A Flash X-Ray Facility for the Naval Postgraduate School

A Pulsar Model 112A flash X-ray machine has been acquired by the Naval Postgraduate School. This brief report describes the technical aspects of the accelerator and provides. documentation so that interested and affected parties may be informed on safety precautions, potential uses and practical considerations for the "effective utilization of a major resource for education and research. This report is not required by NAVPGSCOLINST 5100.5A and 5100.6A which pertains to the radiation protection program 1,2 at NPS, but is submitted as a matter of courtesy and prudence as some aspects of the use of the flash X-ray machine may fall within the responsibility of safety organizations at NPS. This "document. constitutes a report to the Safety Manager, the Radiation Protection Officer and, the Radiological, Safety and "Isotopes Committee (RSIC). The device does not fall under the "licensing authority of the Nuclear Regulatory' Commission as' radioactive sources are not involvedApproved for public release; distribution unlimited

Higher order parametric X-ray spectra in mosaic graphite and single silicon crystals

We have observed up to eight orders (n) in the spectra of parametric x-radiation, in the range 5-40 keV, produced by the interaction of a 90 Mev electron beam with mosaic graphite and 90 and 35 Mev beams with single silicon crystals. The measured yields and intensity ratios, I(2)/I(n= I), in graphite are not in agreement with the theory of PXR for mosaic crystals. In comparison, the yield and ratios of intensities in silicon are close to the predictions of PXR theory for perfect crystals. The bandwidths of spectral lines measured in both silicon and graphite are in good agreement with theoretical predictions, and are determined by the angular field of view of the detector.U.S. Department of EnergyDNANaval Postgraduate SchoolContract No. DE-FG03-91ER8109

Proton propagation in nuclei studied in the (e,e’p) reaction

Proton propagation in nuclei was studied using the (e,e’p) reaction in the quasifree region. The coincidence (e,e’p) cross sections were measured at an electron angle of 50.4° and proton angles of 50.1°, 58.2°, 67.9°, and 72.9° for 12C, 27Al, 58Ni, and 181Ta targets at a beam energy of 779.5 MeV. The average outgoing proton energy was 180 MeV. The ratio of the (e,e’p) yield to the simultaneously measured (e,e’) yield was compared to that calculated in the plane-wave impulse approximation and an experimental transmission defined. These experimental transmissions are considerably larger (a factor of ∼2 for 181Ta) than those one would calculate from the free N-N cross sections folded into the nuclear density distribution. A new calculation that includes medium effects (N-N correlations, density dependence of the N-N cross sections and Pauli suppression) accounts for this increase

Precision measurement of the deuteron spin structure function g1dg^{d}_{1}

We report on a high-statistics measurement of the deuteron spin structure function g[sup d][sub 1] at a beam energy of 29 GeV in the kinematic range 0.029 < x < 0.8 and 1 < Q2 < 10 (GeV/c)2. The integral Gamma [sup d][sub 1] = (integral)[sup 1][sub 0]g[sup d][sub 1]dx evaluated at fixed Q2 = 3 (GeV/c)2 gives 0.042 ± 0.003(stat) ± 0.004(syst). Combining this result with our earlier measurement of g[sup p][sub 1], we find Gamma [sup p][sub 1]- Gamma [sup n][sub 1] = 0.163 ± 0.010(stat) ± 0.016(syst), which agrees with the prediction of the Bjorken sum rule with O( alpha [sup 3][sub s]) corrections, Gamma [sup p][sub 1]- Gamma [sup n][sub 1] = 0.171 ± 0.008. We find the quark contribution to the proton helicity to be Delta q = 0.30 ± 0.06

Measurements of R=sigma_L/sigma_T for 0.03<x<0.1 and Fit to World Data

Measurements were made at SLAC of the cross section for scattering 29 GeV electrons from carbon at a laboratory angle of 4.5 degrees, corresponding to 0.03<x<0.1 and 1.3<Q^2<2.7 GeV^2. Values of R=sigma_L/sigma_T were extracted in this kinematic range by comparing these data to cross sections measured at a higher beam energy by the NMC collaboration. The results are in reasonable agreement with pQCD calculations and with extrapolations of the R1990 parameterization of previous data. A new fit is made including these data and other recent results.Comment: 8 pages, 4 figures, late

Cherenkov x Rays: Recent Experimental Results

The 11th Werner Brandt Workshop on Charged Particle Penetration PhenomenaPreliminary experimental results show the measurement of Cherenkov x rays for silicon and carbon foils. The measured distributions demonstrate grazing-angle enhancement of the emission flux, where relativistic electrons are incident on the foils at near-grazing angles. This behavior was predicted in a paper presented at the preceding Werner Brandt Workshop.Oak Ridge National LaboratoryNaval Postgraduate School FoundationU.S. Department of Energy by the Lawrence Livermore National Laboratory under Contract number W7405-ENG-4

Production of x-rays by the interaction of charged particle beams with periodic structures and crystalline materials

We describe our recent experimental study of the production of x-rays by an electron beam interacting with a crystal lattice, i.e. parametric x-ray (PX) generation. In this radiation process the virtual photon field associated with a relativistic electron traveling in a crystal is diffracted by the crystal lattice in the same way that real x-rays are diffracted by crystals. The radiation produced satisfies the Bragg condition associated with the diffraction of the virtual photons which are nearly parallel to the velocity of the electrons. This phenomenon is associated with a more general class of radiation production mechanisms which include transition radiation (TR), diffraction radiation (DR), and Smith-Purcell radiation. In each case, radiation is produced when the particle's fields are altered by interacting with a material whose dielectric constant varies along or near the particle's trajectory. The usual acceleration mechanism for the production of radiation is not involved in these phenomena. In the case of a crystal, the periodic electric susceptibility interacting with the particle's field produces parametric x-rays. We will also present a theoretical overview of this phenomenon which can be used to generate monochromatic, linearly polarized, directional x-rays. Accelerators with energies ranging from a few MeV to hundreds of MeV may be used as drivers for novel parametric x-ray generators for various applications requiring the unique properties of these sources

Electroexcitation of Giant Multipole Resonances in Au197 and Pb208 between 5 and 40 MeV Excitation Energy with 90-MeV Electrons

Ever since Goldhaber and Teller explained the giant dipole resonance as a collective oscillation of neutrons against protons, extensions of their model have raised the question of the existence of giant resonances with other multipolarities, especially those with quadrupole and monopole characters

Excitation of M1 and M2 states in (22)Ne by 180° electron scattering

States in (22)Ne have been studies by 180° inelastic electron scattering with incident energies of 37, 50, and 60 MeV. Prominent magnetic dipole and quadrupole states are observed below 13 MeV excitation energy. Reduced transition probabilities, transition radii, and spin and parity assignments are presented for these states and compared to shell model calculations.Approved for public release; distribution is unlimited

A method for measuring dark current electron beams in an RF linac

X-ray fluorescence from thin foils inserted into the Naval Postgraduate School linac has been used to measure the integrated electron beam intensity when the accelerator is operating with dark current. The measured x-ray flux, the known inner shell ionization cross sections and radiative transition probabilities are used to obtain measurements of dark currents of the order of 10-14 Amperes. The same arrangement allows continuous, in-situ energy calibration of our SiLi detector in the electromagnetic noise environment of the linac. This technique was originally developed to perform absolute production efficiency measurements of parametric x-ray generation in the 5 - 50 keV range.This work was partially supported by the Defense Nuclear Agency, the Naval Postgraduate School and USDOE SBIR Contract (No. DE-FGO3- 9 1ER8 1099)