Bursts Of Radiation Research Articles

Developing an accurate model of spot-scanning treatment delivery time and sequence for a compact superconducting synchrocyclotron proton therapy system

BackgroundA new compact superconducting synchrocyclotron single-room proton solution delivers pulsed proton beams to each spot through several irradiation bursts calculated by an iterative layer delivery algorithm. Such a mechanism results in a new beam parameter, burst switching time (BST) in the total beam delivery time (BDT) which has never been studied before. In this study, we propose an experimental approach to build an accurate BDT and sequence prediction model for this new proton solution.MethodsTest fields and clinical treatment plans were used to investigate each beam delivery parameter that impacted BDT. The machine delivery log files were retrospectively analyzed to quantitatively model energy layer switching time (ELST), spot switching time (SSWT), spot spill time (SSPT), and BST. A total of 102 clinical IMPT treatment fields’ log files were processed to validate the accuracy of the BDT prediction model in comparison with the result from the current commercial system. Interplay effect is also investigated as a clinical application by comparing this new delivery system model with a conventional cyclotron accelerator model.ResultsThe study finds that BST depends on the amount of data to be transmitted between two sequential radiation bursts, including a machine irradiation log file of the previous burst and a command file to instruct the proton system to deliver the next burst. The 102 clinical treatment fields showed that the accuracy of each component of the BDT matches well between machine log files and BDT prediction model. More specifically, the difference of ELST, SSWT, SSPT, and BST were (− 3.1 ± 5.7)%, (5.9 ± 3.9)%, (2.6 ± 8.7)%, and (− 2.3 ± 5.3)%, respectively. The average total BDT was about (2.1 ± 3.0)% difference compared to the treatment log files, which was significantly improved from the current commercial proton system prediction (58 ± 15)%. Compared to the conventional cyclotron system, the burst technique from synchrocyclotron effectively reduced the interplay effect in mobile tumor treatment.ConclusionAn accurate BDT and sequence prediction model was established for this new clinical compact superconducting synchrocyclotron single-room proton solution. Its application could help users of similar facilities better assess the interplay effect and estimate daily patient treatment throughput.

Radiation burst by axion star collision with star in the Andromeda Galaxy

Axion is a promising candidate of dark matter in the universe. A fraction of dark matter axion may form axion star with radius ∼102 km. We show that the axion star emits radiation burst by the collision with K and M types main sequence star in the Andromeda Galaxy. The emission arises in the atmosphere of the star, in which electrons coherently oscillate due to oscillating electric field of the axion star. The electric field is produced under magnetic field B of the star. We estimate the flux density of the radiation ∼1.6×10−3Jy(10−12M⊙/Ma)2(10−5eV/ma)3(B/102G)23×103K/T and the rate of the collision per hour ∼0.06/hour(10−12M⊙/Ma) in the galaxy, where Ma (ma) denotes the mass of axion star (axion) and T does temperature of the electrons. We assume the number 1011 of the stars with B∼102 G and radius ∼3.5×105 km in the galaxy. We also assume that a half of the dark matter is composed of axion star. We show that the emission of the radiation burst only arises in the atmosphere in which the plasma frequency mp≃ma. The duration of the burst lasts for the period which it takes the axion star to pass the region with mp≃ma. It would be longer than 1 second.

Exploring the Circular Polarisation of Low\u2013Frequency Solar Radio Bursts with LOFAR

