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Smith, K.

Publications and source records attributed to Smith, K..

At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Experimental Demonstration of Hadron Beam Cooling Using Radio-Frequency Accelerated Electron Bunches

Cooling of beams of gold ions using electron bunches accelerated with radio-frequency systems was recently experimentally demonstrated in the Relativistic Heavy Ion Collider at Brookhaven National Laboratory. Such an approach is new and opens the possibility of using this technique at higher energies than possible with electrostatic acceleration of electron beams. The challenges of this approach include generation of electron beams suitable for cooling, delivery of electron bunches of the required quality to the cooling sections without degradation of beam angular divergence and energy spread, achieving the required small angles between electron and ion trajectories in the cooling sections, precise velocity matching between the two beams, high-current operation of the electron accelerator, as well as several physics effects related to bunched-beam cooling. Here we report on the first demonstration of cooling hadron beams using this new approach.

43 PARTICLE ACCELERATORS↗
DOE OSTI2020

γ -ray spectroscopy of astrophysically important states in Ca 39

Background: Nova explosions synthesize elements up to A ≃ 40 , and discrepancies exist between calculated and observed abundances of Ar and Ca created in the explosion. The K 38 ( p , γ ) Ca 39 reaction rate has been illustrated to be influential on these isotopic abundances at the endpoint of nova nucleosynthesis. The energies of the three most important resonances, corresponding to J π = 5 / 2 + excited states in the Ca 39 nucleus above the proton separation threshold, are uncertain and one has been measured with conflicting values [ E r = 679 ( 2 ) versus E r = 701 ( 2 ) keV] in previous experiments. Purpose: Reducing the uncertainties on the resonance energies would allow for a better understanding of the reaction rate. To improve these uncertainties, we searched for γ rays from the depopulation of the corresponding excited states in Ca 39 . Methods: We report a new measurement of these resonance energies via the observation of previously unobserved γ -ray transitions. These transitions were observed by studying the Ca 40 ( 3 He , α γ ) Ca 39 reaction with Gammasphere ORRUBA Dual Detectors for Experimental Structure Studies (GODDESS). The updated resonance energies were then used to calculate the K 38 ( p , γ ) Ca 39 reaction rate and assess its uncertainties. Results: In total, 23 new transitions were found, including three γ -ray transitions corresponding to the three J π = 5 / 2 + states of astrophysical interest at energies of 6156.2(16), 6268.8(22), and 6470.8(19) keV. These correspond to resonance energies in the K 38 ( p , γ ) Ca 39 reaction of 386(2), 498(2), and 701(2) keV. Conclusions: Updated K 38 ( p , γ ) Ca 39 reaction rate calculations reflect a reduced upper limit at nova temperatures. However, the lower-than-previously-measured energy of the 498-keV resonance and uncertainty in its resonance strength increases the upper limit of the rate close to previous estimates at 0.4 GK.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2019

Preparation for the Beam Energy Scan II at RHIC in 2020

RHIC will provide Au-Au collisions at beam energies of 5.75, 4.59 GeV/nucleon for physics program in 2020, and at beam energy of 3.85 GeV/nucleon for physics program in 2021 as part of the BeamEnergy Scan II (BES-II). The oper- ational experience gained in the first year (2019) of BES-II operation will be applied toward operations in the coming years. This article will present some technical details and the outlook of the BES-II operations in the coming years.

