I am a member of Filomena Nunes's research group at the Facility for Rare Isotope Beams at Michigan State University. We are currently working on the development of theoretical tools to study direct nuclear reactions. 

My graduate school work was on the calculation of microscopic nucleon-nucleus optical potentials based on two- and three-nucleon interactions from chiral effective field theory.  A python script for using the Whitehead-Lim-Holt global optical potential can be downloaded here.

A full list of my publications may be found here: https://inspirehep.net/authors/1621981

Recent Papers

Prediction of (p,n) Charge-Exchange Reactions with Uncertainty Quantification

T.R. WhiteheadT. Poxon-PearsonF.M. NunesG. Potel


Background: Charge-exchange reactions are a powerful tool for exploring nuclear structure and nuclear astrophysics, however, a robust charge-exchange reaction theory with quantified uncertainties is essential to extracting reliable physics. Purpose: The goal of this work is to determine the uncertainties due to optical potentials used in the theory for charge-exchange reactions to isobaric analogue states. Method: We implement a two-body reaction model to study (p,n) charge-exchange transitions and perform a Bayesian analysis. We study the (p,n) reaction to the isobaric analog states of 14C, 48Ca, and 90Zr targets over a range of beam energies. We compare predictions using standard phenomenological optical potentials with those obtained microscopically. Results: Charge-exchange cross sections are reasonably reproduced by modern optical potentials. However, when uncertainties in the optical potentials are accounted for, the resulting predictions of charge-exchange cross sections have very large uncertainties. Conclusions: The charge-exchange reaction cross section is strongly sensitive to the input interactions, making it a good candidate to further constrain nuclear forces and aspects of bulk nuclear matter. However, further constraints on the optical potentials are necessary for a robust connection between this tool and the underlying isovector properties of nuclei.

Global Microscopic Description of Nucleon-Nucleus Scattering with Quantified Uncertainties

T.R. WhiteheadY. Lim, and J.W. Holt

Phys. Rev. Lett. 127, 182502

We develop for the first time a microscopic global nucleon-nucleus optical potential with quantified uncertainties suitable for analyzing nuclear reaction experiments at next-generation rare-isotope beam facilities. Within the improved local density approximation and without any adjustable parameters, we begin by computing proton-nucleus and neutron-nucleus optical potentials from a set of five nuclear forces from chiral effective field theory for 1800 target nuclei in the mass range 12≤A≤242 for energies between 0  MeV<E≲150  MeV. We then parameterize a global optical potential for each chiral force that depends smoothly on the projectile energy as well as the target nucleus mass number and isospin asymmetry. Uncertainty bands for elastic scattering observables are generated from a full covariance analysis of the parameters entering in the description of our global optical potential and benchmarked against existing experimental data for stable target nuclei. Since our approach is purely microscopic, we anticipate a similar quality of the model for nucleon scattering on unstable isotopes.

Neutron elastic scattering on calcium isotopes from chiral nuclear optical potentials

T.R. WhiteheadY. Lim, and J.W. Holt

Phys. Rev. C 101, 064613

We formulate microscopic neutron-nucleus optical potentials from many-body perturbation theory based on chiral two- and three-body forces. The neutron self-energy is first calculated in homogeneous matter to second order in perturbation theory, which gives the central real and imaginary terms of the optical potential. The real spin-orbit term is calculated separately from the density matrix expansion using the same chiral interaction as in the self-energy. Finally, the full neutronnucleus optical potential is derived within the improved local density approximation utilizing mean field models consistent with the chiral nuclear force employed. We compare the results of the microscopic calculations to phenomenological models and experimental data up to projectile energies of E = 200 MeV. Experimental elastic differential scattering cross sections and vector analyzing powers are generally well reproduced by the chiral optical potential, but we find that total cross sections are overestimated at high energies.

Proton elastic scattering on calcium isotopes from chiral nuclear optical potentials

T. R. Whitehead, Y. Lim, and J. W. Holt

Phys. Rev. C 100, 014601

We formulate microscopic optical potentials for nucleon-nucleus scattering from chiral two- and three-nucleon forces. The real and imaginary central terms of the optical potentials are obtained from the nucleon self energy in infinite nuclear matter at a given density and isospin asymmetry, calculated self-consistently to second order in many-body perturbation theory. The real spin-orbit term is extracted from the same chiral potential using an improved density matrix expansion. The densitydependent optical potential is then folded with the nuclear density distributions of 40,42,44,48Ca from which we study proton-nucleus elastic scattering and total reaction cross sections using the reaction code TALYS. We compare the results of the microscopic calculations to those of phenomenological models and experimental data up to projectile energies of E = 180 MeV. While overall satisfactory agreement with the available experimental data is obtained, we find that the elastic scattering and total reaction cross sections can be significantly improved with a weaker imaginary optical potential, particularly for larger projectile energies.

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