The Sun is an active star that often produces numerous bursts of electromagnetic radiation at radio wavelengths. Low frequency radio bursts have recently been brought back to light with the advancement of novel radio interferometers. However, their polarisation properties have not yet been explored in detail, especially with the Low Frequency Array (LOFAR), due to difficulties in calibrating the data and accounting for instrumental leakage. Here, using a unique method to correct the polarisation observations, we explore the circular polarisation of different sub-types of solar type III radio bursts and a type I noise storm observed with LOFAR, which occurred during March–April 2019. We analysed six individual radio bursts from two different dates. We present the first Stokes V low frequency images of the Sun with LOFAR in tied-array mode observations. We find that the degree of circular polarisation for each of the selected bursts increases with frequency for fundamental emission, while this trend is either not clear or absent for harmonic emission. The type III bursts studied, that are part of a long–lasting type III storm, can have different senses of circular polarisation, occur at different locations and have different propagation directions. This indicates that the type III bursts forming a classical type III storm do not necessarily have a common origin, but instead they indicate the existence of multiple, possibly unrelated acceleration processes originating from solar minimum active regions.

How do spherical black holes grow monopole hair?

Black holes in certain modified gravity theories that contain a scalar field coupled to curvature invariants are known to possess (monopole) scalar hair while non-black-hole spacetimes (like neutron stars) do not. Therefore, as a neutron star collapses to a black hole, scalar hair must grow until it settles to the stationary black hole solution with (monopole) hair. In this paper, we study this process in detail and show that the growth of scalar hair is tied to the appearance and growth of the event horizon (before an apparent horizon forms), which forces scalar modes that would otherwise (in the future) become divergent to be radiated away. We prove this result rigorously in general first for a large class of modified theories, and then we exemplify the results by studying the temporal evolution of the scalar field in scalar Gauss-Bonnet gravity in two backgrounds: (i) a collapsing Oppenheimer-Snyder background, and (ii) a collapsing neutron star background. In case (i), we find an exact scalar field solution analytically, while in case (ii) we solve for the temporal evolution of the scalar field numerically, with both cases supporting the conclusion presented above. Our results suggest that the emission of a burst of scalar field radiation is a necessary condition for black hole formation in a large class of modified theories of gravity.

Particle-in-cell simulations of THz emission from plasma by oblique collision of two-electron beams

We studied the THz radiation generated by a beam-plasma system using two-dimensional (2D) particle-in-cell (PIC) simulations. The Langmuir waves excited by two counterpropagating electron beams, via two-stream instability, collide with each other at an oblique angle, which forms a high beam-density modulation near the collision region, where both beam electrons become trapped. As a result, spatially localized Langmuir wave packets with large longitudinal-electric field amplitudes are formed, which give rise to bursts of electromagnetic radiation. Our 2D PIC simulations of the two thin, low-density, asymmetric, electron beams colliding obliquely show that a strong THz emission is obtained at the second harmonic of the plasma frequency (f = 1.0 THz), with a narrow spectral width (∼0.80%) in vacuum and significantly higher efficiency than the head-on-collision case. The efficiency of power conversion from electron beams to THz radiation measured in vacuum reaches around ∼0.0289, for a continuous injection of beams into the plasma, making it suitable for applications requiring high-power narrow-band THz radiation sources.

Immune Checkpoint Inhibition in GBM Primed with Radiation by Engineered Extracellular Vesicles.

The lack of safe and effective delivery across the blood-brain barrier and the profound immune suppressive microenvironment are two main hurdles to glioblastoma (GBM) therapies. Extracellular vesicles (EVs) have been used as therapeutic delivery vehicles to GBM but with limited efficacy. We hypothesized that EV delivery to GBM can be enhanced by (i) modifying the EV surface with a brain-tumor-targeting cyclic RGDyK peptide (RGD-EV) and (ii) using bursts of radiation for enhanced accumulation. In addition, EVs were loaded with small interfering RNA (siRNA) against programmed cell death ligand-1 (PD-L1) for immune checkpoint blockade. We show that this EV-based strategy dramatically enhanced the targeting efficiency of RGD-EV to murine GBM, while the loaded siRNA reversed radiation-stimulated PD-L1 expression on tumor cells and recruited tumor-associated myeloid cells, offering a synergistic effect. The combined therapy significantly increased CD8+ cytotoxic T cells activity, halting tumor growth and prolonging animal survival. The selected cell source for EVs isolation and the presented functionalization strategy are suitable for large-scale production. These results provide an EV-based therapeutic strategy for GBM immune checkpoint therapy which can be translated to clinical applications.

