High X-ray Yield Research Articles

Comparative study of X-ray emission from plasma focus relative to different preionization schemes

A 2.7-kJ Mather-type plasma focus has been investigated for X-ray emission with preionization produced by an α-source, a β-source, and a shunt resistor. Time-resolved and time integrated measurements are carried out using a PIN-diode-based X-ray spectrometer and pinhole camera. The β-source (28Ni63) assisted preionization enhances the X-ray emission up to 25%, while preionization induced by depleted uranium (92U238) increases both Cu-Kα and total X-ray yield of about 100%. The preionization caused by the optimum shunt resistor enhances the Cu-Kα and total X-ray yield of about 53%. It is found that preionization also broadens the working pressure range for the high X-ray yield and improves the shot-to-shot reproducibility of the system. Pinhole images reveal that the X-ray emission from the anode tip is dominant owing to impact of electron bombardment, while the X-ray emission from hot spots is also visible.

Investigation of the hydrogen multilayered target H/T−D2 and muonic X-ray yields in ion implantation

This paper extends applications of the multilayered solid target H/T−D2, which is kept at 3 K. The time evolutions of muonic tritium atoms (μt) are obtained, by taking into account μt production rate at different places of deuterium material. The apparatus H/T−D2 can be used for checking nuclear properties of implanted ions, which take part at muon transfer. Electromagnetic X-rays are generated by muon atomic transitions. The muonic X-ray transition energies are strongly affected by the size of nuclei. Here, a solid hydrogen–tritium (H/T) with a ≈1 mm thick is used for μt production. For ion implantation, the required amount of deuterium material is determined to be about 3.2 μm. Moreover, the muonic X-ray yields are estimated and compared with those of the arrangement H/T−D2. While the present target requires argon ion beam intensity nearly a factor of 2 times smaller; gives a relatively higher X-ray yield (15% enhancement per hour) at the energy 644 keV with the detection efficiency of ≈1%.

Symmetric multilayer megampere X-pinch

Raising the power of X-ray emission from an X-pinch by increasing the pinch current to the megampere level requires the corresponding increase in the initial linear mass of the load. This can be achieved by increasing either the number of wires or their diameter. In both cases, special measures should be undertaken to prevent the formation of a complicated configuration with an uncontrolled spatial structure in the region of wire crossing, because such a structure breaks the symmetry of the neck formed in the crossing region, destabilizes plasma formation, and degrades X-ray generation. To improve the symmetry of the wire crossing region, X-pinch configurations with a regular multilayer arrangement of wires in this region were proposed and implemented. The results of experiments with various symmetric X-pinch configurations on the COBRA facility at currents of ∼1MA are presented. It is shown that an X-pinch with a symmetric crossing region consisting of several layers of wires made of different materials can be successfully used in megampere facilities. The most efficient combinations of wires in symmetric multilayer X-pinches are found in which only one hot spot forms and that are characterized by a high and stable soft X-ray yield.

Soft X-ray emissions from neon gas-puff Z-pinch powered by Qiang Guang-I accelerator

AbstractThe X-ray emission, especially the K-shell emission, from a neon gas-puff Z-pinch powered by the Qiang Guang-I accelerator, about 1.5 MA in amplitude and 100 ns in rise time, were calculated based on the two-level model and measured with X-ray diodes and an eight-frame X-ray pinhole camera. The simulation results showed that the K-shell yield is highly sensitive to the peak current. The experimental results confirmed that the matching of the Z-pinch load (mass and initial radius) to the current is crucial for getting a higher X-ray yield. Being determined by the imploding time, the pinch current plays a more important role than the current amplitude in K-shell emission. It seems that the preferable imploding time is about 110 ns. The K-shell radiation power with double shells, as a whole, is higher than that using single neon shell. While an implosion of a light (32 µg/cm) and small (20 mm in diameter) neon shell evolves with rather twist and asymmetries, a heavier (41 µg/cm) and bigger (25 mm in diameter) neon shell implodes more symmetrically. The double neon shells, 30 mm and 30 µg/cm for the outer shell, and 15-mm and 10 µg/cm for the inner shell, create almost “perfect” implosions evidenced by the early-time plasma shells with little perturbation and late stagnated pinch liners with a good axial uniformity. It was found that the “Zippering” effect leads to an earlier K-shell emission in the cathode region than that in the anode region, which extends the pulse width of K-shell emission.

