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Nuclear Reactions of Arsenic with 190 Mev Deuterons

Description: Isotopes formed in the bombardment of {sub 33}As{sup 75} with 190 Mev deuterons range in atomic number up to 24 (or more) mass units lighter than As{sup 75}. Identification of these isotopes was based on chemical behavior and half-life determination. Relative yields have been calculated and show that 80% of the observed reactions produce isotopes within 8 mass units of As{sup 75}. Three new isotopes have been observed: 9.5 d. Se{sup 72} (K), 44 m, Se{sup 71} ({beta}{sup +}), and 52 m, As{sup 71} ({beta}{sup +}).
Date: January 21, 1948
Creator: Hopkins Jr, H.H. & Cunningham, B.B.
Partner: UNT Libraries Government Documents Department


Description: Gamma-ray multiplicities have been measured as a function of the light-fragment atomic number Z{sub 3} for the above reactions. The events associated with sequential fission of the heavy fragment were distinguished from binary events by means of a triple coincidence. The failure of the measured y-multiplicities for deep-inelastic collisions to rise with decreasing Z{sub 3}, according to the rigid-rotation limit, appears more likely to be associated with a selective population of the low Z fragments by the lower {ell}-waves rather than to an incomplete relaxation of the rotational energy.
Date: October 1, 1977
Creator: Aleonard, M.M.; Wozniak, G.J.; Glassel, P.; Deleplanque, M.A.; Diamond, R.M.; Moretto, L.G. et al.
Partner: UNT Libraries Government Documents Department

The New ELement Mendelevium, Atomic Number 101

Description: We have produced and chemically identified for the first time a few atoms of the element with atomic number 101. Very intense helium ion bombardments of tiny targets of 99{sup 253} have produced a few spontaneously fissionable atoms which elute in the eka-thulium position on a cation resin column.
Date: April 4, 1955
Creator: Ghiorso, A.; Harvey, B.G.; Choppin, G.R.; Thompson, S.G. & Seaborg, G.T.
Partner: UNT Libraries Government Documents Department

Case for an Improved Effective-Atomic-Number for the Electronic Baggage Scanning Program

Description: Z{sub eff}, a parameter representing an 'effective atomic number' for a material, plays an important role in the Electronic Baggage Scanning Program (EBSP) to detect threats in dual-energy computed tomography (CT) baggage-scanning systems. We believe that Z{sub eff}, as defined and used on this program, does not provide the accurate representation of a material's x-ray absorption properties that is needed by the EBSP. We present the case for a new method that defines an effective atomic number for compounds and mixtures, which we refer to as Z{sub e}. Unlike Z{sub eff}, Z{sub e} is tied by definition to the x-ray absorption properties of each specific material. Use of this alternative will provide a more accurate scale for calibrating Micro-CT and EDS systems against standard reference materials and will provide a more accurate physical characterization of the x-ray properties of materials evaluated on those systems. This document: (1) Describes the current usage of the Z{sub eff} parameter; (2) Details problems entailed in the use of the Z{sub eff} parameter; (3) Proposes a well-defined alternative - Z{sub e}; (4) Proposes and demonstrates an algorithm for optimally associating Z{sub e} with any specified compound or mixture; (5) Discusses issues that can impact the usefulness of an effective-Z model; and (6) Recommends that, in order that the chosen effective-Z parameter not materially impact the accuracy of data produced by the EBSP program, the use of Z{sub eff} be replaced by Z{sub e}.
Date: April 5, 2011
Creator: Smith, J A; Martz, H E & Kallman, J S
Partner: UNT Libraries Government Documents Department

Nanocrystal Thickness Information from Z-Stem: 3-D Imaging in One Shot

Description: The authors have applied Atomic Number Contrast Scanning Transmission Electron Microscopy (Z-Contrast STEM) towards the study of colloidal CdSe semiconductor nanocrystals embedded in MEH-PPV polymer films. For typical nanocrystal thicknesses, the image intensity is a monotonic function of thickness. Hence an atomic column-resolved image provides information both on the lateral shape of the nanocrystal, as well as the relative thickness of the individual columns. They show that the Z-Contrast image of a single CdSe nanocrystal is consistent with the predicted 3-D model derived from considering HRTEM images of several nanocrystals in different orientations. They further discuss the possibility of measuring absolute thicknesses of atomic columns if the crystal structure is known.
Date: November 29, 1999
Creator: Kadavanich, A.V.; Kippeny, Tl; Erwin, M.; Rosenthal, S.J. & Pennycook, S.J.
Partner: UNT Libraries Government Documents Department

