W. W. Beeman

Small-angle X-ray scattering from turnip yellow mosaic virus☆

Abstract The small-angle X-ray scattering has been measured from solutions of turnip yellow mosaic virus and the associated protein. The data indicate that both particles are near spherical and about 140 A in radius. The virus is approximately uniform electron density. The protein is a water-filled spherical shell with a ratio of inner to outer radius of 0.75. The 140 A quoted represents the radius of the protein structure excluding external hydration. Thus both particles have large internal hydrations. A reasonable assignment of hydration to the protein and nucleic acid fractions of the virus particle is possible, which gives the particle an approximately uniform electron density.

An X‐Ray Investigation of the Shapes and Hydrations of Several Protein Molecules in Solution

The x‐ray scattering curves of five proteins in solution have been measured at small angles. The radii of gyration of the protein molecules are determined from the scattering curves. These data together with the known molecular weights, densities, and frictional ratios are used to estimate the axial ratios and hydrations of the molecules. Some possibilities and limitations of the method are pointed out.

The X‐Ray K Absorption Edges of Covalently Bonded Cr, Mn, Fe, and Ni

We discuss some recently measured absorption edges of covalent nickel complexes and edges of Cr, Mn, and Fe in similar complexes already in the literature. Low energy absorption (generally resolved as a line) is observed in all complexes where empty 4p orbital is expected from chemical or magnetic data. From the position of the line it is concluded that the metal ion is near neutral in the covalent complex. Where the 4p orbital is completely used in bonding, no low energy absorption line is observed. The method may be useful as an additional experimental check on the assignment of bonding orbitals.

An X-ray investigation of the sizes and hydrations of three spherical virus macromolecules in solution

Abstract We have measured the small-angle X-ray scattering from dilute aqueous solutions of southern bean mosaic virus, tobacco necrosis virus, and tomato bushy stunt virus. All of these virus particles are nearly spherical. Values of the sphere diameter obtained by a comparison of our curves with curves of the exact scattering function for spheres are SBMV = 286 A, TNV = 280 A and TBSV = 309 A. A comparison of these values with other molecular constants strongly suggests that they are internally hydrated. The effects upon the experimental curves of interparticle interference and of slit dimensions for the X-ray collimating system are considerable and have been taken into account.

Double Crystal and Slit Methods in Small Angle X-ray Scattering

An angular resolution of about 10 seconds of arc may be obtained with a double calcite crystal spectrometer for Cu Kα‐radiation. However, the shape of the rocking curve at large angles is such as to make the detection of radiation from weakly scattering materials difficult. Of the order of 106 counts per second are detected with a stationary, water‐cooled copper target and parallel crystals. Wing intensities, even at large angles, do not fall much below 102 counts per second. Wing heights may be considerably reduced by the addition of a third calcite crystal. With this modification the crystal spectrometer is a useful instrument for most scattering experiments in which extremely high resolution is desired. It is inferior to a slit system and Geiger counter arrangement when poorer resolution may be tolerated but high sensitivity is required. A slit instrument with an angular resolution of 4 or 5 minutes of arc provides an effective incident flux of more than 106 counts per second while wing intensities may...

Secondary electron emission from beams of polystyrene latex spheres

Polystyrene latex spheres suspended in a carrier gas of nitrogen are accelerated through a nozzle‐skimmer system into a vacuum chamber and ionized in a crossed electron beam. Measurements of the particle beam current as a function of the primary electron energy and current give information on the secondary electron emission yield of the spheres and on the energy distribution of the secondaries. The positively charged spheres provide their own retarding potential for the energy scan of the secondaries. For 260‐eV primaries the distribution in energy of the secondaries from polystyrene peaks between 1 and 2 eV. At 5 eV it has fallen to about 40% of its peak value. The yield per incident primary of secondaries (or scattered primaries) whose energy is greater than 5 eV is unity. Some advantages and limitations of the method are discussed.

X-ray studies on top component a and bottom component of alfalfa mosaic virus.

Abstract Small-angle X-ray-scattering measurements have been made on dilute solutions of two of the separated components of alfalfa mosaic virus. Top component a has an electronic radius of gyration of 129 A and bottom component 216 A. These results are accurate to about 5%. The extended scattering curve is in best agreement with a prolate, roughly cylindrical, shape for each particle. Top component a has a diameter of about 230 A and a length of 350 A. For bottom component the diameter is 220 A and the length 700 A. These results are not as reliable as the radii of gyration. Rather large hydrations are indicated for both particles.

On the Mechanism of the Small Angle X‐Ray Scattering from Cold Worked Metals

The characteristic small angle x‐ray scattering from cold worked polycrystalline foils of Cu, Al, and Ni is found to appear immediately when the foil is stretched in the x‐ray beam at liquid air temperature. The scattering at a fixed angle is a reversible function of foil temperature as long as recrystallization temperatures are not exceeded. The temperature dependence is about twice that expected from the Debye temperature factor of an average Bragg reflection. It is postulated that the small angle scattering is the result of two successive Bragg reflections from two slightly misoriented subgrains of the same grain. The small angle scattering is found to be polarized. This can be understood only on the double Bragg scattering model. The double Bragg model was suggested by our observation of occasional isolated small angle peaks from annealed foils. These have unusual characteristics which quickly eliminate any possible single scattering source. They are double scattering from two large annealed grains wh...