Collisionless phenomena in heteronuclear clusters

Argon K-shell x-ray yields and electron fluxes are measured for water doped Ar clusters as a function of laser pulse width. The high energy electron and x-ray yields are significantly enhanced in doped clusters. We show that doping of the clusters can be used to enhance collisionless absorption.

K -shell and extreme ultraviolet spectroscopic signatures of structured Ar puff Z-pinch loads with high K-shell x-ray yield

Structured 12-cm-diam Ar gas-puff loads have recently produced Z-pinch implosions with reduced Rayleigh-Taylor instability growth and increased K-shell x-ray yield [H. Sze, J. Banister, B. H. Failor, J. S. Levine, N. Qi, A. L. Velikovich, J. Davis, D. Lojewski, and P. Sincerny, Phys. Rev. Lett. 95, 105001 (2005)]. To better understand the dynamics of these loads, we have measured the extreme ultraviolet (XUV) emission resolved radially, spectrally, and axially. Radial measurements indicated a compressed diameter of ≈3mm, consistent with the observed load inductance change and an imploded-mass consisting of a ≈1.5-mm-diam, hot, K-shell-emitting core and a cooler surrounding blanket. Spectral measurements indicate that, if the load is insufficiently heated, then radiation from the core will rapidly photoheat the outer blanket, producing a strong increase in XUV emission. Also, adding a massive center jet (⩾20% of load mass) increases the rise and fall times of the XUV emission to ⩾40ns, consistent with a more adiabatic compression and heating of the load. Axial measurements show that, despite differences in the XUV and K-shell emission time histories, the K-shell x-ray yield is insensitive to axial variations in load mass.

F21 Abnormal X-ray Emission from Insulators Bombarded with Low Energy Ions

An abnormal phenomenon, low energy ion induced X-ray emission from insulators is reported and discussed. Irradiation with He + , Ga + , Ar + , and Xe + ions in energy from 5 to 100 keV induces strong characteristic X-ray emission from insulator targets but not from conductive ones. The phenomenon is different from the high energy ion induced X-rays, such as PIXE (particle induced X-ray emission) in several aspects, such as very low energy of the used ions, existence of upper limit energy for the ion to induce X-rays. It is implied that the phenomenon relates not only to plus charging-up on surface of the irradiated specimen but may also to ion irradiation related process, such as sputtering. However, further study has to be done for a precise mechanism of the phenomenon. Features, such as high X-ray yields, suggest the phenomenon has potential applications in element analysis and studying ion-solid interaction.

Plasma Focus as a High Intensity Flash X-Ray Source for Biological Radiography

A study on X-ray emission from a low energy (3.3 kJ) plasma focus (PF) device operated with hydrogen is reported. X-ray are detected by using an X-ray detector consisting of three Quantrad Si PIN-diodes with differential filtering and with a pinhole camera. The X-ray yield in different energy windows is measured as a function of hydrogen filling pressure. The maximum yield in 4π-geometry is found to be 46.6 J and corresponding wall plug efficiency for X-ray generation is 1.40%. In particular, to demonstrate feasibility of the present PF as a high intensity flash X-ray source for good contrast biological radiography, an X-ray radiogram of a fish, is presented. The fine structure of the specimen can be seen in different parts. The PF, because of its high X-ray yield and good reproducibility is particularly suited for this application.

Interaction of intense, femtosecond laser pulse with small-sized Ne clusters

We report the first observation of X-ray emission (4 - 18 nm) from small-sized Ne clusters heated by high-intensity, 25-100 fs laser pulses. The Ne spectrum started to drastically change in emitting ions from Ne 5+ to Ne 7+ below the pre-expansion temperature of -120 °C. The significant change in the spectrum is attributed to the collisional heating of small-sized Ne clusters formed in the cryogenically cooled gas jet. Though the size of Ne clusters in our experiment is estimated to be quite small, i.e. a few tens of atoms per cluster, and thus they were undetectable by the standard Rayleigh scattering technique, the appearance of spectral lines of Ne 7+ ions presented clear evidence of collisional heating that occurred in near-solid-density cluster. By extending the laser pulse length from 25 fs to 100 fs, considerably higher X-ray yield from the highest charge state Ne 7+ was observed in the covered spectral region, showing more efficient absorption of 100 fs laser pulse.

