arXiv subjects

T. N. Massey

Publications and source records attributed to T. N. Massey.

13 recordsLinked to original sources

arXiv2026

Differential cross sections for ${{^{12}\mathrm{C}(n,α_{0})}}$, ${{^{16}\mathrm{O}(n,α_{0})}}$ and ${{^{16}\mathrm{O}(n,α_{1,2,3})}}$ between ${E_n}$ = 7.2 and 10 MeV with an active-target Time Projection Chamber

Data for the ${{^{12}\mathrm{C}(n,α_{0})}}$, ${{^{16}\mathrm{O}(n,α_{0})}}$ and ${{^{16}\mathrm{O}(n,α_{1,2,3})}}$ differential cross sections are important for several different areas of nuclear physics such as understanding neutron transmutation in nuclear reactors. The TexAT Time Projection Chamber was used to measure the differential and angle-integrated cross sections in active-target mode. The chamber was filled with CO$_2$ gas and used a quasi-monoenergetic neutron beam from the $d(d,n)$ reaction at Edwards Accelerator Lab at Ohio University. A comparison between our current and previous results at overlapping energies and angles which showed good agreement in angular dependence and absolute cross section. A broader angular coverage than previous results demonstrated that the integrated cross section for the \po16 reaction deviates from ENDFVIII.0 evaluations. This first instance of neutron-induced measurements with an active-target Time Projection Chamber demonstrates the use of this method for high-quality differential cross section data across a broad angular range, generating good statistics with a relatively low-intensity beam.

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arXiv2022

Measurements of the $^{27}{\rm Al}(α,n)$ Thick Target Yield Near Threshold

We present results from direct measurements of the $^{27}{\rm Al}(α,n)$ thick target yield from laboratory incident energies $E_α\approx$ 3$-$5~MeV, performed with the $^{3}$HeBF$_{3}$ Giant Barrel (HeBGB) neutron detector at the Edwards Accelerator Laboratory. Our measurements have a small energy cadence in order to address discrepancies and sparseness of thick-target yield data sets existing for this energy region. We find general agreement with existing data sets, including yields derived from cross section data, while resolving a discrepancy between existing thick-target yield data sets for $E_α\approx4-5$~MeV. However, for $E_α<3.5$~MeV, our results are substantially lower than previous thick-target yield data and somewhat larger than yields calculated from existing cross section data. Our data complete the energy-range needed for estimates of the $^{27}{\rm Al}(α,n)$ contribution to neutrino and dark matter detector backgrounds and result in increased viability of $^{27}{\rm Al}(α,n)$ as a plasma diagnostic tool at fusion facilities such as the National Ignition Facility.

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arXiv2022

The $^{3}$He BF$_{3}$ Giant Barrel (HeBGB) Neutron Detector

$(α,n)$ reactions play an important role in nuclear astrophysics and applications and are an important background source in neutrino and dark matter detectors. Measurements of total $(α,n)$ cross sections employing direct neutron detection often have a considerable systematic uncertainty associated with the energy-dependent neutron detection efficiency and the unknown initial neutron energy distribution. The $^{3}{\rm He}\,{\rm BF}_{3}$ Giant Barrel (HeBGB) neutron detector was built at the Edwards Accelerator Laboratory at Ohio University to overcome this challenge. HeBGB offers a near-constant neutron detection efficiency of ($7.5\pm 1.2$) \% over the neutron energy range 0.01 MeV -- 9.00 MeV, removing a significant source of systematic uncertainty present in earlier $(α,n)$ cross section measurements.

