X-ray Yield Research Articles

Efficient fast electron generation in an interaction of Intense, ultrashort laser with metal nanoparticle coated dielectric target

Hot electron generation in intense laser-matter interaction studies is a topic of great interest due in significant part to its applications in fast ignitor scheme in Inertial Confinement Fusion (ICF). We measure the hot electron energy spectrum from Ag nanoparticle coated fused silica target (100 μm thick) interacting with an intense (I∼1018W/cm2), short pulse (τ∼ 30× 10-15s) laser and compare the results with those of an uncoated fused silica. Enhancement in hot electron energy and hard x-ray yield is measured as a function of thickness of Ag nano-coating, varied from tens of nm to hundreds of nm. The hot electron temperatures and integrated x-ray yield are observed to be greater for subwavelength film thicknesses for the case of a p-polarized laser. Such results indicate that metal nanoparticle layers have an important role to play in the enhancement of laser-plasma coupling efficiency for short scale-length plasmas created in femtosecond laser interactions.

Target optimisation for the yield of X-rays of desired hardness under femtosecond pulse irradiation

Different regimes of electron acceleration from solid foils and low-density targets are investigated using three-dimensional numerical simulations. The size of the plasma corona is shown to be the main parameter characterising the temperature and number of hot electrons, which determine the yield of X-ray radiation and its hardness. Also studied is the generation of X-ray radiation by laser-accelerated electrons, which bombard the converter target located behind the laser target.

K-series X-ray yield measurement of kaonic hydrogen atoms in a gaseous target

We measured the K-series X-rays of the K−p exotic atom in the SIDDHARTA experiment with a gaseous hydrogen target of 1.3 g/l, which is about 15 times the ρSTP of hydrogen gas. At this density, the absolute yields of kaonic X-rays, when a negatively charged kaon stopped inside the target, were determined to be 0.012−0.003+0.004 for Kα and 0.043−0.011+0.012 for all the K-series transitions Ktot. These results, together with the KEK E228 experiment results, confirm for the first time a target density dependence of the yield predicted by the cascade models, and provide valuable information to refine the parameters used in the cascade models for the kaonic atoms.

Study of the angular distribution of W-L X-ray intensity ratios in photoionization

The angular distribution of W-[Formula: see text], [Formula: see text] and [Formula: see text] X-rays induced by 13.1 keV bremsstrahlung has been measured at different emission angles from 110[Formula: see text] to 140[Formula: see text] at intervals of 10[Formula: see text]. The investigation of angular dependence of [Formula: see text] X-ray intensity ratios by bremsstrahlung is barely found in previous works. The [Formula: see text] X-ray yield shows isotropic emission, while the measured [Formula: see text] and [Formula: see text] X-ray yields are found to be spatially anisotropic. At last, the anisotropy parameters for [Formula: see text] and [Formula: see text] X-rays have been derived.

Study of x-rays produced from debris-free sources with Ar, Kr and Kr/Ar mixture linear gas jets irradiated by UNR Leopard laser beam with fs and ns pulse duration

Experiments of x-ray emission from Ar, Kr, and Ar/Kr gas jet mixture were performed at the UNR Leopard Laser Facility operated with 350 fs pulses at laser intensity of 2 × 1019 W/cm2 and 0.8 ns pulses at an intensity of 1016 W/cm2. Debris free x-ray source with supersonic linear nozzle generated clusters/monomer jet with an average density of ≥1019 cm−3 was compared to cylindrical tube subsonic nozzle, which produced only monomer jet with average density 1.5–2 times higher. The linear (elongated) cluster/gas jet provides the capability to study x-ray yield anisotropy and laser beam self-focusing with plasma channel formation that are interconnecting with efficient x-ray generation. Diagnostics include x-ray diodes, pinhole cameras and spectrometers. It was observed that the emission in the 1–9 keV spectral region was strongly anisotropic depending on the directions of laser beam polarization for sub-ps laser pulse and supersonic linear jet. The energy yield in the 1–3 keV region produced by a linear nozzle was an order of magnitude higher than from a tube nozzle. Non-LTE models and 3D molecular dynamic simulations of Ar and Kr clusters irradiated by sub-ps laser pulses have been implemented to analyze obtained data. A potential evidence of electron beam generation in jets' plasma was discussed. Note that the described debris-free gas-puff x-ray source can generate x-ray pulses in a high repetition regime. This is a great advantage compared to solid laser targets.

