The photon analyzing power for the photodisintegration of the deuteron was measured for seven gamma-ray energies between 2.39 and 4.05 MeV using the linearly polarized gamma-ray beam of the High-Intensity Gamma-ray Source at the Duke Free-Electron Laser Laboratory. The data provide a stringent test of theoretical calculations for the inverse reaction, the neutron-proton radiative capture reaction at energies important for Big-Bang Nucleosynthesis. Our data are in excellent agreement with potential model and effective field theory calculations. Therefore, the uncertainty in the baryon density ΩBh 2 obtained from Big-Bang Nucleosynthesis can be reduced at least by 20%. 24.70.+s, 27.10.+h, 21.45.+v Big-Bang Nucleosynthesis (BBN) is an observational cornerstone of the hot Big-Bang (BB) cosmology. According to [1] the neutron(n)-proton(p) capture reaction p(n, γ)d with a deuteron (d) and a 2.225 MeV γ ray in the exit channel is of special interest, because the BB abundance of deuterium provides direct information on the baryon density in the early universe at times between about 0.01 and 200 seconds after the BB. Knowing accurately the n-p capture cross section in the energy range from 25 to 200 keV in the center-of-mass (c.m.) system and using the experimental value for the primeval deuterium number density (D/H) p [2, 3], would allow for an accurate determination of the baryon density Ω B h 2 (h is the Hubble constant in units of 100 km/s/Mpc). From Ω B h 2 one can predict the abundances of the three light elements 3 He, 4 He, and 7 Li. According to [1], the 10% uncertainty in the deuterium-inferred baryon density Ω B h 2 = 0.019 ± 0.002 comes in almost equal parts from the (D/H) measurements and theoretical uncertainties in predicting the deuterium abundance. For the latter, the knowledge of the n-p capture cross section is of crucial importance. Unfortunately, there is a near-complete lack of data at energies relevant to BBN. Aside from thermal energies, data exist only at n-p c.m. energies of 275 keV and above. As a consequence, the ENDF-B/VI [4] evaluation has been used [1] in the BBN energy range. This evaluation is normalized to the high-precision thermal n-p capture cross-section measurements. The 5% uncertainty that is assigned in this approach contributes a significant fraction to the uncertainty in the baryon density and consequently in the abundances of the light elements produced in BBN.Very recently, with the precision results from WMAP (Wilkinson Microwave Anisotropy Probe) for the Cosmic Microwave Background (CMB) and its anisotropies an independent and even more accurate result became available: Ω B h 2 = 0.0224 ± 0.0009 [5,6]. The comparison of the baryon density predictions from BBN and the CMB is a fundamental test of BB cosmology [7]. Any deviation points to either unknown systematics or the need for new physics. Therefore, it is of crucial importance to reduce the uncertainty in Ω B h 2 obtained from BBN. As stated above, 50% of the uncertainty is due to the uncertainty in the n-p capture cr...

The (n, 2n) cross section of the radioactive isotope 241 Am (T 1/2 = 432.6 y) has been measured in the incident neutron energy range from 7.6 to 14.5 MeV in steps of a few MeV using the activation technique. Monoenergetic neutron beams were produced via the 2 H(d, n) 3 He reaction by bombarding a pressurized deuterium gas cell with an energetic deuteron beam at the TUNL 10-MV Van de Graaff accelerator facility. The induced γ -ray activity of 240 Am was measured with high-resolution HPGe detectors. The cross section was determined relative to Al, Ni, and Au neutron activation monitor foils, measured in the same geometry. Good agreement is obtained with previous measurements at around 9 and 14 MeV, whereas for a large discrepancy is observed when our data are compared to those reported by Perdikakis et al. near 11 MeV. Very good agreement is found with the END-B/VII evaluation, whereas the JENDL-3.3 evaluation is in fair agreement with our data.

The Mobile Imaging and Spectroscopic Threat Identification (MISTI) system developed to locate radiological threats in urban and rural environments is currently undergoing characterization activities. MISTI is a mobile source detection and imaging system designed to identify and localize a radiological source to within +/-10m in range. This requirement is based on a 1 mCi Cs-137 source at 100 m in 20s, while maintaining a false alarm rate of less than one per day. MISTI utilizes the cost effective collection power of NaI for imaging and the sensitivity of high resolution HPGe for spectroscopy. MISTI's data acquisition system was developed with the latest commercially availed hardware that met MISTI's requirements. The performance of crucial software and hardware components is presented along with overall system performance. A synopsis and example of the initial characterization results are presented here.

The low-lying structure of 94 40 Zr was studied with the (n, n γ ) reaction, and a level scheme was established based on excitation function and γ γ coincidence measurements. Branching ratios, multipole mixing ratios, and spin assignments were determined from angular distribution measurements. Lifetimes of levels up to 3.4 MeV were measured by the Doppler-shift attenuation method, and for many transitions the reduced transition probabilities were determined. In addition to the anomalous 2 + 2 state, which has a larger B(E2; 2 + 2 → 0 + 1 ) value than the B(E2; 2 + 1 → 0 + 1 ), the experimental results revealed interesting and unusual properties of the low-lying states in 94 Zr. In a simple interpretation, the excited states are classified in two distinct categories, i.e., those populating the 2 + 2 state and those decaying to the 2 + 1 state.