Ross Filter Research Articles

X-Ray and electron spectra from the double inverse pinch device

X-ray measurements are reported for the double inverse pinch device (Mark I) which develops an X-type neutral point through argon plasma flow. An x-ray pulse ( E>3 keV) is observed at a critical phase of field line reconnection. Differential absorber measurements with two proportional counters indicate an x-ray energy spectrum of the form (dN / dE)E = aE−s, where S is 3.0±0.2 and a is (1.4±0.7) ×106 (keV)3.0. E is the energy, expressed in keV. The proportional counters are also operated in the Ross filter (K-edge) mode. The x rays appear to be produced by thick target bremsstrahlung of the electrons on the copper anode in the immediate area of the X-type neutral point. An electron energy spectrum of the form (dN / dE) E = bE−γ where γ 4.0±0.2 is and b is (6.8±3.4) × 104 (keV)4.0 is deduced from the x ray spectrum. The x-ray signal starts less than 0.2 μsec after the resitivity minimum and continues for less than 0.25 μsec. The results suggest that runaway electrons are produced then later braked probably by the same wave-particle interactions that have been considered responsible for the current disruption at the neutral point.

A Time-Resolved Ross Filter System for Measuring X-Ray Spectra in Z-Pinch Plasma Focus Devices

The development of plasma pinch and other flash x-ray devices has created the need for a system capable of measuring the spectra of 50 nsec x-ray pulses. A Ross filter system used in conjunction with silicon diode x-ray detectors gives nanosecond time resolution in spectral intervals between 5.46 and 115.6 keV.

X-Ray Spectra from Dense Plasma Focus Devices

X-ray spectra with energies up to 350 keV are reported for two paraboloidal plasma focus devices, the Mark I and Mark III device. Low energy x rays with energies between 5.46 and 29.2 keV were measured with Ross filters. Both time resolved and time integrated spectra were obtained. The higher energy x rays from 60 to 350 keV were measured with K-5 nuclear emulsions. The energies of the individual electrons produced by the photoelectric effect and by Compton scattering in the nuclear emulsion were measured and the x-ray spectra were deduced. The x-ray spectra from each device can be represented by the function (dN/dE)E = AE−m. In the Mark I device, A = (0.85 ± 0.28) × 108 ergs (keV)1.5 and m = (2.5 ± 0.8); in the Mark III device, A = (3.8 ± 1.0) × 108 ergs (keV)1.5 and m = (2.5 ± 1.0), where E is the photon energy in kiloelectron volts. Both spectra are similar in shape, but the x-ray intensity from Mark III, with four times the bank energy, is greater. The x rays appear to be produced by thick target bremsstrahlung on the anode surface by electrons with maximum energies greater than 350 keV and total energy distributions that vary as E−3.3. The start of the x-ray pulse is found to be coincident in time with the current discontinuity in the plasma pinch device.

Experimental continuous and L-characteristic X-ray spectra for tungsten target tubes operated at 15 to 30 kV

Distributions of energy fluence with respect to energy were measured by three methods for x-rays produced in a tungsten target tube with a 1 mm beryllium window. The tube was energized by a constant potential generator operated at 15, 20, 25 and 30 kv. The methods used were gas proportional counting, scintillation counting and attenuation analysis. The percentage of the total energy fluence due to tungsten L-characteristic radiation was measured by each of the above techniques and also by using balanced (Ross) filters. It reached a maximum of about 33%. The methods gave results which were in reasonable agreement with one another and with theory.

A method for balancing Ross filters in x-ray diffraction of liquids

In x-ray diffraction techniques for liquids, balanced (Ross) filters can be used for obtaining an essentially monochromatic beam. This article describes how correct balancing can be tested experimentally. The method is based on the use of a strongly fluorescent solution (e.g. for Mo Kα radiation a solution containing Y). The filters are then balanced until the fluorescent radiation is equally absorbed by both filters. The measurements are carried out under conditions identical to those existing in the actual experiments.

An automatic balanced filter device for X-ray diffraction experiments

An automatic balanced filter box which may be used on most standard X-ray diffraction tubes is described. It is designed to be used in conjunction with a wide variety of automated X-ray diffraction experiments to change Ross filters and insert attenuators into the incident X-ray beam on receipt of appropriate commands from the control system. The positions of the filters and attenuators may be displayed at all times by using feedback signals generated by a combination of light sources and photocells.

