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Measurement of neutron attenuation through thick shields and comparison with calculation

Description: The large neutrino experiments conducted over the last several years at the Los Alamos Neutron Science Center (LANSCE) have provided the opportunity to measure the effects of neutron attenuation in very thick shields. These experiments have featured detectors with active masses of 6 to 150 tons and shield thicknesses ranging from 3000 to 5280 g/cm{sup 2}. An absolute measurement of the high-energy neutron flux was made from the beam stop in a neutrino cave at ninety degrees and nine meters from the beam stop. Differential neutron shielding measurements in iron were also performed, resulting in an attenuation length of 148 g/cm{sup 2}. These measurements allow for the testing of radiation shielding codes for deep penetration problems. The measured flux and attenuation length is compared to calculations using the LAHET Code System (LCS). These codes incorporate biasing techniques, allowing for direct calculation of deep penetration shielding problems. Calculations of the neutron current and attenuation length are presented and compared with measured values. Results from the shielding codes show good agreement with the measured values.
Date: December 31, 1998
Creator: Bull, J.S.; Donahue, J.B. & Burman, R.L.
Partner: UNT Libraries Government Documents Department

Spallation source neutron target systems

Description: This is the final report for a two-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The project sought to design a next-generation spallation source neutron target system for the Manuel Lujan, Jr., Neutron Scattering Center (LANSCE) at Los Alamos. It has been recognized for some time that new advanced neutron sources are needed in the US if the country is to maintain a competitive position in several important scientific and technological areas. A recent DOE panel concluded that the proposed Advanced Neutron Source (a nuclear reactor at Oak Ridge National Laboratory) and a high-power pulsed spallation source are both needed in the near future. One of the most technically challenging designs for a spallation source is the target station itself and, more specifically, the target-moderator-reflector arrangement. Los Alamos has demonstrated capabilities in designing, building, and operating high-power spallation-neutron-source target stations. Most of the new design ideas proposed worldwide for target system design for the next generation pulsed spallation source have either been conceived and implemented at LANSCE or proposed by LANSCE target system designers. These concepts include split targets, flux-trap moderators, back scattering and composite moderators, and composite reflectors.
Date: July 1, 1996
Creator: Russell, G.; Brown, R.; Collier, M. & Donahue, J.
Partner: UNT Libraries Government Documents Department

Comparison of F(2)-Based Gases for High-Rate Dry Etching of Si

Description: Four different F{sub 2}-based gases (SF{sub 6}, NF{sub 3}, PF{sub 5}, and BF{sub 3}) were examined for high rate Inductively Coupled Plasma etching of Si. Etch rates up to {approximately}8 {micro}m/min were achieved with pure SF{sub 6} discharges at high source power (1500W) and pressure (35mTorr). A direct comparison of the four feedstock gases under the same plasma conditions showed the Si etch rate to increase in the order BF{sub 3} < NF{sub 3} < PF{sub 5} < SF{sub 6}. This is in good correlation with the average bond energies of the gases, except for NF{sub 3}, which is the least strongly bound. Optical emission spectroscopy showed that the ICP source efficiently dissociated NF{sub 3}, but the etched Si surface morphologies were significantly worse with this gas than with the other 3 gases.
Date: March 31, 1999
Creator: Donahue, J.; Hahn, Y.B.; Hays, D.C.; Johnson, D.; Jung, K.B.; Lambers, E.S. et al.
Partner: UNT Libraries Government Documents Department

LANSCE short-pulse spallation source target upgrade

Description: A project to upgrade the short-pulse spallation source target at the Los Alamos Neutron Scattering Center (LANSCE) is in progress. This upgrade will reduce the target change out time from about a year to about three weeks and permit the proton beam current to be raised to 200 {mu}A. The project includes a new target-moderator-reflector system, a new suite of moderators for four new flight paths, improved auxiliary systems, remote handling capability, and a new crane and service building. The project has also supported calculations and experiments for target neutronics, rod-target thermo-hydraulics, and corrosion-related measurements in a proton beam. The final engineering design is now complete and the project has begun fabrication and procurement. Installation will begin in the fall of this year.
Date: September 1, 1997
Creator: Donahue, J.B.; Baker, G.D. & Bultman, N.K.
Partner: UNT Libraries Government Documents Department

