G. H. Miller

Simultaneous Integral Measurement of Electron Energy and Charge Albedos

Electron energy and charge albedos were obtained for Be, Al, Ti, Mo, Ta, and U targets over the range of incident energies from 0.1 to 1.0 MeV. In the case of Al, Ta, and U the measurements were extended down to approximately 25 keV. Measurements were made for incident angles from 0° (normal) to 60°, and in some cases 75°, in 15° increments. The results agree well with existing experimental data and with Monte Carlo predictions, except at low energies where the discrepancies are only partially understood.

Optimization of Bremsstrahlung Energy Deposition

Thick-target bremsstrahlung energy deposition in a thin, gold calorimeter has been measured as a function of converter foil thickness for Mo, Sn, La, Ce, Pr, Nd, and Ta converters at source electron energies of 0.5, 0.75, and 1.0 MeV. The thickness-maximized deposition is not a monotonically increasing function of converter atomic number, but instead exhibits a broad maximum near the type 4f rare-earth region. This maximum is substantially greater than the deposition from the Ta converter--Ta being a material routinely employed in flash x-ray sources. Theoretical models also predict higher deposition from La converters than from Ta converters and are used to show that this enhancement is a consequence of higher characteristic x-ray production in La. Nevertheless, there remain significant discrepancies between theoretical predictions and measured data, even when improved numerical cross sections which have just become available are employed in the calculations.

Improved calorimetric method for energy deposition measurement

An improved technique has been developed for the measurement of electron energy deposition versus depth profiles using thin foil calorimeters. A square-wave modulated beam is employed, and the time derivative of the thermocouple signal is measured at a specified time after beam switch. The method and apparatus are described, and results are presented for Al and Ta for 0.3, 0.5, and 1.0 MeV normally incident electrons. Data are also presented for the same energies and 60° (relative to normal) incidence in Al. Deposition data in a layered Ta and Al system at 1.0 and 0.5 MeV energy (normal incidence) are also presented.

Electron Energy Deposition in Multilayer Geometries

A high precision calorimetric method has been employed to measure electron energy deposition profiles in multilayer configurations for normally incident source electrons at an energy of 1.0 MeV. The results are compared with the predictions of a coupled electron/ photon Monte Carlo transport model. Excellent agreement between theory and experiment is obtained for an Al/Au/Al configuration, while significant discrepancies are observed in the case of C/Au/C and Be/Au/Be configurations. Several potential problems are discussed but no satisfactory explanation for the discrepancies has been found.

Absolute Measurement of Low Energy Electron Deposition Profiles in Semi-Infinite Geometries

Two different techniques have been used to measure absolute electron energy deposition profiles in semi-infinite geometries. The first, employing an ionization chamber, was used to measure energy deposition by normally incident electrons at incident energies of 1.0, 0.5, and 0.3 MeV in aluminum, and 1.0 MeV in tantalum. The second method is unique in that it represents the first calorimetric measurement of energy deposition from a monoenergetic D. C. source. Results are given for normally incident electrons at an incident energy of 1.0 MeV in aluminum, and at incident energies of 1.0 and 0.5 MeV in tantalum. The latter method circumvents some of the difficulties inherent in the ion chamber technique and provides more precise results.

Electron Transport in Reactor Materials

The transport method used in the analysis of pulsed electron beam experiments to determine the equations of state of Liquid-Metal-Fast-Breeder-Reactor materials has been verified experimentally. A calorimetric technique has been employed in conjunction with a steady-state monoenergetic (¿ 1.0 MeV) accelerator to measure electron albedos and high-resolution energy deposition profiles in reactor materials. Energy deposition profiles have been obtained in a multilayer carbon-uranium-carbon configuration and in semi-infinite uranium. Systematic measurements of the saturated number and energy albedos for UO2 have been obtained as a function of source energy and incident angle. All experimental results have been compared with predictions of the Monte Carlo code employed in the analysis of the pulsed-beam experiments. The good agreement substantially enhances our confidence in the resulting equation-of-state data, as well as in the more general predictive capability of the transport technique.

Calorimetric Determination of Beam Energy

A high-precision calorimetric system has been developed for determining beam energy. The beam is square-wave (on-off) modulated and the time derivative of the calorimeter temperature is determined at a time late in the modulation half-cycle. This avoids sensitivity variations associated with beam size and location on the calorimeter. The data are collected and analyzed in a small on-line computer. The use of beryllium, with its very small backscatter coefficient for electrons, permits the use of the method for electron accelerators. Using such a calorimeter with a high-stability electron accelerator, standard deviations of the order of 0.03 percent for series of 20 measurements were achieved for energies from 0.025 to 1 MeV over several hours time period. The calorimeter system is usually calibrated with a low energy (~ 20 keV) positive ion beam whose energy is well established. Where lower accuracy is acceptable, the sensitivity may be determined from first principles to within 1 percent. The method will be described and the optimization of the various parameters discussed.

Temperature measurement in symmetric top polyatomic gases using spontaneous rotational Raman spectra

Abstract A method is described for rapidly obtaining the rotational temperature from the spontaneous rotational Raman spectra of polyatomic symmetric top molecules in the gas phase. The method utilizes the odd-numbered R -branch lines in order to eliminate the complication resulting from S -branch interference. The temperature dependence is then approximated over the range of interest by a two-parameter expression of the same form used for the diatomic case. This approach is applied to NH 3 gas flowing in a chemical vapor deposition cell.