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Portrait of William Clyde Martin, Jr.
No full textWilliam Clyde Martin, Jr. was inducted into the NIST Gallery of Distinguished Scientists, Engineers, and Administrators in 2002. He was recognized “For many publications concerned with measurement and energy-level analysis of atomic spectra and for direction of the Atomic Energy Levels Data Center.
Birth: 1929, Cullman, Alabama.
Tenure at NIST:
1957-1998.
Positions at NIST:
Chief, Spectroscopy Section, Atomic Physics Division
Director, Atomic Energy Levels Data Center
Leader, Atomic Spectroscopy
NIST Scientist Emeritus.
Education:
B.S., Physics, University of Richmond, 1951
M.A., Physics, Princeton University, 1953
Ph.D., Physics, Princeton University, 195
A Ramsey's method with pulsed neutrons for a T-violation experiment
No full textA Ramsey's method with pulsed neutrons is discussed for neutron spin manipulation in a time reversal (T) symmetry violation experiment. The neutron spin (s(n)) is aligned to the direction of a vector product of the nuclear spin (I) and the neutron momentum (k(n)) for the measurement of a T-odd correlation term, which is represented as s(n) center dot (k(n) x I), during propagation through a polarized nuclear target. The phase control and amplitude modulation of separated oscillatory fields are discussed for the measurement of the T-odd correlation term
On the absorption spectrum of noble gases at the arc spectrum limit
No full textRydberg spectral lines of an atom are sometimes superimposed on the continuous spectrum of a different configuration. Effects of interaction among different configurations in one of these cases are theoretically investigated, and a formula is obtained that describes the behavior of absorption spectrum intensity. This offers qualitative justification of some experimental results obtained by BEUTLER in studies of absorption arc spectra of noble gases and I-b spectra of some metal vapors
A gamma polarimeter for neutron polarization measurement in a liquid deuterium target for parity violation in polarized neutron capture on deuterium
No full textA measurement of the parity-violating gamma asymmetry in n-D capture would yield information on N-N parity violation independent of the n-p system. Since cold neutrons will depolarize in a liquid deuterium target in which the scattering cross section is much larger than the absorption cross section, it will be necessary to quantify the loss of polarization before capture. One way to do this is to use the large circular polarization of the gamma from n-D capture and analyze the circular polarization of the gamma in a gamma polarimeter. We describe the design of this polarimeter
Measurement of the neutron lifetime by counting trapped protons
No full textWe measured the neutron decay lifetime by counting in-beam neutron decay recoil protons trapped in a quasi-Penning trap. The absolute neutron beam fluence was measured by capture in a thin (LiF)-Li-6 foil detector with known efficiency. The combination of these measurements gives the neutron lifetime: tau(n)=(886.8 +/- 1.2 +/- 3.2) s, where the first (second) uncertainty is statistical (systematic) in nature. This is the most precise neutron lifetime determination to date using an in-beam method
Re-analysis of the uncertainty of the 0.895 micrometer diameter (NIST SRM (R) 1690) and the 0.269 micro-m diameter (NIST SRM (R) 1691) sphere standards
No full textThe uncertainties of the mean diameters of the nominal 1.0 micro-m SRM(R) 1690 polystyrene spheres and of the nominal 0.3 micro-m SRM(R) 1691 polystyrene spheres are recomputed using the current NIST Guidelines for computing uncertainty. The revised expanded uncertainty ( approximately 95% confidence level) for SRM(R) 1690 polystyrene spheres is equal to 0.005 micro-m compared to previous value of 0.008 micro-m. The revised expanded uncertainty for SRM(R) 1691 is equal to 0.004 micro-m compared to the previous value of 0.007 micro-m. The major cause of the reduction in the uncertainty for the 1.0 micro-m spheres is from a decrease in the recomputed uncertainty of the refractive index of the polystyrene spheres. The 1.0 micro-m spheres were used in calibrating the electron microscope used to size the 0.3 micro-m spheres, and the reduction in the uncertainty of 1.0 micro-m SRM(R) uncertainty was the biggest factor in the decrease in the uncertainty of the 0.3 micro-m spheres
The fundamental neutron physics facilities at NIST
No full textThe program in fundamental neutron physics at the National Institute of Standards and Technology (NIST) began nearly two decades ago. The Neutron Interactions and Dosimetry Group currently maintains four neutron beam lines dedicated to studies of fundamental neutron interactions. The neutrons are provided by the NIST Center for Neutron Research, a national user facility for studies that include condensed matter physics, materials science, nuclear chemistry, and biological science. The beam lines for fundamental physics experiments include a high-intensity polychromatic beam, a 0.496 nm monochromatic beam, a 0.89 nm monochromatic beam, and a neutron interferometer and optics facility. This paper discusses some of the parameters of the beam lines along with brief presentations of some of the experiments performed at the facilities
Neutron measurements and the weak nucleon-nucleon interaction
No full textThe weak interaction between nucleons remains one of the most poorly-understood sectors of the Standard Model. A quantitative description of this interaction is needed to understand weak interaction phenomena in atomic, nuclear, and hadronic systems. This paper summarizes briefly what is known about the weak nucleon-nucleon interaction, tries to place this phenomenon in the context of other studies of the weak and strong interactions, and outlines a set of measurements involving low energy neutrons which can lead to significant experimental progress
Measurement of the coherent neutron scattering length of He-3
No full textBy means of neutron interferometry the s-wave neutron scattering length of the He-3 nucleus was re-measured at the Institut Laue-Langevin ( ILL). Using a skew symmetrical perfect crystal Si-interferometer and a linear twin chamber cell, false phase shifts due to sample misalignment were reduced to a negligible level. Simulation calculations suggest an asymmetrically alternating measuring sequence in order to compensate for systematic errors caused by thermal phase drifts. There is evidence in the experiment's data that this procedure is indeed effective. The neutron refractive index in terms of Sears' exact expression for the scattering amplitude has been analyzed in order to evaluate the measured phase shifts. The result of our measurement, b(c)' = (6.000 +/- 0.009) fm, shows a deviation towards a greater value compared to the presently accepted value of b(c)' = (5.74 +/- 0.07) fm, confirming the observation of the partner experiment at NIST. On the other hand, the results of both precision measurements at NIST and ILL exhibit a serious 12 sigma ( 12 standard uncertainties) deviation, the reason for which is not clear yet
Investigation of the neutron quantum states in the Earth's gravitational field
No full textWe studied the neutron quantum states in the potential well formed by the Earth's gravitational field and a horizontal mirror. The estimated characteristic sizes of the neutron wave functions in two lowest quantum states correspond to their expectations with an accuracy of approximate to 25 %. The spatial density distribution in a standing neutron wave above a mirror was measured for a set of a few lowest quantum states. A position-sensitive neutron detector with an extra high spatial resolution of 1 micro-m to 2 micro-m was developed and tested for this particular task. Although this experiment was not designed or optimized to search for an additional short-range force, nevertheless it allowed us to slightly improve the published boundary in the nanometer range of characteristic distances. We studied systematical uncertainties in the chosen "flow-through" method as well as the feasibility to improve further the accuracy in this experiment