Surrogate ratio methodology for the indirect determination of neutron capture cross sections

Abstract

The relative γ -decay probabilities of the 162 Dy to 161 Dy and 162 Dy to 164 Dy residual nuclei, produced using light-ion-induced direct reactions, were measured as a function of excitation energy using the CACTUS array at the Oslo Cyclotron Laboratory. The external surrogate ratio method (SRM) was used to convert these relative γ -decay probabilities into the 161 Dy(n,γ ) cross section in an equivalent neutron energy range of 130-560 keV. The directly measured 161 Dy(n,γ ) cross section, obtained from the Evaluated Nuclear Data Files (ENDF/B-VII.0), was compared to the experimentally determined surrogate 161 Dy(n,γ ) cross section obtained using compound-nucleus pairs with both similar ( 162 Dy to 164 Dy) and dissimilar ( 162 Dy to 161 Dy) nuclear structures. A γ -ray energy threshold was identified, based upon pairing gap parameters, that provides a first-order correction to the statistical γ -ray tagging approach and improves the agreement between the surrogate cross-section data and the evaluated result.

Spin-dependent observables in surrogate reactions

“…Generally speaking, however, decay branching ratios are sensitive to the spin value of the decaying compound system. Therefore, a great care must be paid to the condition in which the surrogate method can yield the correct neutron cross sections [2,3].…”

Indirect determination of neutron capture cross sections on spherical and near-spherical nuclei using the surrogate method

“…Contribution from carbon contamination was determined to comprise no more than ≈ 1% of the total singles spectrum in the excitation energy range relevant for the surrogate cross section measurement. Given that there are no conflicting 13 C γ rays observed in the γ-ray energy regions of interest, no carbon contamination was present in the particle-γ coincident data relevant for the surrogate cross section measurements.…”

“…This effort was recently expanded to include the determination of neutron capture cross sections. Two approaches have been applied to tag the γ-decay channel in the indirect determination of neutron capture cross sections using the surrogate method: discrete tagging [8][9][10][11] and statistical tagging [12,13].…”

Development of a measurement system for the determination of (n,γ) cross-sections using multi-nucleon transfer reactions

“…The cross-section thus obtained agrees with the neutron induced data of the 170 Yb(n, γ) 171 Yb reaction within their uncertainties. Goldblum et al [15] also used the same surrogate reactions as above to obtain the ratio of 162 Dy relative to 161 Dy. In parallel, the ratio of the P γ ðE x Þ of 162 Dy relative to 164 Dy was obtained from the ( 3 He, 3 He'γ) reaction.…”