43 PARTICLE ACCELERATORS↗
DOE OSTI2019

M4SF-19LL010302042: Pu Incorporation into Reduced Iron Oxide Phases

The research is focused on actinide and radionuclide sequestration in steel corrosion products. The effort described herein was focused on identifying synthesis methods for reduced Fe-oxide phases and performing Pu sorption and coprecipitation experiments to determine the fractionation of Pu into and onto these phases. Specifically, we are: Quantifying the rate of Pu incorporation to magnetite and green rust, and Characterizing the nature and morphology of sorbed and coprecipitated Pu on these phases.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2019

New γ -ray transitions observed in Ne 19 with implications for the O 15 ( α , γ ) Ne 19 reaction rate

The 15 O(α,γ) 19 Ne reaction is responsible for breakout from the hot CNO cycle in type I x-ray bursts. Understanding the properties of resonances between E x =4 and 5 MeV in 19 Ne is crucial in the calculation of this reaction rate. The spins and parities of these states are well known, with the exception of the 4.14- and 4.20-MeV states, which have adopted spin-parities of 9/2 - and 7/2 - , respectively. γ-ray transitions from these states were studied using triton-γ – γ coincidences from the 19 F( 3 He,tγ) 19 Ne reaction measured with the GODDESS (Gammasphere ORRUBA Dual Detectors for Experimental Structure Studies) at Argonne National Laboratory. The observed transitions from the 4.14- and 4.20-MeV states provide strong evidence that the J π values are actually 7/2 - and 9/2 - , respectively. These assignments are consistent with the values in the 19 F mirror nucleus and in contrast to previously accepted assignments.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2019

Towards Neutron Capture on Exotic Nuclei: Demonstrating ( d , p γ ) as a Surrogate Reaction for ( n , γ )

The neutron-capture reaction plays a critical role in the synthesis of the elements in stars and is important for societal applications including nuclear power generation and stockpile-stewardship science. However, it is difficult—if not impossible—to directly measure neutron capture cross sections for the exotic, short-lived nuclei that participate in these processes. We demonstrate a new technique which can be used to indirectly determine neutron-capture cross sections for exotic systems. This technique makes use of the $(d,p)$ transfer reaction, which has long been used as a tool to study the structure of nuclei. Recent advances in reaction theory, together with data collected using this reaction, enable the determination of neutron-capture cross sections for short-lived nuclei. A benchmark study of the $^{95}\mathrm{Mo}(d,p)$ reaction is presented, which illustrates the approach and provides guidance for future applications of the method with short-lived isotopes produced at rare isotope accelerators.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2019

Key Ne 19 States Identified Affecting γ -Ray Emission from F 18 in Novae

Detection of nuclear-decay γ rays provides a sensitive thermometer of nova nucleosynthesis. The most intense γ-ray flux is thought to be annihilation radiation from the β + decay of 18 F, which is destroyed prior to decay by the 18 F(p,α) 15 O reaction. Estimates of 18 F production had been uncertain, however, because key near-threshold levels in the compound nucleus, 19 Ne, had yet to be identified. We report the first measurement of the 19 F( 3 He, tγ ) 19 Ne reaction, in which the placement of two long-sought 3/2 + levels is suggested via triton-γ–γ coincidences. Furthermore, the precise determination of their resonance energies reduces the upper limit of the rate by a factor of 1.5–17 at nova temperatures and reduces the average uncertainty on the nova detection probability by a factor of 2.1.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2018

Status of the JENSA gas-jet target for experiments with rare isotope beams

The JENSA gas-jet target was designed for experiments with radioactive beams provided by the rare isotope re-accelerator ReA3 at the National Superconducting Cyclotron Laboratory. The gas jet will be the main target for the Separator for Capture Reactions SECAR at the Facility for Rare Isotope Beams on the campus of Michigan State University, USA. We describe the advantages of a gas-jet target, detail the current recirculating gas system, and report recent measurements of helium jet thicknesses of up to about 10 19 atoms/cm 2 . A comparison with other supersonic gas-jet targets is presented.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2017

Synthesis, Vibrational Spectra, and DFT Simulations of 3-bromo-2-methyl-5-(4-nitrophenyl)thiophene

