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Lifetime measurements in 178-Hf
No full textLifetimes of levels from K-pi = 2(+), K-pi = 4(+) and several K-pi = 0(+) bands have been measured in the 178-Hf nucleus using the GRID technique. Lifetimes of the 2(+) and 3(+) levels were measured within the K-pi = 2(+) gamma band. A lower limit was established for the lifetime of the 4(+) level of the K-pi = 4(+) band. The resulting upper limits for the absolute B(E2) values exclude collective transitions from the K-pi = 4(+) to the ground state band but not to the K-pi = 2(+) gamma band. Level lifetimes were also measured for several states within three separate K-pi = 0(+) bands. Evidence is presented for a previously unobserved case of two excited K-pi = 0(+) bands being connected via collective E2 transitions
Study of interatomic potentials using the crystal-GRID method on oriented single crystals of Ni, Fe, and Cr
No full textThe Crystal-GRID method is used to study interatomic collisions at low energy in metals and such to probe the repulsive interatomic potential. Line shapes of gamma rays, emitted by the recoiling Ni-59 isotope after thermal neutron capture in Ni single crystals, were measured and compared to results obtained by molecular dynamics simulations of the slowing down. The same procedure is also used for recoiling Fe-57 and Cr-54 atoms in Fe and Cr single crystals, respectively. Different potentials (including several from the embedded atom method) are investigated using the observed fine structure of the line shape which depends on the crystal orientations. From the detailed study of the lineshapes measured in two different orientations, a new potential is then derived for each element. Nuclear state lifetimes for the excited isotopes are also deduced with a higher precision than obtained with standard nuclear techniques
Computation of Fresnel integrals. II
No full textThis paper describes an improved method for computing Fresnel integrals with an error of less than 1 x 10(-9). The method is based on a known approximate formula for a different integral which is due to Boersma and referenced by Abramowitz and Stegun
Comparison of the NIST and NPL air kerma standards used for X-ray measurements between 10 kV and 80 kV
No full textA direct comparison was made between the air kerma primary standards used for the measurements of low-energy x rays at the National Institute of Standards and Technology (NIST) and the National Physical Laboratory (NPL). The comparison was conducted at the NPL using NPL reference radiation qualities between 10 kV and 80 kV. The results show the primary air-kerma standards to agree within 0.6 % of their values for beam qualities up to 80 kV
Calibration of high-resolution X-ray tomography with atomic force microscopy
No full textFor two-dimensional x-ray imaging of thin films, the technique of scanning transmission x-ray microscopy (STXM) has achieved images with feature sizes as small as 40 nm in recent years. However, calibration of three-dimensional tomographic images that are produced with STXM data at this scale has not yet been described in the scientific literature, and the calibration procedure has novel problems that have not been encountered by x-ray tomography carried out at a larger scale. In x-ray microtomography, for example, one always has the option of using optical imaging on a section of the object to verify the x-ray projection measurements. with STXM, on the other hand, the sample Features are too small to be resolved by light at optical wavelengths. This fact implies that one must rely on procedures with higher resolution, such as atomic force microscopy (AFM), for the calibration. Such procedures, however, generally depend on a highly destructive sectioning of the sample, and are difficult to interpret because they give surface information rather than depth information. In this article, a procedure for calibration is described that overcomes these limitations and achieves a calibration of an STXM tomography image with an AFM image and a scanning electron microscopy image of the same object. A Ge star-shaped pattern was imaged at a synchrotron with a scanning transmission x-ray microscope. Nineteen high-resolution projection images of 200x200 pixels were tomographically reconstructed into a three-dimensional image. Features in two-dimensional images as small as 40 nm and features as small as 80 nm in the three-dimensional reconstruction were resolved. Transverse length scales based on atomic force microscopy, scanning electron microscopy, x-ray transmission and tomographic reconstruction agreed to within 10 nm. Toward the center of the sample, the pattern thickness calculated from projection images was (51 +/- 15) nm vs (80 +/- 52) nm for tomographic reconstruction, where the uncertainties are evaluated at the level of two standard deviations
Portrait of Nancy Trahey
No full textNancy Trahey
Nancy Trahey was born on January 31, 1941, in Las Vegas, New Mexico, and grew up in Long Beach, CA. There, Nancy attended St. Anthony’s High School where she excelled scholastically. Upon graduation, she was awarded a four-year scholarship to Immaculate Heart College, graduating in 1962 with a B.S. in chemistry. Trahey’s professional career began as a chemist with Rockwell International Atomic Division, then as a project manager with the New Brunswick Laboratory, followed by the Department of Energy Argonne Laboratory.
In 1995, Trahey joined the National Institute of Standards and Technology’s (NIST) Office of Measurement Services. In 1999, she received a Bronze Medal “for outstanding efforts in forging a stronger partnership between NIST, American Society for Testing and Materials (ASTM) and U.S. industry regarding production of standard reference materials.”
Trahey was a member of the American Association for the Advancement of Science, the American Chemical Society, the American Nuclear Society, and the Standards Engineering Society. She was listed as a noteworthy chemist by Marquis Who’s Who of American Women. She retired in 2001 and died December 23, 2024.
Source: Standards Alumni Association Newsletter, April 2025, p.2