83 Matching Results

Search Results

Advanced search parameters have been applied.

Charged particles produced in neutron reactions on nuclei from beryllium to gold

Description: Charged-particle production in reactions of neutrons with nuclei has been studied over the past several years with the spallation source of neutrons from 1 to 50 MeV at the Los Alamos Neutron Science Center (LANSCE). Target nuclides include 9Be, C, 27Al, Si, 56Fe, 59Co, 58,60Ni, 93Nb and 197Au. Proton, deuteron, triton, 3He and 4He emission spectra, angular distributions and production cross sections have been measured. Transitions from the compound nuclear reaction mechanism to precompound reactions are clearly seen in the data. The data are compared with data from the literature where available, with evaluated nuclear data libraries, and with calculations where the selection of the nuclear level density prescription is of great importance. Calculations normalized at En = 14 MeV can differ from the present data by a factor of 2 for neutron energies between 5 and 10 MeV.
Date: August 1, 1997
Creator: Haight, R.C.
Partner: UNT Libraries Government Documents Department

HOTSPUR progress report: neutron source spectrum characterization, and /sup 6/Li(n,x. cap alpha. ) and /sup 7/Li(n,x. cap alpha. ) cross section determination

Description: As a prerequisite to high accuracy measurements involving the bulk configuration of /sup 6/LiD we must have a good grasp of the details of the RTNS-I neutron source energy spectrum. Experiments to this end involving neutron yield vs deuteron energy, ratios of foil activation of selected elements, and pulse height distributions of a Si surface barrier detector are described. With this knowledge, the /sup 4/He-production cross sections for /sup 6/Li and /sup 7/Li are found experimentally to be 0.512b and 0.336b, respectively, at anti E/sub N/ = 15.0 MeV in free-field geometry. 14 references.
Date: April 2, 1984
Creator: Goldberg, E. & Haight, R.
Partner: UNT Libraries Government Documents Department

Neutron cross sections for fusion. [Review]

Description: First generation fusion reactors will most likely be based on the /sup 3/H(d,n)/sup 4/He reaction, which produces 14-MeV neutrons. In these reactors, both the number of neutrons and the average neutron energy will be significantly higher than for fission reactors of the same power. Accurate neutron cross section data are therefore of great importance. They are needed in present conceptual designs to calculate neutron transport, energy deposition, nuclear transmutation including tritium breeding and activation, and radiation damage. They are also needed for the interpretation of radiation damage experiments, some of which use neutrons up to 40 MeV. In addition, certain diagnostic measurements of plasma experiments require nuclear cross sections. The quality of currently available data for these applications will be reviewed and current experimental programs will be outlined. The utility of nuclear models to provide these data also will be discussed. 65 references.
Date: October 1, 1979
Creator: Haight, R.C.
Partner: UNT Libraries Government Documents Department

(n, charged particle) reactions on lp-shell nuclides at 14 MeV

Description: The reactions (n,p), (n,d), (n,t) and (n,..cap alpha..) of 14-MeV neutrons with 1p-shell nuclides are of interest in several areas: they can provide tests of charge symmetry by comparisons with proton-induced reactions (on T=O nuclides); they allow study of the complex, often many-body decay of excited nuclear states; and they yield information on final-state interactions. As part of the program in (n, charged particle) reaction studies, several 1p-shell nuclides were investigated: /sup 9/Be, /sup 12/C, /sup 14/N, and /sup 16/O at E/sub n/ = 14 MeV (Haight et. al. 1981). These measurements, with the newly developed magnetic quadrupole charged-particle spectrometer, provide data with a much higher signal-to-background than heretofore available. Experimental methods and results are briefly described. (WHK)
Date: June 1, 1981
Creator: Haight, R.C.
Partner: UNT Libraries Government Documents Department

Comments on (n, charged particle) reactions at E/sub n/ = 14 MeV

Description: The study of charged particles produced by bombarding materials with 14 MeV neutrons is important for the development of fusion reactors and for biomedical applications as well as for the basic understanding of nuclear reactions. Several experimental techniques for investigating these reactions are discussed here. The interpretation of the data requires the consideration of several possible reaction mechanisms including equilibrium and preequilibrium particle emission and, for light nuclei, sequential particle emission, final state interactions, and the effect of resonances. 17 references.
Date: January 1, 1984
Creator: Haight, R.C.
Partner: UNT Libraries Government Documents Department

Nuclear-data needs for inertial-confinement fusion (ICF)

Description: Our survey was limited to ICF programs in the United States. It included researchers in laser and heavy ion fusion, target design, target diagnostics, and conceptual reactor design. We asked each of these people to read the current data needs for magnetic fusion energy and to comment on additional data that they require.
Date: May 9, 1983
Creator: Haight, R.C. & Motz, H.T.
Partner: UNT Libraries Government Documents Department

