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Microfabrication of a microarcjet with Fifth-harmonic generation Nd:YAG pulses (wavelength 213 nm) and its plasma acceleration characteristics was investigated. The microarcjet with a rectangular exit of 0.44 mm in height was machined in a 1.2 mm thick quartz plate. For electrodes, Au films of 100 nm in thickness were coated on a divergent part of the nozzle for anode and an inner wall surface for cathode. In operational tests, a stable discharge was observed for mass flow of 1.0 mg/s, discharge current of 6 mA, discharge voltage of 600 V, or 3.6 W input power. With the 3.6 W input power, plasma speed of 1441 m/s and an energy efficiency of 7% were obtained.

Absolute leakage neutron spectrum in the energy range between 0.1 and 15 MeV from a silicon spherical pile of 60-cm diameter was measured using an intense 14 MeV pulsed neutron source, OKTAVIAN, for the purpose of the benchmark validation of the nuclear data of silicon in JENDL-3.2, JENDL-3.3, ENDF/B-VI (release 2), ENDF/B-VI (release 5) and EFF-2.4. The neutron spectrum was compared with the calculated results using MCNP with different nuclear data. For estimating sensitivity of the individual cross section, the calculations were also performed using modified JENDL-3.2 based data libraries. It was found that the all nuclear data could predict the measured spectrum with the measurement fairly well. ENDF/B-VI (release 2) gave considerably large discrepancy over the whole energy region presumably caused by the inadequate inelastic scattering cross section values. The discrepancy found in the JENDL-3.2, JENDL-3.3 and EFF-2.4 between 5 and 10 MeV could be attributed to the too low values of the discrete inelastic scattering cross section values. The prediction with ENDF/B-VI (release 5) was almost satisfactory over whole energy region.

Investigations on optimum operational conditions of very low-power DC micro-arcjet, or micro-plasmajet, were conducted. It was shown that with an electrically insulating material for a constrictor stable discharges below 5 W could be achieved. Also, microfabrication of micro-arcjet nozzles with fifth-harmonic Nd:YAG pulses (wavelength 213 nm) were conducted. Micro-arcjet nozzles were machined in a 1.2 mm thick quartz plate. Sizes of the nozzle exit were 0.44 mm in height and constrictor height of 0.1 mm. For an anode, a thin film of Au (∼100 nm thick) was coated in vacuum on divergent part of the nozzle. As for a cathode, an Au film was also coated on inner wall surface. In discharging operational tests, a stable discharge was observed for mass flow of 1.0 mg/s, discharge current of 6 mA, discharge voltage of 600 V or 3.6 W input power. In this case, plenum pressure of the discharge chamber was 80 kPa. Thrust obtained was 1.4 mN giving specific impulse of 138 s with thrust efficiency of 24% with 3.6 W input power.

An assessment of a novel laser-assisted pulsed plasma thruster (PPT) was conducted, in which a laser-induced plasma was induced through laser-beam irradiation onto a solid target and accelerated by electrical means instead of direct acceleration using only a laser beam. It was found that the discharge duration at low-voltage cases was as long as that of laser-induced plasma. However, in high-voltage cases, the discharge duration was much longer than that of laser-induced plasma. In this case, the laser-induced plasma should be leading the main discharge from a capacitor, where a certain amount of neutral components of vaporized propellant must be ionized through the discharge. At 8.65-J discharge energy, the maximum current reached about 8000 A. With a newly developed torsion-balance-type thrust stand, thrust performances of laser-assisted PPTs could be estimated. The impulse bit and the specific impulse linearly increased. On the other hand, the coupling coefficient and the thrust efficiency did not increase linearly. The coupling coefficient decreased with energy showing a maximum value (20.8 μN s/J) at 0 J, or in a pure laser ablation case. The thrust efficiency first decreased with energy from 0 to 1.4 J and then increased linearly with energy from 1.4 J to 8.6 J. At 8.65-J operation, an impulse bit of 38.1 μN s, a specific impulse of 3791 s, a thrust efficiency of 8%, and a coupling coefficient of 4.3 μN s/J were obtained.

An investigation on effects of a focused laser pulse for combustion enhancement characteristics was conducted for supersonic airstreams with a transverse hydrogen-fuel injection. In order to estimate behaviors of a laser-induced plasma, temporal variations of its emission distribution were measured with an ICCD camera and photodiodes. From these measurements, characteristic time scales of an absorption process of an incident laser pulse and a plasma formation process were also estimated. Numerical simulations using a time-dependant Navier–Stokes equation with finite-rate chemistry were also conducted to elucidate laser-induced ignition and mixing enhancement characteristics in supersonic airstreams with a transverse hydrogen injection. From the results, it was confirmed that, depending on the laser energy density and focal points, radicals, a shock wave, and shock-induced local turbulences were being formed through laser irradiation. Then, recirculation zones with flamelets were induced. Moreover, it was shown that these flamelets were growing in moving upstream and downstream from the focal point up to 1 ms. Consequently, it was shown that laser-induced plasmas could be effective in both combustion reaction and mixing enhancements for the supersonic combustion.

