II. SURROGATE “ABSOLUTE” AND “RATIO” METHODS 3 nore the difference; the so-called Weisskopf-Ewing condition, or to assume schematic (rather arbitrary) spin-parity distributions for the surrogate reaction and argue that they do not affect the decay branching ratio sensitively. Both of these approaches, however, are based on arbitrary assumptions which have not been justified theoretically nor experimentally. On the other hand, it is also true that the surrogate method has yielded a rather accurate cross sections, verified when the corresponding neutron data are available. Therefore, it is natural to expect that there is a certain condition to equate the results from the surro- gate method and the neutron-induced reactions. However, the condition under which the surrogate method works is not clearly understood yet. In this paper, we investigate the spin-parity dependence of the branching ratios of Ura- nium isotopes to the fission and capture channels and clarify the condition for the surrogate (ratio) method to work, and estimate the accuracy achievable by it. R S i ? = σ n i σ n R , (1) In the surrogate method, we measure a branching ratio to a specific decay channel, normally the fission or capture channel by populating the same kind of compound nucleus as the desired neutron-induced reactions . We denote the decay channel by a subscript i ( i = fission or capture), and then the surrogate method hopefully gives a ratio of the neutron cross section σ n i to the total neutron reaction cross section σ n R of the compound system, namely, The symbol R S i denotes the branching ratio of the nucleus decaying to channel i populated by the surrogate reaction, and is defined later by Eq. (6). By multiplying it the total reaction cross section σ n R calculated by the optical or coupled-channel model, we can determine the neutron cross section σ n i . Here, a question mark is explicitly shown since it is not obvious if this equality holds or not. It is due to the reason that the spin-parity distributions populated in the surrogate (left-hand-side) and neutron-induced (right-hand-side) reactions are different, and the branching ratio is dependent on them in general. This is the very fundamental problem to be resolved for the surrogate method to yield correct neutron- indeed cross sections. This method is referred to as the surrogate absolute method. On the contrary, these ratios can be measured for two nearby nuclei 1 and 2 by using the same