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Papers by Melvin Piestrup

Review of Scientific Instruments, 2004

We have fabricated and tested short focal-length compound refractive lenses (CRLs) composed of mi... more We have fabricated and tested short focal-length compound refractive lenses (CRLs) composed of microbubbles embedded in epoxy encased in glass capillaries. The interface between the bubbles formed 90 to 350 spherical biconcave microlenses reducing the overall focal length inversely by the number of lenses or bubbles. When compared with CRLs manufactured using other methods, the microbubble lenses have shorter focal lengths with higher transmissions and larger gains for moderate energy x rays (e.g., 7-20 keV). We used beamline 2-3 at the Stanford Synchrotron Radiation Laboratory and beamline 5BM-D-DND at the Advanced Photon Source to measure focal lengths between 100-250 mm with lens apertures varying between 97 and 321 m. Transmission profiles were measured giving, for example, a peak transmission of 46% for a 240 mm focal length CRL at 20 keV. The focal-spot sizes were also measured yielding, for example, a vertical spot size of 1.2 m resulting from an approximate 20-fold demagnification of the APS 23 m source size. The measured gains in intensity over that of unfocused beam were between 9 and 26.

A new kind of hard X-ray / gamma-ray optic is proposed. This optics may be useful for collecting ... more A new kind of hard X-ray / gamma-ray optic is proposed. This optics may be useful for collecting primary X-rays or gammarays from a point source and direct secondary hard X-rays into a given direction. The main element of the proposed optic is a multichannel collimator, which is a glass poly-capillary tube. Incident gamma-rays or hard X-rays with energy E from a point source cross the channel walls of the collimator at a given angle to channel axis and produce secondary Comptonscattered hard X-rays with energy E1 < E. A small portion of the secondary, Compton-scattered hard X-rays, which are emitted in parallel to the center axis of each channel, transmit through the collimator without absorption, forming a hard Xray beam.

We have developed a technique for measuring the energy-resolved angular distribution of longitudi... more We have developed a technique for measuring the energy-resolved angular distribution of longitudinally coherent transition radiation generated in multiple-foil targets. This paper will demonstrate how data generated by these measurements can be used to determine the dielectric constants of materials in the soft x-ray spectral region. Ongoing advances in the development of x-ray technology have attached increasing importance to measurement of the dielectric constant £( 0)) of materials in the x-ray spectral region. Data of this type has been obtained in the past by a number of different techniques. ~3 These techniques have been applied to a number of different materials/­ and with the advent of intense synchrotron x-ray sources, the range of availble data has expanded greatly. The purpose of this paper is to describe how coherent transition radiation can be used as the basis of a complementary technique for measuring x-ray dielectric constants. The measurements are most useful when t...

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2007

The spectral and angular distributions from parametric X-radiation (PXR) from non-relativistic el... more The spectral and angular distributions from parametric X-radiation (PXR) from non-relativistic electrons penetrating a multilayer nanostructure are calculated while accounting for contributions of ordinary and diffracted transition radiation. The PXR emission mechanism is shown to be the dominant emission mechanism. The calculation also demonstrates the possibility of a tunable quasi-monochromatic extreme ultraviolet (EUV) source using only non-relativistic electrons whose efficiency can be large enough for practical applications.

Review of Scientific Instruments, 2002

We present experimental evidence that electrons of modest energy are making multiple passes throu... more We present experimental evidence that electrons of modest energy are making multiple passes through thin targets placed inside a betatron toroid, thus increasing their bremsstrahlung emission efficiency. Thin Cu, Be, W, and Mylar targets of thicknesses between 10-5 to 3.5×10-3 radiation lengths were used. The number of passes through the thin radiators were obtained using either the bremsstrahlung photon densities

Radiation Protection Dosimetry, 2017

Neutron generators are an excellent tool that can be effectively utilized in educational institut... more Neutron generators are an excellent tool that can be effectively utilized in educational institutions for applications such as neutron activation analysis, neutron radiography, and profiling and irradiation effects. For safety purposes, it is imperative that appropriate measures are taken in order to minimize the radiation dose from such devices to the operators, students and the public. This work presents the simulation and measurement results for the neutron and photon dose rates in the vicinity of the neutron generator installed at the University of Sharjah. A very good agreement is found between the simulated and measured dose rates. All of the public dose constraints were found to be met. The occupational dose constraint was also met after imposing a 200 cm no entry zone around the generator room.

