Neutron-capture cross sections of four stable tungsten isotopes were measured as a function of energy by time of flight at the Oak Ridge Electron Linear Accelerator. The resolution achieved, ..delta..E/E about 1/750 FWHM, has allowed the analysis of several hundred resonance peaks at energies a few kiloelectron volts above the neutron-binding energy. Strength functions were fitted to the average cross sections up to about 100 keV, and average cross sections were extended with less precision from 100 to 2000 keV. The capture cross section of natural tungsten was calculated from measurements for individual isotopes. Compound nucleus calculations have been made with deformed optical model parameters for comparison with experimental cross sections.
Six angular distributions and the zero degree excitation function of the reaction /sup 1/H(t,n)/sup 3/He between 5.95 and 19.15 MeV were measured to provide back angle data for the /sup 3/H(p,n)/sup 3/He reaction between 2.0 and 6.4 MeV proton energy. Together with relative angular distributions at 2.22 and 3.00 MeV these data are the backbone of the new evaluation which gives appreciably higher angle yields than previous ones. Consistency of the data base is not very good resulting in maximum scale errors of +-4% and maximum shape error of the angular distributions of +-3%. Data of the reaction /sup 4/He(t,n/sub x/)/sup 6/Li can contribute to the knowledge of the cross section standard /sup 6/Li(n,t)/sup 4/He, the time-reversed reaction. New data for triton energies between 11.9 and 16.4 MeV (corresponding to neutron energies for N-/sup 6/Li between 2.3 and 5.3 MeV) are presented both for the population of the ground state in /sup 6/Li and the first excited state. In addition, data of the same reaction obtained in a previous experiment were revised above 12.8 MeV taking a 0.1% impurity of hydrogen into account.
Date: May 1, 1985
Creator: Drosg, M.; Haouat, G.; Stoeffel, W. & Drake, D.M.
Fast neutron capture cross sections of /sup 169/Tm, /sup 191/Ir, /sup 193/Ir, and /sup 175/Lu, and the /sup 6/Li(n,..cap alpha..)/sup 3/H cross sections to which they are normalized are presented in tabular form for neutron energies between 3 and 2000 keV.
Two neutron detectors are described that can function in a continuous radiation background. Both detectors identify neutrons by recording a proton recoil pulse followed by a characteristic capture pulse. This peculiar signature indicates that the neutron has lost all its energy in the scintillator. Resolutions and efficiencies have been measured for both detectors.
Using the time-of-flight technique, the /sup 10/B and /sup 11/B neutron emission spectra at incident neutron energies of 6.00 and 10.00 MeV for angles between 20/sup 0/ and 145/sup 0/ have been measured. Double differential cross sections and their integrated values have been extracted and are presented in tables and graphs. The integrated values (corrected for charged particle cross sections, if necessary) are in excellent agreement with measured total cross sections. 15 refs., 39 figs., 14 tabs.
The forward-to-backward asymmetry of high-energy photons, emitted in the radiative capture of neutrons with energies up to 20 MeV, was measured for /sup 208/Pb. The asymmetry increases abruptly from small values to large ones near E..gamma.. approx. 23 MeV, supporting the location in that neighborhood of the E2 giant isovector resonance.
Date: November 1, 1981
Creator: Drake, D.M.; Aniol, K.; Halpern, I.; Joly, S.; Nilsson, L.; Storm, D. et al.
Neutron emission spectra of /sup 10/B and /sup 11/B were measured at 6, 10, and 14.1 MeV and those of /sup 6/Li, /sup 7/Li and carbon at 14.1 MeV using time-of-flight technique. Absolute double differential cross sections were obtained by using scattering from hydrogen as a cross section reference. Integration over energy ranges and solid angle yielded integrated elastic and total neutron emission cross sections. At 6 and 10 MeV excellent agreement with total cross section data is found, at 14.1 MeV the new data tend to be higher than expected. The biggest error source in the continuous spectra stems from uncertainties in the input library (ENDF/B-IV) of the Monte Carlo correction for multiple scattering. In particular, the library for /sup 11/B appears to be very unrealistic, with a total elastic cross section at 14.1 MeV which should be higher by 50%.
Date: January 1, 1985
Creator: Drosg, M.; Lisowski, P.W.; Hardekopf, R.A.; Drake, D.M. & Treitl, K.
Differential cross sections of the reaction /sup 4/He(t,n)/sup 6/Li, including some data of the first and second excited states of /sup 6/Li, were measured and compared with an R-matrix analysis of previous data in the /sup 7/Li system. Excellent agreement is observed for the angular distribution at the 0.24-MeV resonance of n-/sup 6/Li, and the shape of the angular distribution for /sup 4/He(t,n/sub 1/)/sup 6/Li at 12.9 MeV is predicted qualitatively by the R-matrix analysis. However, for neutron energies greater than 0.5 MeV for /sup 6/Li(n,t)/sup 4/He the zero-degree excitation function is consistently lower (about 30%) in the R-matrix analysis.
Date: January 1, 1982
Creator: Drosg, M.; Drake, D.M.; Hardekopf, R.A. & Hale, G.M.
Using the time-of-flight technique, we have measured neutron emission spectra for /sup 6/Li, /sup 7/Li, /sup 10/B, /sup 11/B and carbon at an incident neutron energy of 14.1 MeV and at 10 angles between 30/degree/ and 143/degree/. Double differential cross sections and their integrated values have been extracted and are presented in tables and graphs. The nonelastic portion of the neutron emission spectra is noticeably higher than expected which may be due to uncertainties in the input library (ENDF/B-IV) used in the Monte Carlo correction for multiple scattering. In particular, the library for /sup 11/B appears to be very unrealistic with an integrated elastic cross section which should be higher by 50%. 20 refs., 1 fig., 12 tabs.