For validation of nuclear data files for Nb, the absolute leakage neutron spectrum from a spherical pile of Nb was measured in the energy range between 0.1 and 16MeV at OKTAVIAN. A sensitivity analysis was performed with MCNP-4A and the modified JENDL-3.2 libraries. The measured spectrum was compared with the MCNP-4A calculation with two nuclear data libraries processed from JENDL-3.2 and ENDF/B-VI. The comparison was made by the spectrum shape and the C/E values in four energy regions. The JENDL-3.2 calculation gives satisfactory prediction except below 0.8 MeV, but that with ENDF/B-VI considerably overestimates the spectrum above 1 MeV. From the observation of the calculated and measured spectra and of the secondary energy distribution spectra (SED) of the (n, 2n) and inelastic scattering in JENDL-3.2 and ENDF/B-VI, the discrepancies in the calculations are probably due to improper SED of the (n, 2n) reaction for that below 0.8 MeV in JENDL-3.2 and that between 0.8 and 6 MeV and SED of inelastic scatter...

The displacement cross-section of iron was calculated for gamma-ray irradiation with the energy range of 1 to 15 MeV, which corresponds to radiation fields in fission reactors. Three gamma-material interactions, Compton scattering, pair production and photoelectric effect were considered. The displacements induced by both electrons and positrons were included. For damage function the modified Kinchin-Pease model with the displacement energy of 40 eV was applied, which are used as the standard damage model in neutron-induced displacement calculations. The standard damage model gave a lower cross-section by a factor of 1.3 compared to Kinchin-Pease model, and the exact treatment of positron contribution gave a lower cross-section by a factor 1.1 compared to an approximation treating positrons as electrons. The present cross-section was lower by a factor of 1.1–2.0 than the cross-sections previously proposed in the literatures.

Recent advances of laser plasma accelerators that promise very high gradients of the accelerating fields and enable small sized accelerators were reviewed, and a feasibility study of the utilization of these accelerators for space propulsion was conducted. Forward plasma acceleration through a foil target with a low-power laser pulse was observed, and resultant impulse was measured for various targets. The significant merit of this thruster was discussed in the case of operation of this type of thruster on earth and/or solar orbit, in which solar power is available. Related issues on this point were also discussed.

Gallium arsenide was anodically oxidized in a mixture of ethylene glycol and tartaric acid as an electrolyte. The numbers of Ga and As atoms in the anodic oxide films and in the used electrolytes were measured by radioactivation analysis. During the anodic oxidation, GaAs dissolved into the electrolyte. The numbers of Ga and As atoms that dissolved into the electrolytes was proportional to the anodic voltage, and the number of Ga atoms in the electrolyte was about five times more than that of As atoms. The composition of the anodic oxide films varied with depth. However, the atomic profiles measured by Auger electron spectroscopy displayed As atoms much less than Ga atoms throughout the anodic oxide films, because Ga oxides were lost from the anodic oxide films into the vacuum during the Auger electron spectroscopy, accompanying sputtered thin film removal.

The neutron-induced fission cross-sections of 242mAm were measured relative to that of 235U from 0.003 eV to 10 keV with a back-to-back type double fission chamber. These measurements were performed from 0.03 eV to 10 keV, at 0.025 eV and from 0.003 to 35 eV using the Kyoto University lead slowing-down spectrometer, the thermal neutron facility of Kyoto University Reactor and the time-of-flight method, respectively. The results were compared with both the evaluated data of JENDL-3.2, ENDF/B-VI and JEF-2.2, and the existing experimental data. The validity of the cross-section in the files was discussed through the comparison.

The multiplicity and energy of the prompt neutrons emitted from the fission fragments for 239Pu(nth, f) were measured as functions of the fragment mass and total kinetic energy. The results were compared with those for 233U(nth, f) and with the predicted values by the multi-channel fission theory with the random neck rupture model. The measured and predicted values of the neutron multiplicity, ⟨V⟩(m*), show the saw-tooth trend and agree with each other. The total neutron multiplicity decreases linearly with increasing total kinetic energy resulting in —d⟨TKE⟩/d⟨Vtot⟩=16.5±0.4MeV/neutron. The slope of the neutron multiplicity vs. the total kinetic energy, —d⟨V⟩/d⟨TKE⟩, was plotted against the fragment mass. Its shape agrees with that for 233U(nth, f). The average neutron emission energy, ⟨η⟩(m*), follows a bell shape about the symmetric fission accompanying higher values for very asymmetric fissions and agrees with that for 233U (nth, f). The total excitation energy (TXE)(m*) was determined by two manners:...

An experimental study was performed to evaluate the feasibility of DC arcjet/plasma jet operation at very low-power levels ranging from 40 to 90 W, using nozzles with different materials and geometries. Nitrogen gas was used as the propellant. The thermal characteristics were evaluated for conventional nozzles and partially insulated nozzles, consisting of a ceramic insulator and a tungsten anode. Stable arcjet operations at very low-power levels ranging from 40 to 90 W were confirmed. It was observed that the temperature of molecular nitrogen estimated at the center of the exit is high, about 4000–6000 K. Higher thermal performance was obtained at very low-power operation combined with the use of insulated constrictors of reduced length and diameter. Furthermore, it was found that both temperature and thermal efficiency increase with the electrode gap.