Fluorescence concerns in high energy x-ray yield scaling and imaging studies

X rays at high photon energies are needed to backlight and image large objects of high opacity on large lasers, such as the National Ignition Facility, or large pulsed power facilities, such as ATLAS. Attenuators and filters are usually used to bring the signals to scale and to filter the x rays from un-needed low energy components. As the x-ray energy increases, the secondary effect of the interactions of the x rays with the filter or attenuator material must be addressed. This is especially true when one considers using the very high energy x rays from the hot electrons generated during the interaction of intense lasers with high Z materials. We will show how these concerns can be quantified and reduced in at least one case; an experiment on the OMEGA laser facility, designed to investigate the scaling of absolute x-ray yield and conversion efficiency with laser energy and power. This investigation is part of the study to determine the feasibility of high-energy backlighters using Ge emission near 10.3 keV. We will also show how these results apply to imaging at larger x-ray energies.

A spray technique for preparing uniform large-area PIXE calibration standards from aqueous solutions

We describe a procedure for preparing reference standards that can be used to calibrate PIXE spectra of aerosol deposits collected on suitable backing films made, for example, of synthesised polymers (polypropylene, polycarbonate etc.) or chemically modified biopolymers (e.g., cellulose actetate). Aqueous solutions of well defined concentration were prepared from metal salts. The solutions were spray-deposited on cellulose acetate backings using a nebuliser. Lateral uniformity of the deposited layer over areas ranging from several mm to several cm was accomplished by raster scanning the table on which the backing was mounted. By optimising the experimental parameters, deposition could be accomplished without any detectable wetting of delicate substrates like paper. The areal density of the deposited material was calculated from the concentration of the solute, the volume of the consumed solution and the raster scanned area. The reference standards were analysed by PIXE using an external beam chamber backfilled with helium. The Si(Li) based detection system contained a thin funny filter so that X-ray spectra could be measured down to 1 keV. The proton energy on impact was 1.1 MeV. This relatively low probe energy has the advantage of producing favourable elemental X-ray peak heights relative to the bremsstrahlung-background, notably at energies between 2 and 7 keV. Under the same conditions sufficiently high X-ray yields were achieved for heavy elements like Zn and Pb. Using large area beams, bombardment-induced stress in the backing films could be kept at a low level so that very reproducible background spectra were obtained. Hence a straightforward background subtraction routine could be employed. Sensitivities were determined for 23 elements ranging from Na to Pb. Advantages and problems associated with the different metal salts are discussed briefly.

Enhanced X-ray yields from insulating samples

Some insulating samples under proton bombardment produce a very large bremsstrahlung background and enhanced X-ray lines. X-ray energy spectra of several insulating samples (fluorides of metals with valence 4, 3, 2 and 1, a fluoride glass and three fluoride free samples) are presented for proton energies from 0.175 to 2.00 MeV. Also, multiscaling spectra have been collected in order to relate the X-ray yield enhancement with the sample charging up process. It may be concluded that the enhancement effect is obtained during the charged state of the samples and not during the discharge and that structural properties of the samples rather than their insulating properties play an important role in producing and keeping that charged state. Considerations of ionization cross section values suggest high energy electrons as the main ionizing agent. It is also shown that some samples can hold the charged state, with corresponding high X-ray yields, for long periods, suggesting their use as X-ray sources.

Study of sample charging effects on satellite spectra of Ca Kα by means of high-resolution PIXE

High resolution PIXE was applied to measure a sample charging effect on satellite spectra of Ca Kα. A Ca diagram line KL 0) of 3690 eV was observed mainly with an anomaly high X-ray yield when an electric insulator sample of CaF 2 was bombarded with 1.8 MeV He + ions. The yield of KL 0 line decreases drastically when the sample charging is eliminated by applying an electron shower and the KL 1 satellite was distinguished from the KL 0 diagram line. The intensity ratio of KL 1/KL 0 for CaF 2 without charge up is the same as for semiconducting CaB 6.

Production of charge-induced X-rays during PIXE studies using light and heavy ion-beams

A recently discovered phenomenon of excessively high X-ray production is discussed. The high yield is attributed to the build-up of potential on non-conducting targets irradiated with accelerated ion beams, and the subsequent discharge. Ion-beams of1H+,1H2+,2H+,2H2+,3He+,3He2+,4He+,14N+,14N2+,16O+ and20Ne+ were used. A new mechanism of X-ray excitation is proposed. The increased X-ray fluxes produced by this process are suitable for analytical applications of high specificity. The mechanism of excitation associated with the process, factors affecting the high X-ray yields, applications and a general overview of the studies undertaken with the various ion beams are given.

