ABSTRACT Cross-section measurements of (n,xγ) reactions on ^natCu were carried out at TUNL using ... more ABSTRACT Cross-section measurements of (n,xγ) reactions on ^natCu were carried out at TUNL using monoenergetic neutrons at six energies of En = 6, 8, 10, 12, 14, 16 MeV. These studies were performed to provide accurate cross-section data on materials abundant in experimental setups involving HPGe detectors used to search for rare events, like the neutrino-less double-beta decay of ^76Ge. Spallation and (α,n) neutrons are expected to cause the largest source of external background in the energy region of interest. At TUNL pulsed neutron beams were produced via the ^2H(d,n)^3He reaction and the deexcitation γ rays from the reaction ^natCu(n,xγ) were detected with clover HPGe detectors. Our cross-section data will be compared to theoretical calculations and to data recently obtained at LANL with a white neutron beam.
Neutron Stimulated Emission Computed Tomography (NSECT) was evaluated as a potential technique fo... more Neutron Stimulated Emission Computed Tomography (NSECT) was evaluated as a potential technique for breast cancer diagnosis. NSECT can form a 3D tomographic image with an elemental (isotopic) spectrum provided at each reconstructed voxel. The target is illuminated (in ...
Medical Imaging 2006: Physics of Medical Imaging, 2006
Certain elements (such as Fe, Cu, Zn, etc.) are vital to the body and an imbalance of such elemen... more Certain elements (such as Fe, Cu, Zn, etc.) are vital to the body and an imbalance of such elements can either be a symptom or cause of certain pathologies. Neutron Stimulated Emission Computed Tomography (NSECT) is a spectroscopic imaging technique whereby the body is illuminated via a beam of neutrons causing elemental nuclei to become excited and emit characteristic gamma
The polarization observables have been determined for the Li7(d-->,n0)Be8 and Li7(d--&... more The polarization observables have been determined for the Li7(d-->,n0)Be8 and Li7(d-->,n1)Be8 reactions at beam energies between 80 and 160 keV. A Transition Matrix Element (TME) analysis revealed unique, dominant p-wave solutions for both neutron channels. The polarization observables were compared with distorted wave Born approximation (DWBA) and coupled reaction channels (CRC) calculations. The general features of the data can be
AbstractWe measured the analyzing power and the efficiency of a new neutron polarimeter that was... more AbstractWe measured the analyzing power and the efficiency of a new neutron polarimeter that was designed to measure GnE, the neutron electric form factor. The polarimeter calibration was performed as experiment E377 at the Indiana University Cyclotron Facility (IUCF) ...
The European Physical Journal A - Hadrons and Nuclei, 2003
The ratio of the electric to the magnetic form factor of the neutron, g ≡ GEn/GMn, was measured v... more The ratio of the electric to the magnetic form factor of the neutron, g ≡ GEn/GMn, was measured via recoil polarimetry (R.G. Arnold, C.E. Carlson, F. Gross, Phys. Rev. C 23, 363 (1981)) from the quasielastic 2 H(e, e n) 1 H reaction at three values of Q 2 (viz, 0.45, 1.15, and 1.47 (GeV/c) 2) in Hall C of the Thomas Jefferson National Accelerator Facility. The data reveal that GEn continues to follow the Galster parameterization up to Q 2 = 1.15 (GeV/c) 2 and rises above the Galster parameterization at Q 2 = 1.47 (GeV/c) 2 .
Angular distributions of the analyzing power A~(0) have been measured for neutron elastic scatter... more Angular distributions of the analyzing power A~(0) have been measured for neutron elastic scattering and for neutron inelastic scattering to the first 2+i states of ' ' Fe and ' Ni at 10 MeV, and for ' Fe and "Ni at 14 and 17 MeV. The differential cross sections o. (8) for the same processes were measured at 17 MeV for ' Fe and "Ni. These measurements have been combined with other measurements of o. (0) and A~(0) and also with total cross sections to form a sizable data set for incident neutron energies up to 80 MeV. This data set has been described in the context of the coupled channels formalism to determine the energy dependences of the various terms of the deformed optical potential. Some emphasis was placed on investigating the magnitude of the deformation parameter /3"of the neutron spin-orbit potential and the possibility that it might be energy dependent.