Development plan for the Nucleon Physics Laboratory Facility at LAMPF

Description: A 3- to 4-year plan is described for upgrading the LAMPF Nucleon Physics Laboratory including a neutron time-of-flight facility for the (p,n) reaction, a medium-resolution spectrometer for (p,p') and n,p) studies, and a dedicated facility for atomic beam studies. Development of these facilities and relationships to other ongoing developments are detailed. The scope of the new physics programs supported by such a facility is discussed.
Date: February 1, 1986
Creator: McClelland, J.B.; Bacher, A.; Boudrie, R.L.; Carey, T.A.; Donahue, J.; Goodman, C.D. et al.
Partner: UNT Libraries Government Documents Department

Photodetachment of relativistic ions

Description: A series of fundamental laser ion beam experiments has been made feasible by the high-quality, relativistic (..beta.. = 0.842) H/sup -/ ion beam available at the Clinton P. Anderson Meson Physics Facility (LAMPF). The relatavistic Doppler shift of the light from an ordinary ultraviolet laser provides what is, in effect, a continuously tunable vacuum-ultraviolet laser in the rest frame of the moving ions. The Lorentz transformation of a modest laboratory magnetic field provides an electric field of several megavolts/centimeter. The latest results of photo-detachment work with H/sup -/ beams and our spectroscopic work with H/sup 0/ beams are presented. Plans for future work are discussed.
Date: January 1, 1980
Creator: Donahue, J.B.; Gram, P.A.M.; Hamm, M.E.; Hamm, R.W.; Bryant, H.C.; Butterfield, K.B. et al.
Partner: UNT Libraries Government Documents Department

Overview of progress on the improvement projects for the LANSCE accelerator and target facilities

Description: Three projects have been initiated since 1994 to improve the performance of the accelerator and target facilities for the Los Alamos Neutron Science Center (LANSCE). The LANSCE Reliability Improvement Project (LRIP) was separated into two phases. Phase 1, completed in 1995, targeted near-term improvements to beam reliability and availability that could be completed in one-year`s time. Phase 2, now underway and scheduled for completion in May 1998, consists of two projects: (a) implementation of direct H-injection for the Proton Storage Ring (PSR) and (b) an upgrade of the target/moderator system for the short pulse spallation neutron (SPSS) source. The latter will reduce the target change-out time from about 10 months to about three weeks. The third project, the SPSS Enhancement Project, is aimed at increasing the PSR output beam current to 200 {micro}A at 30 Hz and providing up to seven new neutron scattering instruments.
Date: June 1, 1997
Creator: Macek, R. J.; Browne, J.; Brun, T.; Donahue, J. B.; Fitzgerald, D. H.; Hoffman, E. et al.
Partner: UNT Libraries Government Documents Department

Measurement of H zero excited states produced by foil stripping of 800-MeV H{sup {minus}} ions

Description: Foil stripping of H{sup {minus}} directly to H{sup +} is being considered for proton injection in the next generation of high-current proton storage rings. This technique can result in significant losses because excited states of HO, which are also produced in the foil, are field stripped in the downstream bending magnets. Without due care in the injection system design, many of the resulting protons will be outside the acceptance of the storage ring and will be quickly lost. We measured the production of such H{sup 0} excited states at the LAMPF High Resolution Atomic Beam Facility. An 800-MeV H{sup {minus}} beam was passed through carbon foils of thicknesses 70, 100, 200, and 300 {mu}g/cm{sup 2}, and the excited states were analyzed by a special magnet downstream of the foil. The magnet had a linear field gradient so that the trajectories of the outgoing protons could be used to reconstruct the field values at which the various H{sup 0} stripped. We found that about 1% of the H{sup 0} emerge in excited states which can be stripped to protons by ring-bending magnets.
Date: June 1, 1993
Creator: Donahue, J. B.; Clark, D. A.; Cohen, S.; Fitzgerald, D.; Frankle, S. C.; Huston, R. L. et al.
Partner: UNT Libraries Government Documents Department

Measurement of H zero excited states produced by foil stripping of 800-MeV H[sup [minus]] ions

Description: Foil stripping of H[sup [minus]] directly to H[sup +] is being considered for proton injection in the next generation of high-current proton storage rings. This technique can result in significant losses because excited states of HO, which are also produced in the foil, are field stripped in the downstream bending magnets. Without due care in the injection system design, many of the resulting protons will be outside the acceptance of the storage ring and will be quickly lost. We measured the production of such H[sup 0] excited states at the LAMPF High Resolution Atomic Beam Facility. An 800-MeV H[sup [minus]] beam was passed through carbon foils of thicknesses 70, 100, 200, and 300 [mu]g/cm[sup 2], and the excited states were analyzed by a special magnet downstream of the foil. The magnet had a linear field gradient so that the trajectories of the outgoing protons could be used to reconstruct the field values at which the various H[sup 0] stripped. We found that about 1% of the H[sup 0] emerge in excited states which can be stripped to protons by ring-bending magnets.
Date: January 1, 1993
Creator: Donahue, J.B.; Clark, D.A.; Cohen, S.; Fitzgerald, D.; Frankle, S.C.; Huston, R.L. et al.
Partner: UNT Libraries Government Documents Department