Physical Review B, 1990

%e report the results of channeling-radiation experiments performed with high-current electron be... more %e report the results of channeling-radiation experiments performed with high-current electron beams. The research shows that electron channeling can produce a useful source of hard x rays that is highly directional, polarized, intense, tunable, with a 10-15% linewidth, and of picosecond duration. On a picosecond time scale, using a 30-MeV electron beam with a peak current of 50 A channeled in Si, photon Auxes of 1.0X10' photons/(sr keV sec) have been measured at a wavelength of 0.42 A.

AIP Conference Proceedings, 1985

The introduction of a gas into the transverse-field accelerator allows the use of realizable heli... more The introduction of a gas into the transverse-field accelerator allows the use of realizable helix magnetic fields while still maintaining good acceleration gradients for ultrarelativistic electron beams. Synchrotron radiation losses can then be kept to acceptable values. To account for elastic scattering in the gas, a Monte-Carlo simulation has been done, and it shows that the introduction of the gas does not effect the interaction appreciably.

Ieee Journal of Quantum Electronics, 1991

AIP Conference Proceedings, 2009

Single ion-beam RF-plasma neutron generators are presented as a laboratory source of intense neut... more Single ion-beam RF-plasma neutron generators are presented as a laboratory source of intense neutrons. The continuous and pulsed operations of such a neutron generator using the deuterium-deuterium fusion reaction are reported. The neutron beam can be pulsed by switching the RF plasma and/or a gate electrode. These generators are actively vacuum pumped so that a continuous supply of deuterium gas is present for the production of ions and neutrons. This contributes to the generator's long life. These single-beam generators are capable of producing up to 10 10 n/s. Previously, Adelphi and LBNL have demonstrated these generators' applications in fast neutron radiography, Prompt Gamma Neutron Activation Analysis (PGNAA) and Neutron Activation Analysis (NAA). Together with an inexpensive compact moderator, these high-output neutron generators extend useful applications to home laboratory operations.

AIP Conference Proceedings, 2000

ABSTRACT One-dimensional and rotationally axisymmetric two-dimensional focusing of x-rays by plas... more ABSTRACT One-dimensional and rotationally axisymmetric two-dimensional focusing of x-rays by plastic Compound Refractive Lens (CRL) systems are demonstrated and theoretical aspects behind the design of x-ray CRLs are presented in this report. X-rays between 8 and 19.5 keV were focused by cylindrical CRLs having focal lengths between 35 and 100 cm and fabricated using acrylic (Lucite) and polyethylene. Focusing of x-rays by a spherical CRL was also demonstrated observing a focal length of 85 cm and an effective aperture of about 320 μm for 8 keV x-rays. The gain, which is the increase in intensity in the image plane relative to the intensity that would have been obtained without a lens on that plane, was 1.5 for 8 keV photons. The gain of this spherical CRL scales about three orders of magnitude higher on undulator beam lines at third generation x-ray sources from the results obtained at the bending magnet x-ray source, with dimensions 445 μm in the vertical and 1700 μm in the horizontal, used in this work. © 2000 American Institute of Physics.

Stanford Univ Report, Jul 1, 1984

Advances in X-Ray/EUV Optics and Components II, 2007

New projection-type X-ray microscope with a compound refractive lens as the optical element is pr... more New projection-type X-ray microscope with a compound refractive lens as the optical element is presented. The microscope consists of an X-ray source that is 1-2 mm in diameter, compound X-ray lens and X-ray camera that are placed in-line to satisfy the lens formula. The lens forms an image of the X-ray source at camera sensitive plate. An object is placed between the X-ray source and the lens as close as possible to the source, and the camera shows a shadow image of the object. Spatial resolution of the microscope depends on the lens focal length, lens aperture and the distance from the source to the object. One to two micron resolution may be achieved by placing the object at a distance of 1-5 mm from the source. The X-ray source may be designed with the target deposited on a 200-µm thick Be window, which permits the object to be placed very close to the emitting surface. The tube focal spot is equal to 1-2 mm. Results of imaging experiments with an ordinary copper anode X-ray tube and a 10-cm focal length spherical compound refractive X-ray lens are discussed.

