13 Search Results

Excited states in ⁵³Cr were studied via the ⁵²Cr ⁢(𝑑, 𝑝⁢𝛾) reaction up to the neutron-separation threshold. Proton-𝛾 angular correlations and 𝛾 decay branching ratios were measured in particle-𝛾 coincidences between the Super-Enge Split-Pole Spectrograph (SE-SPS) and CeBr₃ Array (CeBrA) demonstrator of the John D. Fox Accelerator Laboratory at Florida State University. Previous spin-parity assignments from a (𝑑,𝑝) singles experiment at the SE-SPS are supported and 𝛾-ray transitions in ⁵³Cr are reported. We firmly assign higher-lying excited states to ⁵³Cr because overlapping excited states and contaminants could be identified better due to the complementary 𝛾-decay information. We also correct somemore » of the previously reported excitation energies and present a reanalysis of previously measured ⁵²Cr (𝑑, 𝑝)⁢ ⁵³Cr angular distributions guided by the complementary 𝛾-ray information. Based on this reanalysis, the fragmentation of the neutron 2⁢𝑝_3/2, 2⁢𝑝_1/2, 1⁢𝑓_5/2, 1⁢𝑔_9/2, and 2⁢𝑑_5/2 single-particle strengths is reassessed for ⁵³Cr. Here, a comparison to the corresponding strengths in ⁵⁵Fe is presented.« less

Here, we have measured the 0$$^+_{𝑔⁡𝑠}$$ → 2$$^+_1$$ transition in the neutron-rich 𝑁 = 28 isotope ⁴²Si using the probes of intermediate-energy Coulomb excitation and inelastic proton scattering in inverse kinematics at the Facility for Rare Isotope Beams with beam particle rates of ≈ 5 particles/s. The results of these two measurements allowed us to determine 𝑀_𝑛/𝑀_𝑝, the ratio of the neutron and proton transition matrix elements for the 0$$^+_{𝑔⁡𝑠}$$ → 2$$^+_1$$ transition. In addition, we have measured the 0$$^+_{𝑔⁡𝑠}$$ → 2$$^+_1$$ transition in the isotone ⁴⁴S using inverse kinematics inelastic proton scattering. By comparing the ⁴⁴S proton-scattering result withmore » a recent intermediate-energy Coulomb excitation result on the same transition, we were able to determine 𝑀_𝑛/𝑀_𝑝 for the 0$$^+_{𝑔⁡𝑠}$$ → 2$$^+_1$$ transition in this nucleus as well. This work strengthens the evidence that ⁴²Si has a stable quadrupole deformation in its ground state and that ⁴⁴S does not. Both conclusions are further supported by shell-model calculations carried out with the FSU interaction.« less

For this work, single-neutron adding data was collected in order to determine the distribution of the single-neutron strength of the 0ƒ_7/2 , 1p_3/2 , 1p_1/2 and 0ƒ_5/2 orbitals outside of Z = 16, N = 18, ³⁴S. The ³⁴S(d,p) ³⁵S reaction has been measured at 8 MeV/u to investigate cross sections to excited states in ³⁵S. Outgoing proton yields and momenta were analyzed by the Super-Enge Split-Pole Spectrograph in conjunction with the CeBrA demonstrator located at the John D. Fox Laboratory at Florida State University. Angular distributions were compared with Distorted Wave Born Approximation calculations in order to extract single-neutronmore » spectroscopic overlaps. Spectroscopic overlaps and strengths were determined for states in S up through 6 MeV in excitation energy. Each orbital was observed to have fragmented strength where a single level carried the majority. The single-neutron centroids of the 0ƒ_7/2, 1p_3/2, 1p_1/2 and 0ƒ_5/2 orbitals were determined to be 2360$$^{+90}_{-40}$$ keV, 3280$$^{+80}_{-50}$$ keV, 4780$$^{+60}_{-40}$$ keV, and ≳7500 keV, respectively. A previous discrepancy in the literature with respect to the distribution of the neutron 1p_1/2 strength was resolved. The integration of the normalized spectroscopic strengths, up to 5.1 MeV in excitation energy, revealed fully-vacant occupancies for the 0ƒ_7/2, 1p_3/2, and 1p_1/2 orbitals, as expected. The spacing in the single-neutron energies highlighted a reduction in the traditional N = 28 shell-gap, relative to both the 1p spin-orbit energy difference (N = 32) and the lower limit on the N = 34 shell spacing.« less

