J. M. Schwantes

Acquisition-analysis system for the DANCE (detector for advanced neutron capture experiments) BaF/sub 2/ gamma-ray calorimeter

The DANCE detector is a segmented 4/spl pi/ gamma-ray calorimeter for measuring (n, /spl gamma/) and (n,fission) cross-sections of stable and long-lived radioactive isotopes. DANCE uses waveform digitization to acquire the basic gamma-ray data, which maximizes the information available for event reconstruction, but has necessitated the development of several techniques for handling the resulting high data rates. This paper describes the basic experimental requirements for acquisition and analysis and how we have satisfied these requirements primarily by extending existing acquisition and analysis frameworks.

Acquisition-analysis system for the DANCE (detector for advanced neutron capture experiment) BaF/sub 2/ gamma-ray calorimeter

The DANCE detector is a segmented 4pi gamma-ray calorimeter for measuring (n, gamma) and (n, fission) cross-sections of stable and long-lived radioactive isotopes. DANCE uses waveform digitization to acquire the basic gamma-ray data, which maximizes the information available for event reconstruction, but has necessitated the development of several techniques for handling the resulting high data rates. This paper describes the basic experimental requirements for acquisition and analysis and how we have satisfied these requirements primarily by extending existing acquisition and analysis frameworks

The Detector for Advanced Neutron Capture Experiments: A 4π BaF2 Detector for Neutron Capture Measurements at LANSCE

The Detector for Advanced Neutron Capture Experiments (DANCE) is a 162‐element 4π BaF2 array designed to make neutron capture cross‐section measurements on rare or radioactive targets with masses as little as one milligram. Accurate capture cross sections are needed in many research areas, including stellar nucleosynthesis, advanced nuclear fuel cycles, waste transmutation, and other applied programs. These cross sections are difficult to calculate accurately and must be measured. The design and initial performance results of DANCE is discussed.

Nuclear Astrophysics at DANCE

One of the most interesting nuclear physics challenges is obtaining a detailed understanding of the nucleosynthesis processes of the elements. Knowledge about the stellar sites, and how they are governed by stellar evolution and cosmology are crucial in understanding the overall picture. Information on reaction rates for neutron‐ and charged‐particle‐induced reactions have a direct impact on existing stellar models. Except for the stable isotopes, very few neutron‐induced reactions in the energy range of interest have been measured to date. DANCE measurements on stable and unstable isotopes will provide many of the missing key reactions that are needed to understand the nucleosynthesis of the heavy elements.

First Measurements with a Lead Slowing‐Down Spectrometer at LANSCE

The characteristics of a Lead Slowing‐Down Spectrometer (LSDS) installed at the Los Alamos Neutron Science Center (LANSCE) are presented in this paper. This instrument is designed to study neutron‐induced fission on ultra small quantities of actinides, on the order of tens of nanograms or less. The measurements of the energy‐time relation, energy resolution and neutron flux are compared to simulations performed with MCNPX. Results on neutron‐induced fission of 235U and 239Pu with tens of micrograms and tens of nanograms, respectively, are presented. Finally, a digital filter designed to improve the detection of fission events at short time after the proton pulses is described.

Neutron Capture Cross Sections of 236U and 234U

Accurate neutron capture cross sections of the actinide elements at neutron energies up to 1 MeV are needed to better interpret archived nuclear test data, for post‐detonation nuclear attribution, and the Advanced Fuel Cycle Initiative. The Detector for Advance Neutron Capture Experiments, DANCE, has unique capabilities that allow the differentiation of capture gamma rays from fission gamma rays and background gamma rays from scattered neutrons captured by barium isotopes in the barium fluoride scintillators. The DANCE array has a high granularity, 160 scintillators, high efficiency, and nearly 4‐π solid angle. Through the use of cuts in cluster multiplicity and calorimetric energy the capture gamma‐rays are differentiated from other sources of gamma rays. The preliminary results for the capture cross sections of 236U are in agreement with the ENDF/B‐VI evaluation. The preliminary results for 234U lower are than ENDF/B‐VI evaluation and are closer to older evaluations.

Simultaneous measurement of (n,γ) and (n,fission) cross sections with the DANCE 4π BaF2 array

Neutron capture cross section measurements on many of the actinides are complicated by low‐energy neutron‐induced fission, which competes with neutron capture to varying degrees depending on the nuclide of interest. Measurements of neutron capture on 235U using the Detector for Advanced Neutron Capture Experiments (DANCE) have shown that we can partially resolve capture from fission events based on total photon calorimetry (i.e. total γ‐ray energy and γ‐ray multiplicity per event). The addition of a fission‐tagging detector to the DANCE array will greatly improve our ability to separate these two competing processes so that improved neutron capture and (n,γ)/(n,fission) cross section ratio measurements can be obtained. The addition of a fission‐tagging detector to the DANCE array will also provide a means to study several important issues associated with neutron‐induced fission, including (n,fission) cross sections as a function of incident neutron energy, and total energy and multiplicity of prompt fission photons. We have focused on two detector designs with complementary capabilities, a parallel‐plate avalanche counter and an array of solar cells.