ABSTRACT We are continuing a program to measure cross sections for ^187Re(n,2ngamma) reactions wi... more ABSTRACT We are continuing a program to measure cross sections for ^187Re(n,2ngamma) reactions with particular interest in confirming a transition that has tentatively been identified as a doorway transition feeding the ^186Re Ex=149(7) keV isomeric state. The cross sections are being measured using pulsed, nearly mono-energetic neutron beams, as well as an array of planar HPGe gamma-ray detectors. At present, the reaction cross sections for ^187Re(n,2ngamma) are poorly known, so measuring the cross sections have positive implications, for example, on reactor physics since Re is a common fission fragment. Furthermore, refining the cross section measurements may reduce uncertainties in the Re/Os cosmochronometer. Funding provided by NSF grant NSF-PHY-08-51813.
Proceedings of the 2005 Particle Accelerator Conference
The Duke FEL lab operates a unique UV/VUV storage ring FEL and an FEL driven nearly monochromatic... more The Duke FEL lab operates a unique UV/VUV storage ring FEL and an FEL driven nearly monochromatic, highly polarized, high intensity Compton gamma-ray source. The Duke storage ring light source is undergoing several phases of upgrade in order to significantly improve its light source capabilities and performance. The recent upgrade in 2004 included an upgrade of the RF system with a high-order mode damped RF cavity and a new 34 meter long straight section lattice designed to host new FEL wigglers. This upgrade was completed in August 2004, followed by the storage ring and light source commissioning. This paper provides an overview of this upgrade project and reports the commissioning experience of the Duke storage ring and light sources.
Cross-section values for Compton scattering on the proton were measured at 25 kinematic settings ... more Cross-section values for Compton scattering on the proton were measured at 25 kinematic settings over the range s = 5-11 and-t = 2-7 GeV 2 with statistical accuracy of a few percent. The scaling power for the s-dependence of the cross section at fixed center of mass angle was found to be 8.0±0.2, strongly inconsistent with the prediction of perturbative QCD. The observed cross-section values are in fair agreement with the calculations using the handbag mechanism, in which the external photons couple to a single quark.
ABSTRACT The nuclear resonance fluorescence experiments have been performed at the High Intensity... more ABSTRACT The nuclear resonance fluorescence experiments have been performed at the High Intensity Gamma Source (HIgammaS) on 138Ba nuclei using four 60% efficient HPGe detectors. Excitation energies, spin, parities, and decay branching ratios were measured for the low-energy dipole modes of excitations. Experimental results on the parity measurement below the neutron separation energy shows that all dipole states in this energy region exhibit E1 excitation. These results are consistent with theoretical prediction of the collective isoscalar nature of this low-energy mode of excitation.
We have measured the transverse asymmetry A T ′ in 3 He(e, e ′) quasi-elastic scattering in Hall ... more We have measured the transverse asymmetry A T ′ in 3 He(e, e ′) quasi-elastic scattering in Hall A at Jefferson Lab with high statistical and systematic precision for Q 2-values from 0.1 to 0.6 (GeV/c) 2. The neutron magnetic form factor G n M was extracted based on Faddeev calculations for Q 2 = 0.1 and 0.2 (GeV/c) 2 with an experimental uncertainty of less than 2%.
The analyzirg power A~(0) for scattering of neutrons from deuterons at 10 MeV for 30 to 145 (c.m.... more The analyzirg power A~(0) for scattering of neutrons from deuterons at 10 MeV for 30 to 145 (c.m.) was measured to an accuracy better than + 0.005. The results are compared to published p-d data at 10 MeV, and convincirg differences are noted for the first time. These differences provide a sensitive test both of calculations for the three-nucleon system and, more importantly, of the fundamental nucleon-nucleon interaction.