Strong interaction studies with kaonic atoms

The strong interaction of antikaons with nucleons and nuclei in the low-energy regime represents an active research field connected intrinsically with few-body physics. There are important open questions like the question of antikaon nuclear bound states. A unique and rather direct experimental access to the antikaon-nucleon scattering lengths is provided by precision X-ray spectroscopy of transitions in low-lying states of light kaonic atoms like kaonic hydrogen isotopes. In the SIDDHARTA experiment at the electron-positron collider DAFNE of LNF-INFN we measured the most precise values of the strong interaction observables, i.e. the strong interaction on the 1s ground state of the electromagnetically bound kaonic hydrogen atom leading to a hadronic shift and a hadronic broadening of the 1s state. The SIDDHARTA result triggered new theoretical work which achieved major progress in the understanding of the low-energy strong interaction with strangeness. Antikaon-nucleon scattering lengths have been calculated constrained by the SIDDHARTA data on kaonic hydrogen. For the extraction of the isospin-dependent scattering lengths a measurement of the hadronic shift and width of kaonic deuterium is necessary. Therefore, new X-ray studies with the focus on kaonic deuterium are in preparation (SIDDHARTA2). Many improvements in the experimental setup will allow to measure kaonic deuterium which is challenging due to the anticipated low X-ray yield. Especially important are the data on the X-ray yields of kaonic deuterium extracted from a exploratory experiment within SIDDHARTA.

Experimental investigation on the electrical explosion of single aluminum wire in vacuum

The electrical explosion of single wire occurs in many application fields, such as wire-array Z-pinch, synthesis of the nanopowder, high-intensity magnetic field source, etc. The initial stage of the electrical explosion of single wire has a critical influence on the stagnation and X-ray yield in the wire-array Z-pinch. The impressive result of X-ray yield from wire-array Z-pinch is a major motivation to promote the research in this field. Although numerous studies have been carried out to gain a deep insight into the physics of the electrical explosion of single wire, more experimental investigations are necessary to optimize the energy deposition and expansion rate. It is important to investigate the characteristics of the electrical explosion of single wire under the negative polarity pulsed-current, which is adopted in many Z-pinch facilities. In this paper, the electrical explosion of aluminum wire under negative polarity pulsed-current in vacuum is investigated. In the present experiments, the light emission is measured by the photomultiplier and streak camera. A laser probe EKSPLA-PL2251C (30 ps, 532 nm) is adopted to perform the shadowgraphy, schlieren and interferometry diagnostics. The radial knife-edge schlieren scheme is employed to translate the regions with plasma refractivity and gas-type refractivity. The interferometry is constructed based on Mach-Zehnder interferometer. The shadowgram, schlieren image and interferogram are recorded by Canon cameras. The typical waveforms of the voltage, current and light emission from the electrical explosion of 15 m-diameter, 2 cm-long aluminum wire are derived. The energy deposition at the instant of voltage collapse is about 2.4 eV/atom (vaporization energy is about 4 eV/atom). In order to increase the energy deposited into the wire, the 15 m-diameter, 2 cm-long aluminum wire with 2 m polyimide coating is exploded with the same electrical parameters. The energy deposition in the coated wire is about 5 eV/atom. From the shadowgram of the electrical explosion of uncoated aluminum wire, the expansion velocity of the high-density region can be estimated to be about 2.2 km/s. However, the expansion velocity of the high-density region of the polyimide-coated aluminum wire is about 5 km/s. The schlieren images show that the wire is exploded into a binary structure, i.e., a high-density core surrounded by the low-density corona. It should be noted that the energy deposition in the coated wire is larger than the vaporization energy, indicating that the aluminum wire is totally in gaseous state. Thus, the plasma region in the schlieren image of electrical explosion of coated wire is not distinct. The core-corona structure is depressed by the insulating coatings to a certain extent. The configuration of the parallel wire is adopted to estimate the expansion velocity of the plasma shell. The expansion velocity of the low-density plasma is about 5.8 km/s. Two-dimensional distribution of the phase shift is derived through the interferogram. The central part of the gas-type material with a radius of 0.1 cm exhibits a large positive phase shift, while the peripheral plasma shows a small negative phase shift. The three-dimensional atomic density distribution is reconstructed in the gas-type distribution area in which the contribution of electrons is negligible. In our experiments, the energy deposition of the electrical explosion of uncoated wire ranges from 2 to 4 eV/atom. This may be caused by the initial conditions of the wire surface and the connection between the wire and electrode. Further research should be carried out for a better understanding of this phenomenon.