Gravitational memory and compact extra dimensions

We develop a general formalism for treating radiative degrees of freedom near ${\mathcal{I}}^{+}$ in theories with an arbitrary Ricci-flat internal space. These radiative modes are encoded in a generalized news tensor which decomposes into gravitational, electromagnetic, and scalar components. We find a preferred gauge which simplifies the asymptotic analysis of the full nonlinear Einstein equations and makes the asymptotic symmetry group transparent. This asymptotic symmetry group extends the Bondi--Metzner--Sachs (BMS) group to include angle-dependent isometries of the internal space. We apply this formalism to study memory effects, which are expected to be observed in future experiments, that arise from bursts of higher-dimensional gravitational radiation. We outline how measurements made by gravitational wave observatories might probe properties of the compact extra dimensions.

Multiframe point-projection radiography imaging based on hybrid X-pinch.

This paper demonstrates the possibility of using a new configuration of the hybrid X-pinch to produce a set of spatially and temporarily separate x-ray bursts that could be used for the radiography of dynamic events. To achieve this, a longer than normal wire is placed between the conical electrodes of the hybrid X-pinch, and a set of small spacers (fishing weights) is placed along the wire. Each subsection of the wire then acts as a unique X-pinch, producing its own radiation burst from a small (∼3 µm) spot. The timing between bursts is 20-50ns, and each is <2ns in duration. For comparison, if a longer wire is simply employed without spacers, hotspots of radiation occur in random positions and the time between any two bursts does not exceed 20ns. Examples of two and three frame point-projection radiography of solid-state and plasma test objects are given.

The Infrared Echo of SN2010jl and Its Implications for Shock Breakout Characteristics

Abstract SN 2010jl is a Type IIn core-collapse supernova whose radiative output is powered by the interaction of the supernova (SN) shock wave with its surrounding dense circumstellar medium (CSM). After day ∼60, its light curve developed a near-infrared (NIR) excess emission from dust. This excess could be a thermal IR echo from preexisting CSM dust, or emission from newly formed dust either in the cooling post-shock region of the CSM, or in the cooling SN ejecta. Recent analysis has shown that dust formation in the CSM can commence only after day ∼380, and has also ruled out newly formed ejecta dust as the source of the NIR emission. The early (&lt;380 days) NIR emission can therefore only be attributed to an IR echo. The H–K color temperature of the echo is about 1250 K. The best-fitting model requires the presence of about 1.6 × 10−4 M ⊙ of amorphous carbon dust at a distance of 2.2 × 1016 cm from the explosion. The CSM-powered luminosity is preceded by an intense burst of hard radiation generated by the breakout of the SN shock through the stellar surface. The peak burst luminosity seen by the CSM dust is significantly reduced by Thomson scattering in the CSM, but still has the potential of evaporating the dust needed to produce the echo. We show that the survival of the echo-producing dust provides important constraints on the intensity, effective temperature, and duration of the burst.

Dose reduction for minimizing radiation in displaced paediatric supracondylar humerus fractures: single vs. automated pulse mode.

