has performed a set of absolute Fission Product Yield (FPY) measurements. Using monoenergetic neutron at energies between 0.5 and 14.8 MeV, the excitation functions of a number of fission products from 235 U, 238 U and 239 Pu have begun to be mapped out. This work has practical applications for the determination of weapon yields and the rate of burn-up in nuclear reactors, while also providing important insight into the fission process. Combining the use of a dual-fission ionization chamber and-ray spectroscopy, absolute FPYs have been determined for approximately 15 di↵erent fission products. The dual-fission chamber is a back-to-back ionization chamber system with a 'thin' actinide foil in each chamber as a monitor or reference foil. The chamber holds a 'thick' target in the center of the system such that the target and reference foils are of the same actinide isotope. This allows for simple mass scaling between the recorded number of fissions in the individual chambers and the number of fissions in the center thick target, eliminating the need for the knowledge of the absolute fission cross section and its uncertainty. The 'thick' target was removed after activation and-rays counted with well shielded High Purity Germanium (HPGe) detectors for a period of 1.5-2 months.

A high-resolution study of the electromagnetic response of 206 Pb below the neutron separation energy is performed using a ( γ,γ ) experiment at the HI γS facility. Nuclear resonance fluorescence with 100% linearly polarized photon beams is used to measure spins, parities, branching ratios, and decay widths of excited states in 206 Pb from 4.9 to 8.1 MeV. The extracted ΣB(E1)↑ and ΣB(M1)↑ values for the total electric and magnetic dipole strength below the neutron separation energy are 0.9±0.2 e 2 fm 2 and 8.3 ± 2.0 µ 2 N , respectively. These measurements are found to be in very good agreement with the predictions from an energy-density functional (EDF) plus quasiparticle phonon model (QPM). Such a detailed theoretical analysis allows to separate the pygmy dipole resonance from both the tail of the giant dipole resonance and multi-phonon excitations. Combined with earlier photonuclear experiments above the neutron separation energy, one extracts a value for the electric dipole polarizability of 206 Pb of α D = 122 ± 10 mb/MeV. When compared to predictions from both the EDF+QPM and accurately calibrated relativistic EDFs, one deduces a range for the neutron-skin thickness of R 206 skin = 0.12-0.19 fm and a corresponding range for the slope of the symmetry energy of L = 48-60 MeV. This newly obtained information is also used to estimate the Maxwellian-averaged radiative cross section 205 Pb(n,γ) 206 Pb at 30 keV to be σ = 130±25 mb. The astrophysical impact of this measurement-on both the s-process in stellar nucleosynthesis and on the equation of state of neutron-rich matter-is discussed.

The SPectrometer for Ion DEtermination in fission Research (SPIDER) has been developed for measuring mass yield distributions of fission products from spontaneous and neutron-induced fission. The 2E-2v method of measuring the kinetic energy (E) and velocity (v) of both outgoing fission products has been utilized, with the goal of measuring the mass of the fission products with an average resolution of 1 atomic mass unit (amu). The SPIDER instrument, consisting of detector components for time-of-flight, trajectory, and energy measurements has been assembled and tested using 229 Th and 252 Cf radioactive decay sources. For commissioning, the fully assembled system measured fission products from spontaneous fission of 252 Cf. Individual measurement resolutions were met for time-of-flight (250 ps FWHM), spacial resolution (2 mm FHWM), and energy (92 keV FWHM for 8.376 MeV). Mass yield results measured from 252 Cf spontaneous fission products are reported from an E-v measurment.

Angular distributions for the target spin-dependent observables A0y, Axx, and Ayy have been measured using polarized proton beams at several energies between 2 and 6 MeV and a spin-exchange optical pumping polarized 3 He target. These measurements have been included in a global phaseshift analysis following that of George and Knutson, who reported two best-fit phase-shift solutions to the previous global p+ 3 He elastic scattering database below 12 MeV. These new measurements, along with measurements of cross-section and beam-analyzing power made over a similar energy range by Fisher et al., allowed a single, unique solution to be obtained. The new measurements and phase-shifts are compared with theoretical calculations using realistic nucleon-nucleon potential models.

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11A neutron counter designed for assay of radioactive materials has been adapted for beam exper-12 iments at TUNL. The cylindrical geometry and 60% maximum efficiency make it well suited for 13 (γ, n) cross-section measurements near the neutron emission threshold. A high precision charac-14 terization of the counter has been made using neutrons from several sources. Using a combination 15 of measurements and simulations, the absolute detection efficiency of the neutron counter was de-16 termined to an accuracy of ± 3% in the neutron energy range between 0.1 and 1 MeV. It is shown 17 that this efficiency characterization is generally valid for a wide range of targets.

The48 Ca(γ,n) cross section was measured using γ-ray beams of energies between 9.5 and 15.3 MeV generated at the Triangle Universities Nuclear Laboratory (TUNL) high-intensity γ-ray source (HIγS). Prior to this experiment, no direct measurements had been made with γ-ray beams of sufficiently low energy spread to observe structure in this energy range. The cross sections were measured at thirty-four different γ-ray energies with an enriched 48 Ca target. Neutron emission is the dominant decay mechanism in the measured energy range that spans from threshold, across the previously identified M1 strength, and up the low-energy edge of the E1 giant dipole resonance (GDR). This work found B(M 1) = 6.8 ± 0.5 µ 2 N for the 10.23 MeV resonance, a value greater than previously measured. Structures in the cross section commensurate with extended random-phase approximation (ERPA) calculations have also been observed whose magnitudes are in agreement with existing data.