[en] The mechanism of excitation of isomeric h11/2 states in nuclei around the closed shell at N=82 have been studied at the High-Intensity Gamma Source (HIγS). We have taken advantage of the monoenergetic (ΔE/E=1.5%) and pulsed γ-ray-beam from HIγS to perform in-beam spectroscopy measurements with an improved level of precision and sensitivity. The giant dipole resonances at 15 MeV in the N=82 target isotones 138Ba, 140Ce, and 142Nd have been excited, and following neutron emission the γ-ray cascades leading to the isomeric h11/2 state and the ground state were observed in the N=81 isotones. For all three nuclei a very similar de-excitation scheme was found. The only level observed from which the isomeric state was populated was found to be Jπ = 7/2-. The ground state is principally populated from the states with spin and parities Jπ = 1/2+, 5/2+, and 7/2+. The structure of the N=81 isotones and the role of the gateway states in isomer population will be discussed. The results of the measurements will be compared with statistical model calculations

[en] We provide a detailed experimental validation of the concept of transmission-based isotope detection. The dominant background processes in this class of systems were measured by studying the detection of ²³⁸U with a quasimonochromatic (ΔE/E∼3%) photon beam. A notch develops in the spectrum transmitted through our test objects due to the preferential attenuation of photons with an energy that resonantly excites a bound nuclear state in ²³⁸U near 2 MeV. The notch was measured downstream of our test objects by means of resonant photon scattering from a secondary ²³⁸U target. The dominant backgrounds measured in the notch detector due to radioactive decay and elastic scattering of the transmitted beam are presented. Processes that refill the notch with off-resonance photons will obscure the signal and result in a higher probability of false negatives. A measurement of the refill process produced a null result, and we report an upper limit on the magnitude of the notch fill factor.

[en] M1 excitations in the ⁹⁰Zr nucleus have been studied in a photon-scattering experiment with monoenergetic and 100% linearly-polarized beams from 7 to 11 MeV. More than 40 J^π = 1+ states were identified for the first time from the observed ground-state transitions revealing the fine structure of the giant M1 resonance with center of gravity of 9 MeV and sum strength of 3.8(3) μ²_N. The results of the present work are compared with predictions from the shell model and the quasi-particle random-phase approximation.

[en] Measurements of neutron-deuteron (n-d) analyzing power A_y(θ) at E_n=19.0 MeV are reported at 16 angles from θ_c.m.=46.7 to 152.0 deg. The objective of the experiment is to better characterize the discrepancies between n-d data and the predictions of three-nucleon calculations for neutron energies above 16.0 MeV. The experiment used a shielded neutron source, which produced polarized neutrons via the ²H(d-vector,n-vector)³He reaction, a deuterated liquid scintillator center detector (CD) and liquid-scintillator neutron side detectors. A coincidence between the CD and the side detectors isolated the elastic-scattering events. The CD pulse height spectrum associated with each side detector was sorted by using pulse-shape discrimination, time-of-flight techniques, and by removing accidental coincidences. A Monte Carlo computer simulation of the experiment accounted for effects due to finite geometry, multiple scattering, and CD edge effects. The resulting high-precision data (with absolute uncertainties ranging from 0.0022 to 0.0132) have a somewhat lower discrepancy with the predictions of three-body calculations, as compared to those found at lower energies.

[en] TUNL is responsible for data evaluations in the mass range A = 3-20. Since the last NSDD/IAEA meeting in 2003, the final reviews for the masses A = 8,9,10 were published in 'Energy Levels of Light Nuclei, A = 8,9,10', Nuclear Physics A745 (2004) 155. Preliminary reviews of A = 3 and A = 11, 12 are under way. Since 2003, we have published a review of Energy Levels of Light Nuclei, A = 8-10; the corresponding ENSDF files are in progress. The ENSDF file for A = 8 was submitted in April, and files for A = 9 and 10 are nearly completed. TUNL continues to develop new WWW services for the nuclear science and applications communities. PDF and HTML documents are online for TUNL and Fay Ajzenberg-Selove reviews for 1968-present, A = 5-7 (1966) and A = 5-10 (1959). Energy Level Diagrams are provided in GIF, PDF and EPS/PS formats for the publication years 1966-present and A = 5-10 (1959). General tables that reference theoretical work related to TUNL?s most recent reviews are available on our website for masses A = 5-10. Information on the TUNL web pages make extensive use of the NSR link manager. We have also begun a new effort to organize and provide information on Thermal Neutron Capture evaluated data

[en] Cross section measurements for the neutron induced reactions on GaAs have been carried out at ten different neutron energies from 7.5 to 15 MeV, using the activation technique. The monoenergetic neutron beams were produced via the ²H(d,n)³He reaction, known for it's high neutron yield in the chosen energy regime. GaAs samples were activated along with the Au and Al monitor foils, for estimating the incident neutron flux. The induced activity was measured using high resolution γ-ray spectroscopy. Five reaction channels viz., ⁶⁹Ga(n, 2n) Ga, ⁶⁹Ga(n,p)^69mZn, ⁷¹Ga(n,p)^71mZn, ⁷⁵As(n, 2n)⁷⁴As and ⁷⁵As(n,p)⁷⁵Ge, have been reported for the comprehensive cross section measurements. The results are compared with the existing literature data and the available evaluations. Statistical model calculations, based on the Hauser-Feshbach formalism, have been carried out using the TALYS and EMPIRE codes and are compared with the experimental values.

[en] High resolution and sensitivity studies of the nuclear dipole response in ¹³⁸Ba have been performed in (γ, γ') experiment. The electric dipole character of the 'pygmy' mode was experimentally verified for excitations from 4.0 to 8.5 MeV. Experimental findings have been compared with the quasiparticle phonon model. A new understanding about the character and the evolution of the pygmy resonance emerges from comparison of the experimental results with the theoretical calculations.

[en] High-sensitivity studies of E1 and M1 excitations observed in the ¹³⁸Ba(γ,γ') reaction at energies below the neutron emission threshold have been performed. The electric dipole character of the so-called ''pygmy'' mode was experimentally verified for excitations from 4.0-8.6 MeV. The fine structure of the M1 ''spin-flip'' mode was observed for the first time in N = 82 nuclei.

[en] The photodisintegration cross section of radioactive ²⁴¹Am has been obtained for the first time using monoenergetic γ-ray beams from the HIγS facility. The induced activity of ²⁴⁰Am produced via the ²⁴¹Am(γ,n) reaction in the γ-ray energy range from 9.5 to 16 MeV was measured by the activation technique utilizing high resolution HPGe detectors. The ²⁴¹Am(γ,n) cross section was determined both by measuring the absolute γ-ray flux and by comparison to the ¹⁹⁷Au(γ,n) and ⁵⁸Ni(γ,n) cross section standards. The experimental data for the ²⁴¹Am(γ,n) reaction in the giant dipole resonance energy region is compared with statistical nuclear-model calculations.

[en] For the first time, cross-section measurements were carried out for the ⁸⁶Kr(γ, n) reaction in order to probe the s-process branching point nucleus ⁸⁵Kr. The branching point nuclei in the s-process path are of importance in testing and constraining the nucleosynthesis models. Cross-section measurement for the photoneutron reaction on the neighbouring stable isotope is carried out to deduce the aforesaid neutron capture cross-section, as has been adopted in the present case of ⁸⁵Kr branching point. The cross-section results from the ⁸⁶Kr(γ, n) reaction were compared with the statistical model calculations using TALYS code.