Experimental studies of (n, charged particle) cross sections, angular distributions and spectra with a magnetic quadrupole spectrometer

Description: The charged-particle-producing reactions of 15-MeV neutrons with structural materials have been studied with a new type of spectrometer based around a magnetic quadrupole lens. Significant improvements in signal-to-background have permitted the detection of protons with energies as low as 800 keV. In several materials charged particles emitted with energies well below the Coulomb barrier contribute significantly to the total hydrogen and helium production cross sections. The production mechanism for these low-energy particles is second-chance emission in (n,n'p) and (n,n'..cap alpha..) reactions. At the high-energy end of the proton and alpha-particle spectra and for the entire deuteron spectra, non-statistical reaction mechanisms are indicated. Results for Al, Ti, V, Fe, Ni, Cu, Nb, and stainless steel 316 are compared with data from other experimental methods.
Date: December 1, 1977
Creator: Haight, R.C. & Grimes, S.M.
Partner: UNT Libraries Government Documents Department

Status of (n, charged particle) measurements at LLL. [14 MeV]

Description: A charged-particle magnetic-quadrupole spectrometer was used to study (n, charged particle) reactions on materials bombarded with 14- to 15-MeV neutrons. Charged-particle production cross sections, angular distributions, and spectra were measured. The materials investigated to date include most of those proposed for fusion reactor structures, Al, Ti, Cr, V, Fe, Ni, Cu, Nb, and stainless steels 304 and 316. Isotopic data on /sup 46/ /sup 48/Ti, /sup 50/ /sup 52/Cr, /sup 54/ /sup 56/Fe, /sup 58/ /sup 60/Ni, and /sup 63/ /sup 65/Cu and on the monoisotopic elements /sup 27/Al, /sup 51/V, and /sup 93/Nb provided stringent tests of reaction model calculations. Equilibrium and pre-equilibrium reaction mechanisms were identified and quantified. Preliminary data on /sup 92/ /sup 94/ /sup 95/ /sup 96/Mo and on light nuclides including /sup 12/C and /sup 7/Li were obtained recently. 8 figures, 1 table.
Date: January 1, 1980
Creator: Haight, R.C. & Grimes, S.M.
Partner: UNT Libraries Government Documents Department

Office of Basic Energy Sciences program to meet high priority nuclear data needs of the Office of Fusion Energy 1983 review

Description: This review was prepared during a coordination meeting held at Oak Ridge National Laboratory on September 28-29, 1983. Participants included research scientists working for this program, a representative from the OFE's Coordination of Magnetic Fusion Energy (MFE) Nuclear Data Needs Activities, and invited specialists.
Date: November 1, 1983
Creator: Haight, R.C. & Larson, D.C.
Partner: UNT Libraries Government Documents Department

Status report to DOE Nuclear Data Committee

Description: This status report from Lawrence Livermore Laboratory covers work in the areas of nuclear data applications - measurements, nuclear data application - calculations, nuclear data for reactor safety, fission physics, and data evaluation and compilation. Separate abstracts were prepared for seven of the contributions to this report. 7 figures, 3 tables. (RWR)
Date: March 13, 1980
Creator: Haight, R.C. & Struble, G.L.
Partner: UNT Libraries Government Documents Department

Secondary standards (non-activation) for neutron data measurements above 20 MeV

Description: In addition to H(n,p) scattering and {sup 235,238}U(n,f) reactions, secondary standards for neutron flux determination may be useful for neutron energies above 20 MeV. For experiments where gamma rays are detected, reference gamma-ray production cross sections are relevant. For neutron-induced charged particle production, standard (n,p) and (n,alpha) cross sections would be helpful. Total cross section standards would serve to check the accuracy of these measurements. These secondary standards are desirable because they can be used with the same detector systems employed in measuring the quantities of interest. Uncertainties due to detector efficiency, geometrical effects, timing and length of flight paths can therefore be significantly reduced. Several secondary standards that do not depend on activation techniques are proposed. 14 refs.
Date: January 1, 1991
Creator: Haight, R.C.
Partner: UNT Libraries Government Documents Department

