[en] A brief summary of the Surrogate reaction method, an indirect approach for determining compound-nuclear reaction cross sections, is presented. The possibilities for obtaining accurate (n,f) cross sections from Surrogate measurements that are analyzed in the Weisskopf-Ewing and Ratio approximations are considered. Theoretical studies and benchmark experiments that provide new insights into the validity and limitations of the Surrogate approach, are discussed

[en] The STARS/LiBerACE collaboration has been exploring the surrogate technique with success in the actinide region. This method uses a direct reaction to measure the decay probability of the same compound nucleus produced via a neutron-induced channel. This paper serves as an overview of these activities. Using the STARS array at 88-inch Cyclotron at Lawrence Berkeley National Laboratory we have explored the following surrogate reactions: ²³⁴U(α, α(prime)f), ²³⁵U(³He, αf), ²³⁶U(α, α(prime)f), ²³⁸U (α,α(prime)f), ²³⁸U(³He,αf), ²³⁸U(³He, tf) surrogates for ²³³U(n,f), ²³³U(n,f), ²³⁵U(n,f), ²³⁷U(n,f), ²³⁶U(n,f), and ²³⁷Np(n,f), respectively

[en] The desire to build nuclear clocks with an unprecedented accuracy of 1 part in ${10}^{19}$ is currently driving the interest in accurate measurements of the first excited nuclear state in ${}^{229}$Th. We have used superconducting tunnel junction (STJ) radiation detectors to search for the associated decay of ${}^{229m}$Th and measure its energy accurately. In this experiment, recoiling ${}^{229m}$Th ions from the alpha decay of ${}^{233}$U are embedded in the STJ detectors, and their subsequent decay into the ground state is expected to produce a signal at an energy of $7.8\pm <!--\; ??\; -->0.5$ eV. This approach is particularly promising, because all decay products are captured inside the STJ so that the measured energy does not depend on the decay mode or on chemical effects. Although this approach works well to characterize the decay of metastable ${}^{235m}$U, no signal from ${}^{229m}$Th has been observed. This negative result can be explained by recent measurements of the ${}^{229m}$Th half-life of only 7±1μs. We discuss our experiments and the modifications required to measure the energy of metastable ${}^{229m}$Th with an accuracy of order ± 10 meV.

[en] Fission product yields can be extracted from an irradiated sample by performing gamma ray spectroscopy on the whole sample post irradiation. There are several pitfalls to avoid when trying to determine a specific isotope's fission product yield.

[en] Cross sections for compound-nuclear reactions are required for many applications. The surrogate nuclear reactions method provides an indirect approach for determining cross sections for reactions on unstable isotopes, which are difficult or impossible to measure otherwise. Current implementations of the method provide useful cross sections for (n,f) reactions, but need to be improved upon for applications to capture reactions.

[en] We are studying the gamma ray and neutron multiplicity of various fission processes, beginning with the spontaneous fission of ²⁵²Cf, for a variety of basic and applied science purposes. The Livermore-Berkeley Array for Collaborative Experiments (LiBerACE) consists of six high-purity germanium Clover detectors (HPGe) each enclosed by an array of 16 bismuth-germanate (BGO) detectors. These detectors were arranged in a cubic pattern around a 1 (micro)Ci ²⁵²Cf source to attempt to cover as much solid angle of gamma ray emission as possible with a high level of segmentation. The single-gamma detector response function is determined at several energies by tagging in a HPGe detector on the photopeak of one of two gamma rays in two-gamma ray calibration sources and observing the multiplicity of the remainder of the array. Summing these single-gamma responses in groups yields the response function of the array to higher multiplicity events, which are convolved with multiplicity distributions from theoretical models and compared to the measured results to test the models validity

[en] This report serves as a compendium of the time dependent populations of every isotope produced from the fissioning of the uranium-235 nucleus. All isotope populations, ground state and isomeric state, are plotted as a function of time from microseconds to a week after creation.

[en] This report serves as a compendium of the time dependent populations of every isotope produced from the fissioning of the uranium-238 nucleus. All isotope populations, ground state and isomeric state, are plotted as a function of time from microseconds to a week after creation.

[en] This report serves as a compendium of the time dependent populations of every isotope produced from the ssioning of the Plutonium-239 nucleus. All isotope populations, ground state and isomeric state, are plotted as a function of time from microseconds to a week after creation.

[en] We measured the ratio of the fission probabilities of ²³⁴U* relative to ²³⁶U* formed via an (α,α(prime)) direct reactions using the STARS array at the 88-inch cyclotron at the Lawrence Berkeley National Laboratory. This ratio has a shape similar to the ratio of neutron capture probabilities from ²³³U(n; f) and ²³⁵U(n; f), indicating the alpha reactions likely formed a compound nucleus. This result indicates that the ratios of fission exit channel probabilities for two actinide nuclei populated via (α, α(prime)) can be used to determine an unknown fission cross section relative to a known one. The validity of the External Surrogate Ratio Method (ESRM) is tested and the results support the conclusions of Burke et al. [1]