Abstract
We present the results of two experiments where we have measured for the first time simultaneously the fission and gamma-decay probabilities induced by different surrogate reactions. In particular, we have investigated the 238 U(d,p), 238 U( 3 He,t) and 238 U( 3 He, 4 He) reactions as surrogates for the neutron-induced n + 238 U, n + 237 Np and n + 236 U reactions, respectively. In the region where gamma emission, neutron emission and fission compete, our results for the fission probabilities agree fairly well with the neutron-induced data, whereas our gamma-decay probabilities are significantly higher than the neutron-induced data. The interpretation of these results is not obvious and is discussed within the framework of the statistical model with preliminary results for calculated spin-parity distributions populated in surrogate reactions. We also present future plans for surrogate-reaction studies in inverse kinematics with radioactive-ion beams at storage rings.
Highlights
Neutron-induced cross sections of short-lived nuclei are key input information for applications in nuclear technology and for nuclear astrophysics
Note that 238Np has a half-life of only 2.1 days and there are no fission or capture cross sections data for this nucleus at fast neutron energies
We used a model based on the Distorted-Wave Born approximation (DWBA) to obtain a first estimate of the average spin populated in the 238U(d,p) reaction [5]
Summary
Neutron-induced cross sections of short-lived nuclei are key input information for applications in nuclear technology and for nuclear astrophysics. In many cases the measurement of these cross sections is very difficult or even impossible, due to the radioactivity of the targets involved. The surrogate-reaction method can help to overcome these difficulties. This indirect method consists in using an alternative (or surrogate) reaction to produce the same decaying nucleus A∗ as the one formed in the neutron-induced reaction of interest. The decay probability induced by the surrogate reaction is measured, and the desired neutron-induced reaction is “simulated” by multiplying the measured decay probability by the calculated cross section for the formation of a compound nucleus after neutron absorption. The usefulness of the surrogate method is that in some cases it is possible to find a surrogate reaction where the needed target is stable or less radioactive than the target of the corresponding neutron-induced reaction
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