Flash X-ray Source Research Articles

Flash x-ray source for plasma shutter diagnostics

A flash x-ray source has been fabricated to examine the plasma-driven shutter for the Nova Fusion Laser System at the Lawrence Livermore National Laboratory. This source has a 20-ns pulse width and 1.5- and 4.5-keV x rays. It has been used to characterize plasma moving at 1–5 cm/μs with areal densities down to 0.1 mg/cm2 and a spatial resolution of 2.5 μm. By using this x-ray source to diagnose the Nova plasma shutter, the authors were able to discover and cure sources of plasma nonuniformity and empirically select the foil dimensions and the current required for Nova.

Radiation Output and Dose Predictions for Flash X-Ray Sources

Calculations are made of target parameters required to maximize the photon fluence from flash x-ray sources for electron energies from 0.5 to 15.0 MeV. Doses and effective absorption coefficients for critical materials located downstream of the target are also obtained.

Two-frame flash x-radiography device for the study of particle beam fusion target implosions

A two-frame flash x-radiography (FXR) system has been developed for studying the implosion hydrodynamics of particle beam driven, inertial confinement fusion (ICF) targets. This system consists of two micropoint flash x-ray sources, two gated x-ray cameras, and a mechanical framework for aligning these components with respect to the target. The tungsten micropoint sources yield a bremsstrahlung spectrum with an end-point energy of 600 keV, an x-ray dose of 8 mrad at 61 cm, a spot size of ∼100 μm, and an exposure time of ∼3 ns. A geometric magnification of 4× was employed in this radiographic arrangement, with an overall system resolving power of 4 line pairs/mm. This system has been used successfully to observe relativistic electron beam (REB) driven, ablative pusher target implosions.

Reducing Errors in Dosimetry Caused by Low Energy Components of Co-60 and Flash X-Ray Sources

Radiation effects testing for electronic devices is commonly performed using Co-60 sources and flash x-ray (FXR) sources. Dosimetry for such irradiation is usually done by measuring the dose in TLD's and then converting to dose in SiO/sub 2/ using energy deposition coefficients. This dosimetry method is useful because it is simple, it requires little knowledge of the source spectrum, and it requires little knowledge of the details of the source spectrum, and it requires little knowledge of the details of the device geometry. However, this method can lead to large errors for some Co-60 sources and most FXR sources because they have significant low energy components. The goal of this paper is to determine whether dosimetry can be performed using the usual method with an acceptable level of error. The authors show to what extent errors can be reduced using a filter to remove low energy components from the incident spectra. Finally, the implications of these results for dosimetry methods and standards. The approach used in this paper is to perform a series of calculations which lead to an estimate of the maximum error in the dosimetry. Further, it has been assumed that errors of up to about 30-40% aremore » acceptable for an important class of engineering problems where the attainment of better accuracy is difficult or expensive.« less

A Characterization and Optimization Study of Gamble II as an X-Ray Bremsstrahlung Source

The adverse effects of radiation on solid state devices are strongly spectrum dependent. It is thus essential that the radiation spectrum from flash x-ray sources be available when they are used as facilities for testing electronic components. This paper describes a preliminary study in which previously developed computer codes were used to calculate the radiation spectrum produced by NRL's Gamble II pulsed power generator. To determine how well the calculated spectrum matched the experimental one, doses in CaF2-Mn TLD's were computed for the dosimeters placed behind various thicknesses of Cu and Pb filters and compared with the experimentally measured doses. Using a diode model that was consistent with presently understood electron beam behavior, a spectrum was generated which predicted TLD doses to within about 15% of the experimentally measured values.

High Resolution X-Ray Contact Microscopy of Hydrated Muscle Filaments

Soft x-ray contact microscopy is a relatively new method for imaging biological materials at resolutions of 5-30 nm. By using a wet cell, and flash x-ray source to reduce the exposure time, we have been able to obtain high contrast images of hydrated biological specimens at better than 30 nm resolution. This paper describes the technique and results of using this type of “wet” microscopy for the examination of hydrated invertebrate isolated myosin filament, and paramyosin paracrystal,preparations.Paramyosin paracrystals and myosin filaments were isolated from telson muscle of the horseshoe crab, Limulus polyphemus L. The muscle was homogenized and the cellular debris and filaments segregated by differential centrifugation. Isolated filaments were resuspended in buffer (Tris, pH 7.4-7.5), and dialyzed overnight against buffer containing EDTA at 4°C. Tissue taken from the white adductor muscle of the clam, Mercenaria mercenaria, was similarly homogenized and isolated by standard methods.

Improved Flash X-Ray Simulation Using the Grad-B Interaction

A new concept for improving the simulation capabilities of flash x-ray sources has been analyzed. The method makes use of adiabatic, single-particle drift in externally applied azimuthal magnetic fields in order to focus, reflex, and stagnate a relativistic electron beam at a converter foil. It yields higher extraction efficiencies and softer spectra than those obtained from more conventional schemes. Power deposition in standard dosimetry is enhanced by factors of 2 to 3. Additional enhancement of time-dependent effects may be achieved through bunching.

Dose and Dose Rate Dependence of 8080a Microprocessor Failures

The occurrence of transient upset and catastrophic failure in 8080A microprocessors was investigated over a dose-rate range of 6 × 10-4 to 3 × 10+10 rads/sec. The transient upset and catastrophic failure levels depended on both dose and dose-rate. For example, the dose at which catastrophic failure occurs is 10 times greater at the highest dose-rates investigated than at the lowest. Irradiation was performed using both low energy (45 kV x-ray tube, 200 kV flash x-ray source) and high energy (Co 60, Linac) sources. The observed transient upset and catastrophic failure levels were significantly higher for low energy irradiation than for high energy irradiation. These results have important implications for models of ionizing radiation effects in MOS devices.

