Fluorescence excited in a thunderstorm atmosphere by relativistic runaway electron avalanches

The spectrum and spatiotemporal evolution of the fluorescence of an atmospheric discharge developing in the regime of relativistic runaway electron avalanche (RREA) generation have been calculated without involving the relativistic feedback. The discharges generating narrow bipolar pulses, along with the discharges responsible for terrestrial gamma-ray flashes, are shown to be relatively dark. Nevertheless, the fluorescence excited by a discharge involving RREAs can be recorded with cameras used to record high-altitude optical phenomena. A possible connection between a certain class of optical phenomena observed at the tops of thunderclouds and RREA emission is pointed out.     

Photomultiplier-Based Scintillation Radiation Detectors of Increased Sensitivity and Time Resolution for Measurements under Conditions of High Electromagnetic Interference

Scintillation detectors for detecting X-ray, gamma, and neutron radiation with time resolutions of 3–4 ns and having high noise stability have been developed. The detector housings are shielded from the strong electromagnetic interference produced at the moment of discharge. The detector design features an original voltage divider. With these detectors, the parameters of the high-energy radiation from a megavolt atmospheric nanosecond discharge can be studied at the limit of sensitivity of this class of devices.     

常压窄间隙介质阻挡放电等离子体辐射特性

利用带有透明电极与可测向观察的一个介质阻挡放电(DBD)实验装置对它的常压窄间隙等离子体辐射特性进行了实验研究。结果表明：这一DBD装置的辐射特性会受激励电压、激励频率、DBD结构等多种因素影响。在频率为10～20kHz高压电源激励下,采用窄间隙、薄电介质层结构DBD可以大幅度提高放电空间的电场强度,增加放电功率密度,提高了放电装置性能。     

Characteristics of a stilbene scintillation crystal in a neutron spectrometer

Various organic scintillators are commonly used as the detecting material for neutrons, but these detectors are less sensitive to gamma rays. In particular, stilbene crystals and BC501A (NE213, EJ301) have good pulse-shape discrimination (PSD) between neutron and gamma-ray events, and have been selected as the media for fast-neutron detection among the organic, inorganic and plastic materials in a mixed radiation field. Although some of the scintillation characteristics of stilbene crystals have been studied, the detailed scintillation characteristics of the crystal are not completely understood. In this study, the light yield, decay time and pulse shape discrimination capability of a stilbene crystal were measured because this crystal is an optimized detector in a large flux of neutrons such as those might be found in cyclotron and charged particle accelerator facilities. The pulse-shape discrimination of neutrons and gamma rays with a stilbene crystal was measured using a ²⁵²Cf neutron source at room temperature. A neutron tagger module was used for the neutron and gamma separation using the charge comparison method in real time. The total pulse width for the charge integration and the delay from the peak-to tail start time were optimized for a better neutron and gamma separation. The relative light yield and decay time of the stilbene crystal scintillator were also measured.     

High-energy neutrinos from gamma ray bursts

We treat high-energy neutrino production in gamma ray bursts (GRBs). Detailed calculations of photomeson neutrino production are presented for the collapsar model, where internal nonthermal synchrotron radiation is the primary target photon field, and the supranova model, where external pulsar-wind synchrotron radiation provides important additional target photons. Detection of greater, similar 10 TeV neutrinos from GRBs with Doppler factors > or approximately 200, inferred from gamma-ray observations, would support the supranova model. Detection of < or approximately 10 TeV neutrinos is possible for neutrinos formed from nuclear production. Only the most powerful bursts at fluence levels > or approximately 3 x 10(-4) erg cm(-2) offer a realistic prospect for detection of nu(mu).     

