Bremsstrahlung X-ray Research Articles

Development of a YAP(Ce) camera for the imaging of secondary electron bremsstrahlung x-ray emitted during carbon-ion irradiation toward the use of clinical conditions

Low-energy x-ray imaging of the secondary electron bremsstrahlung (SEB) x-ray emitted during carbon-ion irradiation is a promising method for range estimation. However, it remains unclear whether the method can be used for imaging with the clinical dose levels of carbon-ion and whether the bremsstrahlung x-ray can be detected from the deeper part of the body. To clarify these points, we developed a new high resolution low-energy x-ray camera and conducted imaging of the SEB x-ray during the irradiation of carbon-ions of different energies and intensities. Imaging was also tried with an x-ray camera using a human-head-sized, 17 cm diameter cylindrical phantom. To develop a high resolution imaging detector for a low-energy x-ray, we used a 20 × 20 × 0.5 mm thick cerium-doped yttrium aluminum perovskite, YA1O3 (YAP(Ce)) scintillator plate, which was optically coupled to a 25 mm square high quantum efficiency (HQE) type position sensitive photomultiplier tube (PSPMT). The imaging detector was encased in a 2 cm thick tungsten container and a pinhole collimator was attached to its camera head. After evaluating the camera’s performance, SEB x-ray imaging was tried during irradiation of the carbon-ion and compared the results with a Monte Carlo simulation. We imaged the beam tracks by the SEB x-ray in real-time during irradiation of the carbon-ion and imaging and range estimation were possible even with near clinical dose level of 7.5 × 108 particles of carbon-ion. Clear images of a SEB x-ray were also obtained for a 17 cm diameter cylindrical phantom. The measured images were good agreement with the Monte Carlo simulation. We confirmed that our developed YAP(Ce) camera is promising for imaging SEB x-rays during irradiation of carbon-ions even near clinical conditions.

Absolute cross sections of ultra-soft x-ray radiation in electron scattering upon atoms and the soft-photons approximation

We calculated the cross sections of ultra-soft x-ray bremsstrahlung in electron scattering upon Ar, Kr and Xe. The results are consistent with the absolute values of the differential cross sections measured by Gnatchenko et al. (2009) [17] for scattering electrons with an energy of 600 eV on these atoms.

Measurements of electron beam ring structures from laser wakefield accelerators

Laser-plasma interaction experiments using a 70 TW short-pulse laser were conducted to investigate the properties of electron beams produced from laser wakefield acceleration. In addition to narrow divergence electron beams in excess of 200 MeV, lower energy components of the electron beam were observed to have an annular emission pattern with much larger divergence. This ring-shaped component of the beam is up to several MeV in energy and gives rise to a corresponding increase in the divergence of bremsstrahlung x-rays while producing more background radiation. Scaling measurements of the emission angle of the beam with respect to plasma density were also made. From 3D numerical simulations of the interaction, it is shown that this phenomenon results from energetic electrons in the laser-driven wakefield which are not trapped by the plasma wave, but which can still obtain some longitudinal momentum from the interaction.

Measurement of Total Energy of Pulsed Electron Beam From a Plasma Focus Device Using Dosimetry of Bremsstrahlung X-Ray

In this paper, the total energy of pulsed electron beam from a plasma focus device was studied by measurement of the Bremsstrahlung X-ray dose. The Bremsstrahlung X-ray dose caused by collision of electrons to a copper foil was measured by GR-200A TLD dosimeters. Using the Monte Carlo code, the relationship between the absorbed dose and energy of the colliding electron was determined in the experimental conditions. This relationship is approximately linear and is independent of the electron energy within the energy range of 0–300 keV. The measurements were performed at different charging voltages and different pressures of argon and air as working gases. The mean value of the X-ray dose was higher at experiments with air gas. The maximum X-ray dose of 3.3 mGy, which corresponds to total energy of 48 mJ for electron beam, was measured at 23 kV and 0.9 mbar of air. The total energy of the electron beam at different shots of the same experimental conditions showed large fluctuations around the mean value. This makes it hopelessly difficult to predict the energy of the electron beam in one shot of the plasma focus device. On the other hand, a direct relationship between the energy of the electron pulse and depth of spike on the current signal was observed. The predictability of the energy was significantly improved by increasing the number of shots. The relative standard deviation of the measured energies from the mean value was decreased from 74% for a single shot to 8% for 15 shots, and the mean value of X-ray dose in one shot was significantly increased over the large number of shots.

