During a winter thunderstorm on 24 November 2017, a strong burst of gamma rays with energies up to ∼10 MeV was detected coincident with a lightning discharge, by scintillation detectors installed at ...the Kashiwazaki-Kariwa Nuclear Power Station at sea level in Japan. The burst had a subsecond duration, which is suggestive of photoneutron production. The leading part of the burst was resolved into four intense gamma-ray bunches, each coincident with a low-frequency radio pulse. These bunches were separated by 0.7-1.5 ms, with a duration of ≪1 ms each. Thus, the present burst may be considered as a "downward" terrestrial gamma-ray flash (TGF), which is analogous to upgoing TGFs observed from space. Although the scintillation detectors were heavily saturated by these bunches, the total dose associated with them was successfully measured by ionization chambers, employed by nine monitoring posts surrounding the power plant. From this information and Monte Carlo simulations, the present downward TGF is suggested to have taken place at an altitude of 2500±500 m, involving 8_{-4}^{+8}×10^{18} avalanche electrons with energies above 1 MeV. This number is comparable to those in upgoing TGFs.
During a winter thunderstorm on 24 November 2017, a downward terrestrial gamma-ray flash took place and triggered photonuclear reactions with atmospheric nitrogen and oxygen nuclei, coincident with a ...lightning discharge at the Kashiwazaki-Kariwa nuclear power station in Japan. We directly detected neutrons produced by the photonuclear reactions with gadolinium orthosilicate scintillation crystals installed at sea level. Two gadolinium isotopes included in the scintillation crystals, 155Gd and 157Gd, have large cross sections of neutron captures to thermal neutrons such as 155Gd (n,γ) 156Gd and 157Gd (n,γ) 158Gd. Deexcitation gamma rays from 156Gd and 158Gd are self-absorbed in the scintillation crystals, and make spectral-line features which can be distinguished from other non-neutron signals. The neutron burst lasted for ∼ 100 ms, and neutron fluences are estimated to be > 52 and > 31 neutrons cm−2 at two observation points inside the power station. Gadolinium orthosilicate scintillators work as valid detectors for thermal neutrons in lightning.
An on‐ground observation program for high‐energy atmospheric phenomena in winter thunderstorms along the Japan Sea has been performed via measurements of gamma ray radiation, atmospheric electric ...field, and low‐frequency radio band. On 11 February 2017, the radiation detectors recorded gamma ray emission lasting for 75 s, and then abruptly terminated with a nearby lightning discharge. The gamma ray spectrum extended up to 20 MeV and was reproduced by a cutoff power law model with a photon index of
1.36−0.04+0.03, being consistent with Bremsstrahlung radiation from a thundercloud (known as a gamma‐ray glow or a thunderstorm ground enhancement). The low‐frequency radio monitors, installed ∼50 km away from the gamma ray observation site recorded leader development of an intracloud/intercloud discharge spreading over ∼60 km area with a ∼300‐ms duration. The timing of the gamma ray termination coincided with the moment when the leader development of the intracloud/intercloud discharge passed 0.7 km horizontally away from the radiation monitors. The intracloud/intercloud discharge started ∼15 km away from the gamma ray observation site. Therefore, the glow was terminated by the leader development, while it did not trigger the lightning discharge in the present case.
Plain Language Summary
This study presents high‐energy radiation, atmospheric electric field and low‐frequency radio measurements of winter thunderstorms in Japan. Long‐duration gamma ray bursts, called “gamma ray glows,” are thought to originate from electrons accelerated and multiplied by strong electric fields in thunderclouds. There are unsolved questions such as electron‐acceleration mechanisms, position of the acceleration site, lifetime, and life cycle of the bursts. We observed a gamma ray burst lasting for ∼75 s from a thundercloud abruptly terminated with a lightning discharge. The gamma ray source was destroyed by a cloud‐to‐cloud discharge over the gamma ray observation site but not related to the triggering of the discharge in the present case.
Key Points
A gamma ray glow and its termination with a lightning discharge was observed in a Japanese winter thunderstorm
The glow was terminated by leader development of a horizontally long intracloud/intercloud discharge passing nearby overhead
The intracloud/intercloud discharge was not triggered by the glow in the present case because it started far from the gamma ray glow site
•W samples were pre-irradiated with 4.8 and 20MeV W ions to various displacements per atom (dpa).•Under following exposure to D plasmas radiation-induced defects were occupied by diffusing D ...atoms.•At ⩾0.1dpa, the D concentration in the damage zone demonstrated weak dependence on the damage level.
