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Focusing and imaging sharp line x-ray and gamma-ray sources using variable-metric diffraction crystals. [Gamma ray telescopes]

Description: A new method has been devised for focusing and imaging the radiation from sharp-line sources of x-rays and gamma-rays, which makes use of variable-metric diffraction crystals. A variable-metric diffraction crystal is one in which the spacings between the crystalline planes is varied as a function of position in the crystal by either the application of a thermal gradient or by changing the composition of a two component or multiple component crystal. This change in planar spacing changes the Bragg diffraction angle for monochromatic radiation as a function of position in the crystal and makes it possible to obtain focusing and in some cases imaging of a sharp-line point source or parallel beam source. This new approach to focusing x-rays and gamma-rays is used to design a number of gamma ray telescopes suitable for focusing the 511 keV annihilation radiation from the strong source of the center of our galaxy. The new designs are surprisingly efficient with approximately 20% of the radiation incident on the variable-metric diffraction crystals being focused on the image spot. Crystals of Ge, Ge + Si, Si, and quartz are used with mosaic widths of 10 arc sec. The size of the telescope can be scaled up or down without affecting the angular resolution or the energy resolution. The largest model described is 50 m long and has 10 crystal diffraction ring assembles with radii between 71 and 200 cm. The total area of the diffraction crystal is 24,610 cm/sup 2/ and the effective area (total x diffraction coefficient x transmission) is 4745 cm/sup 2/. An example of a smaller telescope is also given that is only 12.5 m long and has an effective area of 297 cm/sup 2/.
Date: January 1, 1982
Creator: Smither, R.K.
Partner: UNT Libraries Government Documents Department

SPECTER: neutron damage calculations for materials irradiations

Description: Neutron displacement damage-energy cross sections have been calculated for 41 isotopes in the energy range from 10/sup -10/ to 20 MeV. Calculations were performed on a 100-point energy grid using nuclear cross sections from ENDF/B-V and the DISCS computer code. Elastic scattering is treated exactly including angular distributions from ENDF/B-V. Inelastic scattering calculations consider both discrete and continuous nuclear level distributions. Multiple (n,xn) reactions use a Monte Carlo technique to derive the recoil distributions. The (n,d) and (n,t) reactions are treated as (n,p) and (n,/sup 3/He) as (n,/sup 4/He). The (n,..gamma..) reaction and subsequent ..beta..-decay are also included, using a new treatment of ..gamma..-..gamma.. coincidences, angular correlations, ..beta..-neutrino correlations, and the incident neutron energy. The Lindhard model was used to compute the energy available for nuclear displacement at each recoil energy. The SPECTER computer code has been developed to simplify damage calculations. The user need only specify a neutron energy spectrum. SPECTER will then calculate spectral-averaged displacements, recoil spectra, gas production, and total damage energy (Kerma). The SPECTER computer code package is readily accessible to the fusion community via the National Magnetic Fusion Energy Computer Center (NMFECC) at Lawrence Livermore National laboratory.
Date: January 1, 1985
Creator: Greenwood, L.R. & Smither, R.K.
Partner: UNT Libraries Government Documents Department

Measurement of the /sup 27/Al(n,2n)/sup 26/Al reaction cross section for fusion-reactor applications

Description: The /sup 27/Al(n,2n)/sup 26/Al reaction is of considerable interest to the fusion reactor program. Aluminum is an attractive material for many structural applications, and the (n,2n) reaction is the major source of long-lived activity (/sup 26/Al, g.s. T/sub 1/2/ = 7.34 x 10/sup 3/ g). The threshold for this reaction falls within the spread of neutron energies generated by a D-T plasma. Its cross section is therefore a steeply rising function of energy for the primary fusion neutrons. This special feature makes it possible to use this reaction to measure plasma ion temperatures as well as neutron yields and neutron spectral shapes. The /sup 27/Al(n,2n)/sup 26/Al reaction is one of the major sources of displacement damage in Al-metal alloys and other aluminum containing fusion materials, thus the cross section near threshold will strongly affect the amount of displacement damage in these materials as well as the long-lived radioactivity.
Date: January 1, 1983
Creator: Smither, R.K. & Greenwood, L.R.
Partner: UNT Libraries Government Documents Department