Enhanced bremsstrahlung X-ray emission from Ag nanoparticles irradiated by ultrashort laser pulses

In this work, an Ag nanoparticle colloidal suspension flowing in the form of a thin jet (250 μm) is irradiated by 150 femtosecond, 800 nm laser pulses to form a plasma which emits bremsstrahlung X-rays of up to 100 keV energy. The flowing jet ensures long-term durability of the plasma source during continuous laser irradiation. The laser pulse is p-polarized and the angle of incidence is normal to the jet surface, to optimize resonance absorption of laser radiation by the plasma electron density gradient. A 30-fold enhancement is observed in the X-ray yield in the nanoparticle suspension, compared to the precursor salt solution. This is because of the local field enhancement (LFE) associated with the localized surface plasmon resonance (LSPR) in Ag nanoparticles. Multiphoton ionization will be greatly enhanced in the presence of LFE, resulting in the generation of a relatively larger number of free electrons, which become “hot” electrons of high kinetic energy by resonance absorption. Bremsstrahlung in the X-ray regime occurs due to the deceleration of these hot electrons. Under identical excitation conditions the corresponding X-ray enhancement measured in Au nanoparticles is relatively lower at 18-fold. This decrease is due to the higher ionization potential of Au (9.22 eV) as compared to Ag (7.58 eV). On the other hand, absorption spectra and SEM images measured after continuous irradiation reveal that Au nanoparticles are more photostable compared to Ag nanoparticles. These studies show that Ag nanoparticles are better suited for X-ray generation compared to Au nanoparticles under the experimental conditions employed. Applications include dynamics studies, microscopy, and lithography.

Possibility analysis of bremsstrahlung x-ray imaging of C-14 radionuclide using a LaGPS radiation imaging system

The in-vivo imaging of C-14 is thought to be impossible because it is a pure beta-emitting radionuclide and the energy of beta particles is low. However, beta particles emit bremsstrahlung x-rays in subjects that may be imaged from the outside subjects. Thus, we imaged bremsstrahlung x-rays from a C-14 solution using a high resolution Ce-doped (Gd, La)2Si2O7 (LaGPS) radiation imaging system. With a LaGPS radiation imaging system, we conducted bremsstrahlung x-ray imaging from a C-14 solution in a plastic container with 37 MBq radioactivity with and without a parallel hole collimator. Without it, images were obtained with a spatial resolution of ∼1 mm FWHM in less than 1 min of acquisition time. The energy spectrum of the bremsstrahlung x-rays from a C-14 solution showed a broad distribution with an average energy of ∼30 keV. With a parallel hole collimator, images of the C-14 solutions were also possible although the detected counts decreased to 2.4% of those without a collimator. The measured sensitivities of the LaGPS imaging system without and with a collimator for bremsstrahlung x-rays from C-14 solutions in a plastic container were 3.5 × 10−5 and 8.5 × 10−7, respectively. We conclude that the imaging of bremsstrahlung x-rays from C-14 might be a new method for the in-vivo distribution imaging of small animals or plants.

Simulations of hard X-ray generation by hot electrons in a silver target

A semi-analytical model is developed for the generation of X-ray bremsstrahlung in metallic targets with the inclusion of hot electron recirculation (refluxing). The hard bremsstrahlung and characteristic X-ray yields are calculated in relation to the thickness of a silver target for an s-polarised subpicosecond laser pulse intensity of 2 × 1019 W cm–2. The effect of hot electron recirculation in thin foils is shown to significantly improve the Kα radiation and bremsstrahlung yields in a photon energy of 10 – 100 keV. By contrast, the 0.1 – 1 MeV bremsstrahlung photon yield from thin foils with hot electron recirculation corresponds approximately to the highest photon yield from those targets in which recirculation is insignificant. We make a comparative analysis of the highest laser-to-X-ray energy conversion efficiencies obtained to date.