Conventional C-arm image intensifiers (CCA) are an essential and indispensable aid in modern orthopaedic surgery. CCAs are defaulted to auto-pulse mode which emit multiple pulses (or bursts) of radiation to obtain optimum image quality. The number of pulses per shot can be configured manually. The purpose of this study is to investigate the efficacy of the single pulse mode of CCA in reducing and fixing paediatric supracondylar humeral fractures (SCHF). A retrospective chart review of 99 paediatric patients who underwent closed reduction and percutaneous pinning of displaced SCHF was performed. Fifty-one consecutive cases operated with auto-pulse mode (group A). Another 48 consecutive cases were operated with the single-pulse mode (group B). Baumann's angle, operative duration and average radiation dose rate were recorded for comparison between both groups. Twenty postpinning images were randomly selected (10 from each group) to study intra- and interobserver reliability. Twelve doctors were recruited and tasked to identify if each X-ray was taken with the auto-pulse or single-pulse mode. This was repeated after 2 weeks. The patients in the auto-pulse mode group had a significantly higher mean radiation dose of 40.4 ± 32.51 cGycm2/min compared to that of 14.8 ± 3.24 cGycm2/min for the single-pulse group (P ≤ 0.001). All patients in both groups had Baumann's angle within normal range of 64-81°. No significant difference was noted in average intraoperative timings between both groups (P = 0.869). In the majority of cases, the doctors were unable to visually differentiate between the modes of CCA used. The single-pulse mode is an excellent alternative to the auto-pulse mode in fixing SCHF. It gives significantly lower radiation without compromising the surgical outcome. Level of evidence: Level III retrospective comparative study.

GPS L1 signals absorption in high-latitude lower ionosphere during severe geomagnetic storm in June 2015

Based on the results of an analysis of FORMOSAT-3/COSMIC radio occultation measurements, the absorption of DM-radio waves (wavelength ∼19 cm) in the lower high-latitude ionosphere of the Earth was detected. The maximum absorption value is ∼3 dB in the range from ∼60 to ∼90 km and, in some cases, it reaches ∼10 dB at altitudes from ∼90 to ∼95 km. A method for determining the vertical profiles of the absorption coefficient by solving the inverse problem of radiosonding in the Earth’s lower ionosphere is proposed. The absorption layers, caused by powerful bursts of X-ray radiation and strong changes in geomagnetic conditions during the storm, were reliably identified in individual sessions. It was found that, at altitudes from ∼90 to ∼100 km, the value of the absorption coefficient of DM-radio waves reached values (5.69 ± 1.35)·10−3 dB/km.

Black hole S-matrix for a scalar field

We describe a unitary scattering process, as observed from spatial infinity, of massless scalar particles on an asymptotically flat Schwarzschild black hole background. In order to do so, we split the problem in two different regimes governing the dynamics of the scattering process. The first describes the evolution of the modes in the region away from the horizon and can be analysed in terms of the effective Regge-Wheeler potential. In the near horizon region, where the Regge-Wheeler potential becomes insignificant, the WKB geometric optics approximation of Hawking’s is replaced by the near-horizon gravitational scattering matrix that captures non-perturbative soft graviton exchanges near the horizon. We perform an appropriate matching for the scattering solutions of these two dynamical problems and compute the resulting Bogoliubov relations, that combines both dynamics. This allows us to formulate an S-matrix for the scattering process that is manifestly unitary. We discuss the analogue of the (quasi)-normal modes in this setup and the emergence of gravitational echoes that follow an original burst of radiation as the excited black hole relaxes to equilibrium.

On the possibilities of amplification and radiation of harmonics in modern X-ray free electron lasers

X-ray free electron lasers (FELs) produce ultra short bursts of coherent radiation at the wavelengths ∼1–100 Å. In the absence of ready seed in this range, the fundamental tone is usually radiated in self-amplified spontaneous emission (SASE) FELs. During the last decade, the quality of modern FELs has improved in all aspects, and this offers possibility to use the harmonic radiation more effectively. With the goal to achieve maximum performance in minimum size and cost of a FEL, we study the harmonic multiplication in resonating undulator cascades as viable alternative to the SASE fundamental radiation. The harmonic power evolution along FELs is analyzed for the SASE and the harmonic self-seed. The analytical results are compared with available data for soft X-rays FLASH2. The possibility of harmonic radiation is studied for FELs with variable deflection parameter k: FLASH2, European FEL, SACLA, SwissFEL and currently built LCLS-II. We demonstrate earlier growth of the harmonic power in a buncher as compared with the SASE regime at the same wavelength. The difference is explained theoretically by the bunching. We find it impossible to use harmonics at the SACLA due to high initial energy spread. Excellent characteristics of the SwissFEL allow amplification of the third FEL harmonic. We propose the harmonic self-seed for it, which would allow 10 m shorter undulator length for saturation at the same power, and up to 30% shorter radiation wavelength with the existing electron beam. The amplification of the third harmonic is possible also at the European FEL; theoretical calculations show for it ∼10 m shorter saturation length, while the saturated power does not change. At the LCLS-II, good bunching at the third harmonic wavelength can be achieved in a dedicated buncher with minimal gap of the undulators. However, further amplification and radiation of the third harmonic in the undulators with small parameter k appear less efficient than its direct amplification in the FEL, where the bunching of the fundamental is disrupted between the undulator cascades.