High resolution monochromator systems using thermal gradient induced variable Bragg spacing

Description: The vertical divergences of bending magnet and wiggler synchrotron sources are generally considerably larger than the acceptance angles of typical monochromator systems. This is particularly true at high energies (E greater than or equal to 14 keV) where the Darwin widths of perfect crystals are of the order 10/sup -6/ radians. By imposing a thermal gradient on the crystal, an efficient, wide acceptance angle monochromator can be obtained. The necessary condition being that the resulting d . sin theta is a constant across the beam. Gains in intensity of 3 to 100 can be realized relative to standard flat crystal systems. A number of possible designs are presented for both two and four crystal monochromator systems. The use of Si, Ge, and quartz monochromators are discussed.
Date: July 1, 1985
Creator: Knapp, G.S. & Smither, R.K.
Partner: UNT Libraries Government Documents Department

Liquid metal cooling of synchrotron optics

Description: The installation of insertion devices at existing synchrotron facilities around the world has stimulated the development of new ways to cool the optical elements in the associated x-ray beamlines. Argonne has been a leader in the development of liquid metal cooling for high heat load x-ray optics for the next generation of synchrotron facilities. The high thermal conductivity, high volume specific heat, low kinematic viscosity, and large working temperature range make liquid metals a very efficient heat transfer fluid. A wide range of liquid metals were considered in the initial phase of this work. The most promising liquid metal cooling fluid identified to date is liquid gallium, which appears to have all the desired properties and the fewest number of undesired features of the liquid metals examined. Besides the special features of liquid metals that make them good heat transfer fluids, the very low vapor pressure over a large working temperature range make liquid gallium an ideal cooling fluid for use in a high vacuum environment. A leak of the liquid gallium into the high vacuum and even into very high vacuum areas will not result in any detectable vapor pressure and may even improve the vacuum environment as the liquid gallium combines with any water vapor or oxygen present in the system. The practical use of a liquid metal for cooling silicon crystals and other high heat load applications depends on having a convenient and efficient delivery system. The requirements for a typical cooling system for a silicon crystal used in a monochromator are pumping speeds of 2 to 5 gpm (120 cc per sec to 600 cc per sec) at pressures up to 100 psi.
Date: September 1, 1992
Creator: Smither, R.K.
Partner: UNT Libraries Government Documents Department

Recent developments in neutron dosimetry and damage calculations for fusion materials irradiations

Description: Fusion materials experiments require accurate neutron dosimetry measurements and damage calculations. Neutron cross section measurements are described for application at fission reactors, accelerator neutron sources, fusion reactors, and spallation neutron sources. For fission reactors work is in progress to resolve integral/differential discrepancies and to develop new reactions for dosimetry. Reactions for fusion reactors are designed for plasma diagnostics and waste generation. Spallation reactions are being measured to extend our techniques to 800 MeV for spallation neutron sources. The SPECTER computer code has been developed to routinely calculate displacement damage, gas production, recoil spectra, and total dose for 38 elements with a user specified neutron spectrum. New helium measurements and calculations are described. A new procedure is discussed for the thermal production of helium by nickel including previously neglected damage from the energetic /sup 56/Fe recoils.
Date: January 1, 1984
Creator: Greenwood, L.R. & Smither, R.K.
Partner: UNT Libraries Government Documents Department

Crystal diffraction lens for medical imaging

Description: A crystal diffraction lens for focusing energetic gamma rays has been developed at Argonne National Laboratory for use in medical imaging of radioactivity in the human body. A common method for locating possible cancerous growths in the body is to inject radioactivity into the blood stream of the patient and then look for any concentration of radioactivity that could be associated with the fast growing cancer cells. Often there are borderline indications of possible cancers that could be due to statistical functions in the measured counting rates. In order to determine if these indications are false or real, one must resort to surgical means and take tissue samples in the suspect area. They are developing a system of crystal diffraction lenses that will be incorporated into a 3-D imaging system with better sensitivity (factors of 10 to 100) and better spatial resolution (a few mm in both vertical and horizontal directions) than most systems presently in use. The use of this new imaging system will allow one to eliminate 90% of the false indications and both locate and determine the size of the cancer with mm precision. The lens consists of 900 single crystals of copper, 4 mm x 4 mm on a side and 2--4 mm thick, mounted in 13 concentric rings.
Date: February 25, 2000
Creator: Smither, R. K. & Roa, D. E.
Partner: UNT Libraries Government Documents Department

