Adon A. Gordus

Factors affecting the trace-metal content of human hair

Both present-day and historical head-hair samples up to 300 years old are being analysed by neutron activation for more than 30 trace elements. This study, designed to determine an historical base-line for the human intake of trace metals and to provide an evaluation of the present-day rate of increase and sources of environmental pollution, has direct forensic applicability. Modern samples being analysed in this study include hair from U. S. Naval Academy midshipmen and U.S. Air Force Academy cadets obtained upon arrival at the Academies in mid-1971 and again at later intervals during which trace-metal equilibration due to fixed diets and environmental conditions is presumed to occur. A wide variety of factors such as age, sex, hair structure and color, geographic location, general diet, socieconomic status are being considered in evaluating the analysis data. Examples of some of the initial data obtained from the analysis of the first three sets of Naval Academy midshipmen hair are presented.

Obsidian Sources Characterized by Neutron-Activation Analysis

Concentrations of elements such as manganese, scandium, lanthanum, rubidium, samarium, barium, and zirconium in obsidian samples from different flows show ranges of 1000 percent or more, whereas the variation in element content in obsidian samples from a single flow appears to be less than 40 percent. Neutron-activation analysis of these elements, as well as of sodium and iron, provides a means of identifying the geologic source of an archeological artifact of obsidian.

A Closed General Solution of the Probability Distribution Function for Three‐Dimensional Random Walk Processes

A closed general solution of the probability distribution function for three‐dimensional random walk processes is derived. In addition: (1) For the particular case of equal‐length displacements, the exact solution is compared with the Gaussian approximation for n=3, 5, and 10 steps. (2) The general solution is utilized in calculating the probability distribution of gamma‐ray energies resulting in the Cl35 (n, γ) Cl36 process. (3) For five unequal steps of fractional length: 0.582, 0.135, 0.131, 0.092, and 0.060 (which is somewhat characteristic of the fractional energies of gamma rays resulting from neutron capture), the exact solution is compared with a Gaussian, a modified Gaussian, and a five equal‐step approximation. (4) There are presented the specific solutions for all possible unequal‐length random displacements involving n=2, 3, and 4 steps.

Failure to Bond Rupture and Nuclear Recoil Following (n, γ) Activation

Following the absorption of a thermal neutron by 127I or 79Br, the neutron‐binding energy is frequently released in the form of a gamma‐ray cascade. As a result of partial cancellation of gamma‐ray momenta, a small fraction of the activated halogens will not receive sufficient recoil momentum to rupture from their parent compound. The gas‐phase failures to bond rupture following 127I(n, γ) 128I, and 79Br(n, γ) 80Br activation were found experimentally to be: CH3I—1.09, CD3I—0.68, CF3I—0.12, CH2I2—0.068, C2H5I—0.082, n‐C3H7I—0.66, i‐C3H7I—0.30, CH3Br—0.25, CD3Br—0.20, CH2Br2—0.12, CF3Br—0.11, CF2Br2—0.093, CHClBr2—0.087, CCl3Br—0.066, CHBr3—0.05, CBr4—0.03, C2H5Br—0.33, and 1,1‐C2H4Br2—0.17%. These data are correlated with the calculated recoil energies required for bond rupture (preceding article). Using as a basis the distribution of net gamma‐ray energies calculated by the random‐walk method for the 35Cl(n, γ) 36Cl process, the kinetic‐energy distributions of the dissociated 128I or 80Br are approximate...

Neutron Activation Analysis of Obsidian: An Example of Its Relevance to Northwestern Plains Archaeology

AbstractBy a process of neutron activation, obsidian samples from an archaeological site may be traced to their quarry sources. The potential of this type of information remains largely unexplored ...

Energy‐Distribution Function for Hot Atoms Produced by Nuclear Transformations

The energy‐distribution function for hot atoms produced by nuclear transformations is examined in terms of the fraction of the initial hot‐atom energy. Energy dependent and independent asymmetric scattering is specifically considered. For gaseous tritium generated by the 3He(n, p) process, the asymptotic solution probably can serve as a reasonable approximation of the distribution function in the energy range 2–20 eV. For hot atoms produced with an initial distribution of energies, such as 79Br(n, γ)‐produced 80Br, the asymptotic solution will be less valid than for tritium, but may still be a valid approximation.

Momentum Transfer to an Atom in a Molecule: Internal Excitation and Bond Dissociation

An atom will dissociate from a compound if the atom receives a recoil momentum greater than some average value Q0. Considering a polyatomic molecule as composed of point‐mass atoms, there is derived an equation which relates Q0 to the bond energy, bond angles and distances, and masses of the atoms in the molecule. The minimum net recoil energy required for bond rupture, the kinetic energy of the recoiling radicals, and the internal energy of the radical originally bonded to the activated atom are calculated for a series of simple alkyl halides.

Reactions of High‐Energy, Excited I128 Ions with Gaseous Molecules

The manner in which molecular additives inhibit the reaction of (n, γ) activated I128 with CH4 was determined in an effort to observe indirectly reactions of I128 with the additives. The data suggest that (1) O2, N2, and CF4 serve only to remove excess I128 kinetic energy; (2) the ionization potential of O2 is greater than 12.16 ev, the potential energy of I+(1D2); (3) the ionization potential of C2F6 is less than 12.16 ev; (4) CH3I, CF3I, n‐C3H7I, and C6H6 inhibit the reaction principally as a result of I++additive ion‐molecule reactions and/or physical quenching.

Neutron Activation Analysis of Microgram Samples of Sasanian Coins and Metallic Art

Neutron activation analysis of microgram metal-rubbing samples from over 2,000 Sasanian (Persia: 224-651 AD) silver coins and a few hundred art objects allow grouping the data in terms of the gold-impurity levels. About 1,000 of the silver coins were from the reign of Khusrau ∥ (591-628 AD) and represent various mints and dates. For the early coins, mg gold/100 silver values of less than 0.3 are associated with relatively modern fakes. The authentic coins and authentic silver Sasanian art almost always have values in the range of 0.3-1.0. Questionable ‘Sasanian’ art objects in private collections usually have goldimpurity levels of less than 0.3.

C13 and Deuterium Isotope Effects in the Photolysis of Methyl and Ethyl Bromide

Relative rates of formation of isotopic radicals in the photolysis of gaseous methyl and ethyl bromide have been measured. Photolyses (2537 A) were carried out in a large excess of cyclopentane. Methyl (or ethyl) radicals formed in the primary C–Br bond scission abstract H from cyclopentane to form methane (or ethane). For methyl bromide, the C12/C13 enrichment factor for the first fraction of the methane was 1.039±0.003. The corresponding factor for the α‐carbon—Br rupture in ethyl bromide was 1.041±0.004. In the deuterium experiments, CH3Br—CD3Br mixtures in excess cyclopentane were photolyzed. The H/D fractionation factor (based on CH4/CD3H) was 1.41±0.01.The difference in rates of formation of isotopic radicals is due to the difference in ultraviolet absorption coefficients of the isotopic alkyl bromides. At 2537 A the observed ratio of the extinction coefficient of CH3Br relative to that of CD3Br is 1.38±0.05.