W samples were irradiated at 300 and 573K with 4.8 and 20MeV W ions to displacement damage levels in the range from 0.022 to 50 displacements per atom at the damage peak. 50μm thick W samples were exposed to high flux D plasma at 550K on the side opposite to the damaged one, whereas 2mm thick W samples were exposed to low flux D plasma at 403K on the damaged side. Trapping of deuterium at displacement damage was examined by the D(3He, p)4He nuclear reaction with 3He energies between 0.69 and 4.0MeV allowing determination of the D concentration up to a depth of 6μm. It was found that (i) at the damage level above 0.1dpa, the concentration of the W-ion-induced defects responsible for trapping of diffusing D atoms depended very weakly on the numbers of displacements per atom, and (ii) the quasi-saturation concentration of the defects decreased by a factor of two as the W-ion irradiation temperature increased from 300 to 573K.
We report simulation results of photonuclear reactions in the atmosphere triggered by a downward terrestrial gamma ray flash in lightning. Possible channels of reactions in the atmosphere and their ...cross‐sections are verified with the ENDF/B‐VII.1 library. Monte Carlo simulations with two stages are then performed with the Geant4 framework. In the first stage, electrons following the relativistic runaway electron avalanche spectrum are produced in a mass model of the atmosphere, and production of photoneutrons and β+‐decay nuclei is calculated based on the nuclear data library. In total 1 × 1013 neutrons and 4 × 1012 β+‐decay nuclei are produced by 1018 energetic electrons above 1 MeV. In the second stage, propagation of the photoneutrons and positrons from the β+‐decay nuclei in the previous stage is calculated. As a result, we model on‐ground distributions of fluxes and energy spectra for neutrons, neutron‐related gamma rays, and annihilation ones. The simulation model is to be compared with photonuclear events detected in low‐charge‐center winter thunderstorms.
Plain Language Summary
Lightning discharges occasionally emit a powerful flash of gamma rays called terrestrial gamma ray flashes. Gamma rays in terrestrial gamma ray flashes have high energies enough to react with atmospheric nuclei such as nitrogen and oxygen. The nuclear reactions in the atmosphere produce neutrons and unstable isotopes that emit positrons. In this paper, we utilize a Monte Carlo simulation framework, calculate a series of reactions and processes in the atmosphere, and then construct a distribution model of neutrons, neutron‐related gamma rays, and positron‐related ones at ground level. The obtained model can be compared with recent observations of nuclear reactions during winter thunderstorms in Japan.
Key Points
Possible channels of atmospheric photonuclear reactions in lightning are surveyed from a nuclear‐reaction data library
Monte Carlo calculations are performed to simulate photoneutron and β+‐decay‐nuclide productions in the atmosphere
On‐ground distributions of fluxes and spectra for neutrons, neutron‐related gamma rays, and annihilation gamma rays are modeled
Objectives To determine the metabolism of favipiravir (T-705, 6-fluoro-3-hydroxy-2-pyrazinecarboxamide) to its ribosylated, triphosphorylated form (T-705 RTP) in uninfected and influenza ...A/Duck/MN/1525/81 (H5N1) virus-infected cells. Effects of treatment on intracellular guanosine triphosphate (GTP) pools and influenza virus-inhibitory activity were also assessed. Methods A strong anion exchange HPLC separation method with UV detection was used to quantify T-705 RTP and GTP levels in Madin–Darby canine kidney cells. Antiviral activity was determined by virus yield reduction assay. Results Accumulation of T-705 RTP in uninfected cells increased linearly from 3 to 320 pmol/106 cells in cells exposed to 1–1000 µM extracellular T-705 for 24 h, approaching maximum levels by 9 h. Virus infection did not result in greater T-705 RTP accumulation compared with uninfected cells. Catabolism of T-705 RTP occurred after removal of T-705 from the extracellular medium, with a half-life of decay of 5.6 ± 0.6 h. Based upon these results, short-term incubation of T-705 with H5N1 virus-infected cells was predicted to provide an antiviral benefit. Indeed, 4–8 h 10–100 µM T-705 treatment of cells resulted in virus yield reductions, but less than continuous exposure. A 100-fold higher extracellular concentration of T-705 was required to inhibit intracellular GTP levels compared with ribavirin, which helps explain ribavirin's greater toxicity. Conclusions The favourable intracellular metabolic properties of T-705 combined with its reduced cell-inhibitory properties make this compound an attractive candidate for treating human influenza virus infections.