Asymmetric-cut monochromator with adjustable asymmetry

Description: A variable incident angle, asymmetric cut, double crystal monochromator was tested for use on beamlines at the Advanced Photon Source (APS). For both undulator and wiggler beams the monochromator can expand area of footprint of beam on surface of the crystals to 50 times the area of incident beam; this will reduce the slope errors by a factor of 2500. The asymmetric cut allows one to increase the acceptance angle for incident radiation and obtain a better match to the opening angle of the incident beam. This can increase intensity of the diffracted beam by a factor of 2 to 5 and can make the beam more monochromatic, as well. The monochromator consists of two matched, asymmetric cut (18 degrees), silicon crystals mounted so that they can be rotated about three independent axes. Rotation around the first axis controls the Bragg angle. The second rotation axis is perpendicular to the diffraction planes and controls the increase of the area of the footprint of the beam on the crystal surface. Rotation around the third axis controls the angle between the surface of the crystal and the wider, horizontal axis for the beam and can make the footprint a rectangle with a minimum. length for this area. The asymmetric cut is 18 degrees for the matched pair of crystals, which allows one to expand the footprint area by a factor of 50 for Bragg angles up to 19.15 degrees (6 keV for Si[111] planes). This monochromator, with proper cooling, will be useful for analyzing the high intensity x-ray beams produced by both undulators and wigglers at the APS.
Date: January 1, 1993
Creator: Smither, R.K. & Fernandez, P.B.
Partner: UNT Libraries Government Documents Department

Liquid metal cooling of synchrotron optics

Description: The installation of insertion devices at existing synchrotron facilities around the world has stimulated the development of new ways to cool the optical elements in the associated x-ray beamlines. Argonne has been a leader in the development of liquid metal cooling for high heat load x-ray optics for the next generation of synchrotron facilities. The high thermal conductivity, high volume specific heat, low kinematic viscosity, and large working temperature range make liquid metals a very efficient heat transfer fluid. A wide range of liquid metals were considered in the initial phase of this work. The most promising liquid metal cooling fluid identified to date is liquid gallium, which appears to have all the desired properties and the fewest number of undesired features of the liquid metals examined. Besides the special features of liquid metals that make them good heat transfer fluids, the very low vapor pressure over a large working temperature range make liquid gallium an ideal cooling fluid for use in a high vacuum environment. A leak of the liquid gallium into the high vacuum and even into very high vacuum areas will not result in any detectable vapor pressure and may even improve the vacuum environment as the liquid gallium combines with any water vapor or oxygen present in the system. The practical use of a liquid metal for cooling silicon crystals and other high heat load applications depends on having a convenient and efficient delivery system. The requirements for a typical cooling system for a silicon crystal used in a monochromator are pumping speeds of 2 to 5 gpm (120 cc per sec to 600 cc per sec) at pressures up to 100 psi.
Date: September 1, 1992
Creator: Smither, R. K.
Partner: UNT Libraries Government Documents Department

Potential of a beryllium x-ray lens

Description: The use of refractive lenses for focusing x-ray beams has been the subject of publications since the early 1980s. Detailed calculations have been made for different shapes for the refractive lens: cylindrical, spherical, parabolic, and for a Fresnel-type refractive lens. The main drawback to the use of a single refractive lens to focus x-rays is that the index of refraction (n = 1 {minus} {delta}) is very close to 1, which results in a lens with a very long focal length. Recently Snigerov and others have suggested and experimentally demonstrated, using cylindrical-shaped lenses, that this problem of long focal lengths can be overcome by using many lenses in series. Each lens refracts the photon through a small angle, but the sum of these sequential changes in direction can be moderately larger. This increase in effective refraction angle reduces the focal length of the lens to a few meters or less and makes the multi-element lens a much more useful instrument for focusing x-rays. This paper, annualizes the expected performance of a lens consisting of a series of aligned hollow spheres in a beryllium substrate. The use of hollow spheres rather than hollow cylinders produces focusing of the x rays into a small focal spot in contrast to the single-directional focusing of the hollow cylinders, which produces a line focus. Two multi-element lenses have been constructed: one with 20 1-mm-diameter hollow spheres in an aluminum substrate, and one with 50 hollow spheres, 1 mm in diameter, in a beryllium substrate. Some construction details and calculations of the expected performance, are given for these two multi-element lenses.
Date: September 1, 1997
Creator: Smither, R.K.; Khounsary, A.M. & Xu, S.
Partner: UNT Libraries Government Documents Department

