1,237 Matching Results

Search Results

Advanced search parameters have been applied.

Measurements of MeV photon flashes in petawatt laser experiments

Description: Planar targets illuminated by the Petawatt laser system emit directed beams of photons with energies of MeVs. The laser pulses have durations of 0.5 or 5 psec, on target energies in excess of 100 joules, and focal-spot sizes that vary from 10 to 100 µm, producing peak intensities greater than 10<sup>19</sup> watts/cm<sup>;2</sup>. Arrays of PIN diodes, dosimeters and nuclear-activation detectors measure the angular distributions of photons with energies greater than 0.5 MeV. The PIN diodes, with 1 cm<sup>2</sup> by 500-µm sensitive volume, are housed in lead pigs with 2.5-cm thick walls. Measured emission intensities have been as high as 5x10<sup>13</sup> (gamma) MeV/steradian. The angular distributions are highly directed in forward directions, with significant variations on a shot-to-shot basis. Backward radiated intensities tend to be more than a decade lower than in forward direct
Date: November 10, 1998
Creator: Phillips, T.; Brown, C. G.; Cowan, T.; Hatchett, S.; Hunt, A.; Key, M. et al.
Partner: UNT Libraries Government Documents Department


Description: Despite the essentially independent development of the Cosmotron and Bevatron, these two accelerators have general specifications which are the same within a factor of 2-3 in their pertinent characteristics. An electron analogue of the Bevatron would be an electron synchrotron operating in the 5 kev to 3 Mev range.
Date: October 20, 1953
Creator: Smith, Lloyd
Partner: UNT Libraries Government Documents Department

Development of a novel neutron source with applications in calibration and monitoring. Final report

Description: The objective of this research project, development of a unique portable inertial electrostatic confinement (IEC) neutron source (10{sup 6} 2.5-MeV neutrons/second-level) has been achieved. A majority of the experimental work required for the project was reported in the 1993 Annual Report. (The abstract and table of contents for that report arc included here as Appendix A for convenience. Full copies can be obtained upon request to the PI.) Unfortunately, the DOE program providing support for the project was canceled and funding was not available to continue the project in 199495. However, to provide time to explore some innovative potential applications for upgraded versions of the IEC, a no-cost extension of the contract was requested and granted in 1994. This follow-on work, mostly involving conceptual design studies, is reported here.
Date: April 1, 1995
Creator: Miley, G.H.
Partner: UNT Libraries Government Documents Department

Measurements of the {sup 235}U(n,f) cross section in the 3 to 30 MeV neutron energy region

Description: To improve the accuracy of the {sup 235}U(n,f) cross section, measurements have been made of this standard cross section at the target 4 facility at Los Alamos National Laboratory (LANL). The data were obtained at the 20-meter flight path of that facility. The fission reaction rate was determined with a fast parallel plate ionization chamber and the neutron fluence was measured with an annular proton recoil telescope. The measurements provide the shape of the {sup 235}U(n,f) cross section relative to the hydrogen scattering cross section for neutron energies from about 3 to 30 MeV neutron energy. The data have been normalized to the very accurately known value near 14 MeV. The results are in good agreement with the ENDF/B-VI evaluation up to about 15 MeV neutron energy. Above this energy differences as large as 5% are observed.
Date: December 31, 1991
Creator: Carlson, A.D.; Wasson, O.A. & Lisowski, P.W.
Partner: UNT Libraries Government Documents Department

Intense positron beams: linacs. Preworkshop copy

Description: Beams of monoenergetic positrons with energies of a few eV to many keV have been used in experiments in atomic physics, solid state physics and materials science. The production of positron beams from a new source, an electron linac, is described. Intense, pulsed beams of low-energy positrons have been produced by a high-energy beam from an electron linac. The production efficiency, moderator geometry, beam spot size and other positron beam parameters have been determined for electrons with energies from 60 to 120 MeV. Low-energy positron beams produced with a high-energy electron linac can be of much higher intensity than those beams currently derived from radioactive sources. These higher intensity beams will make possible positron experiments previously infeasible.
Date: September 1, 1983
Creator: Howell, R.H.; Alvarez, R.A.; Woodle, K.A.; Dhawan, S.; Egan, P.O.; Hughes, V.W. et al.
Partner: UNT Libraries Government Documents Department

Phenomenology of preequilibrium angular distributions

Description: The systematics of continuum angular distributions from a wide variety of light ion nuclear reactions have been studied. To first order, the shape of the angular distributions have been found to depend only on the energy of the outgoing particle and on the division of the cross section into multi-step direct and multi-step compound parts. The angular distributions can be described in terms of Legendre polynomials with the reduced polynomial coefficients exhibiting a simple dependence on the outgoing particle energy. Two integer and four continuous parameters with universal values are needed to describe the coefficients for outgoing energies of 2 to 60 MeV in all the reaction types studied. This parameterization combined with a modified Griffin model computer code permits the calculation of double differential cross sections for light ion continuum reactions where no data is available.
Date: May 1, 1980
Creator: Kalbach, C. & Mann, F.M.
Partner: UNT Libraries Government Documents Department