X-ray analysis methods for sources from self-modulated laser wakefield acceleration driven by picosecond lasers.

A versatile set of methods for analyzing x-ray energy spectra and photon flux has been developed for laser plasma accelerator experiments driven by picosecond lasers. Forward fit provides extrapolated broad energy spectrum measurements, while Ross pair and differential average transmission analysis provide directly measured data points using a particular diagnostic. Combining these methods allows the measurement of x-ray energy spectra with improved confidence. We apply the methods to three diagnostics (filter wheel, stacked image plate spectrometer, and step wedge), each sensitive to a different region of x-ray energies (<40 keV, 35-100 keV, and 60-1000 keV, respectively), to characterize the analysis methods using laser-driven bremsstrahlung x-rays. We then apply the methods to measure three x-ray mechanisms, betatron, inverse Compton scattering, and bremsstrahlung, driven by a laser plasma accelerator. The analysis results in the measurement of x-ray energy spectra ranging from 10 keV to 1 MeV with peak flux greater than 1010 photons/keV/Sr. The combined analysis methods provide a robust tool to accurately measure broadband x-ray sources (keV to MeV) driven by laser plasma acceleration with picosecond, kilojoule-class lasers.

Relativistic laser driven electron accelerator using micro-channel plasma targets

We present an experimental demonstration of the efficient acceleration of electrons beyond 60 MeV using micro-channel plasma targets. We employed a high-contrast, 2.5 J, 32 fs short pulse laser interacting with a 5 μm inner diameter, 300 μm long micro-channel plasma target. The micro-channel was aligned to be collinear with the incident laser pulse, confining the majority of the laser energy within the channel. The measured electron spectrum showed a large increase in the cut-off energy and slope temperature when compared to that from a 2 μm flat Copper target, with the cutoff energy more than doubled and the total energy in electrons &amp;gt;5 MeV enhanced by over 10 times. Three-dimensional particle-in-cell simulations confirm efficient direct laser acceleration enabled by the novel structure as the dominant acceleration mechanism for the high energy electrons. The simulations further reveal the guiding effect of the channel that successfully explains preferential acceleration on the laser/channel axis observed in experiments. Finally, systematic simulations provide scalings for the energy and charge of the electron pulses. Our results show that the micro-channel plasma target is a promising electron source for applications such as ion acceleration, Bremsstrahlung X-ray radiation, and THZ generation.

Study on eccentricity effects of the rod-pinch diode radiography source.

The rod pinch diode (RPD) is a cylindrical pinched beam diode that generates intense pulsed bremsstrahlung X-ray radiation with a small diameter. In practice, the anode and cathode structures of the RPD may be eccentric due to the mechanical deformation and mounting errors. In theory, this eccentricity changes the physical characteristics of the RPD, which in turn affects the X-ray production. To study the performance variation induced by eccentric electrodes, the electrode concentricity evaluation system is used to quantify the concentricity of the anode and cathode. Then a series of experiments are carried out with different concentricity deviations, and the electrical performance, the radiation dose, and the X-ray pulse signal among different shots are analyzed. These results have shown that, within a certain eccentricity range, the overall performances of the RPD, including the diode impedance and the X-ray production, change very little. Going beyond this range, the average impedance decay rate increases significantly, resulting in accelerated impedance collapse and shortened voltage pulse width. Consequently, X-ray dose distribution and the X-ray pulse width are both reduced. These results are helpful in understanding the RPD characteristics from a different perspective as well as providing a method to determine the designing and mounting criteria of the electrodes of rod-pinch diode.