Review of Scientific Instruments, 2004

We have fabricated and tested short focal-length compound refractive lenses (CRLs) composed of mi... more We have fabricated and tested short focal-length compound refractive lenses (CRLs) composed of microbubbles embedded in epoxy encased in glass capillaries. The interface between the bubbles formed 90 to 350 spherical biconcave microlenses reducing the overall focal length inversely by the number of lenses or bubbles. When compared with CRLs manufactured using other methods, the microbubble lenses have shorter focal lengths with higher transmissions and larger gains for moderate energy x rays (e.g., 7-20 keV). We used beamline 2-3 at the Stanford Synchrotron Radiation Laboratory and beamline 5BM-D-DND at the Advanced Photon Source to measure focal lengths between 100-250 mm with lens apertures varying between 97 and 321 m. Transmission profiles were measured giving, for example, a peak transmission of 46% for a 240 mm focal length CRL at 20 keV. The focal-spot sizes were also measured yielding, for example, a vertical spot size of 1.2 m resulting from an approximate 20-fold demagnification of the APS 23 m source size. The measured gains in intensity over that of unfocused beam were between 9 and 26.

A new kind of hard X-ray / gamma-ray optic is proposed. This optics may be useful for collecting ... more A new kind of hard X-ray / gamma-ray optic is proposed. This optics may be useful for collecting primary X-rays or gammarays from a point source and direct secondary hard X-rays into a given direction. The main element of the proposed optic is a multichannel collimator, which is a glass poly-capillary tube. Incident gamma-rays or hard X-rays with energy E from a point source cross the channel walls of the collimator at a given angle to channel axis and produce secondary Comptonscattered hard X-rays with energy E1 < E. A small portion of the secondary, Compton-scattered hard X-rays, which are emitted in parallel to the center axis of each channel, transmit through the collimator without absorption, forming a hard Xray beam.

We have developed a technique for measuring the energy-resolved angular distribution of longitudi... more We have developed a technique for measuring the energy-resolved angular distribution of longitudinally coherent transition radiation generated in multiple-foil targets. This paper will demonstrate how data generated by these measurements can be used to determine the dielectric constants of materials in the soft x-ray spectral region. Ongoing advances in the development of x-ray technology have attached increasing importance to measurement of the dielectric constant £( 0)) of materials in the x-ray spectral region. Data of this type has been obtained in the past by a number of different techniques. ~3 These techniques have been applied to a number of different materials/­ and with the advent of intense synchrotron x-ray sources, the range of availble data has expanded greatly. The purpose of this paper is to describe how coherent transition radiation can be used as the basis of a complementary technique for measuring x-ray dielectric constants. The measurements are most useful when t...

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2007

The spectral and angular distributions from parametric X-radiation (PXR) from non-relativistic el... more The spectral and angular distributions from parametric X-radiation (PXR) from non-relativistic electrons penetrating a multilayer nanostructure are calculated while accounting for contributions of ordinary and diffracted transition radiation. The PXR emission mechanism is shown to be the dominant emission mechanism. The calculation also demonstrates the possibility of a tunable quasi-monochromatic extreme ultraviolet (EUV) source using only non-relativistic electrons whose efficiency can be large enough for practical applications.

Review of Scientific Instruments, 2002

We present experimental evidence that electrons of modest energy are making multiple passes throu... more We present experimental evidence that electrons of modest energy are making multiple passes through thin targets placed inside a betatron toroid, thus increasing their bremsstrahlung emission efficiency. Thin Cu, Be, W, and Mylar targets of thicknesses between 10-5 to 3.5×10-3 radiation lengths were used. The number of passes through the thin radiators were obtained using either the bremsstrahlung photon densities

Radiation Protection Dosimetry, 2017

Neutron generators are an excellent tool that can be effectively utilized in educational institut... more Neutron generators are an excellent tool that can be effectively utilized in educational institutions for applications such as neutron activation analysis, neutron radiography, and profiling and irradiation effects. For safety purposes, it is imperative that appropriate measures are taken in order to minimize the radiation dose from such devices to the operators, students and the public. This work presents the simulation and measurement results for the neutron and photon dose rates in the vicinity of the neutron generator installed at the University of Sharjah. A very good agreement is found between the simulated and measured dose rates. All of the public dose constraints were found to be met. The occupational dose constraint was also met after imposing a 200 cm no entry zone around the generator room.