During a winter thunderstorm on 6 February 2017 in Japan, photonuclear reactions such as 14N(γ, n)13N were triggered by a downward terrestrial gamma‐ray flash (TGF), as reported by Enoto et al. ...(2017, https://doi.org/10.1038/nature24630). In the present paper, we compare the observation with a simulation model of downward TGFs and subsequent photonuclear reactions constructed by the first paper of the series and Wada, Enoto, Nakazawa, et al. (2019, https://doi.org/10.1103/physrevlett.123.061103). The observation and model consist of three components: annihilation gamma rays from positrons produced by β+‐decay nuclei, deexcitation gamma rays originating from neutron captures, and radiation doses by TGF photons. Each component of the observation is reproduced by the simulation model, and we constrain a relation between the number of avalanche electrons and their production altitude of the downward TGF. The constraints by three components match within an order of magnitude. The downward TGF is estimated to comprise (0.5–2.5) × 1019 avalanche electrons above 1 MeV produced at an altitude of 1.4–2.7 km. Despite differences in altitude, direction, and season, downward TGFs in winter thunderstorms are thought to have the same mechanism of electron acceleration and multiplication in lightning as TGFs observed by in‐orbit satellites.
Plain Language Summary
Lightning flashes are sometimes accompanied by strong high‐energy emission called “terrestrial gamma‐ray flashes” (TGFs). The energy of gamma rays in TGFs is high enough to trigger nuclear reactions with atmospheric nuclei such as nitrogen and oxygen. The nuclear reactions produce neutrons and unstable isotopes that emit positrons. In the companion paper of this series, we calculated the nuclear reactions and propagation processes of their products such as positrons and neutrons and modeled their characteristics at ground level by simulations. In the present paper, the simulation model is compared with the actual observation of a TGF and nuclear reactions during winter thunderstorms in Japan. The model successfully reproduces the observation and estimate the production altitude the number of energetic electrons involved in the TGF.
Key Points
A simulation model of photonuclear reactions in lightning is compared with an observation during a winter thunderstorm reported by Enoto et al. (2017, https://doi.org/10.1038/nature24630)
Three detected signatures originating from positrons, neutrons, and TGF photons are reproduced by the simulation model
A downward TGF triggering photonuclear reactions comprised 1018 to 1019 avalanche electrons produced at 1.4–2.7 km above sea level
In 2015, the Gamma-Ray Observation of Winter Thunderstorms (GROWTH) collaboration launched a mapping observation campaign for high-energy atmospheric phenomena related to thunderstorms and lightning ...discharges. This campaign has developed a detection network of gamma rays with up to 10 radiation monitors installed in the cities of Kanazawa and Komatsu, Ishikawa Prefecture, Japan, where low-charge-center winter thunderstorms frequently occur. During four winter seasons from October 2016 to April 2020, a total of 70 gamma-ray glows, i.e., minute-lasting bursts of gamma rays originating from thunderclouds, were detected. Their average duration is 58.9 s. Among the detected events, 77% were observed at night. The gamma-ray glows can be classified into temporally symmetric, temporally asymmetric, and lightning-terminated types based on their count-rate histories. An averaged energy spectrum of the gamma-ray glows is well fitted with a power-law function with an exponential cutoff, whose photon index, cutoff energy, and flux are 0.613±0.009 MeV, 4.68±0.04 MeV, and (1.013±0.003)×10^{−5} erg cm^{−2}s^{−1} (0.2–20.0 MeV), respectively. The present paper provides a catalog of gamma-ray glows and their statistical analysis detected during winter thunderstorms in the Kanazawa and Komatsu areas.
Bone Morphogenetic Proteins (BMPs) play crucial roles in a variety of developmental processes, but their functions during early vertebrate brain development are largely unknown. To investigate this ...problem, we have compared by in situ hybridization the expression of five Bmp genes belonging to the Drosophila Decapentaplegic (Bmp2 and Bmp4) and 60A subgroups (Bmp5, Bmp6 and Bmp7). Striking co-expression of these Bmps is observed within the dorsomedial telencephalon, coincident with a future site of choroid plexus development. Bmp co-expression overlaps that of Msx1 and Hfh4, and is complementary to that of Bf1. The domain of Bmp co-expression is also associated with limited growth of the neuroectoderm, as revealed by morphological observation, reduced cell proliferation, and increased local programmed cell death. In vitro experiments using explants from the embryonic lateral telencephalic neuroectoderm reveal that exogenous BMP proteins (BMP4 and BMP2) induce expression of Msx1 and inhibit Bf1 expression, a finding consistent with their specific expression patterns in vivo. Moreover, BMP proteins locally inhibit cell proliferation and increase apoptosis in the explants. These results provide evidence that BMPs function during regional morphogenesis of the dorsal telencephalon by regulating specific gene expression, cell proliferation and local cell death.
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