Measurement of the Dose Rate Using Dosimeters in Interventional Radiology and Its Difficulty

In equipment used for interventional radiology (IVR), automatic exposure control (AEC) is incorporated to obtain the X-ray output suitable for the treatment of targeted lesions. For the AEC, users select a region as the signal sensing region (measuring field, MF) in the flat panel detector; MFs with various sizes and shapes were pre-defined and prepared in the system. The aim of this study was to examine the change of measured dose rate with the selection of MFs, the type of dosimeters (the ionization chamber dosimeter and the semiconductor dosimeter), and the dosimeter placement relative to the direction of X-ray tube (from cathode to anode). The IVR equipment was Allura Xper FD20/10 (Philips Medical Systems), and six kinds of built-in MFs were used. It was found that dose rate measured by the ionization chamber dosimeter showed a variation of -2 mGy/min with the MFs and the ionization chamber dosimeter placement. The dose rate measured by the semiconductor dosimeter showed more variation than the ionization chamber dosimeter. The change of dose rate with the dosimeter placement would be caused by the MF overlapping the dosimeter which would affect the AEC (the X-ray output). Also, the change of dose rate with the dosimeter placement was considered to be related to the heel effect of the X-ray beam. When performing dose rate measurements, we should notice that the selection of MFs, the type of dosimeters, and the dosimeter placement would affect the measured values.

A rare cause of tube arcing artifact seen in computed tomography image of a positron emission tomography/computed tomography scanner.

Tube arcing artifact is known to be caused by a temporary short circuit in the X-ray tube causing momentary loss of X-ray output. It is seen as near-parallel and an equidistant streak pattern on transaxial computed tomography (CT) images and as a “horizontal” hypodense band on the coronal and sagittal CT images. This artifact can be a random occurrence and was caused in this particular case due to voltage fluctuations in the high-voltage supply transformer supplying the rotor of the anode in the X-ray tube. This problem was initially corrected by reducing the tube voltage to 120 kV from the original 140 kV and, subsequently, replacing the faulty transformer. This kind of artifact, which is a very rare situation, can affect the image quality, and could also be an early sign of equipment failure. To the authors’ knowledge, such an artifact has not been reported till date in a clinical scenario. Hence, we would like to report a rare situation of tube arcing artifact along with a unique remedy.

Development of a Lead-covered Case for a Wireless X-ray Output Analyzer to Perform CT Half-value Layer Measurements

Measurement of the half-value layer (HVL) is a difficult task in computed tomography (CT) , because a nonrotating X-ray tube must be used. The purpose of this study is to develop a lead-covered case, which enables HVL measurements with a rotating CT X-ray tube. The lead-covered case was manufactured from acrylic and lead plates, which are 3 mm thick and have a slit. The slit-detector distance can be selected between 14 mm and 122 mm. HVL measurements were performed using a wireless X-ray output analyzer "Piranha." We used the following exposure conditions: tube voltages of 80, 100, and 120 kV; a tube current of 550 mA; and an exposure time of 1.0 s. The HVLs were measured by using the following two methods: (a) Nonrotating method-a conventional method that uses the nonrotating exposure mode. (b) Rotating method-a new method that uses the lead-covered case and the rotating exposure mode. As a result, when the slit-detector distance was 58 mm, the HVL values obtained by the nonrotating and rotating methods were 4.38 and 4.24 mmAl at 80 kV, 5.51 and 5.37 mmAl at 100 kV, 6.61 and 6.48 mmAl at 120 kV, respectively. A lead-covered case, which enables the measurement of the HVL in a rotating X-ray tube, was developed. The case is useful in measuring the HVLs at facilities that cannot fix the X-ray tube.