Secondary Fluorescence Correction for Characteristic and Bremsstrahlung X-Rays Using Monte Carlo X-ray Depth Distributions Applied to Bulk and Multilayer Materials

Secondary fluorescence effects are important sources of characteristic X-ray emissions, especially for materials with complicated geometries. Currently, three approaches are used to calculate fluorescence X-ray intensities. One is using Monte Carlo simulations, which are accurate but have drawbacks such as long computation times. The second one is to use analytical models, which are computationally efficient, but limited to specific geometries. The last approach is a hybrid model, which combines Monte Carlo simulations and analytical calculations. In this article, a program is developed by combining Monte Carlo simulations for X-ray depth distributions and an analytical model to calculate the secondary fluorescence. The X-ray depth distribution curves of both the characteristic and bremsstrahlung X-rays obtained from Monte Carlo program MC X-ray allow us to quickly calculate the total fluorescence X-ray intensities. The fluorescence correction program can be applied to both bulk and multilayer materials. Examples for both cases are shown. Simulated results of our program are compared with both experimental data from the literature and simulation data from PENEPMA and DTSA-II. The practical application of the hybrid model is presented by comparing with the complete Monte Carlo program.

Bremsstrahlung emission profile from intense laser-solid interactions as a function of laser focal spot size

The bremsstrahlung x-ray emission profile from high intensity laser-solid interactions provides valuable insight to the internal fast electron transport. Using penumbral imaging, we characterise the spatial profile of this bremsstrahlung source as a function of laser intensity by incrementally increasing the laser focal spot size on target. The experimental data shows a dual-source structure; one from the central channel of electrons, the second a larger substrate source from the recirculating electron current. The results demonstrate than an order of magnitude improvement in the intensity contrast between the two x-ray sources is achieved with a large focal spot, indicating preferable conditions for applications in radiography. An analytical model is derived to describe the transport of suprathermal electron populations that contribute to substrate and central channel sources through a target. The model is in good agreement with the experimental results presented here and furthermore is applied to predict laser intensities for achieving optimum spatial contrast for a variety of target materials and thicknesses.

The Electromagnetic Compatibility of the VISAR Laser Interferometer with the Angara-5-1 Facility

Experiments on the creation of megabar pressures and acceleration of metal flyers by the pressure of a pulsed magnetic field are being carried out at the Angara-5-1 facility. Velocities of up to 10 km/s were achieved. The velocities of flyers were recorded using the VISAR laser interferometer (velocity interferometer system for any reflector). The issues of the electromagnetic compatibility of the VISAR with the Angara-5-1 facility are considered, since the operation of this facility causes electromagnetic interference and when the magnetic self-isolation is established in the vacuum transmission lines, X-ray bremsstrahlung is generated and influences the optics, fiber-optic cables, and photomultipliers. The suppression of these two sources of interference made it possible to reliably register the VISAR signals and determine the velocity of a flyer.

Pre and post operative radiation protection in Ru-106 brachytherapy ophthalmic plaque surgery and related material shielding properties

Pre and post-operative exposure levels of medical staff and people from public in intra-operative Ru-106 ophthalmic brachytherapy are reported, together with attenuation properties of selected shielding materials. In particular radiation exposure of workers during plaque transportation and during medical assistance of implanted plaque patient was measured. Taking into account dose rates and considering standard assistance procedure of hospitalized patients, the exposure of medical staff and people of the public were evaluated for a given workload.In order to provide tools to optimize radiation protection, considering social and economic aspects due to possible hospital discharge or hospital stay, the attenuation properties of common shielding materials (lead, concrete, red brick, PMMA and gypsum) were measured, considering both narrow and broad beam setups. The eye was simulated using a water equivalent phantom and plaque was fixed on it. All measurements were performed with calibrated survey meters. Results were compared with numerical simulation of bremsstrahlung X-ray radiation spectra emitted from patient eye.Exposure levels measured at 1 m distance in front of the implanted eye are 0.05 µSv/h/MBq, at 10 cm from patient head, 0.44 µSv/h/MBq (plaque side), 0.4 µSv/h/MBq (front), 0.25 µSv/h/MBq (lateral, opposed to plaque), 0.2 µSv/h/MBq (back).Average exposure levels, under conservative assumptions, for medical staff is 17 µSv/patient and less than 23 µSv/patient for careers and comforters. TVLs in lead and concrete are about 1.6 cm and 11.5 cm respectively.

