Interaction losses in sodium iodide crystals have been directly measured for protons in the range of energies from 139 to 444 MeV and for deuterons of 277 MeV. Calculations of the expected loss were made for protons over the range 151-500 MeV using the best currently available reaction cross section data. Our experimental values are typically about 21% lower than the calculated values. The interaction loss for 277 MeV deuteron in Nal is about 8% lower than the calculated value obtained using the deuteron cross section value of Measday and Schneider. Using their calculated value of 100 MeV deuteron interaction loss as a reference point, we calculated the loss for 277 MeV deuterons and from a fit to our data we obtained the cross section for deuterons at an average energy of 188.4 MeV to be 2590 ± 180 mb, which is about 20% lower than the cross section obtained from the empirical relation that σ(d-A) is 2σ(p-A) at half the energy. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Measurements of the angular distribution and total reaction rate in neutron-proton scattering are described. The emphasis of this work has been to obtain an accurate normalization of the distribution, which is difficult to achieve with neutral beams. Nearly monoenergetic neutrons from the d(p,n)pp reaction were scattered from a liquid hydrogen target. The neutron beam energy was determined from the time of flight with respect to the radio frequency signal of the TRIUMF cyclotron. The differential cross section was measured at 319 and 493 MeV from 10 to 180 degrees in the centre of mass (CM.). Calibrated neutron beam monitors upstream of the scattering target provided an absolute normalization over the whole angular range. Between 10 and 100 degrees CM. a neutron detector consisting of a charged particle veto, a carbon convertor and two trigger scintillators sandwiching 7 multiwire proportional chambers was used to select elastic neutrons by time of flight techniques. The neutron angular distribution was measured with an average precision of 5% and an uncertainty on the normalization of 1.3%. An associated particle experiment (neutrons and recoil protons detected in coincidence) determined the efficiency of the neutron detector and the monitors were calibrated by measuring the incident neutron flux with the neutron detector in the beam, i.e. at zero degrees. The recoil protons were detected in the angular range between 60 and 180 degrees CM. with a precision of 1% to 2% and an error on the normalization of 2.8% at 319 MeV and 3.7% at 493 MeV. Elastic events were selected by time of flight and by either a measurement of magnetic rigidity (momentum) or total energy. The absolute normalization of the two experimental techniques is verified by the overlap of the two measurements and by comparing the integrated differential cross section with the measured total cross section. The neutron-proton total cross section was measured at six energies between 200 and 500 MeV by a transmission type experiment to a precision of 1% to 3%. The systematic corrections were small, of the order of 1%, and the statistical errors were increased to include monitor and beam instabilities. The measurements show a smooth quadratic energy dependence. The data was included in a phase shift analysis and a dispersion relation analysis along with the previous world data. Agreement between the real part of the forward scattering amplitude predicted by the phase shift analysis and by the dispersion relation analysis is improved. The errors on the 1=0 (isoscalar) phase shifts are decreased and to a lesser extent on the 1=1 phase shifts. There is a marked improvement in the smooth variation with energy of the 1=0 phase shifts and a better agreement of the higher partial waves with the theoretical predictions of the Paris potential. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

No description available.

<p> A measurement of the cross section for the interaction of electromagnetic radiation with matter has been undertaken. Total cross sections for 29 photon energies from 121 keV to 10.8 MeV in 9 target elements from carbon to uranium have been realized and pair production cross sections, for energies above 2 MeV, deduced from the results. A direct measurement of the partial pair cross section for photons with energies from 1120 to 2754 keV in 6 target elements from titanium to lead has also been included.</p> / Thesis / Doctor of Philosophy (PhD)

The K-shell x-ray and ionization cross sections are measured for protons on Ag, Cd, Sn, Sb, Te, Ba, and La over the ion energy range of 0.6 to 2.0 MeV. The data are compared to the predictions of the PWBA, the PWBA with corrections for binding energy and/or Coulomb deflection, the BEA, and the constrained BEA predictions. In general, the non-relativistic PWBA with binding energy correction gives the best overall agreement with the measurements of proton-induced x-ray processes for the K-shell of the elements studied in this work. The data further suggest the need for relativistic PWBA treatment of the interactions in the K-shell for the range of binding energies represented by the elements investigated in this work.

K-Shell ionization cross section for protons over the energy range of 0.4 to 2.0 MeV have been measured on thin targets of the elements Se, Br, Rb, Sr, Y, Mo and Pd. Total x-ray and ionization cross sections for the K-shell are reported. The experimental values of the ionization cross sections are compared to the non-relativistic plane-wave Born approximation, the binary-encounter approximation, the constrained binary-encounter approximation, and the plane-wave Born approximation with corrections for Coulomb-deflection and binding energy effects.