The transmission of differing energy beta particles through various materials

Description: The transmission of beta particles is frequently calculated in the same fashion as that of gamma rays, where the mass attenuation coefficient is defined by the slope of the exponential function. Numerous authors have used this approximation including Evans (1955), Loevinger (1952), and Chabot et. al. (1988). Recent work by McCarthy et. al. (1995) indicated that the exponential function seemed to fit well over a particular region of the transmission curve. Upon further investigation, the author decided to verify McCarthy`s results by the use of different absorber materials and attempt to reproduce the experiments. A theoretical method will be used to estimate the transmission of the beta particles through the three absorbers, aluminum, zirconium, and iron. An alternate Monte Carlo code, the Electron Gamma Shower version 4 code (EGS4) will also be used to verify that the experiment is approximating a pencil beam of beta particles. Although these two methods offer a good cross check for the experimental data, they pose a conflict in regards to the type of beam that is to be generated. The experimental lab setup uses a collimated beam of electrons that will impinge upon the absorber, while the codes are written using a pencil beam. A minor discrepancy is expected to be observed in the experimental results and is currently under investigation by McCarthy. The results of this project supported the theory that the beta mass attenuation coefficient was accurately represented by the slope of an exponential function, but only for that particular region of the transmission curve that has a minimal absorber thickness. By fitting the data beyond 50% of the beta particle range this theory does not hold true. The theory generated by McCarthy (1995) and the EGS4 Monte Carlo code indicated that the transmission curve for a pencil beam was not accurately ...
Date: April 1, 1996
Creator: Quayle, D.R.
Partner: UNT Libraries Government Documents Department

Coulomb sum rule for {sup 4}He

Description: We determine the Coulomb sum for {sup 4}He using world data on {sup 4}He(e, e') and compare the results to calculations based on realistic interactions and including two-body components in the nuclear charge operator. We find good agreement between theory and experiment using free-nucleon form factors. The apparent reduction of the in-medium G{sub ep} implied by IA-interpretation of the L/T-ratios measured in {sup 4}He(e,e'p) and {sup 4}He([vec]e, e'p) is not confirmed.
Date: October 1, 2002
Creator: Carlson, J.; Jourdan, J.; Schiavilla, R. & Sick, I.
Partner: UNT Libraries Government Documents Department

Curvature of the Lanthanide Contraction: An Explanation

Description: A number of studies have shown that for isostructural series of the lanthanides (elements La through Lu), a plot of equivalent metal-ligand bond lengths versus atomic number differs significantly from linearity and can be better fit as a quadratic equation. However, for hydrogen type wave functions, it is the inverse of the average distance of the electron from the nucleus (an estimate of size) that varies linearly with effective nuclear charge. This generates an apparent quadratic dependence of radius with atomic number. Plotting the inverse of lanthanide ion radii (the observed distance minus the ligand size) as a function of effective nuclear charge gives very good linear fits for a variety of lanthanide complexes and materials. Parameters obtained from this fit are in excellent agreement with the calculated Slater shielding constant, k.
Date: December 21, 2009
Creator: Raymond, Kenneth; Wellman, Daniel; Sgarlata, Carmelo & Hill, Aru
Partner: UNT Libraries Government Documents Department

High Energy Proton Spallation -- Fission of Uranium

Description: The fission and spallation reactions caused in uranium by bombardment with high energy protons (340 t o 350 MeV) were investigated. The reaction products were separated from the target by chemical processes and identified by their radioactive properties. The relative yields of the observed fission products were measured, and the results plotted as a function of mass number. Several of the spallation products were identified and their yields estimated. An attempt was made to determine the most probable atomic number for a nuclide of given mass formed directly from fission. Studies were made of the relative yields along several isobaric chains as a function of atomic number. From these data predictions of the mass and charge of the fissioning nucleus are made.
Date: May 28, 1951
Creator: Folger, R.L.; Stevenson, P.C. & Seaborg, G.T.
Partner: UNT Libraries Government Documents Department