Charge-induced X-ray yields from some metal salts with proton and alpha beams

Previous studies reporting abnormally high X-ray yields from the fluorides of some transition metals were extended to include a variety of other compounds. Using proton beams of 700 and 2000 keV and α-beams of 1000 keV the production of abnormally high X-ray yields were critically examined for reproducibility and under different vaccum and bombarding beam conditions.

Isobar discrimination in accelerator mass spectrometry by detecting characteristic projectile X-rays

The measurement of long-lived radioisotopes by accelerator mass spectrometry (AMS) is often limited by interferences of isobars, which cannot be separated easily (e.g. 36C1/ 36S, 59Ni/ 59Co, 60Fe/ 60Ni,…). Standard isobar separation techniques using ionisation chambers, gas-filled magnets and complete ion stripping can be applied only at sufficiently high energies. It is not possible to achieve enough discrimination for heavier isobars with small AMS accelerators. Recently, the detection of characteristic projectile X-rays during the stopping of ions in matter has been proposed by H. Artigalas et al. [H. Artigalas et al., Nucl. Instr. and Meth. B 79 (1993) 617.] as another isobar separation technique. In this case the discrimination does not depend on the ion energy. A high X-ray yield can be obtained with targets having a nuclear charge close to that of the projectile because inner shell vacancies are produced by molecular orbital formation. We present first results performed at the ETH/PSI 6 MV EN-tandem accelerator applying this technique in the detection of 59Ni and 60Fe. Efficiency, suppression factors and detection limits are discussed.

A PIXE study of abnormal X-rays from binary fluorides with protons in the range 0.4–2 MeV

Previously reported abnormally high X-ray yields from the fluorides of some transition metals were confirmed. Using proton beams and beams of the molecule-ion 1H2+, at equivalent proton energies between 400 and 2000 keV the conditions for the production of abnormally high X-ray yields were studied for the effect of ion beam energy, beam current, charge, target thickness and atomic number of the target metal. The effect was probably due to buildup of potential and discharge with the production of a flux of energetic electrons, with an energy distribution peaking above 10 keV.

Application of a laser differential interferometer to plasma focus

A laser differential interferometer, a modification of an ordinary Schlieren system, is used to study the evolution of plasma sheath structure and the influence of X-ray emission in a plasma focus, and is found to give good results. From the interferograms it is clear that the filling pressure affects not only the propagation velocity of the plasma sheath, but also its structure, and the different structure of plasma above the anode in turn influences X-ray emission. Whilst the pinched plasma gives higher X-ray yield in a low filling pressure, the turbulent plasma with a protrusion above the plasma layer in a high filling pressure leads to low or no X-ray emission. A high density volume emerges from the target of anode at about t=200 ns, well after the focus is over, which may be the metallic vapour released from the target due to an intense electron beam bombardment. From an experimental point of view it appears that the differential interferometer is simpler to use than other interferometers and has proved to be very useful in the diagnostics of plasma focus.

Effect of plasma sheath structure in plasma focus

The development of plasma sheath in the run-down phase and pinch phase in a plasma focus is studied with laser interferometry. The time-resolved interferograms show that the structures of plasma sheaths in the run-down phase are different at low and high pressures of filling gas. This leads to a distinct plasma pattern above the anode. At low pressure the plasma sheath in the run-down phase has clear boundaries, resulting in better compression in the pinch phase and a higher X-ray yield. At high pressure the plasma sheath is turbulent at the back side and become disordered in the pinch phase, giving little or no X-ray emission. The effect of a ceiling, i.e., a metal plate placed above the anode, is investigated. With the ceiling the reproducibility of X-ray emission is much improved.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Experimental study on the dynamics of a cylindrical plasma sheath in a gas-puff z-pinch device

The dynamics of a hollow cylindrical plasma sheath produced in a gas-puff Z-pinch device were studied with a differential interferometer. The velocity of the imploding plasma during three stages of compression the minimum radius of the pinched plasma column, the hot spots and the X-ray emissions were measured. The effect of the parameters of the gas cylinder on the plasma properties and X-ray emission was investigated with three different nozzles. Not only the gas density but also the distribution may influence the process of implosion. The experiments show that a thinner gas sheath produces a higher velocity of compression and higher X-ray yield. An interesting phenomenon of multiple pinch was observed. X-rays may be emitted at different locations and different instants.