The physics program in Hall A at Jefferson Lab commenced in the summer of 1997 with a detailed in... more The physics program in Hall A at Jefferson Lab commenced in the summer of 1997 with a detailed investigation of the 16 O(e, e ′ p) reaction in quasielastic, constant (q, ω) kinematics at Q 2 ≈ 0.8 (GeV/c) 2 , q ≈ 1 GeV/c, and ω ≈ 445 MeV. Use of a self-calibrating, self-normalizing, thin-film waterfall target enabled a systematically rigorous measurement. Five-fold differential cross-section data for the removal of protons from the 1p-shell have been obtained for 0 < pmiss < 350 MeV/c. Six-fold differential cross-section data for 0 < Emiss < 120 MeV were obtained for 0 < pmiss < 340 MeV/c. These results have been used to extract the ALT asymmetry and the RL, RT , RLT , and RL+T T effective response functions over a large range of Emiss and pmiss. Detailed comparisons of the 1p-shell data with Relativistic Distorted-Wave Impulse Approximation (rdwia), Relativistic Optical-Model Eikonal Approximation (romea), and Relativistic Multiple-Scattering Glauber Approximation (rmsga) calculations indicate that two-body currents stemming from Meson-Exchange Currents (MEC) and Isobar Currents (IC) are not needed to explain the data at this Q 2. Further, dynamical relativistic effects are strongly indicated by the observed structure in ALT at pmiss ≈ 300 MeV/c. For 25 < Emiss < 50 MeV and pmiss ≈ 50 MeV/c, proton knockout from the 1s 1/2-state dominates, and romea calculations do an excellent job of explaining the data. However, as pmiss increases, the single-particle behavior of the reaction is increasingly hidden by more complicated processes, and for 280 < pmiss < 340 MeV/c, romea calculations together with two-body currents stemming from MEC and IC account for the shape and transverse nature of the data, but only about half the magnitude of the measured cross section. For 50 < Emiss < 120 MeV and 145 < pmiss < 340 MeV/c, (e, e ′ pN) calculations which include the contributions of central and tensor correlations (two-nucleon correlations) together with MEC and IC (two-nucleon currents) account for only about half of the measured cross section. The kinematic consistency of the 1p-shell normalization factors extracted from these data with respect to all available 16 O(e, e ′ p) data is also examined in detail. Finally, the Q 2-dependence of the normalization factors is discussed.
We have measured the transverse asymmetry A T ′ in the quasi-elastic 3 He(e, e ′) process with hi... more We have measured the transverse asymmetry A T ′ in the quasi-elastic 3 He(e, e ′) process with high precision at Q 2-values from 0.1 to 0.6 (GeV/c) 2. The neutron magnetic form factor G n M was extracted at Q 2-values of 0.1 and 0.2 (GeV/c) 2 using a non-relativistic Faddeev calculation which includes both final-state interactions (FSI) and meson-exchange currents (MEC). Theoretical uncertainties due to the FSI and MEC effects were constrained with a precision measurement of the spin-dependent asymmetry in the threshold region of 3 He(e, e ′). We also extracted the neutron magnetic form factor G n M at Q 2-values of 0.3 to 0.6 (GeV/c) 2 based on Plane Wave Impulse Approximation calculations.
The photo-distingration of ^9Be plays a crucial role in modeling nucleosynthesis in neutron-rich ... more The photo-distingration of ^9Be plays a crucial role in modeling nucleosynthesis in neutron-rich environments, in particular, places suitable for the r-process to occur. Cross-section and analyzing-power measurements for the ^9Be(gamma,n) reaction are being developed using the 100% polarized and nearly mono-energetic gamma-ray beam at the High-Intensity Gamma-ray Source (HIgammaS) at Duke University. In this talk we report the results of our first development run in which the analyzing power at 8 gamma-ray energies between 2.44 and 3.60 MeV was measured. This energy range covers the broad J^pi = 5/2^+ resonance at E_x=3.05 MeV in ^9Be. The experimental technique, preliminary results and our plans for future measurements will be presented.
