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Cottle, P. D.

Publications and source records attributed to Cottle, P. D..

13 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Single-neutron adding on $^{34}$S

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, 34 S. The 34 S(d,p) 35 S reaction has been measured at 8 MeV/u to investigate cross sections to excited states in 35 S. 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-neutron 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.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Measurement of g 9/2 strength in the stretched 8 – state and other negative parity states via the 51 V (d,p) 52 V reaction

We performed a measurement of the 51 V (d,p) 52 V 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 49 Ca, 51 Ti, 53 Cr, and 55 Fe 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 9/2 structure that were systematically observed in the odd-odd N = 29 isotones via the (α,d) reaction. 52 V 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 51 V(d, p) 52 V reaction. Furthermore, this is the first measurement of spectroscopic strength for L = 4 states in 52 V 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 51 Ti, 53 Cr, and 55 Fe. 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.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Proton removal from Br 73 , 75 to Se 72 , 74 at intermediate energies

Herein we report new experimental data for excited states of 72,74 Se obtained from proton removal from 73,75 Br secondary beams on a proton target. The experiments were performed with the Ursinus-NSCL Liquid Hydrogen Target and the combined GRETINA+S800 setup at the Coupled Cyclotron Facility of the National Superconducting Cyclotron Laboratory at Michigan State University. Within uncertainties, the inclusive cross sections for proton removal from 73,75 Br on a proton target are identical suggesting that the same single-particle orbitals contribute to the proton-removal reaction. In addition, details of the partial cross section fragmentation are discussed. The data might suggest that l = 1, 2, 3, and 4 angular momentum transfers are important to understand the population of excited states of 72,74 Se in proton removal. Available data for excited states of 74 Ge populated through the 75 As(d, 3 He) 74 Ge proton-removal reaction in normal kinematics suggest indeed that the fp and sd shell as well as the 1g 9/2 orbital contribute. A comparison to data available for odd-A nuclei supports that the bulk of the spectroscopic strengths could be found at lower energies in the even-even Se isotopes than in, for instance, the even-even Ge isotopes. In addition, the population of high-J states seems to indicate that multi-step processes contribute to proton-removal reactions at intermediate energies in these collective nuclei.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

The CeBrA demonstrator for particle-γ coincidence experiments at the FSU Super-Enge Split-Pole Spectrograph

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 CeBr 3 scintillation detectors of the CeBr 3 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-γ 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.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2023

g 9/2 neutron strength in the N = 29 isotones and the 52 Cr(d,p)⁢ 53 Cr reaction

We performed a measurement of the 52 Cr(d,p)⁢⁢ 53 Cr 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 53 Cr in the present work and in the N = 29 isotones 49 Ca, 51 Ti, and 55 Fe via (d,p) reactions is much smaller than the sum rule for this strength. Most of 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 53 Cr. The (α, 3 He) 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.

39 ≤ A ≤ 58↗
DOE OSTI2023

Hexadecapole strength in the rare isotopes 74,76 Kr

In the Ge-Sr mass region, isotopes with neutron number N ≤ 40 are known to feature rapid shape changes with both nucleon number and angular momentum. To gain new insights into their structure, inelastic proton scattering experiments in inverse kinematics were performed on the rare isotopes 74,76 Kr. This work focuses on observables related to the J π = $4$$^{+}_{1}$ states of the Kr isotopes and, in particular, on the hexadecapole degree of freedom. By performing coupled-channels calculations, hexadecapole deformation parameters β 4 were determined for the J π = $4$$^{+}_{1}$ states of 74,76 Kr from inelastic proton scattering cross sections. Two possible coupled-channels solutions were found. A comparison to predictions from nuclear energy density functional theory, employing both non-relativistic and relativistic functionals, clearly favors the large, positive β 4 solutions. These β 4 values are unambiguously linked to the well deformed prolate configuration. Given the β 2 - β 4 trend, established in this work, it appears that β 4 values could provide a sensitive measure of the nuclear shell structure.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Investigation of octupole collectivity near the A = 72 shape-transitional point

