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The measurement of little g: A fertile ground for precision measurement science
No full textThe occasion of the 100th anniversary of Einstein's "golden year" provides a wonderful opportunity to discuss some aspects of gravity-gravitation being an interest of Einstein's that occurred a few years after 1905. I'll do this by talking about the measurement of little g, the free-fall acceleration on the Earth's surface that is mainly due to the Earth's gravity but whose value is also affected by centrifugal forces that are a result of the Earth's rotation. I will also describe two equivalence experiments and a test of the inverse-square law of gravitation. Finally, I will make some observations on the science of precision measurement-a subject that underpins much of scientific progress
A summary of heat-flux sensor calibration data
No full textThis paper presents a statistical evaluation of the responsivity data on a number of heat-flux sensors, calibrated using an electrical substitution radiometer as a transfer standard up to 5 W.cm(-2). The sensors, furnished by the customers, were of circular-foil or thermopile type. Comparison of the NIST and the customer measured responsivity values showed that the measurements agree within 3 % for more than half the number of sensors tested, so far. Considering the variation in the customer calibration techniques and the wide measuring range of the sensors used in the calibration, the agreement is encouraging
Magnetic field stabilization for magnetically shielded volumes by external field coils
No full textFor highly sensitive magnetic measurements, e. g., a measurement of the neutron electric dipole moment (EDM), the magnetic field has to be stable in time on a level below picoTesla. One of several measures we employ to achieve this uses an external field coil system which can stabilize the ambient external field at a predefined value. Here we report on the construction and characterization of such a system in the magnetic test facility at PSI. The system actively stabilizes the field along the axis of the EDM experiment by means of four coils in a Helmholtz-like configuration. Additional coils serve to compensate for transverse ambient field components. Because of the long integration times in the EDM experiment ( about 100 s or more) only slow disturbances have to be corrected for. The performance of the system has been measured using static and moving magnetic sources and suppression factors in excess of 200 have been observed
Quantitating fluorescence intensity from fluorophore: Assignment of MESF values
No full textA procedure is presented to convert the comparison of measured fluorescence signals into a comparison of fluorescence yields (FY). The fluorescence yield, which is a property of a solution or a suspension, is defined as the product of the fluorophore concentration and the molecular quantum yield. The paper revises the measurement model which relates the measured fluorescence signal to the FY. The equality of FY of two solutions provides an equivalence between the concentrations of fluorophore in the two solutions. The equivalence is the basis for quantitation in terms of molecules of equivalent soluble fluorophore (MESF). The quantitation procedure starts with the measurement of fluorescence signals from a serial dilution of fluorescein solutions to obtain a calibration of a fluorometer. The fluorometer is used to measure the fluorescence signal of a suspension of microspheres with immobilized fluorescein isothiocyanate (FITC). The calibration is used to obtain the concentration of soluble fluorophores which gives the same fluorescence signal as the microsphere suspension. The number concentration of microspheres is measured and the equality of fluorescence yields is used to obtain the number of soluble fluorescein molecules equivalent to a single microsphere
Radiative corrections for neutron decay and search for new physics
No full textThe expected increased accuracy of neutron beta-decay experiments at the new Spallation Neutron Source could result in more stringent tests of the Standard Model. For an unambiguous search for new physics in neutron decay experiments and for a precise determination of fundamental constants, it is necessarily to understand and evaluate all corrections for neutron decay with higher accuracy than the expected experimental precision. We discuss the possibility to estimate the accuracy of radiative corrections. New results based on the applications of effective field theory for neutron decay is presented
The beta-, neutrino- and proton-asymmetry in neutron beta-decay
No full textThis article describes measurements of angular-correlation coefficients in the decay of free neutrons with the superconducting spectrometer PERKEO II. A method for measuring the beta-asymmetry coefficient A is presented, as well as a new method for determining the neutrino-asymmetry coefficient B, which allows a value for the proton-asymmetry coefficient C to be obtained for the first time. An ongoing experiment is trying to improve the accuracy of these quantities
