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A. Henriques et al.
Direct measurements of neutron capture or neutron-induced fission on unstable
isotopes are very difficult and often impossible. One of the main reasons is the production and manipulation of radioactive targets. This can be overcome by inverting
the reaction kinematics with radioactive beams. However, the unavailability of freeneutron targets makes the direct measurement in inverse kinematics impossible.
The most promising approach to overcome the difficulties associated with the
measurement of neutron cross sections of radioactive nuclei is to use surrogate
reactions [1, 2].
2 Surrogate Reactions
The surrogate reaction produces the compound nucleus of interest by a different
reaction than the neutron capture reaction (Fig. 1) and the decay probabilities (e.g.
for γ-emission and fission) are measured. The measured decay probabilities of the
compound nucleus are used to precisely tune model parameters that will lead to
much more accurate predictions of the desired neutron cross sections. Surrogate
reactions of interest are inelastic scattering or transfer reactions with light projectile
nuclei. Indeed, the power of surrogate reactions has been proven very successfully
at high excitation energies for neutron-induced fission in direct kinematics with p,
d, 3 He and 4 He beams [1, 3], and recently also for neutron radiative capture [2].
Since 2000, the CENBG together with other laboratories has been performing
experiments to study the surrogate-reaction method [3–7]. In the past years,
the experimental set-up was improved to simultaneously measure fission and γemission probabilities [8].
Our studies on even–odd and odd–odd fissioning nuclei, e.g. [3, 5] show evidence
of a good agreement in the fission probabilities measured by surrogate and neutroninduced reactions. Thus, in many cases, fission probabilities induced by surrogate
reactions can be used to provide neutron-induced fission cross sections of short-lived
nuclei rather directly through the surrogate method. However, our recent results on
240 Pu show that the surrogate method is not directly applicable to this even–even
Fig. 1 The surrogate
reaction aims to produce the
same compound nucleus as
the neutron-induced reaction.
The study of the different
decay channels (fission, γand particle-emission) of the
compound nucleus can be
used to constrain model
parameters used to predict
neutron cross sections
A. Henriques et al.
Direct measurements of neutron capture or neutron-induced fission on unstable
isotopes are very difficult and often impossible. One of the main reasons is the production and manipulation of radioactive targets. This can be overcome by inverting
the reaction kinematics with radioactive beams. However, the unavailability of freeneutron targets makes the direct measurement in inverse kinematics impossible.
The most promising approach to overcome the difficulties associated with the
measurement of neutron cross sections of radioactive nuclei is to use surrogate
reactions [1, 2].
2 Surrogate Reactions
The surrogate reaction produces the compound nucleus of interest by a different
reaction than the neutron capture reaction (Fig. 1) and the decay probabilities (e.g.
for γ-emission and fission) are measured. The measured decay probabilities of the
compound nucleus are used to precisely tune model parameters that will lead to
much more accurate predictions of the desired neutron cross sections. Surrogate
reactions of interest are inelastic scattering or transfer reactions with light projectile
nuclei. Indeed, the power of surrogate reactions has been proven very successfully
at high excitation energies for neutron-induced fission in direct kinematics with p,
d, 3 He and 4 He beams [1, 3], and recently also for neutron radiative capture [2].
Since 2000, the CENBG together with other laboratories has been performing
experiments to study the surrogate-reaction method [3–7]. In the past years,
the experimental set-up was improved to simultaneously measure fission and γemission probabilities [8].
Our studies on even–odd and odd–odd fissioning nuclei, e.g. [3, 5] show evidence
of a good agreement in the fission probabilities measured by surrogate and neutroninduced reactions. Thus, in many cases, fission probabilities induced by surrogate
reactions can be used to provide neutron-induced fission cross sections of short-lived
nuclei rather directly through the surrogate method. However, our recent results on
240 Pu show that the surrogate method is not directly applicable to this even–even
Fig. 1 The surrogate
reaction aims to produce the
same compound nucleus as
the neutron-induced reaction.
The study of the different
decay channels (fission, γand particle-emission) of the
compound nucleus can be
used to constrain model
parameters used to predict
neutron cross sections