Report to the DOE Nuclear Data Committee, 1983

Description: Measurements for nuclear data applicactions are described including branching ratio in /sup 7/Be decay, kerma factor for carbon, photoneutron cross sections, neutron differential scattering cross sections, half-life of /sup 77/Kr, stellar neutron capture rates for /sup 86/ /sup 87/ /sup 88/Sr, neutron total cross sections, /sup 142/ /sup 143/ /sup 144/Nd neutron capture nucleo-synthesis, half-life of /sup 163/Ho, thermal neutron fission of /sup 236/Np, revised branching ratios in /sup 237/U and /sup 238/Pu decays, and levels of /sup 244/Cm populated by the beta decay of 10-hour /sup 244/Am and 26-minute /sup 244m/Am. Calculations discussed include systematic test of microscopic optical models for nucleon scattering in the range 7 to 60 MeV, Lanczos method shell-model calculations of GamowTeller strength functions, explosive nucleosynthesis and direct radiative capture rates, and calculation of fission cross sections. Evaluated data libraries are briefly discussed. (WHK)
Date: February 1, 1983
Creator: Haight, R.C. & Struble, G.L.
Partner: UNT Libraries Government Documents Department

Report to the DOE nuclear data committee. [EV RANGE 10-100; CROSS SECTIONS; PHOTONEUTRONS; NEUTRONS; GAMMA RADIATION; COUPLED CHANNEL THEORY; DIFFERENTIAL CROSS SECTIONS; MEV RANGE 01-10; ; CAPTURE; GAMMA SPECTRA; THERMAL NEUTRONS; COMPUTER CALCULATIONS; DECAY; FISSION PRODUCTS; FISSION YIELD; SHELL MODELS; NUCLEAR DATA COLLECTIONS]

Description: Topics covered include: studies of (n, charged particle) reactions with 14 to 15 MeV neutrons; photoneutron cross sections for /sup 15/N; neutron radiative capture; Lane-model analysis of (p,p) and (n,n) scattering on the even tin isotopes; neutron scattering cross sections for /sup 181/Ta, /sup 197/Au, /sup 209/Bi, /sup 232/Th, and /sup 238/U inferred from proton scattering and charge exchange cross sections; neutron-induced fission cross sections of /sup 245/Cm and /sup 242/Am; fission neutron multiplicities for /sup 245/Cm and /sup 242/Am; the transport of 14 MeV neutrons through heavy materials 150 < A < 208; /sup 249/Cm energy levels from measurement of thermal neutron capture gamma rays; /sup 231/Th energy levels from neutron capture gamma ray and conversion electron spectroscopy; new measurements of conversion electron binding energies in berkelium and californium; nuclear level densities; relative importance of statistical vs. valence neutron capture in the mass-90 region; determination of properties of short-lived fission products; fission yield of /sup 87/Br and /sup 137/I from 15 nuclei ranging from /sup 232/Th to /sup 249/Cf; evaluation of charged particle data for the ECPL library; evaluation of secondary charged-particle energy and angular distributions for ENDL; and evaluated nuclear structure libraries derived from the table of isotopes. (GHT)
Date: March 1, 1981
Creator: Struble, G.L. & Haight, R.C.
Partner: UNT Libraries Government Documents Department

Hybrid charged-particle guide for studying (n, charged particle) reactions

Description: Charged-particle transport systems consisting of magnetic quadrupole lenses have been employed in recent years in the study of (n, charged particle) reactions. We have completed a new transport system that is based both on magnetic lenses as well as electrostatic fields. The magnetic focusing of this charged-particle guide is provided by six magnetic quadrupole lenses arranged in a CDCCDC sequence (in the vertical plane). The electrostatic field is produced by a wire at high voltage which stretches the length of the guide and is physically at the center of the magnetic axis. The magnetic lenses are used for charged particles above 5 MeV; the electrostatic guide is used for lower energies. This hybrid system possesses the excellent focusing and background rejection properties of other magnetic systems. For low energy charged-particles, the electrostatic transport avoids the narrow band-passes in charged-particle energy which are a problem with purely magnetic transport systems. This system is installed at the LLNL Cyclograaff facility for the study of (n, charged particle) reactions at neutron energies up to 35 MeV.
Date: August 25, 1982
Creator: Haight, R.C.; White, R.M. & Zinkle, S.J.
Partner: UNT Libraries Government Documents Department

New techniques in neutron data measurements above 30 MeV

Description: Recent developments in experimental facilities have enabled new techniques for measurements of neutron interactions above 30 MeV. Foremost is the development of both monoenergetic and continuous neutron sources using accelerators in the medium energy region between 100 and 800 MeV. Measurements of the reaction products have been advanced by the continuous improvement in detector systems, electronics and computers. Corresponding developments in particle transport codes and in the theory of nuclear reactions at these energies have allowed more precise design of neutron sources, experimental shielding and detector response. As a result of these improvements, many new measurements are possible and the data base in this energy range is expanding quickly.
Date: January 1, 1991
Creator: Lisowski, P.W. & Haight, R.C.
Partner: UNT Libraries Government Documents Department