Determination of the electron-antineutrino angular correlation coefficient a(0) in unpolarized neutron beta-decay
No full textThe coefficient a(0) has been derived from a measurement of the integral spectrum of recoil protons stored in a quasi-Penning trap with inhomogeneous magnetic field and adiabatic focusing onto an electro-static mirror of potential variable in 10 V steps between 0 V and 850 V. Correction for incomplete transfer of energy from transverse to longitudinal degrees of freedom, and the violation of the adiabatic conditions on reflection at the mirror, is carried out by alternately measuring the spectrum at trapping times of 1 ms and 2 ms. The results a(0)=-0.1054 +/- 0.0055 and vertical bar lambda vertical bar=1.271 +/- 0.018 are comparable in precision with existing measurements of a(0)
On the measurement of the electron-neutrino correlation in neutron beta decay
No full textI present a new approach to the measurement of a, the electron-neutrino correlation, in neutron beta decay. A precise measurement of a can lead to a precise determination of ratio of the axial vector and vector coupling constants, G(a)/G(v). Coincidences between electrons and protons are detected in a field-expansion spectrometer. The field-expansion spectrometer is designed to make 1/TOF approximate to vertical bar p(p)vertical bar. TOF and p(p) are the proton time of flight and momentum. Two segmented Si detectors view both electrons and protons in 4 pi geometry. The time of flight between the electron and proton are accurately measured in a long, approximate to 1 m, drift distance. The electron energy is accurately measured in the Si detectors. The proton momentum and electron energy determine the electron-neutrino opening angle. I have shown that by sorting the data on proton time of flight and electron energy, a can be determined with a statistical relative standard uncertainty of approximate to 2.4/root n, where n is the number of decays observed. The approach has a number of advantages. The acceptance of the spectrometer is 4p for both particles. Thin-dead-layer segmented Si detectors as well as all other components in the apparatus, are commercially available. There are no material apertures to determine the acceptance of the apparatus. The charged particles interact only with electric and magnetic fields before striking the detectors. Coincident detection of electrons and protons reduces backgrounds, and allows the in situ determination of backgrounds. In the analysis, it is not necessary to sort on the relative electron and proton direction and hence electron back scattering does not cause systematic uncertainties. A time of flight spectrum is obtained for each electron energy. Different parts of the spectra have different sensitivities to a. The medium time of flight parts of the spectra that are insensitive to a can be used to verify the accuracy of the electric and magnetic field determinations
Jack E. Snell
No full textJack E. Snell
Inducted: 2005
Citation:
For outstanding leadership of the NIST Center for Fire Research and the Building and Fire Research Laboratory.
Tenure: 1971-2003
Birth: 1935 Evanston, Illinois
Education:
Princeton University, BSE (Aeronautical Engineering), 1957
Northwestern University, MSE (Industrial Engineering), 1964
Northwestern University, PhD (Civil Engineering), 1966
Positions held:
Chief, Building Service Systems Section, Building Environment Division, 1971-1973
Assistant Chief, Building Environment Division, 1973-1974
Chief, Office of Energy Conservation, 1974-1978
Director, Office of Energy Programs, 1978-1981
Director, Center for Fire Research, 1981-1990
Deputy Director, Building and Fire Research Laboratory, 1990-1999
Director, Building and Fire Research Laboratory, 1999-2003
Honors:
US Department of Commerce, Silver Medal, 1975; Gold Medals, 1987 and 2004
Department of Commerce Federal Engineer of the Year Award, 1987
Chi Epsilon and Sigma Xi Honor Societies
Memberships:
Construction Industry Institute
Founding member of FIATECH
Founding Chair International Forum for Cooperation in Fire Research
National Fire Protection Association (NFPA)
Society of Fire Protection Engineers
American Society of Mechanical Engineers (Fellow)
ASTM Committee E 5 Fire Test Standards.
Publications:
More than 60 publications, including:
Snell, J.E., Achenbach, P.R., Petersen, S.R., Energy Conservation: Influences on New Building Design, Science, vol. 192 No. 4246, June 25, 1976.
Snell, J.E., The Future of Fire Research, Keynote, National Fire Protection Association Annual Conference, Chicago, IL May 13, 1985.
Snell, J.E. and Nelson, H.E., Summary of the National Bureau of Standards Analysis of the DuPont Plaza Hotel Fire, Proceedings from Interflam 88, 4th International Fire Conference, Churchill College, Cambridge, England, March 22-24, 1988.
Snell, J.E., Proposed National Construction Safety Team Act, Fire Protection Strategies for 21st Century Building and Fire Codes Symposium. Proceedings. Society of Fire Protection Engineering and American Institute of Architects, September 17-18, 2002, Baltimore Md