Single-step Coulomb excitation of ^46,48,49,50Ti is presented. A complete set of E2 matrix elements for the quintuplet of states in ⁴⁹Ti, centred on the core excitation, was measured for the first time. A total of nine E2 matrix elements are reported, four of which were previously unknown. $$^{49}_{22}$$Ti₂₇ shows a 20% quenching in electric quadrupole transition strength as compared to its semi-magic $$^{50}_{22}$$Ti₂₈ neighbour. This 20% quenching, while empirically unprecedented, can be explained with a remarkably simple two-state mixing model, which is also consistent with other ground-state properties such as the magnetic dipole moment and electric quadrupole moment. A connectionmore » to nucleon transfer data and the quenching of single-particle strength is also demonstrated. The simplicity of the ⁴⁹Ti-⁵⁰Ti pair (i.e., approximate single-j 0_7/2 valence space and isolation of yrast states from non-yrast states) provides a unique opportunity to disentangle otherwise competing effects in the ground-state properties of atomic nuclei, the emergence of collectivity, and the role of proton-neutron interactions.« less

We performed a measurement of the ⁵¹V (d,p) ⁵²V reaction at 16 MeV using the Florida State University Super-Enge Split-Pole Spectrograph (SE-SPS) to search for single-neutron transfer strength for the g_9/2 intruder orbit. Measurements of νg_9/2 strength with (d, p) reactions in the N = 29 isotones ⁴⁹Ca, ⁵¹Ti, ⁵³Cr, and ⁵⁵Fe have concluded that much of the expected νg_9/2 strength is “missing”; that is, the summed strength is much smaller than the sum rule. In odd-odd N = 29 isotones, we expect a significant amount of νg_9/2 strength to be located in the “stretched” 8^– states with π $$f$$$^{n}_{7/2}$$νg_9/2more » structure that were systematically observed in the odd-odd N = 29 isotones via the (α,d) reaction. ⁵²V is the only one of these odd-odd isotones in which a stable target is available for single-neutron transfer reactions. We report on a determination of νg_9/2 strength for the stretched 8^– state and ten other negative parity states populated via L = 4 transfer in the ⁵¹V(d, p)⁵²V reaction. Furthermore, this is the first measurement of spectroscopic strength for L = 4 states in ⁵²V via (d, p). In total, the L = 4 strength observed here sums to only 28.9(11)% of the sum rule for g_9/2 neutron strength, a result that is consistent with the summed strengths observed in recent (d, p) measurements of the even-Z N = 29 isotones ⁵¹Ti, ⁵³Cr, and ⁵⁵Fe. The (α,3 He) reaction and the use of particle-γ coincidences would provide more sensitivity to search for the missing g_9/2 strength.« less

We performed a measurement of the ⁵²Cr(d,p)⁢⁢ ⁵³Cr reaction at 16 MeV using the Florida State University Super-Enge Split-Pole Spectrograph (SE-SPS) and observed 26 states. While all of the states observed here had been seen in previous (d,p) experiments, we changed five L assignments from those reported previously and determined L values for nine states that had not had such assignments made previously. The g_9/2 neutron strength observed in ⁵³Cr in the present work and in the N = 29 isotones ⁴⁹Ca, ⁵¹Ti, and ⁵⁵Fe via (d,p) reactions is much smaller than the sum rule for this strength. Most ofmore » the observed L = 4 strength in these nuclei is located in states near 4 MeV excitation energy. The remaining g_9/2 strength may be located in the continuum or may be fragmented among many bound states. A covariant density-functional theory calculation provides support for the hypothesis that the g_9/2 neutron orbit is unbound in ⁵³Cr. The (α, ³He) reaction may provide a more sensitive probe for the missing g_9/2 neutron strength. Additionally, particle-γ coincidence experiments may help resolve some remaining questions in this nucleus.« less

