculations and testing nucleon-interaction models. The current focus is on the three-nucleon system, which has highly developed theory and has sufficient complexity to exhibit influences of threenucleon forces.The few-nucleon measurements performed at the High Intensity Gamma-ray Source (HIγS) and in the tandem lab provide complementary information. We have performed the first exclusive differential cross-section measurements for photodisintegration of 3 He at low energy. The measurements were carried out at an incident beam energy of 15 MeV. A difference in the 1 S 0 neutron-proton scattering length determined in this reaction from the value established by two-nucleon scattering data would be potential evidence for three-nucleon interactions that are not included in current calculations. The strength of the neutron-neutron (nn) 1 S 0 interaction is directly evaluated using nn quasi-free scattering in neutron-deuteron breakup. We are performing measurements of this process at two incident neutron beam energies, 10 and 16 MeV, using substantially different detector setups. The experiment methods and preliminary results of these experiments will be presented. The 9th International workshop on Chiral Dynamics 17
Despite their potential for treating type 1 diabetes (T1D), induced pluripotent stem cells (iPSCs... more Despite their potential for treating type 1 diabetes (T1D), induced pluripotent stem cells (iPSCs) have not yet been used successfully in the clinic. In this article, advances in iPSC therapies are reviewed and compared with current methods of treating T1D. Encapsulation of iPSCs is being pursued to address such safety concerns as the possibility of immune rejection or teratoma formation, and provide for retrievability. Issues of material selection, cell differentiation, size of islet aggregates, sites of implantation, animal models, and vascularization are also being addressed. Clinical trials are being conducted to test a variety of new devices with the hope of providing additional therapies for T1D.
The Jefferson Laboratory E93-038 collaboration conducted measurements of the ratio of the electri... more The Jefferson Laboratory E93-038 collaboration conducted measurements of the ratio of the electric form factor to the magnetic form factor of the neutron, G{sup n}E/G{sup n}M, via recoil polarimetry from the quasielastic {sup 2}H({rvec e},e/{rvec n}){sup 1}H reaction at three ...
The most complete set of differential cross sections σ(θ) and vector analyzing power Ay(θ) for ne... more The most complete set of differential cross sections σ(θ) and vector analyzing power Ay(θ) for neutron scattering from 28Si and 32S over the 8 to 40 MeV energy range has been collected and evaluated. These data have been successfully described with the spherical optical model (SOM) and with phenomenological coupled-channels (CC) calculations. For the case of 28Si, various calculations were performed to determine the sensitivity of the data and calculations to the sign of the potential deformation parameters β2 and β4. Comparisons of the present analyses to the corresponding analyses of proton-scattering data have yielded interesting results concerning the magnitudes of the Coulomb corrections to the OM potentials for 28Si and 32S.
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Papers by Calvin Howell