Description: Recent results from the Energetic Gamma-Ray Experiment Telescope (EGRET) aboard the Compton Observatory have generated strong interest in space based high-energy (E{sub {gamma}} > 10 MeV) gamma ray astronomy. This science has wetted the authors` curiosity of what might be observed with an instrument having considerably more capability than EGRET, if such a device were practical in these fiscally difficult times. Advances in silicon technology over the past decade, and the resulting rapid drop in costs, encourage the development of a dramatically new type of high-energy gamma ray space telescope based on silicon strip technology. The GLAST team (GLAST stands for Gamma-ray Large Area Space Telescope) has been working for the past two years on the design of such an instrument, and the development of the silicon strip hardware and readout electronics needed to realize this design. As in previous high-energy instruments, GLAST is a pair spectrometer backed by a total absorption electro-magnetic shower counter. Measurement of the energy and direction of the induced electro-magnetic shower provides information about the energy and direction of the incident gamma-ray. However, due to the flexibility and relatively low cost of the silicon strip technology, the telescope has about a factor of 10 increase in effective area over EGRET, and about a factor of 5 increase in field of view. At the same time, the GLAST design is calculated to have much better point source sensitivity, and to have an energy range of 10 MeV < E{sub {gamma}} < 300 GeV. Due to the economics of silicon technology, along with weight, and size savings compared to gas based detector technology, the authors estimate that this instrument can be built and flown as a Delta II mission. Thus, GLAST would easily fit into the NASA intermediate category with an estimated total cost of about $200 ...
Date: March 1995
Creator: Bloom, E. D.
Partner: UNT Libraries Government Documents Department

Operation and improvements of the Fermilab 400 MeV Linac

Description: The 400 MeV Fermilab Linac Upgrade commissioning began August 28, 1993. High energy physics collider operation (run 1b) began in November 1993 and ended March 1, 1996. The Linac, operating at 98% reliability, provided 400 MeV H{sup -} beam to the Booster and 66 MeV H{sup -} beam to the Neutron Therapy Facility. During this time, the beam intensity, which initially was administratively set to 35 MA, rose to a peak of 50 mA while losses decreased significantly. This paper discusses the Linac operation and reliability since the Upgrade.
Date: September 1, 1996
Creator: Allen, L.J.; Popovic, M. & Schmidt, C.W.
Partner: UNT Libraries Government Documents Department

Analysis of nucleon-induced fission cross sections of lead and bismuth at energies from 45 to 500 MeV

Description: In order to investigate the applicability of the Cascade-Exciton model (CEM) of nuclear reactions to fission cross sections and hoping to learn more about intermediate-energy fission, the authors use an extended version of the CEM, as realized in the code CEM95 to perform a detailed analysis of proton- and neutron-induced fission cross sections of {sup 209}Bi and {sup 208}Pb nuclei and of the linear momentum transfer to the fissioning nuclei in the 45--500 meV energy range.
Date: August 1, 1998
Creator: Prokofyev, A.V.; Mashnik, S.G. & Sierk, A.J.
Partner: UNT Libraries Government Documents Department

Constraints on solar particle events from comparisons of recent events and million-year averages

Description: Several sets of measurements of the fluxes of solar energetic particles (SEPs) above 10 MeV have been used to apply limits to huge solar particle events (SPEs) in the past. Direct measurements of SEPs are used to get event-integrated solar-proton fluences for SPEs since about 1965. Indirect measurements of SEPs in events from 1956 until 1963 have been used with radioactivities measured in lunar rocks to get event-integrated solar-proton fluences for the larger events back to 1956. A cumulative-probability plot of these event-integrated fluences for all energies above 10 MeV shows a fairly smooth trend from fluences of 10{sub 7} protons/cm{sup 2} up to the largest events (3 x 10{sup 10} protons/cm{sup 2}) but there are no events with higher fluences. Activities of radionuclides in the tops of lunar rocks were used to get average fluxes of solar protons for time periods from {approximately} 10{sup 4} to {approximately} 10{sup 7} years, which are similar to those over the last four decades. These proton fluxes from lunar radionuclides indicate that the long-term trend for huge events does not follow the modern trend for event fluences up to {approximately}3 x 10{sup 10} protons/cm{sup 2}, but that huge events (orders of magnitude larger than {approximately}10{sup 11} protons/cm{sup 2}) have been very rare or nonexistent during the last {approximately}10{sup 7} years.
Date: December 1, 1995
Creator: Reedy, R.C.
Partner: UNT Libraries Government Documents Department

Bremsstrahlung pair-production of positrons with low neutron background.