Artificial Collateral Chains to the Thorium and ActiniumFamilies

Description: The authors have produced and identified two new series of alpha-particle emitting radioactive elements; one is a 'collateral' branch of the actinium (4n + 3) radioactive family and the other is collateral to the thorium (4n) family. The series are of considerable interest in that they are the first whose early members lie on the neutron deficient side of beta stability. They have been produced in high yield of irradiation of thorium with deuterons of energy about {sup 80}Mev in the Berkeley 184-inch cyclotron. So far as the present observations are concerned both of these series begin with isotopes of protactinium (atomic number 91), although progenitors with higher atomic numbers are to be expected and will possibly be produced and identified. These protactinium isotopes are Pa{sup 227} and Pa{sup 228} formed by d,7n and d,6n reactions respectively.
Date: July 1, 1948
Creator: Ghiorso, A.; Meinke, W.W. & Seaborg, G.T.
Partner: UNT Libraries Government Documents Department


Description: The total yields of nuclear charge or mass from projectile and target fragments and the fragments from the overlapping region between projectile and target were evaluated based on existing data. These values are compared with simple formulas expected from the participant-spectator model. Agreement is reasonably good, suggesting that the major part of the integrated yields for all reaction products from high-energy heavy-ion collisions are geometrical.
Date: February 1, 1980
Creator: Nagamiya, S. & Morrissey, D.J.
Partner: UNT Libraries Government Documents Department

Including shielding effects in application of the TPCA method for detection of embedded radiation sources.

Description: Conventional full spectrum gamma spectroscopic analysis has the objective of quantitative identification of all the radionuclides present in a measurement. For low-energy resolution detectors such as NaI, when photopeaks alone are not sufficient for complete isotopic identification, such analysis requires template spectra for all the radionuclides present in the measurement. When many radionuclides are present it is difficult to make the correct identification and this process often requires many attempts to obtain a statistically valid solution by highly skilled spectroscopists. A previous report investigated using the targeted principal component analysis method (TPCA) for detection of embedded sources for RPM applications. This method uses spatial/temporal information from multiple spectral measurements to test the hypothesis of the presence of a target spectrum of interest in these measurements without the need to identify all the other radionuclides present. The previous analysis showed that the TPCA method has significant potential for automated detection of target radionuclides of interest, but did not include the effects of shielding. This report complements the previous analysis by including the effects of spectral distortion due to shielding effects for the same problem of detection of embedded sources. Two examples, one with one target radionuclide and the other with two, show that the TPCA method can successfully detect shielded targets in the presence of many other radionuclides. The shielding parameters are determined as part of the optimization process using interpolation of library spectra that are defined on a 2D grid of atomic numbers and areal densities.
Date: December 1, 2011
Creator: Johnson, William C. & Shokair, Isaac R.
Partner: UNT Libraries Government Documents Department

Combined local-density and dynamical mean field theory calculations for the compressed lanthanides Ce, Pr, and Nd

Description: This paper reports calculations for compressed Ce (4f{sup 1}), Pr (4f{sup 2}), and Nd (4f{sup 3}) using a combination of the local-density approximation (LDA) and dynamical mean field theory (DMFT), or LDA+DMFT. The 4f moment, spectra, and the total energy among other properties are examined as functions of volume and atomic number for an assumed face-centered cubic (fcc) structure. These materials are seen to be strongly localized at ambient pressure and for compressions up through the experimentally observed fcc phases ({gamma} phase for Ce), in the sense of having fully formed Hund's rules moments and little 4f spectral weight at the Fermi level. Subsequent compression for all three lanthanides brings about significant deviation of the moments from their Hund's rules values, a growing Kondo resonance at the fermi level, an associated softening in the total energy, and quenching of the spin orbit since the Kondo resonance is of mixed spin-orbit character while the lower Hubbard band is predominantly j = 5/2. while the most dramatic changes for Ce occur within the two-phase region of the {gamma}-{alpha} volume collapse transition, as found in earlier work, those for Pr and Nd occur within the volume range of the experimentally observed distorted fcc (dfcc) phase, which is therefore seen here as transitional and not part of the localized trivalent lanthanide sequence. The experimentally observed collapse to the {alpha}-U structure in Pr occurs only on further compression, and no such collapse is found in Nd. These lanthanides start closer to the localized limit for increasing atomic number, and so the theoretical signatures noted above are also offset to smaller volume as well, which is possibly related to the measured systematics of the size of the volume collapse being 15%, 9%, and none for Ce, Pr, and Nd, respectively.
Date: March 30, 2005
Creator: McMahan, A K
Partner: UNT Libraries Government Documents Department