High-heat-load studies of silicon and diamond monochromators using the APS/CHESS prototype undulator

Description: The results of the latest high-heat-load studies made on the APS/CHESS prototype undulator are summarized. Four different crystals were tested: two slotted, symmetrically cut silicon crystals and a core-drilled, asymmetrically cut silicon crystal and a diamond crystal that was jet cooled using water. The purpose of the silicon crystal tests was to reevaluate the surface power loading at which appreciable degradation of the diffraction efficiency was observed. The diamond tests, allotted only a brief period of time during the testing period, were our first attempt at using diamonds for high-heat-flux x-ray monochromators and were performed primarily to gain first-hand experience with diamond monochromators. Measurements with the silicon crystal at 5 keV reconfirmed our previous measurements of performance degradation at around 4-6 watts/mm{sup 2} using liquid gallium with slotted coolant channels. A value of only 2 watts/mm{sup 2} was observed to cause a degradation of the diffraction performance at 15 keV with the same crystals due to the increased sensitivity to strain because of the reduced Darwin widths. The performance of the asymmetric crystal, with its core-drilled coolant channels, was not found to be as good as that of the slotted crystals. This was probably due to poorer heat transfer properties of the core-drilled geometry in combination with the narrowing of the rocking curves because of the asymmetric cut. Fabrication issues for construction of the gallium-cooled crystals is also discussed. Although the diamonds were only successfully tested at low total power the results were very encouraging and motivated us to accelerate our program on the use of diamonds for high-heat-load monochromators.
Date: September 16, 1994
Creator: Mills, D.M.; Lee, W.K.; Smither, R.K. & Fernandez, P.B.
Partner: UNT Libraries Government Documents Department

Diamond monochromator for high heat flux synchrotron x-ray beams

Description: Single crystal silicon has been the material of choice for x-ray monochromators for the past several decades. However, the need for suitable monochromators to handle the high heat load of the next generation synchrotron x-ray beams on the one hand and the rapid and on-going advances in synthetic diamond technology on the other make a compelling case for the consideration of a diamond monochromator system. In this paper, we consider various aspects, advantages and disadvantages, and promises and pitfalls of such a system and evaluate the comparative performance of a diamond monochromator subjected to the high heat load of the most powerful x-ray beam that will become available in the next few years. The results of experiments performed to evaluate the diffraction properties of a currently available synthetic single crystal diamond are also presented. Fabrication of a diamond-based monochromator is within present technical means.
Date: January 28, 1993
Creator: Khounsary, A.M.; Smither, R.K.; Davey, S. & Purohit, A.
Partner: UNT Libraries Government Documents Department

Liquid gallium metal cooling for optical element with high heat loads

Description: Photon beams from the insertion devices of the Argonne synchrotron facility (APS) have very high total powers, which in some cases will exceed 10 kW, spread over a few cm/sup 2/. These high heat loads require special cooling methods to keep them from degrading the quality of the photon beam. A set of finite element analysis calculations were made in three dimensions to determine the temperature distributions and thermal stresses in a single crystal of silicon with heat loads of 2 kW to 20 kW. Different geometric arrangements and different cooling fluids (water, gallium, oil, Na, etc.) were considered. The two best fluids for room temperature operation were found to be water and liquid gallium metal. The variation in temperature across the face of the crystal and the distortion of the surface was at least a factor of two less for the gallium cooling case than for the water cooling case. The water cooling was effective only for very high flow rates. Efficient cooling and the very low vapor pressure for liquid gallium (less than 10/sup -12/ Torr at 100/sup 0/C) make liquid gallium a very attractive cooling fluid for high vacuum synchrotron applications. A small electromagnetic induction pump for liquid Ga was built to test this cooling method. The new system is portable, controls the output temperature of the Ga and can handle heat loads of 10 kW. 13 figs.
Date: July 1, 1987
Creator: Smither, R.K.; Forster, G.A.; Kot, C.A. & Kuzay, T.M.
Partner: UNT Libraries Government Documents Department