A new thiophene derivative, 3-bromo-2-methyl-5-(4-nitrophenyl)thiophene (2), was synthesized through the Suzuki coupling reaction of 4-bromo-5-methylthiophen-2-ylboronic acid (1) and 4-iodonitrobenzene, and its structure was confirmed by nuclear magnetic resonance (NMR), low and high resolution mass spectrometry (HRMS), Fourier transform infrared spectroscopy (FT-IR), and X-ray investigations of the crystal structure. The FT-IR spectra (4000–400 cm{sup –1}), Raman spectra (4000–100 cm{sup –1}), and theoretical vibrational frequencies of this new substance were investigated. Its theoretically established geometric parameters and calculated vibrational frequencies are in good agreement with the reported experimental data. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energies and other related parameters of the compound were calculated. The ionization potentials given by the B3LYP and HF (Hartree–Fock) methods for this new compound are –0.30456 and –0.30501 eV, respectively.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Direct Reaction Measurements Using GODDESS

GODDESS is a coupling of the charged-particle detection system ORRUBA to the gamma-ray detector array Gammasphere. This coupling has been developed in order to facilitate the high-resolution measurement of direct reactions in normal and inverse kinematics with stable and radioactive beams. GODDESS has been commissioned using a beam of 134 Xe at 10 MeV/A, in a campaign of stable beam measurements. The measurement demonstrates the capabilities of GODDESS under radioactive beam conditions, and provides the first data on the single-neutron states in 135 Xe, including previously unobserved states based on the orbitals above the N=82 shell closure.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2017

Supernovae 2016bdu and 2005gl, and their link with SN 2009ip-like transients: another piece of the puzzle

Supernova (SN) 2016bdu is an unusual transient resembling SN 2009ip. SN 2009ip-like events are characterized by a long-lasting phase of erratic variability that ends with two luminous outbursts a few weeks apart. The second outburst is significantly more luminous (about 3 mag) than the first. In the case of SN 2016bdu, the first outburst (Event A) reached an absolute magnitude Mr ≈ -15.3 mag, while the second one (Event B) occurred over one month later and reached M r ≈ -18 mag. By inspecting archival data, a faint source at the position of SN 2016bdu is several times in the past few years. We interpret these detections as signatures of a phase of erratic variability, similar to that experienced by SN 2009ip between 2008 and mid-2012, and resembling the currently observed variability of the luminous blue variable SN 2000ch in NGC 3432. Spectroscopic monitoring of SN 2016bdu during the second peak initially shows features typical of an SN IIn. One month after the Event B maximum, the spectra develop broad Balmer lines with P Cygni profiles and broad metal features. At these late phases, the spectra resemble those of a typical Type II SN. All members of this SN 2009ip-like group are remarkably similar to the Type IIn SN 2005gl. For this object, the claim of a terminal SN explosion is supported by the disappearance of the progenitor star. While the similarity with SN 2005gl supports a genuine SN explosion scenario for SN 2009ip-like events, the unequivocal detection of nucleosynthesized elements in their nebular spectra is still missing.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Design of SECAR a recoil mass separator for astrophysical capture reactions with radioactive beams

A recoil mass separator SECAR has been designed for the purpose of studying low-energy (p,γ) and (α,γ) reactions in inverse kinematics with radioactive beams for masses up to about A = 65. Their reaction rates are of importance for our understanding of the energy production and nucleosynthesis during explosive hydrogen and helium burning. The radiative capture reactions take place in a windowless hydrogen or He gas target at the entrance of the separator, which consists of four Sections . The first Section selects the charge state of the recoils. The second and third Sections contain Wien Filters providing high mass resolving power to separate efficiently the intense beam from the few reaction products. In the following fourth Section , the reaction products are guided into a detector system capable of position, angle and time-of-flight measurements. In order to accept the complete kinematic cone of recoil particles including multiple scattering in the target in the center of mass energy range of 0.2 MeV to 3.0 MeV, the system must have a large polar angle acceptance of ± 25 mrad. This requires a careful minimization of higher order aberrations. Furthermore, the present system will be installed at the NSCL ReA3 accelerator and will be used with the much higher beam intensities of the FRIB facility when it becomes available.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