Surrogate Reaction Method for Neutron
Capture and Other Reactions on
Unstable Isotopes
J. E. Escher, J. T. Burke, R. O. Hughes, N. D. Scielzo, and R. J. Casperson
1 Introduction
Cross sections for compound-nuclear reactions (a + A → B ∗ → c + C) are
important for many applications, but are often not known. Statistical cross section
calculations can be quite uncertain due to the nuclear structure models describing
the decay of the compound nucleus (CN), B ∗ → c + C. Reaction measurements are
difficult to impossible when the target nucleus is too short-lived or radioactive to be
made into a stationary target. While inverse-kinematics experiments are a promising
development for measuring charged-particle induced reactions directly, the lack of
a neutron target renders this approach out of reach for neutron-induced reactions, at
least for the foreseeable future.
The surrogate method [1] overcomes the challenge of an unstable target by
producing the CN of interest indirectly via a light-ion (inelastic scattering or
transfer) reaction δ (d + D → B ∗ + b) involving a projectile-target combination
more amenable to a measurement. The decay of the CN into the channel of interest,
χ = c + C, is observed in coincidence with the outgoing particle (b) from the
light-ion reaction and the resulting coincidence probability P δχ (E ex ) is measured
as a function of the excitation energy E ex of the CN. This decay probability is then
used, in conjunction with a calculation of the desired fusion process (a + A → B ∗ )
to determine the cross section of interest.
In principle, the surrogate method can employ a variety of light-ion reactions
δ to determine reactions with various decay channels (χ = γ , n, p, α, 2n, . . .).
The primary focus of past applications has been on (n,f) and (n,γ ) reactions. Here,
J. E. Escher () · J. T. Burke · R. O. Hughes · N. D. Scielzo · R. J. Casperson
Lawrence Livermore National Laboratory, Livermore, CA, USA
e-mail: escher1@llnl.gov
© This is a U.S. government work and not under copyright protection
in the U.S.; foreign copyright protection may apply 2021
J. Escher et al. (eds.), Compound-Nuclear Reactions, Springer Proceedings in
Physics 254, https://doi.org/10.1007/978-3-030-58082-7_27
221
Capture and Other Reactions on
Unstable Isotopes
J. E. Escher, J. T. Burke, R. O. Hughes, N. D. Scielzo, and R. J. Casperson
1 Introduction
Cross sections for compound-nuclear reactions (a + A → B ∗ → c + C) are
important for many applications, but are often not known. Statistical cross section
calculations can be quite uncertain due to the nuclear structure models describing
the decay of the compound nucleus (CN), B ∗ → c + C. Reaction measurements are
difficult to impossible when the target nucleus is too short-lived or radioactive to be
made into a stationary target. While inverse-kinematics experiments are a promising
development for measuring charged-particle induced reactions directly, the lack of
a neutron target renders this approach out of reach for neutron-induced reactions, at
least for the foreseeable future.
The surrogate method [1] overcomes the challenge of an unstable target by
producing the CN of interest indirectly via a light-ion (inelastic scattering or
transfer) reaction δ (d + D → B ∗ + b) involving a projectile-target combination
more amenable to a measurement. The decay of the CN into the channel of interest,
χ = c + C, is observed in coincidence with the outgoing particle (b) from the
light-ion reaction and the resulting coincidence probability P δχ (E ex ) is measured
as a function of the excitation energy E ex of the CN. This decay probability is then
used, in conjunction with a calculation of the desired fusion process (a + A → B ∗ )
to determine the cross section of interest.
In principle, the surrogate method can employ a variety of light-ion reactions
δ to determine reactions with various decay channels (χ = γ , n, p, α, 2n, . . .).
The primary focus of past applications has been on (n,f) and (n,γ ) reactions. Here,
J. E. Escher () · J. T. Burke · R. O. Hughes · N. D. Scielzo · R. J. Casperson
Lawrence Livermore National Laboratory, Livermore, CA, USA
e-mail: escher1@llnl.gov
© This is a U.S. government work and not under copyright protection
in the U.S.; foreign copyright protection may apply 2021
J. Escher et al. (eds.), Compound-Nuclear Reactions, Springer Proceedings in
Physics 254, https://doi.org/10.1007/978-3-030-58082-7_27
221