Date: October 1, 1988
Creator: Drosg, M.; Lisowski, P.W.; Drake, D.M.; Hardekopf, R.A. & Muellner, M.
Time-of-flight techniques were used to measure the /sup 6/Li and /sup 7/Li neutron emission spectra at incident neutron energies of 5.96 and 9.83 MeV and at 10 angles from 25/sup 0/ to 144/sup 0/. Differential elastic and inelastic cross sections as well as continuum cross sections that result from three-body breakup and inelastic scatering from unresolved states are presented. 10 figures, 5 tables.
Date: October 1, 1980
Creator: Lisowski, P.W.; Auchampaugh, G.F.; Drake, D.M.; Drosg, M.; Haouat, G.; Hill, N.W. et al.
The Burst Detector Dosimeter (Block) IIR (BDD-IIR) is a multipurpose silicon detector system that is scheduled to fly on two of the first 12 spacecraft of the Global Positioning System (GPS) Block 2 Replenishment series as an alternative to the Burst Detector X-ray (BDX) instrument. This instrument measures energetic-particle fluxes impinging on the GPS space vehicle (SV), primarily energetic electrons trapped in the Earth`s radiation belt, but also solar energetic particles and galactic cosmic rays. Absorbers located in front of eight separate silicon sensors determine energy thresholds for measuring incident particle fluxes, and the magnitude of energy loss in each sensor provides an imperfect but very good separation between ions and electrons over a wide range of energies. For each of two sensors, a conical collimator with a very small opening is used for low-energy particles. For four sensors, five small holes in a thick shield limits the flux on each sensor to manageable levels. For two sensors, solid domes are used to measure high-energy electrons and protons. These eight sensors provide eight channels that determine the electron energy spectrum from 77 keV to > 5 MeV and eight channels determine the proton spectrum from 1.3 to > 54 MeV. The radiation dose rate and total dose for a wide range of equivalent shielding thicknesses is inferred directly from the measured electron energy spectrum. Accumulations times are usually 240 s but can also be 24, 120, or 4,608 s. This report describes the BDD-IIR`s important mechanical and electronic features, its system tests and calibrations, the commands that can be sent to it, and the data that it returns.
Date: September 1, 1998
Creator: Cayton, T.E.; Drake, D.M.; Spencer, K.M.; Herrin, M.; Wehner, T.J. & Reedy, R.C.
Planetary Gamma ray spectroscopy can be used to chemically analyze the top soil from planets in future planetary missions. The production from inelastic neutron interaction plays an effective role in the determination on the C and H at the surface. The gamma ray production cross section from the strongest lines excited in the neutron bombardment of Fe have been measured by the use of a time analyzed quasi-mono-energetic neutron beam and a high purity germanium detector. The results from En=6.5, 32, 43, and 65 MeV are presented.
Date: December 31, 1991
Creator: Castaneda, C. M.; Gearhart, R.; Sanii, B.; Englert, P. A. J.; Drake, D. M. & Reedy, R. C.
The initial purpose of this experiment was to provide a consistent data base of neutron-induced gamma-ray production cross sections over a large energy range for use in estimating elemental composition of the martian surface by observing gamma rays produced by cosmic ray interactions on the planet's surface [Bo02]. However, these data should be useful for other projects such as oil-well logging, accelerator transmutation of nuclear waste, shielding calculations, gamma-ray heating for nuclear reactors and verification of nuclear model calculations and databases. The goal of the measurements was to collect data on the strongest gamma rays from many samples of interest. Because of the available beam time this meant that many of the measurcments were rather short. Despite the short running time the large samples used and the good beam intensity resulted in very satisfactory results. The samples, chosen mainly as common constituents of rock and soil and measured in the same few week period, include: B&, BN, C, Al, Mg, Si, S, Cay Ti, Cr, Mn, and Fe. Be was also used as a neutron scatterer that only produces one gamma ray (478 keV from 7Li) with appreciable intensity. Thus Be can serve as a measure of neutron-induced backgrounds. In this first paper we present results for Fe.
Date: January 1, 2002
Creator: Nelson, R. O. (Ronald O.); Laymon, C. M. (Charles M.); Wender, S. A. (Stephen A.); Drake, D. M. (Darrell M.); Drosg, Manfred; Bobias, S. G. (S. George) et al.
GEANIE is the first large-scale Ge detector array used in conjunction with a high-energy neutron spallation source. GEANIE consists of eleven Compton-suppressed planar detectors, nine suppressed and six unsuppressed co-axial detectors. Spallation neutrons are provided by the LANSCE/WNR facility, and reaction neutron energies are determined via time-of-flight. neutron flux is monitored in-beam with a fission chamber. GEANIE at LANSCE/WNR currently emphasizes the measurement of partial gamma-ray cross sections as a function of neutron energy. Absolute cross section measurements require a complete understanding of array performance. Important effects include intrinsic detector efficiency, beam and detector geometry corrections, target attenuation, and deadtime. Measurements and calculations of these effects will be presented for the specific cases of iron and actinide targets. The use of radioactive targets incurs a large deadtime penalty. In order to increase data throughput they are making plans to move to a triggerless data acquisition system. These modifications and other improvements to the electronics for better timing will be discussed.
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