arXiv subjects

J. Winkelbauer

Publications and source records attributed to J. Winkelbauer.

14 recordsLinked to original sources

arXiv2026

Development of a Modular Current-Mode NaI(Tl) Detector Array for Parity Odd (n,{\gamma}) Cross Section Measurements

The Neutron Optics Parity and Time-Reversal Violation Experiment (NOPTREX) Collaboration has developed a modular array of 24 NaI(Tl) detectors to measure parity and time-reversal symmetry violation in neutron-nucleus interactions. These detectors feature custom electronics that allow for operation in pulse or current mode. This paper describes the design, construction, characterization, and testing of the detectors in this array. We demonstrate the ability of the array to detect parity-odd asymmetries in neutron resonances by observing the known 0.7 eV parity-violating resonance in 139La in measurements at LANSCE.

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arXiv2021

Properties of correlated fission fragments from neutron induced fission of Np-237 at incident neutron energies between 200 keV and 100 MeV

Neutron-induced fission of $^{237}$Np has been measured over a wide range of incident neutron energies using a twin Frisch-gridded ionization chamber (TFGIC) and a thin-backed $^{237}$Np target. These measurements were performed at the Los Alamos Neutron Science Center - Weapons Neutron Research (LANSCE - WNR) facility, which provides a collimated beam of neutrons with energies ranging from 100s of keV to 100s of MeV. The data were analyzed using the double-energy ($2E$) method, with mass-dependent corrections for prompt-fission neutrons and pulse height defect. Pre- and post-neutron evaporation average total kinetic energy ($\langle TKE\rangle$) values are reported for 54 incident neutron energies in the energy range $0.20 \le E_n \le 100.0$ MeV and compared to existing data and evaluations. Pre- and post-neutron evaporation mass yields were extracted with a full width at half maximum (FWHM) resolution of 4u and compared to existing data and evaluations. The present $\langle TKE\rangle$ and mass yield data agree with previous results and also with statistical models of $^{237}$Np$(n,f)$ at incident neutron energies between $E_n = 0.2 - 20.0$ MeV. A flattening of the $\langle TKE\rangle$ data is observed (relative to the prediction of the GEF model) above $E_n = 20.0$ MeV. However, the interpretation of this discrepancy is unclear as the analysis method's neglect of incomplete momentum transfer at high energies, as well as pre-equilibrium pre-fission phenomena likely have a significant impact on the measurement at such high incident neutron energies.

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arXiv2019

Constraining the symmetry energy with heavy-ion collisions and Bayesian analyses

Efficiency corrected single ratios of neutron and proton spectra in central $^{112}$Sn+$^{112}$Sn and $^{124}$Sn+$^{124}$Sn collisions at 120 MeV/u are combined with double ratios to provide constraints on the density and momentum dependencies of the isovector mean-field potential. Bayesian analyses of these data reveal that the isoscalar and isovector nucleon effective masses, $m_s^* - m_v^*$ are strongly correlated. The linear correlation observed in $m_s^* - m_v^*$ yields a nearly independent constraint on the effective mass splitting $Δm_{np}^*= (m_n^*-m_p^*)/m_N = -0.05_{-0.09}^{+0.09}δ$. The correlated constraint on the standard symmetry energy, $S_0$ and the slope, $L$ at saturation density yields the values of symmetry energy $S(ρ_s)=16.8_{-1.2}^{+1.2}$ MeV at a sensitive density of $ρ_s/ρ_0 = 0.43_{-0.05}^{+0.05}$.