Self-absorption of synchrotron radiation in a laser-irradiated plasma

Electrons at the surface of a plasma that is irradiated by a laser with intensity in excess of 1023 W cm−2 are accelerated so strongly that they emit bursts of synchrotron radiation. Although the combination of high photon and electron density and electromagnetic field strength at the plasma surface makes particle–particle interactions possible, these interactions are usually neglected in simulations of the high-intensity regime. Here we demonstrate an implementation of two such processes: photon absorption and stimulated emission. We show that, for plasmas that are opaque to the laser light, photon absorption would cause complete depletion of the multi-keV region of the synchrotron photon spectrum, unless compensated by stimulated emission. Our results motivate further study of the density dependence of quantum electrodynamics phenomena in strong electromagnetic fields.

X-ray quasi-periodic eruptions from two previously quiescent galaxies

Quasi-periodic eruptions (QPEs) are very-high-amplitude bursts of X-ray radiation recurring every few hours and originating near the central supermassive black holes of galactic nuclei1,2. It is currently unknown what triggers these events, how long they last and how they are connected to the physical properties of the inner accretion flows. Previously, only two such sources were known, found either serendipitously or in archival data1,2, with emission lines in their optical spectra classifying their nuclei as hosting an actively accreting supermassive black hole3,4. Here we report observations of QPEs in two further galaxies, obtained with a blind and systematic search of half of the X-ray sky. The optical spectra of these galaxies show no signature of black hole activity, indicating that a pre-existing accretion flow that is typical of active galactic nuclei is not required to trigger these events. Indeed, the periods, amplitudes and profiles of the QPEs reported here are inconsistent with current models that invoke radiation-pressure-driven instabilities in the accretion disk5–9. Instead, QPEs might be driven by an orbiting compact object. Furthermore, their observed properties require the mass of the secondary object to be much smaller than that of the main body10, and future X-ray observations may constrain possible changes in their period owing to orbital evolution. This model could make QPEs a viable candidate for the electromagnetic counterparts of so-called extreme-mass-ratio inspirals11–13, with considerable implications for multi-messenger astrophysics and cosmology14,15.

Extending superposed harmonic initial data to higher spin

Numerical simulations of binary black holes are accompanied by an initial spurious burst of gravitational radiation (called `junk radiation') caused by a failure of the initial data to describe a snapshot of an inspiral that started at an infinite time in the past. A previous study showed that the superposed harmonic (SH) initial data gives rise to significantly smaller junk radiation. However, it is difficult to construct SH initial data for black holes with dimensionless spin $\chi\gtrsim0.7$. We here provide a class of spatial coordinate transformations that extend SH to higher spin. The new spatial coordinate system, which we refer to as superposed modified harmonic (SMH), is characterized by a continuous parameter -- Kerr-Schild and harmonic spatial coordinates are only two special cases of this new gauge. We compare SMH with the superposed Kerr-Schild (SKS) initial data by evolving several binary black hole systems with $\chi=0.8$ and $0.9$. We find that the new initial data still leads to less junk radiation and only small changes of black hole parameters (e.g. mass and spin). We also find that the volume-weighted constraint violations for the new initial data converge with resolution during the junk stage $(t\lesssim700M)$, which means there are fewer high-frequency components in waveforms at outer regions.

