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Professor Ronald Johnson

Emeritus Professor of Physics
+44 (0)1483 682733
06 BC 04

Academic and research departments

Department of Physics.

My publications


Timofeyuk N, Johnson RC (2013) Nonlocality in Deuteron Stripping Reactions,PHYSICAL REVIEW LETTERS 110 (11) ARTN 1 AMER PHYSICAL SOC
We propose a new method for the analysis of deuteron stripping reactions, A(d,p)B, in which the nonlocality of nucleon-nucleus interactions and three-body degrees of freedom are accounted for in a consistent way. The model deals with equivalent local nucleon potentials taken at an energy shifted by
Timofeyuk N, Johnson RC (2013) Nonlocality in the adiabatic model of A(d, p)B reactions,PHYSICAL REVIEW C 87 (6) ARTN 0 AMER PHYSICAL SOC
In a previous publication [Phys. Rev. Lett. 110, 112501 (2013)] we have proposed a generalization of the adiabatic model of (d,p) reactions that allows the nonlocality of the nucleon optical potential to be included in a consistent way together with the deuteron breakup. In this model an effective local d?A potential is constructed from local nucleon optical potentials taken at an energy shifted by
Pang DY, Timofeyuk Natalia, Johnson Ronald, Tostevin Jeffrey (2013) Rapid convergence of the Weinberg expansion of the deuteron stripping amplitude,Physical Review C: Nuclear Physics 87 064613
Theories of (d,p) reactions frequently use a formalism based on a transition amplitude that is dominated by the components of the total three-body scattering wave function where the spatial separation between the incoming neutron and proton is confined by the range of the n-p interaction, Vnp. By comparison with calculations based on the continuum discretized coupled channels method we show that the (d,p) transition amplitude is dominated by the first term of the expansion of the three-body wave function in a complete set of Weinberg states. We use the 132Sn(d,p)133Sn reaction at 30 and 100 MeV as examples of contemporary interest. The generality of this observed dominance and its implications for future theoretical developments are discussed.
Dinmore M. J., Timofeyuk N. K., Al-Khalili J. S., Johnson R. C. (2019) Effects of an induced three-body force in the incident channel of (d,p) reactions,Physical Review C 99 (6) 064612 pp. 064612-1 American Physical Society
A widely accepted practice for treating deuteron breakup in A(d,p)B reactions relies on solving a three-body A+n+p Schrödinger equation with pairwise A?n, A?p and n?p interactions. However, it was shown in Phys. Rev. C 89, 024605 (2014) that projection of the many-body A+2 wave function into the three-body A+n+p channel results in a complicated three-body operator that cannot be reduced to a sum of pairwise potentials. It contains explicit contributions from terms that include interactions between the neutron and proton via excitation of the target A. Such terms are normally neglected. We estimate the first-order contribution of these induced three-body terms and show that applying the adiabatic approximation to solving the A+n+p model results in a simple modification of the two-body nucleon optical potentials. We illustrate the role of these terms for the case of 40Ca(d,p)41Ca transfer reactions at incident deuteron energies of 11.8, 20, and 56 MeV, using several parametrizations of nonlocal optical potentials.
Timofeyuk N.K., Johnson R.C. (2020) Theory of deuteron stripping and pick-up reactions for nuclear structure studies,Progress in Particle and Nuclear Physics 111 103738 Elsevier
Deuteron stripping and pick-up experiments - (d; p) and (p; d) - have been used for a long time
to study the structure of nuclei. Today these experiments are often carried out in inverse kinematics in state-of-the-art radioactive beams facilities around the world, extending the boundaries of
our knowledge of the nuclear chart. The nuclear structure information obtained from these experiments relies entirely on transfer reaction theory. We review the theory of (d; p) and (p; d) reactions
starting from early formulations and ending with the most recent developments. In particular,
we describe the recent progress made in the understanding of the three-body dynamics associated
with the deuteron breakup degrees of freedom, including effects of nonlocality, and discuss the
role of many-body degrees of freedom within the three-body context. We also review advances
in structure model calculations of one-nucleon overlap functions - an important structure input
to (d; p) and (p; d) reaction calculations. We emphasize the physics missing in widely-used standard approaches available to experimentalists and review ideas and efforts aimed at including this
physics, formulating the crucial tasks for further development of deuteron stripping and pickup
reaction theory