Photodetachment of the H sup minus ion

Description: Detachment of electrons from the H{sup {minus}} ion is investigated with an experimental technique whereby an H{sup {minus}} beam moving at a relativistic velocity (2.5 {times} 10{sup 10}cm/sec) is intersected with a fixed frequency laser. The Doppler effect allows systematic variation of the center-of-mass (CM) photon energy over a wide range (factor of 10) by simply adjusting the angle between the ion and laser beams. The focused output from a pulsed, linearly polarized, CO{sub 2} TEA laser operating at 10.6 {mu}m, with peak intensities on the order of 10 GW/cm{sup 2}, was used to examine the multiphoton absorption process in H{sup {minus}}. The fourth harmonic (266 nm) of a ND:YAG laser was used to investigate some of the doubly-excited state resonances in H{sup {minus}}. In the multiphoton absorption work, electron detachment was observed at phonon energies where as few as 2 and as many as 8 photons are required to get above the 1-electron detachment threshold (EDT) of H{sup {minus}} (0.754 eV). Electron yield vs photon energy plots exhibit structure that is laser intensity dependent. Electron yield vs laser pulse energy data was obtained at a few selected CM wavelengths and laser pulse energies. In the single-photon uv laser work, numerous resonances within the H{sup {minus}} photodetachment continuum corresponding to one-photon two-electron excitation processes were observed. The doubly-excited resonances appear to be the Feshbach type. A simple, semi-empirical recursion formula predicts the resonance energy levels. The experimental techniques described here can be used to accurately determine accelerator beam and ion source parameters such as beam energy, energy-spread, and ion density spatial distribution. 7 refs., 5 figs.
Date: January 1, 1990
Creator: Quick, C.R. Jr.; Donahue, J.B.; Cohen, S. (Los Alamos National Lab., NM (USA)); Bryant, H.C.; Tang, C.Y.; Harris, P.G. et al.
Partner: UNT Libraries Government Documents Department

A proposal to search for neutrino oscillations with high sensitivity in the appearance channels. nu. sub. mu. yields. nu. sub e and. nu. sub. mu. yields. nu. sub e

Description: An experiment is proposed to search concurrently for {nu}{sub {mu}} {yields} {nu}{sub e} and {bar {nu}}{sub {mu}} {yields} {bar {nu}{sub e} oscillations with high sensitivity at LAMPF. The detector consists of a tank with 200 tons of dilute liquid scintillator with 850 10-in. photomultiplier tubes mounted on the inside tank covering 28% of the surface. Both Cerenkov light and scintillation light will be detected. The tank will reside inside the existing E645 veto shield and the experiment will make use of the present A6 beam-stop neutrino source. After two years of data collection, 90% confidence level limits on {bar {nu}{sub mu}}({nu}{sub {mu}}) {yields} {bar {nu}}{sub e}({nu}{sub e}) mixing strengths of 2.7(2.7) {times} 10{sup {minus}4} can be obtained for all {Delta}m{sup 2} > 1 eV{sup 2}. Similarly, for maximal mixing the 90% C.L. limits on {Delta}m{sup 2} are 1.7(4.0) {times} 10{sup {minus}2}. This experiment will, therefore, provide the world's best terrestrial limits on {nu}{sub {mu}} {yields} {nu}{sub e}} oscillations. Other physics to be obtained includes measurements of the charged current reactions {nu}{sub e}C {yields} e{sup {minus}}N and {nu}{sub {mu}}C {yields} {mu}{sup {minus}}N, of the inelastic neutral current reaction {nu}C {yields} {nu}C* (15.11- MeV {gamma}), and a search for the rare decays {pi}{sup 0} {yields} {nu}{bar {nu}} and {eta} {yields} {nu}{bar {nu}}.
Date: August 1, 1990
Creator: Lu, X-Q.; Yodh, G. (California Univ., Irvine, CA (USA)); Fung, S.Y.; Kang, J.H.; Shen, B.C.; VanDalen, G.J. (California Univ., Riverside, CA (USA)) et al.
Partner: UNT Libraries Government Documents Department