We report on a highly selective experimental setup for particle-γ coincidence experiments at the Super-Enge Split-Pole Spectrograph (SE-SPS) of the John D. Fox Superconducting Linear Accelerator Laboratory at Florida State University (FSU) using fast CeBr scintillators for γ-ray detection. Specifically, we report on the results of characterization tests for the first five CeBr₃ scintillation detectors of the CeBr₃ Array (CeBrA) with respect to energy resolution and timing characteristics. We also present results from the first particle-γ coincidence experiments successfully performed with the CeBrA demonstrator and the FSU SE-SPS. We show that with the new setup, γ-decay branching ratios and particle-γmore » angular correlations can be measured very selectively using narrow excitation energy gates, which are possible thanks to the excellent particle energy resolution of the SE-SPS. In addition, we highlight that nuclear level lifetimes in the nanoseconds regime can be determined by measuring the time difference between particle detection with the SE-SPS focal-plane scintillator and γ-ray detection with the fast CeBrA detectors. As a result, selective excitation energy gates with the SE-SPS exclude any feeding contributions to these lifetimes.« less

We model the ultraviolet spectra of the Seyfert 1 galaxy NGC 5548 obtained with the Hubble Space Telescope during the 6 month reverberation mapping campaign in 2014. Our model of the emission from NGC 5548 corrects for overlying absorption and deblends the individual emission lines. Using the modeled spectra, we measure the response to continuum variations for the deblended and absorption-corrected individual broad emission lines, the velocity-dependent profiles of Ly$$α$$ and C iv, and the narrow and broad intrinsic absorption features. We find that the time lags for the corrected emission lines are comparable to those for the original data.more » The velocity-binned lag profiles of Ly$$α$$ and C iv have a double-peaked structure indicative of a truncated Keplerian disk. The narrow absorption lines show a delayed response to continuum variations corresponding to recombination in gas with a density of ~10⁵ cm^-3. The high-ionization narrow absorption lines decorrelate from continuum variations during the same period as the broad emission lines. Analyzing the response of these absorption lines during this period shows that the ionizing flux is diminished in strength relative to the far-ultraviolet continuum. The broad absorption lines associated with the X-ray obscurer decrease in strength during this same time interval. The appearance of X-ray obscuration in ~2012 corresponds with an increase in the luminosity of NGC 5548 following an extended low state. We suggest that the obscurer is a disk wind triggered by the brightening of NGC 5548 following the decrease in size of the broad-line region during the preceding low-luminosity state.« less

An in-situ optical pump/x-ray probe technique has been used to study the size dependent lattice parameter of Pt nanoparticles subjected to picosecond duration optical laser pulses. The as-prepared Pt nanoparticles exhibited a contracted lattice parameter consistent with the response of an isolated elastic sphere to a compressive surface stress. During photo-thermally induced sintering and grain growth, however, the Pt lattice parameter did not evolve with the inverse particle size dependence predicted by simple surface stress models. Lastly, the observed behavior could be attributed to the combined effects of a compressive surface/interface stress and a tensile stress arising from intergranular material.

An in situ optical pump and x-ray probe technique has been utilized to study photoinitiated solid-state diffusion in a Ni-Pt multilayer system. Hard x-ray diffraction has been used to follow the systematic growth of the NiPt alloy as a function of laser intensity and total energy deposited. It is observed that new phase growth can be driven in as little as one laser pulse, and that repeated photoexcitation can completely convert the entire multilayer structure into a single metallic alloy. In conclusion, the data suggest that lattice strain relaxation takes place prior to atomic diffusion and the formation of amore » NiPt alloy.« less