Victor H. Ritz

Wavelength-scanning polarization-modulation ellipsometry: some practical considerations

A discussion is presented of the practical considerations involved in wavelength-scanning polarization-modulation ellipsometry. Emphasis is placed on factors affecting accuracy and precision and on the alignment of the optical elements. The system described is used to measure the optical properties of air-cleaved KCI and of clean and tarnished Ag surfaces in ultrahigh vacuum in the 250-650-nm range.

Magnetic properties of amorphous and crystalline GdFe2

The magnetic and structural properties of GdFe2 thin films prepared by electron beam coevaporation have been investigated. The measurements included magnetic resonance, magnetometer, the Mossbauer effect, x‐ray diffraction, and Auger analysis. Comparisons were made between the properties of the as‐deposited amorphous films and films annealed at various temperatures up to 500 °C, at which point crystallization is essentially complete. The measured magnetization for amorphous films was less than the magnetization measured in crystalline films at all temperatures. The magnetic moment of the Gd and Fe ions within their respective magnetic sublattices were determined to be 7.6 and 2.12μβ for crystalline GdFe2. The sublattice moments in the amorphous case do not change appreciably from the crystalline case. The sublattice g values were determined to be slightly temperature dependent below 77 K. The Landau‐Lifshitz magnetic damping parameter was determined to be ∼1×107 and 2×107 Hz for amorphous and crystalline ...

An Ionization Chamber for Kilocurie Source Calibrations

A graphite cavity ionization chamber suitable for measuring the exposure dose rate (r/hr) in kilocurie Co60 gamma -ray sources is described, and the associated techniques involved are discussed in some detail. The chamber has excellent ion saturation properties and can be used to determine the exposure dose rate absolutely to within plus or minus 2% at dose rates up to 1 x 107 r/hr. The use of chambers with walls of different atomic number to determine the influence of low-energy scattered radiation on the absorbed dose (rads) in high-z materials is also described.

Adsorption of O2 on the SrTiO3 (100)−(1 × 1) surface

Abstract Electron energy-loss spectra (ELS) of the SrTiO 3 (100)−(1 × 1) surface have been obtained in UHV and in 5 × 10 −6 Torr O 2 . The most prominent peaks in UHV are at 5.3, 6.8, 10.4 and 13.8 eV. O 2 exposure shifts the 6.8 eV peak to 7.5 eV. It is inferred that the peak shift results from O 2 adsorption near surface strontium ions. Formation of peroxide ions (O 2− 2 ) is consistent with these data and with reflectance and UV photoemission results.

RADIATION INTENSITY MEASUREMENTS WITH SILVER-ACTIVATED GLASS BLOCK DOSIMETERS.

The intensity of radiation at a given place may be defined in general as the energy per unit time entering a small sphere centered at that place per unit cross-sectional area of the sphere (1). In the special case of a unidirectional X-ray or electron beam, the intensity may be defined as the energy per unit time impinging upon a unit crosssectional area oriented at right angles to the direction of the radiation beam. The latter case is frequently encountered experimentally in the form of a plane-parallel X-ray or electron beam. The intensity (ergs/cm2-sec or ev/cm2-sec) at some point of interest may be measured by the total absorption of the radiation arriving there, the absorber being some material that changes in a measurable way as a known function of the energy absorbed per unit area. For example, one might totally absorb an X-ray beam in a calorimeter or large volume of ferrous sulfate solution. Such wellunderstood dosimeters are not always easily employed in many experiments where space is limited and the environment of the specimen under study precludes the use of such absolute dosimetry systems. One can avoid these difficulties by choosing as a dosimeter some material that is more compatible with the environmental conditions of the experiment. Glass that darkens under the influence of ionizing radiation is an example of such a material. This sort of dosimeter need not be absolute in itself, since it can be calibrated against one of the previously mentioned absolute dosimetersthat is, a calorimeter or the Fricke dosimeter. It has the important advantage of small physical size approximating that of many samples, so that it can be employed without alteration of the geometry of the experiment. Rabin and Klick (2) and Ritz (3) have used glass block dosimeters to measure the intensity of low-energy X-ray beams and to determine the fraction of the incident intensity absorbed by thin alkali halide crystals irradiated in a cryostat. These blocks (1 cm X 1 cm X 0.3 cm thick) are made of a silver-activated metaphosphate

Fast‐neutron dosimetry using F centers in MgO

A fast‐neutron dosimeter is described, the operation of which is based on the detection of F centers produced in MgO by displacement collisions. The F‐center production rate is greatly enhanced by hydrogenous surroundings from which recoil protons are ejected. The absorbed dose is measured by means of the 350 °C exoelectron emission peak. The response is linear from 10 to 600 rad (tissue) and approximately independent of neutron energy from 2 to 15 MeV. The response to fast neutrons divided by the response to γ rays is [inverted lazy s] 0.90 on a tissue‐rad basis.

Characterization of degraded hydrogen dissociator envelopes by AES

The performance of hydrogen dissociators used in atomic clocks is known to degrade after prolonged operation, requiring large increases in rf power to maintain a constant output of atomic hydrogen. Auger electron spectroscopy (AES) has been used to characterize the inner surfaces of Pyrex dissociator envelopes. Prolonged operation of the dissociators leads to buildup of a dark film incorporating large quantities of carbon in its amorphous and carbide forms and smaller amounts of nitrogen. Possible mechanisms by which the film could interfere with the operation of the dissociator are given which involve its electrical conductivity and its role as a catalyst in the recombination of atomic hydrogen.

A SOLID STATE BRAGG-GRAY CAVITY CHAMBER

An attempt was made to construct the solid-state analog of a Bragg-Gray cavity ionization chamber. Thin layers of materials sensitive to radiation were placed between walls of C, Al, Cu, Sn, or Pb. Two types of sensing agents were employed; thin layers of anthracene with ultravioletinduced luminescence that degrades upon irradiation, and 6- mu -thick polyethylene terephthalate (Mylar) films with an optical density that at 3250 A increases upon irradiation. Results in a Co/sup 60/ gamma -ray field with the anthracene disagree sharply with theory, while the Mylar film yields excellent agreement ( plus or minus 5%) with theory. A preliminary attempt to discriminate between the fast neutron and gamma -ray dose in a nuclear reactor was unsuccessful. (auth)

Final-state delocalization in the LiF core-valence-(F-center) Auger transition

Abstract The linewidth of the LiF core-valence-(F-center) Auger transition — when compared with that of the valence band photoemission and with those of the core-valence-valence Auger transitions — indicates a delocalized, apparently “band-like”, final state. This is accounted for in terms of various estimates of the final-state correlation energy.