Charge-state dependence of inner-shell processes in collisions between highly charged Xe ions and solids at intermediate energies

The x-ray emission during the penetration of 2--6 MeV ${\mathrm{Xe}}^{q+}$ ($q=20,22,26,30$) ions into thick solid targets of iron and nickel has been measured. An obvious charge-state and incident-energy dependence of the target-to-projectile vacancy-production cross-section ratios was found for the iron target but not for the nickel target. The results are supported by the vacancy-sharing model and direct ionization theory and imply the great importance of level matching for the inner-shell process. The charge equilibration time of ${\mathrm{Xe}}^{30+}$ in solid iron was derived to be around 9 fs from the measured x-ray yields.

Measurements and non-local thermodynamic equilibrium modeling of mid-Z plasma emission

The x-ray yields from laser-irradiated thin foils of iron, copper, zinc, and germanium have been measured in the soft and multi-keV x-ray ranges at the OMEGA laser at the Laboratory for Laser Energetics. The incident laser power had a pre-pulse to enhance the x-ray emission of a 1 ns flat-top main pulse. The experimental results have been compared with post-shot simulations performed with the two-dimensional radiation-hydrodynamics code FCI2. A new non-local thermodynamic equilibrium model, NOO-RAD, have been incorporated into FCI2. In this approach, the plasma ionization state is in-line calculated by the atomic physics NOHEL package. In the soft x-ray bands, both simulations using RADIOM [M. Busquet, Phys. Fluids B 5, 4191 (1993)] and NOO-RAD clearly over-predict the powers and energies measured by a broad-band spectrometer. In one case (the iron foil), the discrepancy between the measured and simulated x-ray output is nevertheless significantly reduced when NOO-RAD is used in the simulations. In the multi-keV x-ray bands, the simulations display a strong sensitivity to the coupling between the electron thermal conductivity and the NLTE models, and for some particular combinations of these, provide a close match to the measured emission. The comparison between the measured and simulated H-like to He-like line-intensity ratios deduced from high-resolution spectra indicates higher experimental electron temperatures were achieved, compared to the simulated ones. Measurements of the plasma conditions have been achieved using the Thomson-scattering diagnostic. The electron temperatures are found to range from 3 to 5 keV at the end of the laser pulse and are greater than predicted by the simulations. The measured flow velocities are in reasonable agreement with the calculated ones. This last finding gives us confidence in our numerical predictions for the plasma parameters, which are over that time mainly determined by hydrodynamics, such as the mass densities and the ion temperatures.

The Effect of Body Mass Index on Fluoroscopic Time and Radiation Dose During Sacroiliac Joint Injections