42 Deposited dose measurement using bremsstrahlung X-rays

Introduction With the development of particle therapy, patient dose verification tools are needed to ensure the accuracy of treatment. Non-invasive methods to measure the deposited energy exist. These are based on the PET-imaging technique, taking advantage of the radionuclides created during the interaction of hadrons with the medium [1] . An alternative method is studied and presented in this work. The detection of bremsstrahlung X-rays (XR) emitted directly by medium [2] is a promising way to obtain all or part of the deposited energy in the medium. This study describes a method to determine the deposited dose by a charged particle beam, for different incident energies. The results obtained for protons and alpha particles of 70 MeV will be presented. Methods The experimental set-up allows the irradiations of a PMMA target by alpha particles or protons delivered by the cyclotron ARRONAX (energy [3] has been developed to model the emitted XR spectrum. Results The first experiment, with alpha particles of 68 MeV, shows a good agreement between theoretical and simulated XR spectrums. The number of bremsstrahlung XR detected for one gray received by the medium is 1060+/−140. Uncertainty includes detection efficiency, the beam charge and the statistical counting fluctuations, and uncertainties about measurement of the number of the incident particles. The simulated spectrum indicates a number of 970 XR/Gy. Thus the number of XR per gray demonstrates a good sensibility. These encouraging results led us to perform experiments using proton beams with different energies. The analyses are in progress and the results will also be presented. Conclusions This work presents an alternative, on-line, non-invasive method based on the measurement of bremsstrahlung XR emitted during the interaction of a particle beam with matter. Proof of concept was obtained for 68 MeV alpha particles. Proton beams with energies from 17 to 70 MeV are under study. The objective is to evaluate the sensitivity of the method, in order to use the bremsstrahlung to monitor the beam and/or the deposited dose at energies close to those used in protontherapy and hadrontherapy.

Piezoelectric Accelerator

Here we propose the conception of small-size piezoelectric accelerator of charged particles that operates due to the piezoelectric effect at varying mechanical force applied to piezoelectrics in vacuum. The accelerating voltage and the energy of accelerated particles are estimated. In the proof-of-principle experiment we demonstrate the effect of the emission of X-ray radiation at the mechanical compression of piezoelectric ceramics in vacuum. The compression leads to the appearance of charges and potentials on the surfaces of the piezoelectrics and also to the arising of the electric field in vacuum. Electrons are accelerated in the electric field, strike the matter and produce the X-ray radiation. In the experiment, we have observed emission of the characteristic and bremsstrahlung X-ray radiation of energy up to 60 keV due to the compression of piezoelectric ceramics in vacuum. This means that electrons are accelerated in the piezoelectric accelerator up to the energy at least of 60 keV. The agreement of calculated and experimental data confirms the conception. Advantages of the piezoelectric accelerator and possibilities of its development and applications are discussed.

Observation of multipath effects in the detection of RF-modulated x-rays

As part of the Air Force Research Laboratory’s ongoing research in particle accelerators and beams, we recently began investigating the interaction of RF-modulated x-ray beams with RF structures. These bremsstrahlung x-rays, produced using an S-band RF electron linac and tungsten foil, were able to drive RF signals at the linac frequency and its integer harmonics in an S-band waveguide. This was interpreted as a result of secondary electron production inside the waveguide by the modulated x-ray beam and implied that the primary electron beam RF modulation was preserved, to at least some degree, through both the processes of x-ray and secondary electron production. The strength of these signals induced on the waveguide varied as the distance of the waveguide from the tungsten foil changed, with the nature of these changes suggesting the existence of an interference process resulting from multipath propagation of the modulated x-rays. Here, we report on our initial attempt to verify this multipath propagation by altering the configuration of shielding and reflective masses in the environment of the waveguide. These measurements support the existence of a multipath propagation effect and further indicate that the RF modulation of the x-rays is preserved as they undergo scattering events inside the accelerator vault.