Search for doubly-charged negative ions via accelerator mass spectrometry

Description: The Argonne FN tandem accelerator in conjunction with an Enge split-pole magnetic spectrograph has been used as a highly sensitive mass spectrometer to search for doubly charged negative ions of /sup 11/B, /sup 12/C and /sup 16/O. No evidence for the formation of these ions in an inverted sputter source and the subsequent acceleration in the tandem has been found. The following limits for the ratio of doubly-charged to singly-charged ions were measured: X/sup - -//X/sup -/ < 1 x 10/sup -15/, /sup 11/B; < 2 x 10/sup -15/, /sup 12/C; < 2 x 10/sup -14/, /sup 16/O. A relatively abundant formation of the short lived, metastable He/sup -/ ion in the sputter source has been observed.
Date: January 1, 1983
Creator: Kutschera, W.; Frekers, D.; Pardo, R.; Rehm, K.E.; Smither, R.K. & Yntema, J.L.
Partner: UNT Libraries Government Documents Department

Diamond monochromator for high heat flux synchrotron x-ray beams

Description: Single crystal silicon has been the material of choice for x-ray monochromators for the past several decades. However, the need for suitable monochromators to handle the high heat load of the next generation synchrotron x-ray beams on the one hand and the rapid and on-going advances in synthetic diamond technology on the other make a compelling case for the consideration of a diamond mollochromator system. In this Paper, we consider various aspects, advantage and disadvantages, and promises and pitfalls of such a system and evaluate the comparative an monochromator subjected to the high heat load of the most powerful x-ray beam that will become available in the next few years. The results of experiments performed to evaluate the diffraction properties of a currently available synthetic single crystal diamond are also presented. Fabrication of diamond-based monochromator is within present technical means.
Date: December 1, 1992
Creator: Khounsary, A.M.; Smither, R.K.; Davey, S. & Purohit, A.
Partner: UNT Libraries Government Documents Department

Accelerator mass spectrometry and radioisotope detection at the Argonne FN tandem facility

Description: The Argonne FN tandem accelerator and standard components of its experimental heavy-ion research facility, have been used as a highly-sensitive mass spectrometer to detect several long-lived radioisotopes and measure their concentration by counting of accelerated ions. Background beams from isobaric nuclei have been eliminated by combining the dispersion from the energy loss in a uniform Al foil stack with the momentum resolution of an Enge split-pole magnetic spectrograph. Radioisotope concentrations in the following ranges have been measured: /sup 14/C//sup 12/C = 10/sup -12/ to 10/sup -13/, /sup 26/Al//sup 27/Al = 10/sup -10/ to 10/sup -12/, /sup 32/Si/Si = 10/sup -8/ to 10/sup -14/, /sup 36/Cl/Cl = 10/sup -10/ to 10/sup -11/. Particular emphasis was put on exploring to what extent the technique of identifying and counting individual ions in an accelerator beam can be conveniently used to determine nuclear quantities of interest when their measurement involves very low radioisotope concentrations. The usefulness of this method can be demonstrated by measuring the /sup 26/Mg(p,n)/sup 26/Al(7.2 x 10/sup 5/ yr) cross section at proton energies in the astrophysically interesting range just above threshold, and by determining the previously poorly known half life of /sup 32/Si.
Date: January 1, 1980
Creator: Henning, W.; Kutschera, W.; Paul, M.; Smither, R.K.; Stephenson, E.J. & Yntema, J.L.
Partner: UNT Libraries Government Documents Department

Apparent temperature versus true temperature of silicon crystals as a function of their thickness using infrared measurements