Description: Minimization of component activation is highly desirable at accelerator-based positron sources. Electrons in the 8- to 14-MeV energy range impinging on a target produce photons energetic enough to create electron-positron pairs; however, few of the photons are energetic enough to produce photoneutrons. Slow positron production by low-energy electrons impinging on a multilayer tungsten target with and without electromagnetic extraction between the layers was studied by simulation. The neutron background from 14-MeV electrons is expected to be significantly lower than that encountered with higher-energy electron beams. Numerical results are presented and some ideas for a low-activation slow-positron source are discussed.
Date: September 16, 1998
Creator: Lessner, E.
Partner: UNT Libraries Government Documents Department

Tests of compressed geometry NEC acceleration tubes

Description: Tests have been performed in the 3 MV Pelletron test machine at NEC on a compressed geometry tube which increases the insulating length of the tube by eliminating the heated electrode assemblies (approx.2.5 cm thick) at the end of each tube section. Some insert electrodes are changed to provide some trapping of secondary ions. The geometry tested provided an 18% increase in live ceramic in the tube. The compressed geometry tube allowed a terminal voltage of 3.55 MV on the 3 MV column at normal gradients of 30.3 kv/tube gap. The tube was also conditioned to more than 4 MV and remained stable in voltage with few sparks and with low x-ray levels for days at about 4 MV. This same performance could be achieved with or without arc discharge cleaning. 4 refs., 4 figs.
Date: January 1, 1985
Creator: Raatz, J.E.; Rathmell, R.D.; Stelson, P.H. & Ziegler, N.F.
Partner: UNT Libraries Government Documents Department

P-P Elastic and Charge-Exchange Scattering at about 120 Mev

Description: Observation of antiprotons in a propane or hydrogen bubble chamber offers the possiblity of studying several phenomena for which counter or photographic emulsion techniques are less suitable. Because there is a high ratio of pions, muons, and electrons to antiprotons in the available momentum-analyzed beams, these beams cannot be used in the bubble chamber without an initial purification, which increases the ratio of antiprotons to other particles. Such a purification has been achieved by utilizing the difference in rates of momentum loss in absorbers between antiprotons and other particles. The principle of the method is to pass a momentum-analyzed beam through an absorber. Since particles of unequal mass do not have the same specific ionization they lose different amounts of momentum, and a further magnetic deflection suffices to separate the particles physically according to mass. In this experiment a desirable momentum for antiprotons entering the bubble chamber was 684 Mev/c; however, at this momentum the ratio of undesirable particles to antiprotons at the target where they are produced is about 6 x 10{sup 5}. By starting with 970-Mev/c particles at the target and using the method of differential absorption, they decreased the ratio of undesirable particles (87% {mu}{sup -}, 105 {pi}{sup -}, 3% e{sup -}) to antiprotons entering the bubble chamber at 684 Mev/c to 1.5 x 10{sup 4}. A system of counters indicatd when an antiproton entered the bubble chamber, and although the chamber was expanded on every Bevatron pulse, the lights were flashed and the chamber photographed only when an antiproton entered.
Date: March 28, 1958
Creator: Agnew Jr., Lewis; Elioff, Tom; Fowler, William B.; Gilly, Louis; Lander, Richard L.; Oswald, Larry et al.
Partner: UNT Libraries Government Documents Department

Mass and charge distributions in Fe-induced reactions

Description: The charge and mass of the projectile-like fragments produced in the 12-MeV/nucleon {sup 56}Fe + {sup 165}Ho reaction were measured at a laboratory scattering angle of 16 degrees. The mass and charge distributions of the projectile-like fragments were generated as a function of total kinetic energy loss (TKEL), and characterized by their neutron and proton centroids and variances, and correlation factors. A weak drift of the system towards mass asymmetry, opposite to the direction which minimizes the potential energy of the composite system, was observed. The increase in the variances with energy loss is consistent with a nucleon exchange mechanism as a means for energy dissipation. Predictions of two nucleon exchange models, Randrup`s and, Tassan-Got`s models, are compared to the experimental results of the 672-MeV {sup 56}Fe + {sup 165}Ho reaction and to other Fe-induced reactions. The proton and neutron centroids were found to be generally better reproduced by Tassan-Got`s model than by Randrup`s model. The variances and correlation factor are well reproduced for asymmetric systems by both models.
Date: February 21, 1995
Creator: Madani, H.; Mignerey, A.C.; Marchetti, A.A.; Weston-Dawkes, A.P.; Kehoe, W.L. & Obenshain, F.
Partner: UNT Libraries Government Documents Department