Electron Acceleration and Jet-facilitated Escape in an M-class Solar Flare on 2002 August 19

Abstract Sudden jets of collimated plasma arise from many locations on the Sun, including active regions. The magnetic field along which a jet emerges is often open to interplanetary space, offering a clear “escape route” for any flare-accelerated electrons, making jets lucrative targets for studying particle acceleration and the solar sources of transient heliospheric events. Bremsstrahlung hard X-rays (HXRs) could, in principle, trace the accelerated electrons that escape along the paths of the jets, but measurements of the escaping electron beams are customarily difficult due to the low densities of the corona. In this work, we augment HXR observations with gyrosynchrotron emission observed in microwaves, as well as extreme ultraviolet (EUV) emission and modeling to investigate flare-accelerated electrons in a coronal jet. HXR and microwave data from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) and the Owens Valley Solar Array (OVSA), respectively, give complementary insight into electron spectra and locations, including the presence of accelerated electrons in the jet itself. High-time-resolution HXR data from the Konus-Wind instrument suggest electron acceleration timescales on the order of 1 s or shorter. We model the energetic electron distributions in the GX Simulator framework using the Solar and Heliospheric Observatory (SOHO)/Michelson Doppler Imager (MDI), the Transition Region and Coronal Explorer (TRACE), RHESSI, and OVSA data as constraints. The result is a modeled distribution, informed and constrained by measurements, of accelerated electrons as they escape the Sun. Combining the detection of microwave gyrosynchrotron emission from an open, rather than closed, magnetic configuration, with realistic 3D modeling constrained by magnetograms, EUV, and X-ray emission, we obtain the most stringent constraints to date on the accelerated electrons within a solar jet.

Bremsstrahlung x-ray generation for high optical depth radiography applications on the National Ignition Facility.

We have tested a set of x-ray sources for use as probes of highly attenuating, laser-driven experiments on the National Ignition Facility (NIF). Unlike traditional x-ray sources that optimize for a characteristic atomic transition (often the n = 2 → n = 1 transition in ionized, He-like atoms), the design presented here maximizes the total photon flux by optimizing for intense, broadband Bremsstrahlung radiation. Three experiments were performed with identical targets, including a uranium x-ray source foil and a tungsten substrate with a narrow (25 μm wide) collimating slit to produce a quasi-1D x-ray source. Two experiments were performed using 12 beams from the NIF laser, each delivering approximately 46 kJ of laser energy but with different laser spatial profiles. This pair yielded similar temporal x-ray emission profiles, spatial resolution, and inferred hot electron temperature. A third experiment with only 6 beams delivering approximately 25 kJ produced a lower hot electron temperature and significantly lower x-ray flux, as well as poorer spatial resolution. The data suggest that laser pointing jitter may have affected the location and intensity of the emitting plasma, producing an emission volume that was not well centered behind the collimating slit and lower intensity than designed. However, the 12-beam design permits x-ray radiography through highly attenuating samples, where lower energy line-emission x-ray sources would be nearly completely attenuated.

Using bremsstrahlung X-Ray for positioning of the filler wire during electron beam surfacing

This work aims to assess the bremsstrahlung X-Ray signal from the processing zone obtained by the use of a solid wire during electron beam surfacing. Applications of the bremsstrahlung X-Ray signal in the control systems allow positioning of the filler wire. During the experiments, a scintillation detector based on monocrystalline iodine cesium and silicone photomultiplier was used for registration of the X-Ray signal. Circle oscillations of the electron beam create the informative component. Synchronous storage method was applied for mathematical treatment of the recorded signal.