BackgroundSacroiliac joint (SIJ) injections are commonly performed under fluoroscopic guidance. Radiation exposure to patients and providers has not been comprehensively studied, particularly the effect of body mass index (BMI). ObjectiveTo identify whether patients with a larger BMI require longer fluoroscopy time or a larger radiation dose during performance of an SIJ injection. DesignRetrospective study of an academic institution database. SettingAcademic outpatient musculoskeletal clinic. PatientsAll patients who underwent SIJ injections during a 10-year period. Main Outcome MeasurementsMachine-reported fluoroscopic time and machine-reported radiation dose. A Bonferroni correction was implemented with P ≤ .01 as statistically significant. ResultsA total of 453 SIJ injections were performed in 359 patients. No statistically significant differences in fluoroscopy time were found between patients with BMI scores identified as normal, overweight, and obese (P = .054). However, the radiation doses were significantly greater for patients with higher BMI scores (χ2 [2, n = 441] = 62.4, P < .001); the median (interquartile range) doses were 1210 (839), 1671 (1240), and 2090 (2170) mGy-cm2 for normal weight, overweight, and obese patients, respectively. Although longer needles were used more often in obese patients (χ2 [2, n = 452] = 31.5, P < .001), fluoroscopy time was not associated with needle length (P = .162). No relationships were identified between fluoroscopy time and first-time (as opposed to repeat) injection (P = .123), trainee involvement (χ2 [1, n = 698] = 3.9, P = .049), or age (P = .337). ConclusionsPatients with an elevated BMI score who are undergoing SIJ injection receive an increased radiation dose despite equivalent fluoroscopic time. This finding suggests that the increased dose is likely due to x-ray output from the fluoroscope traversing a greater tissue mass, as opposed to the physician requiring more fluoroscopic images for proper needle placement. Fortunately, the increased radiation dose delivered to patients with a larger BMI score likely has negligible effects.

Population of post-nova supersoft X-ray sources

Novae undergo a supersoft X-ray phase of varying duration after the optical outburst. Such transient post-nova supersoft X-ray sources (SSSs) are the majority of the observed SSSs in M31. In this paper, we use the post-nova evolutionary models of Wolf et al. to compute the expected population of post-nova SSSs in M31. We predict that depending on the assumptions about the WD mass distribution in novae, at any instant there are about 250-600 post-nova SSSs in M31 with (unabsorbed) 0.2-1.0 keV luminosity L_x>10^36 erg/s. Their combined unabsorbed luminosity is of the order of ~10^39 erg/s. Their luminosity distribution shows significant steepening around log(L_x)~37.7-38 and becomes zero at L_x~2x10^38 erg/s, the maximum L_x achieved in the post-nova evolutionary tracks. Their effective temperature distribution has a roughly power law shape with differential slope of ~4-6 up to the maximum temperature of T_eff~1.5x10^6 K. We compare our predictions with the results of the XMM-Newton monitoring of the central field of M31 between 2006 and 2009. The predicted number of post-nova SSSs exceed the observed number by a factor of ~2-5, depending on the assumed WD mass distribution in novae. This is good agreement, considering the number and magnitude of uncertainties involved in calculations of the post-nova evolutionary models and their X-ray output. Furthermore, only a moderate circumstellar absorption, with hydrogen column density of the order of ~10^21 cm^-2, will remove the discrepancy.

Comparison of line x-ray emission from solid and porous nano-layer coated targets irradiated by double laser pulses

Enhancement of line x-ray emission from both solid and porous iron targets induced by irradiation of single and double laser pulses is studied numerically. The line emission from laser produced plasma is calculated within the extreme ultra-violet lithography wavelength range of 13.5–13.7 nm. The effects of pre-pulse intensity and delay time between two pulses (pre-pulse and main pulse) are examined. The results show that using double pulses irradiation in the conditions of porous target can reduce the x-ray enhancement. According to the results, the use of both pre-pulse and porous target leads to efficient absorption of the laser energy. Calculations also show that such enhanced laser absorption can ionize atoms of the target material to very high degrees of ionization, leading to decrease of the density of appropriate ions that are responsible for line emission in the selected wavelength region. By increasing the target porosity, x-ray yield was more reduced.

High-power laser interaction with low-density C–Cu foams

We study the propagation of high-power laser beams in micro-structured carbon foams by monitoring the x-ray output from deliberately introduced Cu content. In particular, we characterize this phenomenon measuring absolute time-resolved x-ray yields, time-resolved x-ray imaging, and x-ray spectroscopy. New experimental results for C–Cu foams show a faster heat front velocity than simulation that assumed homogeneous plasma. We suggest the foam micro-structure may explain this trend.