ABSTRACT Cross-section measurements of (n,xγ) reactions on ^natCu were carried out at TUNL using ... more ABSTRACT Cross-section measurements of (n,xγ) reactions on ^natCu were carried out at TUNL using monoenergetic neutrons at six energies of En = 6, 8, 10, 12, 14, 16 MeV. These studies were performed to provide accurate cross-section data on materials abundant in experimental setups involving HPGe detectors used to search for rare events, like the neutrino-less double-beta decay of ^76Ge. Spallation and (α,n) neutrons are expected to cause the largest source of external background in the energy region of interest. At TUNL pulsed neutron beams were produced via the ^2H(d,n)^3He reaction and the deexcitation γ rays from the reaction ^natCu(n,xγ) were detected with clover HPGe detectors. Our cross-section data will be compared to theoretical calculations and to data recently obtained at LANL with a white neutron beam.
Neutron Stimulated Emission Computed Tomography (NSECT) was evaluated as a potential technique fo... more Neutron Stimulated Emission Computed Tomography (NSECT) was evaluated as a potential technique for breast cancer diagnosis. NSECT can form a 3D tomographic image with an elemental (isotopic) spectrum provided at each reconstructed voxel. The target is illuminated (in ...
Medical Imaging 2006: Physics of Medical Imaging, 2006
Certain elements (such as Fe, Cu, Zn, etc.) are vital to the body and an imbalance of such elemen... more Certain elements (such as Fe, Cu, Zn, etc.) are vital to the body and an imbalance of such elements can either be a symptom or cause of certain pathologies. Neutron Stimulated Emission Computed Tomography (NSECT) is a spectroscopic imaging technique whereby the body is illuminated via a beam of neutrons causing elemental nuclei to become excited and emit characteristic gamma
The polarization observables have been determined for the Li7(d--&gt;,n0)Be8 and Li7(d--&... more The polarization observables have been determined for the Li7(d--&gt;,n0)Be8 and Li7(d--&gt;,n1)Be8 reactions at beam energies between 80 and 160 keV. A Transition Matrix Element (TME) analysis revealed unique, dominant p-wave solutions for both neutron channels. The polarization observables were compared with distorted wave Born approximation (DWBA) and coupled reaction channels (CRC) calculations. The general features of the data can be
AbstractWe measured the analyzing power and the efficiency of a new neutron polarimeter that was... more AbstractWe measured the analyzing power and the efficiency of a new neutron polarimeter that was designed to measure GnE, the neutron electric form factor. The polarimeter calibration was performed as experiment E377 at the Indiana University Cyclotron Facility (IUCF) ...
The European Physical Journal A - Hadrons and Nuclei, 2003
The ratio of the electric to the magnetic form factor of the neutron, g ≡ GEn/GMn, was measured v... more The ratio of the electric to the magnetic form factor of the neutron, g ≡ GEn/GMn, was measured via recoil polarimetry (R.G. Arnold, C.E. Carlson, F. Gross, Phys. Rev. C 23, 363 (1981)) from the quasielastic 2 H(e, e n) 1 H reaction at three values of Q 2 (viz, 0.45, 1.15, and 1.47 (GeV/c) 2) in Hall C of the Thomas Jefferson National Accelerator Facility. The data reveal that GEn continues to follow the Galster parameterization up to Q 2 = 1.15 (GeV/c) 2 and rises above the Galster parameterization at Q 2 = 1.47 (GeV/c) 2 .
Angular distributions of the analyzing power A~(0) have been measured for neutron elastic scatter... more Angular distributions of the analyzing power A~(0) have been measured for neutron elastic scattering and for neutron inelastic scattering to the first 2+i states of ' ' Fe and ' Ni at 10 MeV, and for ' Fe and "Ni at 14 and 17 MeV. The differential cross sections o. (8) for the same processes were measured at 17 MeV for ' Fe and "Ni. These measurements have been combined with other measurements of o. (0) and A~(0) and also with total cross sections to form a sizable data set for incident neutron energies up to 80 MeV. This data set has been described in the context of the coupled channels formalism to determine the energy dependences of the various terms of the deformed optical potential. Some emphasis was placed on investigating the magnitude of the deformation parameter /3"of the neutron spin-orbit potential and the possibility that it might be energy dependent.