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arXiv2018

Invariant-mass spectroscopy of $^{18}$Ne, $^{16}$O, and $^{10}$C excited states formed in neutron transfer reactions

Neutron transfer reactions with fast secondary beams of $^{17}$Ne, $^{15}$O, and $^9$C have been studied with the HiRA and CAESAR arrays. Excited states of $^{18}$Ne, $^{16}$O, and $^{10}$C in the continuum have been identified using invariant-mass spectroscopy. The best experimental resolution of these states is achieved by selecting events where the decay fragments are emitted transverse to the beam direction. We have confirmed a number of spin assignments made in previous works for the negative-parity states of $^{18}$Ne. In addition we have found new higher-lying excited states in $^{16}$O and $^{18}$Ne, some of which fission into two ground-state $^8$Be fragments. Finally for $^{10}$C, a new excited state was observed. These transfer reactions were found to leave the remnant of the $^9$Be target nuclei at very high excitation energies and maybe associated with the pickup of a deeply-bound $^9$Be neutron.

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arXiv2018

Probing the single-particle character of rotational states in $^{19}$F using a short-lived isomeric beam

A beam containing a substantial component of both the $J^π=5^+$, $T_{1/2}=162$ ns isomeric state of $^{18}$F and its $1^+$, 109.77-min ground state has been utilized to study members of the ground-state rotational band in $^{19}$F through the neutron transfer reaction $(d$,$p)$ in inverse kinematics. The resulting spectroscopic strengths confirm the single-particle nature of the 13/2$^+$ band-terminating state. The agreement between shell-model calculations, using an interaction constructed within the $sd$ shell, and our experimental results reinforces the idea of a single-particle/collective duality in the descriptions of the structure of atomic nuclei.

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arXiv2016

Results of the ASY-EOS experiment at GSI: The symmetry energy at suprasaturation density

Directed and elliptic flows of neutrons and light charged particles were measured for the reaction 197Au+197Au at 400 MeV/nucleon incident energy within the ASY-EOS experimental campaign at the GSI laboratory. The detection system consisted of the Large Area Neutron Detector LAND, combined with parts of the CHIMERA multidetector, of the ALADIN Time-of-flight Wall, and of the Washington-University Microball detector. The latter three arrays were used for the event characterization and reaction-plane reconstruction. In addition, an array of triple telescopes, KRATTA, was used for complementary measurements of the isotopic composition and flows of light charged particles. From the comparison of the elliptic flow ratio of neutrons with respect to charged particles with UrQMD predictions, a value γ= 0.72 \pm 0.19 is obtained for the power-law coefficient describing the density dependence of the potential part in the parametrization of the symmetry energy. It represents a new and more stringent constraint for the regime of supra-saturation density and confirms, with a considerably smaller uncertainty, the moderately soft to linear density dependence deduced from the earlier FOPI-LAND data. The densities probed are shown to reach beyond twice saturation.

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arXiv2014

Elastic breakup cross sections of well-bound nucleons

The 9Be(28Mg,27Na) one-proton removal reaction with a large proton separation energy of Sp(28Mg)=16.79 MeV is studied at intermediate beam energy. Coincidences of the bound 27Na residues with protons and other light charged particles are measured. These data are analyzed to determine the percentage contributions to the proton removal cross section from the elastic and inelastic nucleon removal mechanisms. These deduced contributions are compared with the eikonal reaction model predictions and with the previously measured data for reactions involving the re- moval of more weakly-bound protons from lighter nuclei. The role of transitions of the proton between different bound single-particle configurations upon the elastic breakup cross section is also quantified in this well-bound case. The measured and calculated elastic breakup fractions are found to be in good agreement.

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arXiv2014

Effective Nucleon Masses from Heavy Ion Collisions

We probe the momentum dependence of the isovector mean-field potential by comparing the energy spectra of neutrons and protons emitted in $^{112}$Sn+$^{112}$Sn and $^{124}$Sn+$^{124}$Sn collisions at incident energies of E/A=50 and 120 MeV. We achieve experimental precision that discriminates between different momentum dependencies for the symmetry mean-field potential. Comparisons of the experimental results to Improved Quantum Molecular Dynamics model calculations with Skyrme Interactions indicate small differences between the neutron and proton effective masses.