On the features of bursts of neutrons, hard x-rays and alpha-particles in the pulse vacuum discharge with a virtual cathode and self-organization

In this paper, we continue the discussion of the experimental results on the yield of DD neutrons and hard x-rays in the nanosecond vacuum discharge (NVD) with a virtual cathode, which was started in the previous article of this issue, and previously (Kurilenkov Y K et al 2006 J. Phys. A: Math. Gen. 39 4375). We have considered here the regimes of very dense interelectrode aerosol ensembles, in which diffusion of even hard x-rays is found. The yield of DD neutrons in these regimes is conditioned not only by the head-on deuteron-deuteron collisions in the potential well of virtual cathode, but also by the channel of “deuteron-deuterium cluster” reaction, which exceeds overall yield of neutrons per a shot by more than an order of magnitude, bringing it up to ∼ 107/(4π). Very bright bursts of hard x-rays are also represented and discussed here. Presumably, their nature may be associated with the appearance in the NVD of some properties of random laser in the x-ray spectrum. Good preceding agreeing of the experiment on the DD fusion in the NVD with its particle-in-cell (PIC) simulations provides a basis to begin consideration of nuclear burning “proton-boron” in the NVD, which will be accompanied by the release of alpha particles only. With this objective in view, there has been started the PIC-simulation of aneutronic burning of p-B11, and its preliminary results are presented.

Ag K-shell ionization by electron impact: New cross-section measurements between 50 and 100keV and review of previous experimental data

Abstract We report the measurement of Ag K-shell ionization cross-section by electron impact in the range 50–100 keV and review the experimental data found in the literature. The sample consisted in a thin film of Ag evaporated on a thin C backing. The x-ray spectra generated by electron bombardment in the Sao Paulo Microtron were observed with a planar HPGe detector. The ratios between characteristic and bremsstrahlung x-ray yields were transformed to ionization cross sections with the help of theoretical atomic-field bremsstrahlung cross sections. The measured cross sections are compared with existing experimental values and calculations based on the semi-relativistic distorted-wave Born approximation. According to our experiment, the ratio of Ag K β to K α x-ray intensities is 0.2018(24).

Efficient X-ray emission from laser-irradiated low-density lead target: a substitute for gold in hohlraum design

Numerical experiments are carried out to calculate continuum emissivity and opacity of plasmas produced from laser-irradiated Au and Pb targets as hohlraum wall materials. Targets are considered to be solid or porous with different initial densities. Simulation results show a good agreement compared with the measured data. The results show that under identical conditions, X-ray emission is higher for Au plasma; however, by decreasing initial densities, X-ray yield enhancement is greater for Pb plasma. By using a Pb target with initial density of about 1.14 g cm−3 instead of solid Au target, the same X-ray yield even more can be obtained. Calculations also show that in the conditions of solid density targets, Pb plasma offers a little lower opacity in soft X-ray region. Decreasing initial density of Pb causes its opacity to increase and get closer to the opacity of solid Au which in turn reduces energy losses in hohlraum wall.

Hollow Cathode Electron Beam Formation and Effects on X-Ray Emission in Capillary Discharges

Electron beams produced by the hollow cathode effect are studied in a compact gas filled 24-kV, 5-kA capillary discharge. The characteristics and role of electron beams on X-ray production are studied in order to better understand their impact on X-ray production. X-ray plasma emission is analyzed with a spectrometer, while wideband diodes and Faraday cup probe both electron beams and X-rays. Electron beams of >5 keV are observed early on the discharge and two types of electron beams are identified: a first beam of high energy and low current (with a speed of $\sim 5 \times 10^{7}$ m/s and a current density of $\sim 4\times 10^{\mathrm {-2}}$ A/cm $^{2})$ enhanced by larger cathode apertures, and a second beam of low energy and high current enhanced by smaller cathode apertures. The use of a simple configuration of external magnets prevents X-ray fluorescence production, caused by electron beams, from reaching electronic detectors hence confusion when evaluating X-ray yield from the plasma source is avoided. This is particularly important in extreme ultraviolet lithography and soft X-ray production applications. Furthermore, the presence of the external magnets does not modify line emission, which is detected by means of spectrometry. Therefore, the use of external magnets provides a way to discriminate X-ray diode signals produced by source emitted X-rays and X-ray fluorescence from electron beams.