Terrestrial gamma-ray flashes and neutron pulses from direct simulations of gigantic upward atmospheric discharge

Gamma-ray pulses are calculated from 2D numerical simulations of upward atmospheric discharge in a self-consistent electric field using the multigroup approach to the kinetics of relativistic runaway electrons. Thecalculated numbers and spectra of γ-rays are consistent with the data on terrestrial γ-ray flashes observed aboard spacecraft. The calculated runaway electron flux is concentrated mainly within the domain of the blue jet fluorescence. This proves that exactly this domain is a source of the γ-ray flashes. One γ-ray flash generates ∼10¹⁴-10¹⁵ photonuclear neutrons. The text was submitted by the authors in English     

Hydrogen burning of 17O in classical novae

We report on the observation of a previously unknown resonance at E(lab)(R)=194.1+/-0.6 keV in the 17O(p,alpha)14N reaction, with a measured resonance strength omegagamma(palpha)=1.6 +/- 0.2 meV. We studied in the same experiment the 17O(p,gamma)18F reaction by an activation method and the resonance-strength ratio was found to be omegagamma(palpha)/omegagamma(pgamma) = 470 +/- 50. The corresponding excitation energy in the 18F compound nucleus was determined to be 5789.8 +/- 0.3 keV by gamma-ray measurements using the 14N(alpha, gamma)18F reaction. These new resonance properties have important consequences for 17O nucleosynthesis and gamma-ray astronomy of classical novae.     

Investigation of the X-ray radiation produced by a diffusive discharge in the rod-plane geometry under atmospheric pressure

Spatial parameters of the X-ray radiation produced by a high-voltage nanosecond discharge evolving in air under atmospheric pressure in the rod (cathode)-plane electrode system with a 10-cm electrode spacing are studied experimentally. A ∼170-ns voltage pulse with an amplitude of ∼200 kV and 10-ns rise time is applied to the cathode. The photoelectronic method is used to study, under the same conditions, the integrated (over the gap) characteristics of the radiation, in particular, the duration of its generation. It is found that, when the size of the X-ray source is not smaller than that of the discharge region of diffusive luminescence, radiation from the cathode region of the gap is primarily observed (i.e., from the region where the electric field distribution is sharply inhomogeneous). The X-ray generation is usually observed after the bridging of the discharge gap, the X-ray pulse having a rise time of ∼3 ns, a duration of ∼10 ns, and an effective radiation energy of ∼6 keV.     

Development of a semi-autonomous directional and spectroscopic radiation detection mobile platform

This paper presents a method for a small, inexpensive mobile robot equipped with a single high resolution scintillation detector to quickly survey an area and convey information about local sources of gamma radiation to a remote human operator. This is achieved by surrounding the detector with a lead sheath that blocks all gamma-rays except those incident along the detector's axial direction. A 180° horizontal scan is performed by rotating the detector and a directional profile of gamma radiation is constructed. In addition, a 180° visual panorama of the local area is assembled using a camera mounted on the detector. A plot of the detector count rate versus angle is then overlaid on top of the visual panorama and visible peaks clearly indicate the direction of local gamma radiation sources. Measuring the energy spectrum of gamma-rays in each direction produces a 2D count frequency histogram where distinct peaks indicate the energy and direction of local gamma-ray sources allowing the identification of different radio-isotopes. The mobile robot can use the peaks as goal directions and autonomously move towards gamma-ray sources.     

Experiments with Coherent γ Fields: Gamma Echo and Related Phenomena

The role of coherence played in several phenomena in the gamma energy region has not been well recognised until recently. The Mössbauer source nuclei are noncorrelated, but the absorber response has a well-defined phase relation to the instantaneous source radiation within the relaxation time of the nuclear system. By rapidly changing this phase relation with mechanical displacement, new types of coherent transients in gamma regime have been observed. The gamma echo, replicating and amplifying the enchained decay through a thick sample, is perhaps the best known example of these phenomena. In addition, a simple gamma-ray interferometer based on rapid transit through the resonance has been demonstrated. Fast and intense gamma pulses have been obtained with stepwise phase modulation. These and the gamma-NMR double resonance experiments are reviewed in this paper.     

Polarimetry of short-pulse gamma rays produced through inverse Compton scattering of circularly polarized laser beams

We have developed a polarimetry of ultrashort pulse gamma rays based on the fact that gamma rays penetrating in the forward direction through a magnetized iron carry information on the helicity of the original gamma rays. Polarized, short-pulse gamma rays of (1.1+/-0.2)x10(6)/bunch with a time duration of 31 ps and a maximum energy of 55.9 MeV were produced via Compton scattering of a circularly polarized laser beam of 532 nm off an electron beam of 1.28 GeV. The first demonstration of asymmetry measurements of short-pulse gamma rays was conducted using longitudinally magnetized iron of 15 cm length. It is found that the gamma-ray intensity is in good agreement with the simulated value of 1.0x10(6). Varying the degree of laser polarization, the asymmetry for 100% laser polarization was derived to be (1.29+/-0.12)%, which is also consistent with the expected value of 1.3%.     