X-Ray Fluorescence Yields of Al, Cl, Ar, Sc, Ti, V, Mn, Fe, Co, Y, and Ag

The $K$-fluorescence yields of elements in the range $13\ensuremath{\le}Z\ensuremath{\le}27$ and the $L$-fluorescence yields of yttrium and silver have been measured. A monochromatic x-ray beam obtained through the Ross filter difference method produced the fluorescence in foil targets and argon gas, and some of the fluorescent x rays were detected by a flow counter mounted at right angles to the primary x rays. The incident x-ray flux was determined by a measurement in the same geometry of the x-ray flux scattered by helium. The fluorescence yields and standard deviations are ${\ensuremath{\omega}}_{K}(\mathrm{Al})=0.0379\ifmmode\pm\else\textpm\fi{}0.0023$, ${\ensuremath{\omega}}_{K}(\mathrm{Cl})=0.0970\ifmmode\pm\else\textpm\fi{}0.0054$, ${\ensuremath{\omega}}_{K}(\mathrm{Ar})=0.119\ifmmode\pm\else\textpm\fi{}0.007$, ${\ensuremath{\omega}}_{K}(\mathrm{Sc})=0.190\ifmmode\pm\else\textpm\fi{}0.010$, ${\ensuremath{\omega}}_{K}(\mathrm{Ti})=0.221\ifmmode\pm\else\textpm\fi{}0.012$, ${\ensuremath{\omega}}_{K}(\mathrm{V})=0.250\ifmmode\pm\else\textpm\fi{}0.012$, ${\ensuremath{\omega}}_{K}(\mathrm{Mn})=0.303\ifmmode\pm\else\textpm\fi{}0.017$, ${\ensuremath{\omega}}_{K}(\mathrm{Fe})=0.347\ifmmode\pm\else\textpm\fi{}0.022$, ${\ensuremath{\omega}}_{K}(\mathrm{Co})=0.366\ifmmode\pm\else\textpm\fi{}0.020$, ${\overline{\ensuremath{\omega}}}_{L}(\mathrm{Y})=0.0315\ifmmode\pm\else\textpm\fi{}0.0028$, and ${\overline{\ensuremath{\omega}}}_{L}(\mathrm{Ag})=0.0659\ifmmode\pm\else\textpm\fi{}0.0037$. The uncertainties include a 5% uncertainty in the helium-scattering cross section assumed for the data reduction. These $K$-fluorescence yields and the values for fluorescence yields for $Z\ensuremath{\ge}30$ considered best by Fink, Jopson, Mark, and Swift are fitted with the semiempirical formula ${[\frac{{\ensuremath{\omega}}_{K}}{(1\ensuremath{-}{\ensuremath{\omega}}_{K})}]}^{n}=A+BZ+C{Z}^{3}$, using $n=\frac{1}{4} \mathrm{and} \frac{1}{3}$. The best fit is given by ${[\frac{{\ensuremath{\omega}}_{K}}{(1\ensuremath{-}{\ensuremath{\omega}}_{K})}]}^{\frac{1}{3}}=\ensuremath{-}0.1019+0.03377Z+1.178\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}{Z}^{3}$, with a standard deviation of 2.4%.

AbsoluteK-Ionization Cross Section of the Nickel Atom under Electron Bombardment at 70 kv

Nickel sheets approximately 5\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}6}$ cm in thickness were bombarded with 70 kv electrons and the intensity of the resulting $K\ensuremath{\alpha}$ radiation was measured by a special air-filled ionization chamber connected to a calibrated quadrant electrometer. Isolation of the $K\ensuremath{\alpha}$ line was effected by Ross filters of cobalt and iron, supplemented by additional filters for evaluation of a correction for the continuous background radiation. After due consideration of the effects of electron scattering in the target and all relevant x-ray absorptions, it was concluded from the observed intensities that the cross section of the nickel atom for $K$ ionization by 70 kv electrons is (3.38\ifmmode\pm\else\textpm\fi{}0.2) \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}22}$ ${\mathrm{cm}}^{2}$. From this result and Williams' equation for electron energy loss it is deduced that the efficiency of production of nickel $K$-radiation by electrons of 70 kev energy is 0.35 percent.

Theory and Use of Ross Filters. II

It is often advantageous to use Ross filters of a thickness much greater than that which has been judged to be optimum by the criterion of maximum pass-band transmission. The thicker filters show a larger ratio of measurable pass-band radiation to total spectrum power received and to received power resulting from balance errors. Prefiltration, though useful in connection with thin filters, confers no advantage when thick filters are used. Balance errors caused by the variation with atomic number of the function representing the variation of absorption coefficient with wave-length may, in principle, be eliminated at an indefinite number of chosen wave-lengths by giving one filter a particular type of thickness non-uniformity. Techniques for the construction and adjustment of Ross filters are described.

On the Theory and Use of Ross Filters

Resolving power, preferred thickness and balance errors of Ross filters for x-ray monochromatization are discussed. It is theoretically impossible to balance two filters of elementary composition because of scattering, L limits and K jump, even if the absorption coefficients of the two filters vary similarly with wave-length between the limits, which is not known to be the case. It suffices, however, to obtain good balance for wave-lengths near the pass band since others longer and shorter may be relatively reduced by pre-filtration through a filter whose composition is the same as that of the high atomic number member of the balanced pair. The K jump balance error may be completely removed by adding a slightly absorbing filter of low atomic number to one member of the pair. By employing a specially designed ionization chamber Ross filters may be used simultaneously instead of alternately and a considerable gain in speed and accuracy achieved.