A. Hutcheson

Dipole‐Strength Distributions Below the Giant Dipole Resonance in the Stable Even‐Mass Molybdenum Isotopes

Dipole‐strength distributions in the stable even‐mass molybdenum isotopes up to the neutron‐separation energies have been studied in photon‐scattering experiments with bremsstrahlung at the superconducting electron accelerator ELBE at the Research Center Dresden‐Rossendorf, Germany, and with mono‐energetic photon beams at the High Intensity Gamma‐ray Source facility at Triangle Universities Nuclear Laboratory. In order to determine the dipole‐strength distribution, statistical methods were developed for the analysis of the measured spectra. The data obtained for the stable even‐mass molybdenum isotopes from the present (γ,γ’) experiments are combined with (γ,n) cross sections from the literature resulting in a photoabsorption cross section covering the full range from about 4 to 15 MeV, which is of interest for nuclear structure as well as for nuclear astrophysics network calculations. Novel information about the low‐energy tail of the Giant Dipole Resonance and the energy spreading of its strength is der...

Elemental spectrum of a mouse obtained via neutron stimulation

Several studies have shown that the concentration of certain elements may be a disease indicator. We are developing a spectroscopic imaging technique, Neutron Stimulated Emission Computed Tomography (NSECT), to non-invasively measure and image elemental concentrations within the body. The region of interest is interrogated via a beam of high-energy neutrons that excite elemental nuclei through inelastic scatter. These excited nuclei then relax by emitting characteristic gamma radiation. Acquiring the gamma energy spectrum in a tomographic geometry allows reconstruction of elemental concentration images. Our previous studies have demonstrated NSECTs ability to obtain spectra and images of known elements and phantoms, as well as, initial interrogations of biological tissue. Here, we describe the results obtained from NSECT interrogation of a fixed mouse specimen. The specimen was interrogated via a 5MeV neutron beam for 9.3 hours in order to ensure reasonable counting statistics. The gamma energy spectrum was obtained using two High-Purity Germanium (HPGe) clover detectors. A background spectrum was obtained by interrogating a specimen container containing 50mL of 0.9% NaCl solution. Several elements of biological interest including 12C, 40Ca, 31P, and 39K were identified with greater then 90% confidence. This interrogation demonstrates the feasibility of NSECT interrogation of small animals. Interrogation with a commercial neutron source that provides higher neutron flux and lower energy (~2.5MeV) neutrons would reduce scanning time and eliminate background from certain elements.

Measurement of theAm241(γ,n)Am240reaction in the giant dipole resonance region

The photodisintegration cross section of the radioactive nucleus {sup 241}Am has been obtained using activation techniques and monoenergetic {gamma}-ray beams from the HI{gamma}S facility. The induced activity of {sup 240}Am produced via the {sup 241}Am({gamma},n) reaction was measured in the energy interval from 9 to 16 MeV utilizing high-resolution {gamma}-ray spectroscopy. The experimental data for the {sup 241}Am({gamma},n) reaction in the giant dipole resonance energy region are compared with statistical nuclear-model calculations.

Measurement of the Am-241 (gamma, n) Am-240 reaction in the giant dipole resonance region

The photodisintegration cross section of the radioactive nucleus {sup 241}Am has been obtained using activation techniques and monoenergetic {gamma}-ray beams from the HI{gamma}S facility. The induced activity of {sup 240}Am produced via the {sup 241}Am({gamma},n) reaction was measured in the energy interval from 9 to 16 MeV utilizing high-resolution {gamma}-ray spectroscopy. The experimental data for the {sup 241}Am({gamma},n) reaction in the giant dipole resonance energy region are compared with statistical nuclear-model calculations.

Photodisintegration cross section of241Am

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.

Recent Results from the Excitation of Dipole States at the HIγS Facility

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.

Photodisintegration Cross Section of 241Am

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.

Photodisintegration of the Deuteron between Eγ = 2.4 and 4.0 MeV

Big-bang nucleosynthesis (BBN) is an observational cornerstone of the hot big-bang cosmology. According to [1] the p(n,γ)d reaction is of special interest because the big-bang abundance of deuterium is most sensitive to the baryon density. However, in the most important energy range for BBN, i.e., from 25–200 keV in the c.m. system, experimental data are completely missing. In fact, published data exist only at thermal energies and at n-p c.m. energies above 275 keV. Therefore, theoretical models have been used [1] in the BBN energy range that are normalized to the high-precision thermal neutron capture cross-section data.