Calvin R. Howell
· Professor of PhysicsVerifiedDuke University · Physics
Active 1982–2025
About
Professor Calvin R. Howell's research is in the area of experimental nuclear physics with emphasis on the quantum chromodynamics (QCD) description of low-energy nuclear phenomena, including structure properties of nucleons and nuclei and reaction dynamics in few-nucleon systems. The macroscopic properties of nucleon structure and the residual strong nuclear force between neutrons and protons in nuclei emerge from QCD at distances where the color interactions between quarks and gluons are strong. However, the details of the mechanisms that generate the strong nuclear force are not well understood. Effective field theories (EFT) and Lattice QCD calculations provide theoretical frames that connect low-energy nuclear phenomena to QCD. Professor Howell and collaborators are conducting experiments on few-nucleon systems that test predictions of ab-initio theory calculations for the purpose of providing insight about the QCD descriptions of low-energy nucleon interactions and structure. His current projects include measurements of the electromagnetic and spin-dependent structure properties of nucleons via Compton scattering on the proton and few-nucleon systems and studies of two- and three-nucleon interactions using few-nucleon reactions induced by photons and neutrons. In the coming years, a focus will be on investigating the neutron-neutron interaction in reactions and inside nuclei. In addition, his work includes applications of nuclear physics to national nuclear security, medical isotope production, and plant biology. Most of his research is carried out at the High Intensity Gamma-ray Source and the tandem laboratory at TUNL.
Research topics
- Computer Science
- Physics
- Optics
- Particle physics
- Nuclear physics
- Atomic physics
- Astronomy
Selected publications
Finite-Geometry Corrections for Neutron Scattering Cross Section Measurements
2025-09-01
reportOpen accessIn this report, we describe the corrections necessary for neutron scattering cross section measurements in experiments which use finite-geometry scattering samples.A new Geant4 based framework was developed to calculate these corrections which has been benchmarked against a well-measured test case.This framework also calculates the outgoing neutron energy dependence of the correction factors, which is crucial when resolving individual final states in the scatterer is not possible.
Nuclear Data Sheets · 2025-05-13 · 4 citations
articleEnergy Dependent Fission Product Yields
2025-02-11
reportOpen accessThis project utilized a 10-meter Fast Transfer System (called RABITTS) and Decay Station. FPYs are measured using neutron activation of U-235 and Pu-239 followed by gamma ray spectroscopy. We irradiated targets with mono-energetic neutrons produced at the TUNL tandem accelerator laboratory. The gamma spectra collected in these target irradiations are being analyzed to determine FPY values.
Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment · 2024-03-07 · 4 citations
articleOpen accessEnergy-Dependent Fission-Product Yields in the Region of Second-Chance Fission
EPJ Web of Conferences · 2024-01-01
articleOpen accessThe energy dependence of high-yield fission products has been measured using quasi-monoenergetic neutron beams at energies between 5.5 and 11.0 MeV. The absolute number of fissions during the irradiation period was determined via dual-fission ionization chambers, while the fission products were measured via direct g-ray spectroscopy. This paper presents absolute fission product yields from neutron-induced fission of 235 U, 238 U, and 239 Pu isotopes for five incident energies in the second chance fission region.
Energy Dependent Fission Product Yields (2nd year Milestone and Deliverables)
2024-01-18
reportOpen access1st authorCorrespondingIntroduction to the project: One of the Laboratory missions is to provide consistent, high-precision fission product; yield data critical for testing fission models and maintaining the safety and security of the nation’s nuclear weapons stockpile. However, high-quality, energy-differential fission product yield data is missing for certain actinides and neutron energies important to constrain the new U.S. Nuclear Data Program evaluation effort; It has been shown that the reactor antineutrino anomaly may be at least partially caused by roughly 20 fission products. The fission product yield data is missing or incomplete for many of these isotopes, thus it is necessary to accurately determine these values to better constrain the anomaly; Aitor Bracho is measuring very short-lived (seconds to minutes) fission product yields of 235U and 239Pu using monoenergetic neutron beams at En = 60 and 560 keV; Aitor Bracho is using a direct approach utilizing a state-of-the-art rabbit transfer system, superior HPGe detector, and digital acquisition systems for fission decay measurements. The goals of this project: lop experimental capabilities and data analysis techniques to carry out the gamma-ray spectra analysis necessary for fission product yield calculation; Provide high-precision and energy-dependent fission product data supporting fission theory, neutrino physics, and applied physics.
Photo-nuclear cross sections on $^{197}$Au, an update on the gold standard
arXiv (Cornell University) · 2024-02-23
preprintOpen accessA method was developed for measuring photonuclear reactions concurrently at several discrete photon beam energies on a stack of different target materials via a single irradiation. Concentric ring targets of the materials (in order from front to back targets: Au, TiO$_2$, Zn, Os, and Au) were irradiated at the High Intensity Gamma-ray Source (HI$γ$S). As a proof of principle, we report the result of the cross section measurements from the front Au target. The excitation functions of the $^{197}$Au($γ$,n)$^{196}$Au and $^{197}$Au($γ$,3n)$^{194}$Au reactions were determined in the incident photon energy range of 13-31 MeV using quasi-monoenergetic photon beams provided at HI$γ$S. The cross sections of the combined ground state (2$^{-}$) and short-lived first isomeric state (m1, 5$^{+}$), and of the second isomeric state (m2, 12$^{-}$) in the $^{196}$Au production are obtained separately by subtracting the $γ$ rays from the internal conversion of the second isomeric state. The excitation function of the second isomeric state via the photon-induced reaction $^{197}$Au($γ$,n)$^{196m2}$Au was measured for the first time. By using the activation method rather than direct neutron counting, the exclusive cross sections for the ($γ$,n) and ($γ$,3n) reactions were determined. Comparing the yields from the front and back gold targets validates our ability to simulate the effect of photon scattering in the target stack and provides a method for assessing the systematic uncertainty of our technique.