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arXiv2021

Determination of the $^{60}$Zn level density from neutron evaporation spectra

Nuclear reactions of interest for astrophysics and applications often rely on statistical model calculations for nuclear reaction rates, particularly for nuclei far from $β$-stability. However, statistical model parameters are often poorly constrained, where experimental constraints are particularly sparse for exotic nuclides. For example, our understanding of the breakout from the NiCu cycle in the astrophysical rp-process is currently limited by uncertainties in the statistical properties of the proton-rich nucleus $^{60}$Zn. We have determined the nuclear level density of $^{60}$Zn using neutron evaporation spectra from $^{58}$Ni($^3$He, n) measured at the Edwards Accelerator Laboratory. We compare our results to a number of theoretical predictions, including phenomenological, microscopic, and shell model based approaches. Notably, we find the $^{60}$Zn level density is somewhat lower than expected for excitation energies populated in the $^{59}$Cu(p,$γ$)$^{60}$Zn reaction under rp-process conditions. This includes a level density plateau from roughly 5-6 MeV excitation energy, which is counter to the usual expectation of exponential growth and all theoretical predictions that we explore. A determination of the spin-distribution at the relevant excitation energies in $^{60}$Zn is needed to confirm that the Hauser-Feshbach formalism is appropriate for the $^{59}$Cu(p,$γ$)$^{60}$Zn reaction rate at X-ray burst temperatures.

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arXiv2020

Constraining the destruction rate of $^{40}$K in stellar nucleosynthesis through the study of the $^{40}$Ar(p,n)$^{40}$K reaction

40K plays a significant role in the radiogenic heating of earth-like exoplanets, which can affect the development of a habitable environment on their surfaces. The initial amount of 40K in the interior of these planets depends on the composition of the interstellar clouds from which they formed. Within this context, nuclear reactions that regulate the production of 40K during stellar evolution can play a critical role. In this study, we constrain for the first time the astrophysical reaction rate of 40K(n,p)40Ar, which is responsible for the destruction of 40K during stellar nucleosynthesis. We performed differential cross-section measurements on the 40Ar(p,n)40K reaction, for six energies in the center-of-mass between 3.2 and 4.0 MeV and various angles between 0-deg and 135-deg. The experiment took place at the Edwards Accelerator Laboratory at Ohio University using the beam swinger target location and a standard neutron time-of-flight technique. The total and partial cross-sections varied with energy due to the contribution from isobaric analog states and Ericson type fluctuations. The energy-averaged neutron angular distributions were symmetrical relative to 90-deg and consistent with the theoretical predictions of the statistical model. Based on the experimental data, local transmission coefficients were extracted and were used to calculate the astrophysical reaction rates of 40Ar(p,n)40K and 40K(n,p)40Ar reactions. Our results support that the destruction rate of 40K in massive stars via the 40K(n,p)40Ar reaction is larger compared to previous estimates. This result directly affects the predicted stellar yields of 40K from nucleosynthesis, which is a critical input parameter for the galactic chemical evolution models that are currently employed for the study of significant properties of exoplanets.

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arXiv2018

Measurement of the normalized $^{238}$U(n,f)/$^{235}$U(n,f) cross section ratio from threshold to 30 MeV with the fission Time Projection Chamber

The normalized $^{238}$U(n,f)/$^{235}$U(n,f) cross section ratio has been measured using the NIFFTE fission Time Projection Chamber from the reaction threshold to $30$~MeV. The fissionTPC is a two-volume MICROMEGAS time projection chamber that allows for full three-dimensional reconstruction of fission-fragment ionization profiles from neutron-induced fission. The measurement was performed at the Los Alamos Neutron Science Center, where the neutron energy is determined from neutron time-of-flight. The $^{238}$U(n,f)/$^{235}$U(n,f) ratio reported here is the first cross section measurement made with the fissionTPC, and will provide new experimental data for evaluation of the $^{238}$U(n,f) cross section, an important standard used in neutron-flux measurements. Use of a development target in this work prevented the determination of an absolute normalization, to be addressed in future measurements. Instead, the measured cross section ratio has been normalized to ENDF/B-VIII.$β$5 at 14.5 MeV.

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arXiv2018

The $^{12}$C(n, 2n)$^{11}$C cross section from threshold to 26.5 MeV

The $^{12}$C(n, 2n)$^{11}$C cross section was measured from just below threshold to 26.5 MeV using the Pelletron accelerator at Ohio University. Monoenergetic neutrons, produced via the $^3$H(d,n)$^4$He reaction, were allowed to strike targets of polyethylene and graphite. Activation of both targets was measured by counting positron annihilations resulting from the $β^+$ decay of $^{11}$C. Annihilation gamma rays were detected, both in coincidence and singly, using back-to-back NaI detectors. The incident neutron flux was determined indirectly via $^{1}$H(n,p) protons elastically scattered from the polyethylene target. Previous measurements fall into upper and lower bands, the results of the present measurement are consistent with the upper band.