Description: The very high intensity x-ray beams that will be present at the Advanced Photon Source and other third generation synchrotron sources will require that the first optical element in the beamline and, possibly, the second optical element as well, be cooled to remove the heat deposited by the x-ray beam. In many of the beamlines this heat will be in the 1 to 5 kW range, and any failure of the cooling system will require a quick response from safety control circuits to shut off the beam before damage is done to the optical element. In many cases, this first optical element will be a silicon diffraction crystal. Viewing the surface of objects subjected to high heat fluxes with an infrared camera or infrared sensor has proved to be a very effective method for monitoring the magnitude and distribution of surface temperatures on the object. This approach has been quite useful in studies of cooling silicon crystals in monochromators subject to high heat loads. The main drawback to this method is that single crystals of silicon are partially transparent to the infrared radiation monitored in most infrared cameras. This means that the infrared radiation emitted from the surface contains a component that comes from the interior of the crystal and that the intensity of the emitted radiation and thus the apparent temperature of the surface of the crystal depends on the thickness of the crystal and the kind of coating on the back (and/or the front) of the crystal. The apparent temperature of the crystal increases as the crystal is made thicker. A series of experiments were performed at Argonne National Laboratory to calibrate the apparent surface temperature of the crystal as measured with an infrared camera as a function of the crystal thickness and the type of coating (if ...
Date: December 31, 1993
Creator: Smither, R. K. & Fernandez, P. B.
Partner: UNT Libraries Government Documents Department

Diamond monochromator for high heat flux synchrotron x-ray beams

Description: Single crystal silicon has been the material of choice for x-ray monochromators for the past several decades. However, the need for suitable monochromators to handle the high heat load of the next generation synchrotron x-ray beams on the one hand and the rapid and on-going advances in synthetic diamond technology on the other make a compelling case for the consideration of a diamond mollochromator system. In this Paper, we consider various aspects, advantage and disadvantages, and promises and pitfalls of such a system and evaluate the comparative an monochromator subjected to the high heat load of the most powerful x-ray beam that will become available in the next few years. The results of experiments performed to evaluate the diffraction properties of a currently available synthetic single crystal diamond are also presented. Fabrication of diamond-based monochromator is within present technical means.
Date: December 1, 1992
Creator: Khounsary, A. M.; Smither, R. K.; Davey, S. & Purohit, A.
Partner: UNT Libraries Government Documents Department

Dispersive x-ray synchrotron studies of Pt-C multilayers

Description: We demonstrate the simultaneous acquisition of high-resolution x-ray absorption spectra and scattering data, using a combination of energy-dispersive optics and a two-dimensional CCD detector. Results are presented on the optical constants of Pt and on the reflectivity of a platinum-carbon multilayer at the L/sub III/ absorption edge of Pt. 12 refs., 5 figs.
Date: February 1, 1989
Creator: Smither, R.K.; Rodricks, B.; Lamelas, F.; Medjahed, D.; Dos Passos, W.; Clarke, R. et al.
Partner: UNT Libraries Government Documents Department

A space bourne crystal diffraction telescope for the energy range of nuclear transitions

Description: Recent experimental work of the Toulouse-Argonne collaboration has opened for perspective of a focusing gamma-ray telescope operating in the energy range of nuclear transitions, featuring unprecedented sensitivity, angular and energy resolution. The instrument consists of a tunable crystal diffraction lens situated on a stabilized spacecraft, focusing gamma-rays onto a small array of Germanium detectors perched on an extendible boom. While the weight of such an instrument is less than 500 kg, it features an angular resolution of 15 in., an energy resolution of 2 keV and a 3 {sigma} narrow line sensitivity of a few times 10{sup {minus}7} photons s{sup {minus}1} cm{sup {minus}2} (10{sup 6} sec observation). This instrumental concept permits observation of any identified source at any selected line-energy in a range of typically 200 keV to 1300 keV. The resulting ``sequential`` operation mode makes sites of explosive nucleosynthesis natural scientific objectives for such a telescope: the nuclear lines of extragalactic supernovae ({sup 56}Ni, {sup 44}Ti, {sup 60}Fe) and galactic novae (p{sup {minus}}p{sup +} line, {sup 7}Be) are accessible to observation, one at a time, due to the erratic appearance and the sequence of half-lifes of these events. Other scientific objectives, include the narrow 511 keV line from galactic broad class annihilators (such as 1E1740-29, nova musca) and possible redshifted annihilation lines from AGN`s.
Date: October 1, 1995
Creator: von Ballmoos, P.; Naya, J.E.; Albernhe, F.; Vedrenne, G.; Smither, R.K.; Faiz, M. et al.
Partner: UNT Libraries Government Documents Department