ABSTRACT We are continuing a program to measure cross sections for ^187Re(n,2ngamma) reactions wi... more ABSTRACT We are continuing a program to measure cross sections for ^187Re(n,2ngamma) reactions with particular interest in confirming a transition that has tentatively been identified as a doorway transition feeding the ^186Re Ex=149(7) keV isomeric state. The cross sections are being measured using pulsed, nearly mono-energetic neutron beams, as well as an array of planar HPGe gamma-ray detectors. At present, the reaction cross sections for ^187Re(n,2ngamma) are poorly known, so measuring the cross sections have positive implications, for example, on reactor physics since Re is a common fission fragment. Furthermore, refining the cross section measurements may reduce uncertainties in the Re/Os cosmochronometer. Funding provided by NSF grant NSF-PHY-08-51813.
Proceedings of the 2005 Particle Accelerator Conference
The Duke FEL lab operates a unique UV/VUV storage ring FEL and an FEL driven nearly monochromatic... more The Duke FEL lab operates a unique UV/VUV storage ring FEL and an FEL driven nearly monochromatic, highly polarized, high intensity Compton gamma-ray source. The Duke storage ring light source is undergoing several phases of upgrade in order to significantly improve its light source capabilities and performance. The recent upgrade in 2004 included an upgrade of the RF system with a high-order mode damped RF cavity and a new 34 meter long straight section lattice designed to host new FEL wigglers. This upgrade was completed in August 2004, followed by the storage ring and light source commissioning. This paper provides an overview of this upgrade project and reports the commissioning experience of the Duke storage ring and light sources.
Cross-section values for Compton scattering on the proton were measured at 25 kinematic settings ... more Cross-section values for Compton scattering on the proton were measured at 25 kinematic settings over the range s = 5-11 and-t = 2-7 GeV 2 with statistical accuracy of a few percent. The scaling power for the s-dependence of the cross section at fixed center of mass angle was found to be 8.0±0.2, strongly inconsistent with the prediction of perturbative QCD. The observed cross-section values are in fair agreement with the calculations using the handbag mechanism, in which the external photons couple to a single quark.
ABSTRACT The nuclear resonance fluorescence experiments have been performed at the High Intensity... more ABSTRACT The nuclear resonance fluorescence experiments have been performed at the High Intensity Gamma Source (HIgammaS) on 138Ba nuclei using four 60% efficient HPGe detectors. Excitation energies, spin, parities, and decay branching ratios were measured for the low-energy dipole modes of excitations. Experimental results on the parity measurement below the neutron separation energy shows that all dipole states in this energy region exhibit E1 excitation. These results are consistent with theoretical prediction of the collective isoscalar nature of this low-energy mode of excitation.
We have measured the transverse asymmetry A T ′ in 3 He(e, e ′) quasi-elastic scattering in Hall ... more We have measured the transverse asymmetry A T ′ in 3 He(e, e ′) quasi-elastic scattering in Hall A at Jefferson Lab with high statistical and systematic precision for Q 2-values from 0.1 to 0.6 (GeV/c) 2. The neutron magnetic form factor G n M was extracted based on Faddeev calculations for Q 2 = 0.1 and 0.2 (GeV/c) 2 with an experimental uncertainty of less than 2%.
The analyzirg power A~(0) for scattering of neutrons from deuterons at 10 MeV for 30 to 145 (c.m.... more The analyzirg power A~(0) for scattering of neutrons from deuterons at 10 MeV for 30 to 145 (c.m.) was measured to an accuracy better than + 0.005. The results are compared to published p-d data at 10 MeV, and convincirg differences are noted for the first time. These differences provide a sensitive test both of calculations for the three-nucleon system and, more importantly, of the fundamental nucleon-nucleon interaction.