Physical review. C · 2024-12-05 · 2 citations
articleOpen accessCross sections for the $^{197}\mathrm{Au}(\ensuremath{\gamma},n)$ reaction are broadly used in nuclear physics as a standard for normalizing photonuclear reaction cross-section data at photon beam energies above approximately 8 MeV. In this paper, we report cross-section measurements for the $^{197}\mathrm{Au}{(\ensuremath{\gamma},n)}^{196}{\mathrm{Au}}^{g+m1}$ reaction at beam energies from 13 to 31 MeV. Our measurements provide the first cross-section data for this reaction at beam energies above 20 MeV, enabling the use of this reaction as a cross-section standard up to 30 MeV. Also, this work provides first cross-section measurements for the $^{197}\mathrm{Au}(\ensuremath{\gamma},n)^{196}\mathrm{Au}^{m2}$ reaction. In addition, we measured cross-section data for the $^{197}\mathrm{Au}(\ensuremath{\gamma},3n)^{194}\mathrm{Au}$ reaction, which can be used as a cross-section standard above about 25 MeV. These measurements were performed using a new target activation method that is based on the angle-energy correlation of the laser Compton-scattered photon beams at the High Intensity Gamma-ray Source ($\mathrm{HI}\ensuremath{\gamma}\mathrm{S}$). The technique enables measuring photonuclear reaction cross-sections at several discrete beam energies concurrently via a single irradiation on a stack of different targets. Measurements were carried out by irradiating a stack of concentric-ring targets consisting of Au, ${\mathrm{TiO}}_{2}$, Zn, Os, and Au (in order of the $\ensuremath{\gamma}$-ray beam direction). Our data for the $^{197}\mathrm{Au}(\ensuremath{\gamma},n)^{196}\mathrm{Au}^{g+m1}$ reaction in the energy range of 13 to 20 MeV are in good agreement with existing ones measured using monoenergetic $\ensuremath{\gamma}$-ray beams, but differ from data acquired using a bremsstrahlung $\ensuremath{\gamma}$-ray beam. Also, above 18 MeV, our data for the $^{197}\mathrm{Au}(\ensuremath{\gamma},n)^{196}\mathrm{Au}^{g+m1}$ and $^{197}\mathrm{Au}(\ensuremath{\gamma},n)^{196}\mathrm{Au}^{m2}$ reactions differ significantly from the most recent TENDL and JENDL evaluations, suggesting a need to update these data libraries. The TENDL evaluation and existing data are consistent with our data for the $^{197}\mathrm{Au}(\ensuremath{\gamma},3n)$ reaction, but differ significantly from the JENDL evaluation above 26 MeV.
Proceedings of the Workshop for Applied Nuclear Data Activities WANDA 2022
2024-02-15 · 2 citations
reportOpen accessOn February 28 – March 4, 2022, the Nuclear Data Interagency Working Group (NDIAWG) hosted the 5-day virtual Workshop for Applied Nuclear Data (WANDA2022) to facilitate interagency collaboration on nuclear data for applications. This year’s focus was nuclear data for space applications, but also included photon reactions and transport, reactions on unstable nuclei, and data adjustment topics. The annual WANDA workshops are planned by the Nuclear Data Working Group (NDWG) with the goal of assembling users and producers of nuclear data to provide input to identify and prioritize nuclear data needs and to suggest solutions to address those needs. The workshop consisted of talks by agency program managers, six topic focused road mapping sessions and a review of NDIAWG-funded projects. More than 350 attendees represented national laboratories, universities, and federal agencies, as well as international organizations and industry. The proceedings presented herein summarize the workshop’s content, highlight important outcomes, and document attendees’ recommendations.
Use of the HIFROST Dilution Refrigerator for the $T_{20}$ Experiment
2024-07-30
articleOpen accessI discussed the importance of the $T_{20}$ quantity, a tensor analyzing power, and the basic experimental setup for a measurement of $\stackrel{\leftrightarrow}{d}$ ($\vec{\gamma}$, n)p, the deuteron photodisintegration. Multiple measurements have suggested the existence of a channel around 9 MeV above two nucleon masses. This diverges from calculations from current nuclear theory, and this experiment will focus on this new channel and yield information on the nature of any discrepancy. This experiment will immediately follow the experiment of the GDH measurement on the deuteron and use a lot of the same equipment. While the target will be polarized in the GDH experiment, the target will have the tensor component enhanced for the $T_{20}$ experiment. I will discuss the status of the experiment, as well as the current status of the dilution refrigerator, and the progress being made.
Recent grants
NSF · $297k · 2007–2012
REU Site: Undergraduate Research in Nuclear and Particle Physics at TUNL and Duke University
NSF · $379k · 2012–2015
REU Site: Undergraduate Research in Nuclear and Particle Physics at TUNL and Duke University
NSF · $407k · 2015–2019
REU Site: Undergraduate Research in Nuclear Physics at TUNL/Duke University
NSF · $230k · 2009–2012
Frequent coauthors
- 547 shared
W. Tornow
- 230 shared
R. L. Walter
Duke University
- 213 shared
A. S. Crowell
Triangle Universities Nuclear Laboratory
- 172 shared
A. P. Tonchev
Duke University
- 124 shared
J. H. Kelley
- 106 shared
B. Fallin
Savannah River National Laboratory
- 101 shared
G. J. Weisel
- 92 shared
H. Witała
Jagiellonian University
Awards & honors
- Trinity College Honors Faculty Leadership in the Classroom a…
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