Spatiotemporal parameters of the X-ray radiation from a diffuse atmospheric-pressure discharge

A multichannel photoelectron technique is used to study the X-ray radiation emitted from a nanosecond diffuse discharge initiated in atmospheric pressure air in a point-plane electrode system with a gap width varying from 6 to 12 cm. The discharge is initiated by a voltage pulse with a moderate rate of rise of 1.1 × 10¹³ V/s and an amplitude of 160–280 kV. The radiation detected is found to be anisotropic bremsstrahlung of electrons accelerated to 30–80 keV in the near-cathode region early at the conduction phase. The observed features of the radiation and electrical behavior of the discharge are explained by strengthening of the near-cathode field owing to a short-term disappearance of the space-charge-related screening when the discharge passes from the bridging phase to the conduction one.     

大气压介质阻挡放电的光谱研究

使用水电极介质阻挡放电装置,分别在大气压空气和氦气中实现了稳定的高气压放电。通过水电极观察两种气体的放电,发现大气压空气中放电为空间随机分布的微放电丝,等离子体是不均匀的,而在氦气中放电没有微放电丝,空间分布比较均匀。比较而言,这种均匀放电产生的等离子体具有更广泛的工业应用前景。对两种气体中放电的电流波形进行了比较,发现空气中放电的电流脉冲在时间上是随机出现的而氦气中放电的电流脉冲在时间上具有周期性,并且空气中放电脉冲宽度约为几十ns而氦气中放电的电流持续时间较长,脉冲宽度大约为1μs。文章还对两种气体中介质阻挡放电发射光谱进行了研究,结果表明大气压氦气中均匀放电的N+₂(B2Σ+_u→X2Σ+_g)谱线391.4nm很强而在大气压空气放电中此光谱线很弱。这些研究结果对高气压条件下均匀放电的实现和大气压辉光放电的工业应用具有重要意义。     

DC corona ozone generation enhanced by TiO<Subscript>2</Subscript> photocatalyst

Non-thermal electrical discharges, such as corona discharge are apart of the source of ozone, charged, and excited species and acoustic noise also the source of electromagnetic radiation of different wavelengths. The important component of this radiation from the standpoint of photocatalyst activation is the ultraviolet radiation. We studied the role of UV radiation on corona discharge ozone production by placing the titanium dioxide photocatalyst into the discharge region. We used hollow needle to mesh DC corona discharge at atmospheric pressure with TiO₂ globules on the mesh. The discharge was enhanced by the flow of air through the needle. We found that for the needle biased negatively addition of TiO₂ photocatalyst on the mesh electrode drastically increases discharge ozone production as well as the ozone production yield. These quantities are also influenced by the mass of the used photocatalyst and its distribution in the discharge chamber.     

Studies of cosmic gamma-ray bursts and soft gamma repeaters in the Russian-American Konus-Wind experiment

The studies of the cosmic gamma-ray bursts and soft gamma repeaters that have been performed in the Russian-American Konus-Wind experiment during the last several years have been summarized. The experiment has been continuously performed using the Konus Russian scientific instrument on the Wind American spacecraft since 1994 under the optimal interplanetary space conditions in the absence of noise caused by the Earth’s radiation belts and the shadowing of detectors. Two high-sensitivity detectors have constantly observed the entire celestial sphere and recorded detailed time and spectral characteristics of bursts in a wide range of energies (20 keV–15 MeV). The Konus-Wind data have been widely used in the present-day multiwave studies of gamma-ray bursts.     

Large-area atmospheric Cherenkov detectors for high-energy gamma-ray astronomy

Summary This paper describes the development of new ground-based gammaray detectors to explore the energy region between 20 and 200 GeV. This region in energy is interesting because it is currently unexplored by any experiment. The proposed detectors use the atmospheric Cherenkov technique, in which Cherenkov radiation produced in the gamma-ray air showers is detected using mirrors and light-sensitive devices. The important feature of the proposed experiments is the use of large mirror collection areas, which should allow for a significant improvement (i.e. reduction) in energy threshold over existing experiments. Large mirror areas are available for relatively low cost at central tower solar power plants, and there are two groups developing gamma-ray experiments using solar heliostat arrays. This paper summarizes the progress in the design of experiments using this novel approach. Paper presented at the Special Session on ground-based gamma-ray astronomy of the XXIV International Cosmic-Ray Conference, Rome, August 28–September 8, 1995.     