Toward an Electromagnetic Event Resilient Grid

The threat of a large-scale electromagnetic event having a negative impact on the electric grid is real. Whether human-caused, via the detonation of a nuclear device, or natural, via a high-intensity burst of solar radiation, our historic experience with these phenomena indicates that as a global community, we should be prepared for such events and know how to mitigate their impacts. Current studies and related discussions provide a wide range of damage assessments for these events. We recommend continuing current technical investigations and research as well as strengthening collaboration between stakeholders and experts. This would ensure future threats are addressed in a timely and effective manner.

Gating of charge sensitive preamplifiers for the use at pulsed radiation sources

The development of a switch circuit to gate charge sensitive preamplifiers for use at pulsed radiation sources will be presented. This development was used for the 16O(n,α)13C reaction measurement with a Double Frisch Grid Ionization Chamber (DFGIC) at the neutron time-of-flight facility CERN n_TOF in Geneva, Switzerland. Intense instantaneous radiation which is produced in the spallation target of the n_TOF facility (γ-flash) can saturate charge sensitive preamplifiers and prevent signals from being registered in the detection system. The switch circuit made it possible for the first time to perform a measurement with the DFGIC with γ-flash gated off at n_TOF. Nano-second gating of charge sensitive preamplifiers has a wide range of applicability at pulsed radiation sources, where short bursts of radiation must be gated off to avoid saturation, e.g. with HPGe detectors for γ-ray detection. Nano-second gating requires the stray-capacitance of the wideband reflective switch to be compensated to avoid a strong signal during the switch operation. Spectral analysis of the switch circuit shows that additional noise is insignificant.

An Ultra-High Time Resolution Cosmic-Ray Detection Mode for the Murchison Widefield Array

The radio-wavelength detection of extensive air showers (EASs) initiated by cosmic-ray interactions in the Earth’s atmosphere is a promising technique for investigating the origin of these particles and the physics of their interactions. The Low-frequency Array (LOFAR) and the Owens Valley Long Wavelength Array (OVRO-LWA) have both demonstrated that the dense cores of low-frequency radio telescope arrays yield detailed information on the radiation ground pattern, which can be used to reconstruct key EAS properties and infer the primary cosmic-ray composition. Here, we demonstrate a new observation mode of the Murchison Widefield Array (MWA), tailored to the observation of the sub-microsecond coherent bursts of radiation produced by EAS. We first show how an aggregate 30.72[Formula: see text]MHz bandwidth ([Formula: see text][Formula: see text]kHz frequency channels) recorded at 0.1[Formula: see text]ms resolution with the MWA’s voltage capture system (VCS) can be synthesized back to the full bandwidth Nyquist resolution of 16.3[Formula: see text]ns. This process, which involves “inverting” two sets of polyphase filterbanks, retains 90.5% of the signal-to-noise of a cosmic-ray signal. We then demonstrate the timing and positional accuracy of this mode by resolving the location of a calibrator pulse to within 5[Formula: see text]m. Finally, preliminary observations show that the rate of nanosecond radio-frequency interference (RFI) events is 0.1[Formula: see text]Hz, much lower than that found at the sites of other radio telescopes that study cosmic rays. We conclude that the identification of cosmic rays at the MWA, and hence with the low-frequency component of the Square Kilometre Array, is feasible with minimal loss of efficiency due to RFI.

Thunderstorms spew out gamma rays - these scientists want to know why.

Researchers in Japan are enlisting an army of citizens to explore how storms on Earth create extreme bursts of gamma radiation. Researchers in Japan are enlisting an army of citizens to explore how storms on Earth create extreme bursts of gamma radiation.