Bibliography: leaves 287-294. This thesis addresses preprocessing issues for radar target classification from high resolution radar imagery. High resolution radar imagery of real aircraft in flight and of a MIRAGE aircraft on a turntable is examined. An algorithm to coherently average high resolution range profile is proposed.

Formaldehyde (HCHO) plays a primary role in tropospheric chemistry. Its photochemical activity is an important source of radical species such as HCO, H, and subsequently HO2 as well as molecular hydrogen and carbon monoxide. As a source of hydrogen radicals (HOx = OH + HO2), HCHO plays a significant role in the oxidative capacity of the atmosphere, and an important part in the interrelated chemistries of ozone and the HOx and NOx (NO + NO2) cycles. Accurate atmospheric photolysis rates of HCHO are thus required in order to properly model tropospheric chemistry. Despite extensive studies HCHO’s spectroscopy and photochemistry remains to be well characterized. Absolute room temperature absorption cross sections for the A1A2 – X1A1 electronic transition of formaldehyde have been measured over the spectral range 30285 – 32890 cm-1 (304 – 330 nm) using ultraviolet (UV) laser absorption spectroscopy. Absorption cross sections were obtained at an instrumental resolution better than 0.09 cm-1 which is slightly broader than the Doppler width of a rotational line of HCHO at 300K (~0.07 cm-1) and so we were able to resolve all but the most closely spaced lines. Qualitative comparisons with spectral simulations show varying agreement depending on vibronic band. Refined state origins and transition dipole moments for each vibronic band have been reported. There is evidence of areas of perturbation and the need to optimize higher order spectral constants. Pressure broadening parameters have been measured and increase with the strength of intermolecular interaction between formaldehyde and the collision partner. Comparisons between the available high-resolution studies and spectral simulations indicate that the HCHO absorption cross section is still not well characterized. The relative quantum yield for the production of radical products, H+HCO, from the UV photolysis of formaldehyde (HCHO) has been measured directly using a Pulsed Laser Photolysis – Pulsed Laser Induced Fluorescence (PLP – PLIF) technique across the same spectral region. Relative yields were normalized to a value of 0.69 at 31750 cm-1 based on the current NASA-JPL recommendation. The resulting absolute radical quantum yields agree well with previous experimental studies and show more wavelength dependent behavior than the recommendation. This provides support for the complicated competition among the various HCHO dissociation pathways.

<p>Precision measurements of 238U(n,n'g) and 235,238U(n,2ng) partial cross sections have been performed at Triangle Universities Nuclear Laboratory (TUNL) to improve crucial data for the National Nuclear Security Administration's (NNSA) Stockpile Stewardship Program. Accurate neutron-induced reaction cross-section data are required for many practical applications, including nuclear energy and reactor technology, nuclear transmutation, and explosive nuclear devices. Due to the cessation of underground nuclear testing in the early 1990s, understanding of the performance of nuclear devices is increasingly dependent on precise model calculations which are, in turn, themselves reliant on accurate reaction data to serve as benchmarks for model codes. Direct measurement of (n,n') and (n,2n) reaction cross sections for uranium is extremely difficult due to large neutron background from fission and very close nuclear level spacing. Previous direct measurements of the cross sections are incomplete and/or discrepant over the energy range of interest. However, the (n,n'g) and (n,2ng) partial gamma-ray cross-section data obtained in the present work can be combined with model calculations to infer total (n,n') and (n,2n) reaction-channel cross sections.</p><p>A pulsed and monoenergetic neutron beam was used in combination with high-resolution gamma-ray spectroscopy to measure these partial cross sections for incident neutron energies between 5 and 14 MeV. Gamma-ray yields were measured with high-purity germanium (HPGe) clover and planar detectors. Neutron fluxes were determined from the well-measured 2+ -> 0+ transition in 56Fe to be on the order of 10^4 n/cm^2/s. Detector efficiency and attenuation of gamma rays in the target were simulated using the MCNPX Monte-Carlo radiation transport code.</p><p>Measured partial cross sections were compared with previous measurements and calculations from GNASH and TALYS Hauser-Feshbach statistical-model codes. Results are generally in good agreement with existing data and provide cross-section data for transitions in energy regions where none previously existed. Total reaction-channel cross sections are inferred from statistical-model calculations and compared with existing direct measurement data.</p> / Dissertation

No description available.