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arXiv2014

Scaling properties of light-cluster production

We show that ratios of light-particle energy spectra display scaling properties that can be accu- rately described by effective local chemical potentials. This demonstrates the equivalence of t/3He and n/p spectral ratios and provides an essential test of theoretical predictions of isotopically resolved light-particle spectra. In addition, this approach allows direct comparisons of many theoretical n/p spectral ratios to experiments where charged-particle spectra but not neutron spectra are accurately measured. Such experiments may provide much more quantitative constraints on the density and momentum dependence of the symmetry energy.

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arXiv2012

Democratic decay of 6Be exposed by correlations

The interaction of an E/A=70 - MeV 7Be beam with a Be target was used to populate levels in 6Be following neutron knockout reactions. The three-body decay of the ground and first excited states into the alpha+p+p exit channel were detected in the High Resolution Array. Precise three-body correlations extracted from the experimental data allowed us to obtain insight into the mechanism of the three-body democratic decay. The correlation data are in a good agreement with a three-cluster-model calculation and thus validate this theoretical approach over a broad energy range.

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arXiv2012

Correlations in intermediate-energy two-proton removal reactions

We report final-state-exclusive measurements of the light charged fragments in coincidence with 26Ne residual nuclei following the direct two-proton removal from a neutron-rich 28Mg secondary beam. A Dalitz-plot analysis and comparisons with simulations show that a majority of the triple- coincidence events with two protons display phase-space correlations consistent with the (two-body) kinematics of a spatially-correlated pair-removal mechanism. The fraction of such correlated events, 56(12) %, is consistent with the fraction of the calculated cross section, 64 %, arising from spin S = 0 two-proton configurations in the entrance-channel (shell-model) 28Mg ground state wave function. This result promises access to an additional and more specific probe of the spin and spatial correlations of valence nucleon pairs in exotic nuclei produced as fast secondary beams.

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arXiv2012

Probing elastic and inelastic breakup contributions to intermediate-energy two-proton removal reactions

The two-proton removal reaction from 28Mg projectiles has been studied at 93 MeV/u at the NSCL. First coincidence measurements of the heavy 26Ne projectile residues, the removed protons and other light charged particles enabled the relative cross sections from each of the three possible elastic and inelastic proton removal mechanisms to be determined. These more final-state-exclusive measurements are key for further interrogation of these reaction mechanisms and use of the reaction channel for quantitative spectroscopy of very neutron-rich nuclei. The relative and absolute yields of the three contributing mechanisms are compared to reaction model expectations - based on the use of eikonal dynamics and sd-shell-model structure amplitudes.

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arXiv2011

Investigations of three, four, and five-particle exit channels of levels in light nuclei created using a 9C beam

The interactions of a E/A=70-MeV 9C beam with a Be target was used to populate levels in Be, B, and C isotopes which undergo decay into many-particle exit channels. The decay products were detected in the HiRA array and the level energies were identified from their invariant mass. Correlations between the decay products were examined to deduce the nature of the decays, specifically to what extent all the fragments were created in one prompt step or whether the disintegration proceeded in a sequential fashion through long-lived intermediate states. In the latter case, information on the spin of the level was also obtained. Of particular interest is the 5-body decay of the 8C ground state which was found to disintegrate in two steps of two-proton decay passing through the 6Beg.s. intermediate state. The isobaric analog of 8Cg.s. in 8B was also found to undergo two-proton decay to the isobaric analog of 6Beg.s. in 6Li. A 9.69-MeV state in 10C was found to undergo prompt 4-body decay to the 2p+2alpha exit channel. The two protons were found to have a strong enhancementin the diproton region and the relative energies of all four p-alpha pairs were consistent with the 5Lig.s. resonance.

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arXiv2011

Constraints on the density dependence of the symmetry energy from heavy ion collisions

Constraints on the Equation of State for symmetric matter (equal neutron and proton numbers) have been extracted from energetic collisions of heavy ions over a range of energies. Collisions of neutron-deficient and neutron-rich heavy ions now provide initial constraints on the EoS of neutron-rich matter at sub-saturation densities from isospin diffusions and neutron proton ratios. This article reviews the experimental constraints on the density dependence of Symmetry Energy at sub-saturation density.

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