An Electrical Surge Arrestor (ESA) Model for Electromagnetic Pulse Analysis

Electrical Surge Arrestors (ESA's) have been used extensively for lightning and EMP protection. These components are characterized by (a) presenting an open circuit (high impedance) below the gap breakdown potential, (b) becoming a virtual short-circuit above the gap breakdown and (c) displaying a significantly higher level of apparent gap breakdown for very fast input voltage rise-times (dv/dt). This paper describes a mathematical model for a spark gap surge arrestor which has been used successfully to characterize ESA response to the following stimulus: 1. Below DC Gap Breakdown 2. At or above Gap Breakdown 3. At high apparent Gap Breakdown voltage as a function of increased rise-time 4. Damped Sinewave Input (below and at Gap Breakdown) 5. Exposed to prompt gamma radiation using a Flash X-Ray source and an electrical input

Optimization of Bremsstrahlung Energy Deposition

Thick-target bremsstrahlung energy deposition in a thin, gold calorimeter has been measured as a function of converter foil thickness for Mo, Sn, La, Ce, Pr, Nd, and Ta converters at source electron energies of 0.5, 0.75, and 1.0 MeV. The thickness-maximized deposition is not a monotonically increasing function of converter atomic number, but instead exhibits a broad maximum near the type 4f rare-earth region. This maximum is substantially greater than the deposition from the Ta converter--Ta being a material routinely employed in flash x-ray sources. Theoretical models also predict higher deposition from La converters than from Ta converters and are used to show that this enhancement is a consequence of higher characteristic x-ray production in La. Nevertheless, there remain significant discrepancies between theoretical predictions and measured data, even when improved numerical cross sections which have just become available are employed in the calculations.

X-Ray Emission from Laser-Produced Plasmas

AbstractIntense x-rays are emitted by plasmas formed when sub-nanosecond laser pulses are focused onto materials, Plasmas produced by pulses containing up to 100 J can re-emit over ten percent of the energy as x-rays above about 1.0 keV. These plasmas may be useful flash x-ray sources.

A Depth Dose Calorimeter for High Intensity, Low Voltage Flash X-Ray Machines

A small tantalum foil depth dose calorimeter has been constructed for use with high intensity flash x-ray sources. Incident x-ray energy is deposited in an array of tantalum foils monitored by 25 μ iron-constantan thermocouples. Readout is made with a high speed scanning digital microvoltmeter. Comparison is made between the measured x-ray energy deposition in tantalum and the deposition calculated with a Monte Carlo computer code which takes account of the current and voltage waveforms on the diode.

Proposed Flash X-Ray System for X-Ray Diffraction With Submicrosecond Exposure Time

X-ray diffraction studies have generally used low current, low voltage X-ray tubes (e.g., 50 mA, 50 kV). Consequently, exposure times ranging from seconds to hours have been required, limiting X-ray diffraction techniques to the study of essentially static situations. Using such an X-ray source with a very high speed detector, R. E. Green was able to reduce the exposure time for laue patterns of aluminum crystals to a minimum of 0.003 sec. Nanosecond exposure and pulse timing are required for certain events, e.g., X-ray diffraction study of material under shock compression. Q. Johnson achieved this by using a low voltage, very high current flash X-ray source (approximately 50kV, 50kA, 30 nsec). However, such a system is difficult to build and to synchronize, and is not commercially available.Published X-ray yield data, particularly the recent work of J. W. Motz, indicate that both continuum and characteristic X-ray yields increase rapidly with electron energy, reaching a maximum for an electron energy ranging from 150 keV for titanium to 300 keV for copper to nearly 1 MeV for molybdenum.To take advantage of this property, a 300 kVp, 30 nsec pulse, 5 nsec jitter flash X-ray system has been built which appears to meet the intensity and timing requirements for single pulse laue or Bragg diffraction studies. System design, calculated output and initial tests are represented.

Recent Developments In Flash X-Ray Systems

A new flash X-ray source which penetrates thick objects and records shadowgraphs directly on film is discussed. Radiographs with 20 nanosec. exposure time provide hypervelocity stop motion data. Cineradiographs at frame rates to 10 /sec. are provided by a single X-ray tube. Stereo-cineradiographs are provided by tube pairs activated by a single pulser at 180 kV.

A Pulsed Radiation Energy Spectrometer Using Ferroelectrics

The differential energy spectrum of a flash x-ray source or other pulsed radiation sources may be measured using the ferroelectric radiation detector. The detector, consisting of the poled ceramic lead zirconate titanate, exhibits a pulse charge output which is proportional to the absorbed dose. The spectrorneter system itself employs a filtration technique where a set of energy-selective metal filters is positioned in front of a corresponding set of ferroelectric detectors, and the radiation induced charge output of each detector is measured. From this data the spectrum of the pulsed radiation source is deduced by the use of a numerical unfolding technique. Experimentally, the concept of the ferroelectric spectrometer system was verified by measuring the spectrum of a 0.6 MVP flash x-ray machine. Since the ferroelectric detector exhibits a dynamic response to the incident radiation pulse, the same spectrometer concept is used to measure the spectrum as a function of time. The time-dependent character of tnle flash x-ray machine spectrum was detected experimentally and tne results showed that the energy spectrum is harder during the first portion of the pulse.