Report to the DOE Nuclear Data Committee, 1984

Description: Experimental results are discussed for: /sup 6/ /sup 7/Li(n,/sup 4/He) cross sections at 14 MeV, neutron elastic and inelastic scattering from carbon near 14 MeV, neutron capture cross sections for /sup 46/Ca and /sup 48/Ca at stellar temperatures, revised neutron cross sections for /sup 142/ /sup 143/ /sup 144/Nd, fragment angular distribution for neutron fission of /sup 232/Th, neutron differential scattering measurements in the actinide region, nuclear structure of /sup 244/Am, conversion coefficients of the M4 transition in /sup 193m/Ir, gamma-ray and conversion-electron decay of the /sup 238/U shape isomer, and levels of /sup 244/Cm populated by the beta decay of 10-hr /sup 244g/Am and 26-minute /sup 244m/Am. Calculations described include tests of microscopic optical models for neutron and proton scattering on light nuclei in the range 14 to 45 MeV, a new dynamic model for fission, and the necessity of discrete-level modeling in isomer ratio calculations for neutron-induced reactions on deformed nuclei. Also, a reevaluation for ENDL of sigma(n,f) and anti nu p for /sup 235/U and /sup 239/Pu from 100 keV to 20 MeV is described. 31 references. (WHK)
Date: February 1, 1984
Creator: Wong, C.; Haight, R.C. & Struble, G.L.
Partner: UNT Libraries Government Documents Department

Radiative ion beams: hot stellar reactions in the laboratory

Description: Following our initial production of beams of /sup 7/Be and /sup 13/N, we have improved the purity and intensity of these beams. In addition we have generated beams of /sup 15/O (at 30 MeV) and /sup 8/Li (at 22 MeV). These beams are intended for cross section measurements of proton and alpha-particle capture reactions on unstable species that are important in hot stellar environments. We have begun studies aimed toward measuring the /sup 1/H(/sup 7/Be,/sup 8/B)..gamma.. cross section. As part of the developmental work, we attempted to remeasure the /sup 2/H(/sup 7/Be,/sup 8/B)n cross section with a different technique that pointed out the importance of background /sup 8/Li. We measured the /sup 2/H(/sup 7/Li,/sup 8/Li)/sup 1/H cross section to be 155 +- 20 mb at 12.2 +- 1.3 MeV.
Date: September 1, 1984
Creator: Haight, R.C.; Mathews, G.J. & Bauer, R.W.
Partner: UNT Libraries Government Documents Department

Nuclear transitions induced by atomic excitations

Description: In the two-step pumping scheme for a gamma-ray laser, an essential step is that of exciting the nucleus from a long-lived storage isomer to a nearby short-lived state that then decays to the upper lasing level. For a crystalline structure host, the radiation must be used efficiently so as not to destroy the crystal. High intensity sources of photons are available only for relatively low quantum energy, but it is difficult to couple a long-wavelength photon directly to the much smaller nucleus. An experiment is proposed to induce this transfer by first exciting the atomic electrons. The nuclear excitation should occur by the exchange of a virtual photon in the near field of the electrons. As a test case, the 73 eV /sup 235m/U isomer might be excited by electronic motions induced by a high-brightness uv laser. The conversion electrons from the decay of the isomer would be detected and a 26 minute decay curve would indicate induced nuclear transitions. 5 refs.
Date: January 1, 1986
Creator: Bounds, J.A.; Dyer, P. & Haight, R.C.
Partner: UNT Libraries Government Documents Department

Charged-particle magnetic-quadrupole spectrometer for neutron induced reactions

Description: A spectrometer has been developed for measuring the charged particle production cross sections and spectra in neutron-induced reactions. The spectrometer consists of a magnetic quadrupole doublet which focuses the charged particles onto a silicon surface barrier detector telescope which is 2 meters or more from the irradiated sample. Collimators, shielding, and the large source-to- detector distance reduce the background enough to use the spectrometer with a 14- MeV neutron source producing 4 . 10$sup 12$ n/s. The spectrometer has been used in investigations of proton, deuteron, and alpha particle production by 14-MeV neutrons incident on various materials. Protons with energies as low as 1.1 MeV have been measured. The good resolution of the detectors has also made possible an improved measurement of the neutron- neutron scattering length from the 0$sup 0$ proton spectrum from deuteron breakup by 14-MeV neutrons. (auth)
Date: December 10, 1975
Creator: Haight, R. C.; Grimes, S. M.; Tuckey, B. J. & Anderson, J. D.
Partner: UNT Libraries Government Documents Department