Enhanced octupole collectivity is expected in the neutron-deficient Ge, Se and Kr isotopes with neutron number N ≈ 40 and has indeed been observed for 70,72 Ge. Shape coexistence and configuration mixing are, however, a notorious challenge for theoretical models trying to reliably predict octupole collectivity in this mass region, which is known to feature rapid shape changes with changing nucleon number and spin of the system. To further investigate the microscopic configurations causing the prolate-oblate-triaxial shape transition at A ≈ 72 and their influence on octupole collectivity, the rare isotopes 72 Se and 74,76 Kr were studied via inelastic proton scattering in inverse kinematics. While significantly enhanced octupole strength of ≈32 Weisskopf units (W.u.) was observed for 72 Se, only strengths of ≈15 W.u. were observed for 74,76 Kr. In combination with existing data, the new data clearly question a simple origin of enhanced octupole strengths around N = 40. Furthermore, the present work establishes two regions of distinct octupole strengths with a sudden strength increase around the A = 72 shape transitional point.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2019

Inverse-kinematics proton scattering from S 42 , 44 , P 41 , 43 , and the collapse of the N = 28 major shell closure

Excited states of the neutron-rich isotopes S 42 , 44 and P 41 , 43 have been investigated via inverse-kinematics proton scattering from a liquid hydrogen target, using the GRETINA γ -ray tracking array to extract inelastic-scattering cross sections. Deformation lengths of the 2 1 + excitations in S 42 , 44 have been observed and, when combined with deformation lengths determined with electromagnetic probes, yield the ratio of neutron-to-proton matrix elements M n / M p for the 2 1 + excitations in these nuclei. The present results for P 41 , 43 ( p , p ' ) are used to compare two shell-model interactions, SDPF-U and SDPF-MU. As in a recent study of Si 42 , the present results on P 41 , 43 favor the SDPF-MU interaction.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2019

Spectroscopy and lifetime measurements near the proton drip line: P 26 , 27 , 28

We report on the observation of excited states in the neutron-deficient phosphorus isotopes 26,27,28 P via in-beam gamma-ray spectroscopy with both high-efficiency and high-resolution detector arrays. In 26 P, a previously-unobserved level has been identified at 244(3) keV, two new measurements of the astrophysically-important 3/2 + resonance in 27 P have been performed, gamma decays have been assigned to the proton-unbound levels at 2216 keV and 2483 keV in 28 P, and the gamma-ray lineshape method has been used to make the first determination of the lifetimes of the two lowest-lying excited states in 28P. The expected Thomas-Ehrman shifts were calculated and applied to levels in the mirror nuclei. The resulting level energies from this procedure were then compared with the energies of known states in 26,27,28 P.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

Spectroscopy of Ti 54 and the systematic behavior of low-energy octupole states in Ca and Ti isotopes

We report excited states of the N = 32 nucleus 54 Ti have been studied, via both inverse-kinematics proton scattering and one-neutron knockout from 55 Ti by a liquid hydrogen target, using the GRETINA γ-ray tracking array. Inelastic proton-scattering cross sections and deformation lengths have been determined. A low-lying octupole state has been tentatively identified in 54 Ti for the first time. A comparison of (p,p′) results on low-energy octupole states in the neutron-rich Ca and Ti isotopes with the results of random phase approximation calculations demonstrates that the observed systematic behavior of these states is unexpected.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Isomeric Character of the Lowest Observed 4 + State in S 44

Previous experiments observed a 4 + state in the N=28 nucleus S 44 and suggested that this state may exhibit a hindered E2-decay rate, inconsistent with being a member of the collective ground state band. We populate this state via two-proton knockout from a beam of exotic Ar 46 projectiles and measure its lifetime using the recoil distance method with the GRETINA γ-ray spectrometer. The result, 76(14) stat (20) syst ps, implies a hindered transition of B(E2;4 + →2$+\atop{1}$)=0.61(19) single-particle or Weisskopf units strength and supports the interpretation of the 4 + state as a K=4 isomer, the first example of a high-K isomer in a nucleus of such low mass.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