Casimir Energy in Astrophysics: Gamma-Ray Bursts from QED Vacuum Transitions

Motivated by analogous applications to sonoluminescence, neutron stars mergers are examined in the context of Schwinger's dynamical Casimir effect. When the dielectric properties of the QED vacuum are altered through the introduction of dense matter, energy shifts in the zero-point fluctuations can appear as photon bursts at gamma-ray frequencies. The amount of radiation depends upon the properties and amount of matter in motion and the suddenness of the transition. It is shown that the dynamical Casimir effect can convert sufficient energy of neutron star mergers into gamma rays. Using information extracted from simulations of matter flow in neutron star mergers by Ruffert and Janka, we estimate that the total Casimir energy released can exceed 10 ⁵³ ergs in gamma-ray frequencies. The Casimir energy approach is capable of explaining the most energetic gamma-ray bursts.     

Time-domain, nuclear-resonant, forward scattering: theclassical approach

This paper deals with the interaction of electromagnetic radiation with matter assuming the matter to have nuclear transitions in resonance with incident electromagnetic radiation. The source of the radiation is taken to be of two types; natural radioactive gamma decay and synchrotron radiation. Numerical examples using ⁵⁷Fe are given for the two types of source radiation. Calculated results are contrasted for the two cases. Electromagnetic radiation produced by recoil-free gamma-ray emission has essentially the natural linewidth. Electromagnetic radiation from a synchrotron, even with the best monochromators available, has a relatively broad-band spectrum, essentially constant for these considerations. Polarization effects are considered. In general, the nuclear-resonant medium changes the polarization of the input radiation on traversing the medium. Calculations are presented to illustrate that synchrotron radiation studies using nuclear-resonant forward scattering have the potential for making high-precision measurements of hyperfine fields and recoilless fractions. An interesting aspect of nuclear-resonant forward scattering, relative to possible gamma-ray laser development, is the so-called “speed-up” effect. This revised version was published online in August 2006 with corrections to the Cover Date.     

Quantum optics with nuclear gamma radiation

Some features of quantum optics related to inversionless amplification are translated to nuclear systems. Nuclei and nuclear transitions differ in several ways from atomic systems: gamma radiation has a much shorter wavelength (of the order of lattice-distances), nuclear transitions are many orders of magnitude weaker than atomic ones (making nuclear pumping extremely hard), no coherent gamma-ray sources are available to produce bichromatic gamma radiation. All this makes it very hard to merely translate quantum optical results to nuclear systems. We show that under very specific conditions destructive quantum interferences can occur in the nuclear absorption probability, while the stimulated emission probability is not affected. Nuclear level mixing plays a crucial role in this. This revised version was published online in August 2006 with corrections to the Cover Date.     

Lightning effects at high altitudes: sprites, elves, and terrestrial gamma ray flashes

A fascinating set of newly discovered complex phenomena indicate that thunderstorms and lightning discharges are strongly coupled to the overlying upper atmospheric regions. Lightning discharges at cloud altitudes (<20 km) affect altitudes >40 km either via the release of intense electromagnetic pulses (EMPs) and/or the production of intense quasi-static electric (QE) fields. The intense transient QE fields of up to 1 kV·m⁻¹, which for positive CG discharges is directed downwards, can avalanche accelerate upward-driven runaway MeV electron beams, producing brief (1 ms) flashes of gamma radiation. A spectacular manifestation of these intense fields is the so-called ‘Sprites’, large luminous discharges in the altitude range of 40 km to 90 km, which are produced by the heating of ambient electrons for a few to tens of milliseconds following intense lightning flashes. The so-called ‘Elves’ are optical flashes which last much shorter (<1 ms) than sprites, and are typically limited to 80–95 km altitudes with much larger (up to 600 km) lateral extent, being produced by the heating, ionization, and optical emissions due to the EMPs radiated by both positive and negative lightning discharges. To cite this article: U.S. Inan, C. R. Physique 3 (2002) 1411–1421.