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arXiv2017

The Edwards Accelerator Laboratory at Ohio University

The Edwards Accelerator Laboratory at Ohio University is the hub for a vibrant program in low energy nuclear physics. Research performed with the lab's 4.5MV tandem accelerator spans a variety of topics, including nuclear astrophysics, nuclear structure, nuclear energy, homeland security, and materials science. The Edwards Lab hosts a variety of capabilities, including unique features such as the beam swinger with neutron time-of-flight tunnel and the integrated condensed matter physics facility, enabling experiments to be performed with low-to-medium mass stable ion beams using charged-particle, gamma, and neutron spectroscopy. This article provides an overview of the current and near-future research program in low energy nuclear physics at Ohio University, including a brief discussion of the present and planned technical capabilities.

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arXiv2014

A Time Projection Chamber for High Accuracy and Precision Fission Cross Section Measurements

The fission Time Projection Chamber (fissionTPC) is a compact (15 cm diameter) two-chamber MICROMEGAS TPC designed to make precision cross section measurements of neutron-induced fission. The actinide targets are placed on the central cathode and irradiated with a neutron beam that passes axially through the TPC inducing fission in the target. The 4$π$ acceptance for fission fragments and complete charged particle track reconstruction are powerful features of the fissionTPC which will be used to measure fission cross sections and examine the associated systematic errors. This paper provides a detailed description of the design requirements, the design solutions, and the initial performance of the fissionTPC.

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arXiv2013

Targets for Precision Measurements

The general properties needed in targets (sources) for high precision, high accuracy measurements are reviewed. The application of these principles to the problem of developing targets for the Fission TPC is described. Longer term issues, such as the availability of actinide materials, improved knowledge of energy losses and straggling and the stability of targets during irradiation are also discussed.

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arXiv2011

Equilibrium and pre-equilibrium processes in the 55Mn(6Li,xp) and 57Fe(a,xp) reactions

Spectra of outgoing neutrons and protons from the 6Li+55Mn reaction and protons from the a+57Fe reaction have been measured with beams of 15 MeV 6Li ions and 30 MeV alpha-particles. These reactions proceed through the same 61Ni nucleus at the same excitation energy, thus allowing the difference in reaction mechanism to be studied. It is shown that spectra from the first reaction measured at backward angles are due to emission from a traditional compound nucleus reaction, in which the intermediate nucleus has reached statistical equilibrium; the spectra from the second reaction contain a significant fraction of pre-equilibrium emission at all angles. Level density pa- rameters of the residual nucleus 60Co have been obtained from the first reaction. Both emission spectra and angular distributions have been measured for the second reaction. It was found that the pre-equilibrium component exhibits a forward-peaked angular distribution, as expected, but with a steeper slope than predicted and with an unusual slight rise at angles above 120°. The backward- angle rise is explained qualitatively by the dominance of the multi-step compound mechanism at backward angles.

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arXiv2009

Gamma-strength functions in 60Ni from two-step cascades following proton capture

The two-step cascade method previously used in neutron capture experiments is now applied to a proton capture reaction. The spectrum of two-step cascades populating the first 2+ level of 60Ni has been measured with 59Co(p,2gamma)60Ni reaction. The simulation technique used for the spectrum analysis allows one to reveal the range of possible shapes of both E1 and M1 gamma-strength functions. The low-energy enhancement previously observed in 3He induced reactions is seen to appear in M1 strength functions of 60Ni.

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arXiv2007

Test of nuclear level density inputs for Hauser-Feshbach model calculations

The energy spectra of neutrons, protons, and alpha-particles have been measured from the d+59Co and 3He+58Fe reactions leading to the same compound nucleus, 61$Ni. The experimental cross sections have been compared to Hauser-Feshbach model calculations using different input level density models. None of them have been found to agree with experiment. It manifests the serious problem with available level density parameterizations especially those based on neutron resonance spacings and density of discrete levels. New level densities and corresponding Fermi-gas parameters have been obtained for reaction product nuclei such as 60Ni,60Co, and 57Fe.

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