The physics program in Hall A at Jefferson Lab commenced in the summer of 1997 with a detailed in... more The physics program in Hall A at Jefferson Lab commenced in the summer of 1997 with a detailed investigation of the 16 O(e, e ′ p) reaction in quasielastic, constant (q, ω) kinematics at Q 2 ≈ 0.8 (GeV/c) 2 , q ≈ 1 GeV/c, and ω ≈ 445 MeV. Use of a self-calibrating, self-normalizing, thin-film waterfall target enabled a systematically rigorous measurement. Five-fold differential cross-section data for the removal of protons from the 1p-shell have been obtained for 0 < pmiss < 350 MeV/c. Six-fold differential cross-section data for 0 < Emiss < 120 MeV were obtained for 0 < pmiss < 340 MeV/c. These results have been used to extract the ALT asymmetry and the RL, RT , RLT , and RL+T T effective response functions over a large range of Emiss and pmiss. Detailed comparisons of the 1p-shell data with Relativistic Distorted-Wave Impulse Approximation (rdwia), Relativistic Optical-Model Eikonal Approximation (romea), and Relativistic Multiple-Scattering Glauber Approximation (rmsga) calculations indicate that two-body currents stemming from Meson-Exchange Currents (MEC) and Isobar Currents (IC) are not needed to explain the data at this Q 2. Further, dynamical relativistic effects are strongly indicated by the observed structure in ALT at pmiss ≈ 300 MeV/c. For 25 < Emiss < 50 MeV and pmiss ≈ 50 MeV/c, proton knockout from the 1s 1/2-state dominates, and romea calculations do an excellent job of explaining the data. However, as pmiss increases, the single-particle behavior of the reaction is increasingly hidden by more complicated processes, and for 280 < pmiss < 340 MeV/c, romea calculations together with two-body currents stemming from MEC and IC account for the shape and transverse nature of the data, but only about half the magnitude of the measured cross section. For 50 < Emiss < 120 MeV and 145 < pmiss < 340 MeV/c, (e, e ′ pN) calculations which include the contributions of central and tensor correlations (two-nucleon correlations) together with MEC and IC (two-nucleon currents) account for only about half of the measured cross section. The kinematic consistency of the 1p-shell normalization factors extracted from these data with respect to all available 16 O(e, e ′ p) data is also examined in detail. Finally, the Q 2-dependence of the normalization factors is discussed.
We have measured the transverse asymmetry A T ′ in the quasi-elastic 3 He(e, e ′) process with hi... more We have measured the transverse asymmetry A T ′ in the quasi-elastic 3 He(e, e ′) process with high precision at Q 2-values from 0.1 to 0.6 (GeV/c) 2. The neutron magnetic form factor G n M was extracted at Q 2-values of 0.1 and 0.2 (GeV/c) 2 using a non-relativistic Faddeev calculation which includes both final-state interactions (FSI) and meson-exchange currents (MEC). Theoretical uncertainties due to the FSI and MEC effects were constrained with a precision measurement of the spin-dependent asymmetry in the threshold region of 3 He(e, e ′). We also extracted the neutron magnetic form factor G n M at Q 2-values of 0.3 to 0.6 (GeV/c) 2 based on Plane Wave Impulse Approximation calculations.
The photo-distingration of ^9Be plays a crucial role in modeling nucleosynthesis in neutron-rich ... more The photo-distingration of ^9Be plays a crucial role in modeling nucleosynthesis in neutron-rich environments, in particular, places suitable for the r-process to occur. Cross-section and analyzing-power measurements for the ^9Be(gamma,n) reaction are being developed using the 100% polarized and nearly mono-energetic gamma-ray beam at the High-Intensity Gamma-ray Source (HIgammaS) at Duke University. In this talk we report the results of our first development run in which the analyzing power at 8 gamma-ray energies between 2.44 and 3.60 MeV was measured. This energy range covers the broad J^pi = 5/2^+ resonance at E_x=3.05 MeV in ^9Be. The experimental technique, preliminary results and our plans for future measurements will be presented.
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Papers by C. Howell