Description: Chemical yields of Fe{sup 3+} have been measured from FeSO{sub 4} solutions irradiated in the presence and absence of oxygen with carbon, neon, and argon ions from the Berkeley Bevalac facility. G(Fe{sup 3+}) decreases with increasing beam penetration and with increasing atomic number of the incident ion. The results are compared with current theoretical expectations of the behavior of these particles in an aqueous absorber. The chemical yields are consistently higher than theoretically predicted, by amounts varying from <6.2% (carbon ions) to <13.2% (argon ions). The additional yields are possibly attributable to fragmentation of the primary particle beams.
Date: July 1, 1980
Creator: Christman, E.A.; Appleby, A. & Jayko, M.
Partner: UNT Libraries Government Documents Department

Systematics of Fission-Product Yields

Description: Empirical equations representing systematics of fission-product yields have been derived from experimental data. The systematics give some insight into nuclear-structure effects on yields, and the equations allow estimation of yields from fission of any nuclide with atomic number Z{sub F} = 90 thru 98, mass number A{sub F} = 230 thru 252, and precursor excitation energy (projectile kinetic plus binding energies) PE = 0 thru {approx}200 MeV--the ranges of these quantities for the fissioning nuclei investigated. Calculations can be made with the computer program CYFP. Estimates of uncertainties in the yield estimates are given by equations, also in CYFP, and range from {approx} 15% for the highest yield values to several orders of magnitude for very small yield values. A summation method is used to calculate weighted average parameter values for fast-neutron ({approx} fission spectrum) induced fission reactions.
Date: May 1, 2002
Creator: Wahl, A.C.
Partner: UNT Libraries Government Documents Department

The two-photon decay of 1s2s {sup 1}S{sup 0} states in heavy he-like atomic systems.

Description: In He-like systems the decay of the 1s2s {sup 1}S0 excited state to the 1s{sup 2} {sup 1}S0 ground state is not allowed. This excited state can only decay to the ground state via the emission of two photons. The spectral shape of the emitted continuum is determined by the complete structure of the atomic system as all bound and continuum P states contribute to the 2E1 decay. For very heavy atomic systems the {sup 3}P states ALSO have to be included and the normalized spectral shape changes with atomic number according to the relative strengths of both, the electron-electron interaction and of the relativistic effects. A brief survey on the variation of the spectral shape of the two-photon continuum with atomic number is given and compared to experiments ranging from He-like Ni to He-like Au with special emphasis on the heavy relativistic system. The data compare well with fully relativistic calculations.
Date: August 14, 2002
Creator: Mokler, P. H.; Dunford, R. W. & Kanter, E. P.
Partner: UNT Libraries Government Documents Department

Atomic Resolution Microscopy of Semiconductor Defects and Interfaces

Description: The optical arrangement of the scanning transmission electron microscope (STEM) allows formation of incoherent images by use of a large annular detector. Here we show this capability in the imaging of defects in GaN and the interfacial region of an Au/GaAs ohmic contact. A resolution of around 0.15 nm is attained. Such Z-contrast images show strong atomic number contrast and allow the probe to be positioned accurately at the defect or interface for the purpose of performing high spatial resolution electron energy-loss spectroscopy (EELS).
Date: June 17, 1999
Creator: Baca, A.G.; Browning, N.D.; James, E.M; Reno, J.L. & Xin, Y.
Partner: UNT Libraries Government Documents Department

Progress in table-top transient collisional excitation x-ray lasers at LLNL

Description: We present progress in experiments for high efficiency Ne-like and Ni-like ion x-ray lasers using the transient collisional excitation scheme. Experimental results have been obtained on the COMET 15 TW table-top laser system at the Lawrence Livermore National Laboratory (LLNL). The plasma formation, ionization and collisional excitation of the x-ray laser have been optimized using two sequential laser pulses of 600 ps and 1 ps duration with an optional pre-pulse. We have observed high gains up to 55 cm{sup {minus}1} in Ne-like and Ni-like ion schemes for various atomic numbers. We report strong output for the 4d - 4p line in lower Z Ni-like ion sequence for Mo to Y, lasing from {approximately}190 {angstrom} to 240 {angstrom}, by pumping with less than 5 J energy on target.
Date: February 7, 1999
Creator: Da Silva, L. B.; Dunn, J.; Li, Y.; Nilsen, J.; Osterheld, A.; Shepherd, R. et al.
Partner: UNT Libraries Government Documents Department

