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

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

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)

Polarized angular distributions of parametric x radiation and vacuum-ultraviolet transition radiation from relativistic electrons

We present quantifiable images of the angular distribution (AO's) of parametric X radiation (PXR) and vacuum-ultraviolet transition radiation (vuv TR) from 230 MeV electrons interacting with a silicon crystal. Both AD's are highly polarized. The vuv TR and optical TR data provide measurements of the beam energy and effective divergence angle. Using these quantities and separately known values of the electronic susceptibility |Xo|, we show that the measured PXR AD is in good agreement with the predictions of single crystal theory. Our analysis suggests a method to measure |Xo| using PXR AD's.Ths work was sponsored in part by DOE SBIR Grant No. DE-FG03-91er80199; NCI SBIR Grant no. 1-R43-CA60207-01 and the Canadian Natural Science and Engineering Research Counci

A compact tunable x-ray source based on parametric x-ray generation by moderate energy linacs

Parametric x-radiation can be described as the diffraction of virtual photons associated with the electric field of a relativistic charged particle passing through a crystal. In analogy with Bragg reflection of x-rays, these diffracted photons appear as real photons, with an energy which satisfies Bragg's law for the reflecting crystal planes. We describe the results of experiments performed on the Naval Postgraduate School linac which were designed to explore the basic properties of PXR in order to assess its potential application as a compact tunable x-ray source. Experiments using a mosaic graphite radiator show that this radiator produced multiple order, narrow bandwidth reflections from 5 - 45 keV. The measured production efficiency is found to exceed that predicted for spectral orders n > 1. We demonstrated the tunability of PXR by rotating the crystal in order to change the Bragg angle relative to the incident 90 MeV electron beam.This work was partially supported by the Defense Nuclear Agency, the Naval Postgraduate School and USDOE SBIR Contract (No. DE-FG03-9lER81099

Generation of hard x rays from transition radiation using high-density foils and moderate-energy electrons

In experiments using target consisting of many thin metal foils, we have demonstrated that a narrow, forward-directed cone of transition radiation in the 8- to 60-keV spectral range can be generated by electrons beams with moderate energies (between 100 and 500 MeV). The theory suggests that high-density, moderate-atomic-number metals are the optimum foil materials and that the foil thickness can be chosen to maximize photon production within a desired spectral range. The three targets in the experiments consisted of 10 foils of 1-um-thick gold, 40 foils of 8.5-um stainless steel, and 20 foils of 7.9-um copper. The efficiency with which hard x rays are generated, and the fact that the requisite electron-beam energies are lower by a factor of 5 to 10, make such a radiation source an attractive alternative to synchrotron radiation for applications such as medical imaging, spectroscopy, and microscopy.This work was financed by the National Science Foundation of the Small Business Innovative Research (SBIR) program, Grant No. PHY-8460914This work was financed by the National Science Foundation of the Small Business Innovative Research (SBIR) program, Grant No. PHY-846091

Quasimonochromatic x-ray source using photoabsorption-edge transition radiation

By designing transition radiators to emit x-rays at the foil material's K-, L-, or M-shell photoabsorption edge, the x-ray spectrum is narrowed. The source is quasimonochromatic, directional, and intense and uses an electron beam whose energy is considerably lower than that needed for synchrotron sources. Depending on the selection of foil material, the radiation can be produced wherever there is a photoabsorption edge. In this paper we report the results of the measurement of the x-ray spectrum from a transition radiator composed of 10 foils of 2-um titanium and exposed to low-current, 90.2-MeV electrons, The measured band of emission was from 3.2 5o 5 keV. In addition, a measurement was performed of the total power from a transition radiator composed of 18 foils of 2.o-um copper exposed to a high-average-current electron beam of 40 uA and at energies of 135, 172, and 200 MeV. The maximum measured power was 4.0 mW. The calculated band of emission was from 4 to 9 keV.National Science Foundation of the Small Business Innovative Research (SBIR) program, Grant no. PHY-8460914; Department of Energy SBIR program, Grant No. DE-FG03-90ER80872; Canadian Natural Science and Engineering Research Council and the Naval Postgraduate SchoolThis investigation was supported by a Special Research Opportunity Grant from the U.S. Office of Naval Research, Department of the Navy and by the Foundation Research Program of the Naval Postgraduate School (Monterey, Ca.)Approved for public release; distribution is unlimited

A transition radiation source with a grazing angle optic for step and scan lithography

Using a grazing angle mirror, the collection and collimation of transition radiation into a slit pattern that can be scanned across an image plane for X-ray dose uniformity is demonstrated. An Au-coated grazing-angle optic was used to focus transition radiation into a rectangular or slit pattern (7 mm ´ 16 mm) in the image plane at 631 mm from the optic and 881 mm from the transition radiator. Intensity variation across the longitudinal direction ( 10 mm) of the slit was less than greater or equal to 5%. The grazing angle optic with a transition radiator can be used for step and scan lithography for obtaining circuit resolution patterns below 0.1 um

Technology and Applications of Neutron Generators Developed by Adelphi Technology, Inc

AbstractA standard product line of high yield neutron generators has been developed at Adelphi Technology Inc. The generators use the D-D fusion reaction and are driven by an ion beam supplied by a microwave ion source. Yields of up to 5×109 n/s have been achieved, which are comparable to those obtained using the more efficient D-T reaction. The microwave-driven plasma uses the electron cyclotron resonance (ECR) to produce a high plasma density for high current and high atomic ion species. These generators have an actively pumped vacuum system that allows operation at reduced pressure in the target chamber, increasing the overall system reliability. Variations of these generators have been produced to increase the yield and total flux available. Several of the generators have been enclosed in radiation shielding/moderator structures designed for customer specifications. These generators have been proven to be useful for prompt gamma neutron activation analysis (PGNAA), neutron activation analysis (NAA) and fast neutron radiography. Pulsed and continuous operation has been demonstrated. Larger thermal neutron fluxes are expected to be obtained by multiple ion beams striking a central target that is filled with moderating material. Thus these generators make excellent fast, epithermal and thermal neutron sources for laboratories and industrial applications that require neutrons with safe operation, small footprint, low cost and small regulatory burden

Observation of soft-x-ray spatial coherence from resonance transition radiation

We have observed the spatial distribution of coherent or resonant transition radiation (RTR) in the soft-x-ray region of the spectrum (1-2 keV). Resonance transition radiators were constructed and tested at two accelerators using electron-beam energies ranging from 50 to 228 MeV. These radiators emitted soft x-rays in a circularly symmetrical annulus with a half-angle divergence of 2.5-9.0 mrad. The angle of peak emission was found to increase with electron-beam energy, in contrast to the incoherent case, for which the angle of emission varied inversely with electron-beam energy. By careful selection of foil thickness and spacing, one may design radiators whose angle of emission varies over a range of charged-particle energies. A particular RTR mode (r=m=1) was found to give a sharp annular ring that becomes more accentuated as the number of foils is increased. The RTR effect has application in particle detection, beam diagnostics, x-ray source brightness enhancement, and x-ray free-electron-laser emission.This work was supported by the Department of Energy under the Small Business Innovative Research (SBIR) program, Grant Number DE-AC03-86ER80428, Canadian Natural Science and Engineering Research Council (NSERC), and the Naval Postgraduate SchoolApproved for public release; distribution is unlimited