Physical Review B, 1990

%e report the results of channeling-radiation experiments performed with high-current electron be... more %e report the results of channeling-radiation experiments performed with high-current electron beams. The research shows that electron channeling can produce a useful source of hard x rays that is highly directional, polarized, intense, tunable, with a 10-15% linewidth, and of picosecond duration. On a picosecond time scale, using a 30-MeV electron beam with a peak current of 50 A channeled in Si, photon Auxes of 1.0X10' photons/(sr keV sec) have been measured at a wavelength of 0.42 A.

AIP Conference Proceedings, 1985

The introduction of a gas into the transverse-field accelerator allows the use of realizable heli... more The introduction of a gas into the transverse-field accelerator allows the use of realizable helix magnetic fields while still maintaining good acceleration gradients for ultrarelativistic electron beams. Synchrotron radiation losses can then be kept to acceptable values. To account for elastic scattering in the gas, a Monte-Carlo simulation has been done, and it shows that the introduction of the gas does not effect the interaction appreciably.

Ieee Journal of Quantum Electronics, 1991

AIP Conference Proceedings, 2009

Single ion-beam RF-plasma neutron generators are presented as a laboratory source of intense neut... more Single ion-beam RF-plasma neutron generators are presented as a laboratory source of intense neutrons. The continuous and pulsed operations of such a neutron generator using the deuterium-deuterium fusion reaction are reported. The neutron beam can be pulsed by switching the RF plasma and/or a gate electrode. These generators are actively vacuum pumped so that a continuous supply of deuterium gas is present for the production of ions and neutrons. This contributes to the generator's long life. These single-beam generators are capable of producing up to 10 10 n/s. Previously, Adelphi and LBNL have demonstrated these generators' applications in fast neutron radiography, Prompt Gamma Neutron Activation Analysis (PGNAA) and Neutron Activation Analysis (NAA). Together with an inexpensive compact moderator, these high-output neutron generators extend useful applications to home laboratory operations.

AIP Conference Proceedings, 2000

ABSTRACT One-dimensional and rotationally axisymmetric two-dimensional focusing of x-rays by plas... more ABSTRACT One-dimensional and rotationally axisymmetric two-dimensional focusing of x-rays by plastic Compound Refractive Lens (CRL) systems are demonstrated and theoretical aspects behind the design of x-ray CRLs are presented in this report. X-rays between 8 and 19.5 keV were focused by cylindrical CRLs having focal lengths between 35 and 100 cm and fabricated using acrylic (Lucite) and polyethylene. Focusing of x-rays by a spherical CRL was also demonstrated observing a focal length of 85 cm and an effective aperture of about 320 μm for 8 keV x-rays. The gain, which is the increase in intensity in the image plane relative to the intensity that would have been obtained without a lens on that plane, was 1.5 for 8 keV photons. The gain of this spherical CRL scales about three orders of magnitude higher on undulator beam lines at third generation x-ray sources from the results obtained at the bending magnet x-ray source, with dimensions 445 μm in the vertical and 1700 μm in the horizontal, used in this work. © 2000 American Institute of Physics.

Stanford Univ Report, Jul 1, 1984

Advances in X-Ray/EUV Optics and Components II, 2007

New projection-type X-ray microscope with a compound refractive lens as the optical element is pr... more New projection-type X-ray microscope with a compound refractive lens as the optical element is presented. The microscope consists of an X-ray source that is 1-2 mm in diameter, compound X-ray lens and X-ray camera that are placed in-line to satisfy the lens formula. The lens forms an image of the X-ray source at camera sensitive plate. An object is placed between the X-ray source and the lens as close as possible to the source, and the camera shows a shadow image of the object. Spatial resolution of the microscope depends on the lens focal length, lens aperture and the distance from the source to the object. One to two micron resolution may be achieved by placing the object at a distance of 1-5 mm from the source. The X-ray source may be designed with the target deposited on a 200-µm thick Be window, which permits the object to be placed very close to the emitting surface. The tube focal spot is equal to 1-2 mm. Results of imaging experiments with an ordinary copper anode X-ray tube and a 10-cm focal length spherical compound refractive X-ray lens are discussed.