Solubility Behavior and Phase Stability of Transition Metal Oxides in Alkaline Hydrothermal Environments

Description: The solubility behavior of transition metal oxides in high temperature water is interpreted by recognizing three types of chemical reaction equilibria: metal oxide hydration/dehydration, metal oxide dissolution and metal ion hydroxocomplex formation. The equilibria are quantified using thermodynamic concepts and the thermochemical properties of the metal oxides/ions representative of the most common constituents of construction metal alloys, i.e., element shaving atomic numbers between Z = 22 (Ti) and Z = 30 (Zn), are summarized on the basis of metal oxide solubility studies conducted in the laboratory. Particular attention is devoted to the uncharged metal ion hydrocomplex, M{sup Z}(OH){sub Z}(aq), since its thermochemical properties define minimum solubilities of the metal oxide at a given temperature. Experimentally-extracted values of standard partial molal entropy (S{sup 0}) for the transition metal ion neutral hydroxocomplex are shown to be influenced by ligand field stabilization energies and complex symmetry.
Date: May 18, 2000
Creator: Ziemniak, S.E.
Partner: UNT Libraries Government Documents Department

The Transcalifornium Elements

Description: During the past sixty years, four elements beyond californium on the atomic number scale have been synthesized by the transmutation of lighter elements. The first preparation of einsteinium and fermium occurred in a thermonuclear explosion. Mendelevium and element 102, however, were prepared by a more conventional method, that of charged particle bombardment of elements of high atomic number.
Date: December 8, 1958
Creator: Seaborg, Glenn T.
Partner: UNT Libraries Government Documents Department


Description: The radiation chemistry of heavy particle tracks in dilute aqueous solution is considered in a unified manner. Emphasis is on the physical and chemical phenomena which are involved rather than on the construction of models to be used in actual calculations although the latter problem is discussed. A differential segment of a heavy particle track is composed of two parts which we call 'core' and 'penumbra'; elementary considerations show that all properties of such a differential track can be uniquely specified in terms of a two-parameter system, and we choose energy per nucleon (E) and atomic number (Z) as independent parameters. The nature of heavy-particle track processes varies with the magnitude of the energy deposit (LET), and we discuss three categories of track problems, for low-, intermediate-, and high-LET cases, respectively. Scavenger reactions normally terminate radical recombination in a track, and for heavy particle tracks we find a criterion involving the scavenger concentration for a convenient separation of core and penumbra into essentially noninteracting parts which can be treated independently. Problems of the core expansion in the three regions are considered and it is found that a versatile model can be constructed on concepts previously introduced by Ganguly and Magee. A model for the penumbra, based on the authors electron track theory, is presented and discussed.
Date: March 1, 1980
Creator: Magee, J.L. & Chatterjee, A.
Partner: UNT Libraries Government Documents Department

Atomic-Resolution STEM at Low Primary Energies

Description: Aberration-corrected scanning transmission electron microscopes (STEMs) can now produce electron probes as small as 1 {angstrom} at 60 keV. This level of performance allows individual light atoms to be imaged in various novel materials including graphene, monolayer boron nitride, and carbon nanotubes. Operation at 60 keV avoids direct knock-on damage in such materials, but some radiation damage often remains, and limits the maximum usable electron dose. Elemental identification by electron energy loss spectroscopy (EELS) is then usefully supplemented by annular dark-field (ADF) imaging, for which the signal is much larger and the spatial resolution significantly better. Because of its strong dependence on the atomic number Z, ADF can be used to identify the chemical type of individual atoms, both heavy and light. We review the instrumental requirements for atomic resolution imaging at 60 keV and lower energies, and we illustrate the kinds of studies that have now become possible by ADF images of graphene, monolayer BN, and single-wall carbon nanotubes, and by ADF images and EEL spectra of carbon nanotubes containing nanopods filled with single atoms of Er. We then discuss likely future developments.
Date: January 1, 2011
Creator: Krivanek, Ondrej L.; Chisholm, Matthew F; Dellby, N. & Murfitt, M. F.
Partner: UNT Libraries Government Documents Department