Production efficiency of vacancy-type defects induced in neutron-irradiated silicon carbide single crystals (4H and 6H SiC) is observed as a function of irradiation temperature. The crystals were irradiated at several temperatures (20, 50, 100, 150, 200 and 370 K) using the low temperature irradiation-loop facility of Kyoto University Reactor. In the irradiated crystals, a broad absorption band at 780 nm was observed. The origin of the 780 nm band was attributed to the Si vacancy defect (VSi-type center) because it has similar annealing behavior as a paramagnetic center consisting of a Si vacancy that was identified by electron spin resonance (ESR) measurement. The defect concentration of the VSi-type centers was estimated using the Smakula formula from the absorption intensity of the 780 nm band. The production efficiency of the VSi-type center in SiC crystals irradiated at several temperatures has a maximum at about 200 K. The characterization of the irradiation temperature dependence of the VSi-type center is extremely different from that of MgO or Al2O3 which has a steep negative gradient from 20 to 400 K.

In order to make benchmark validation of the nuclear data for Cr, Mn and Cu in existing modern evaluated nuclear data files, leakage neutron spectra in the energy range from 0.1 to 15 MeV from spherical sample piles were measured by a time-of-flight technique using intense 14 MeV neutron source, OKTAVIAN. To make a qualitative understanding of the dependence of the spectra on individual partial cross sections, a trial calculation was performed by Monte Carlo neutron transport code MCNP-4A along with several kinds of modified cross sections for Mn. The measured spectra were compared with those by theoretical calculation using MCNP-4A with the evaluated nuclear data files. The comparison was made by the spectrum shape and by the C/E values in four energy regions. The calculations for Cr, Mn and Cu using JENDL-3.2, JENDL Fusion File, FENDL-1.0 and EFF-2 give satisfactory predictions with a few exceptions. By checking the result of the trial calculation, it is considered that these disagreement is caused by i...

The effects of DC or AC (14 kHz) corona discharges, formed between tips of opposed needle electrodes, on soot emission of a propane turbulent diffusion flame were investigated experimentally. It is shown that when a DC corona discharge (e.g., 3.6 W; 0.06% of the combustion energy released by the flame) or a discharge system composed of three AC coronas (e.g., 25.5 W in total; 0.43% of the combustion energy) is applied across the lower part of the flame, with a gap width such that the electrode tips are located outside the reaction zone, a marked reduction in soot emission is observed, without noticeable change in the shape of flame luminous region. When corona discharges are applied, increases of the density of charged species and/or charged soot particles are observed in the flame over the whole length downstream of the corona application. It is suggested that, in the case of DC corona application, additional air and inorganic charged species and electrons, produced in the air near the tip of the positive electrode, are carried into the flame mainly by corona winds, whereas in the case of the AC corona application the inorganic charged species and electrons are carried into the flame by diffusion processes. The charged species and electrons carried into the flame may influence the state of charging of incipient soot particles and also reduce the concentration of growing ions, i.e., soot precursors, which directly relate to the soot emission of the flame. In TEM photographs it was found that separate soot particles, or those forming chains in the flame, decrease in mean size with the application of corona discharges. Smaller size soot particles burn faster than larger size particles in the high-temperature oxidizing atmosphere at the flame top region.

The neutron-induced fission cross section of 243Am was measured relative to that of 235U from thermal neutron energy to 15 keV making use of a double fission chamber with 243Am and 235U electrodeposited layers. The data above 0.05 eV were measured using a lead slowing-down spectrometer coupled to an electron linear accelerator. A relative measurement to the 10B(n, α) reaction was also made using a BF3 counter at energies below 1 keV, and normalized to the absolute value obtained by using the cross section of the 235U(n,/) reaction between 200eV and IkeV. The existing experimental data by Wisshak and Kappeler, and by Knitter and Budtz-Jorgensen are in general agreement with the current measurement in the relevant energy region. However, the data by Seeger are considerably higher. The evaluated nuclear data in JENDL-3.2, ENDF/B-VI and JEF-2.2, whose data were broadened by the energy resolution function of the spectrometer, have been compared with the measured result. The fission cross section for thermal ne...

Making use of back-to-back type double fission chambers and a lead slowing-down spectrometer coupled to an electron linear accelerator, the cross section for the 241Am(n,f) reaction has been measur...

核分裂が発見されて60年近くになり,核分裂の連鎖反応は原子炉として実用化して人類に役立っているが,励起された重い原子核が大きく変形し, 2つの核分裂片へと分離していく核分裂過程は,現在でも十分に解明されていない。これは,物理的に興味ある課題であるとともに,核燃料サイクルの基礎データとしても重要である。最近,理論と実験の両面で核分裂過程の研究が進展しつつある。本稿では,まずBrosaらが提唱したマルチチャンネル(モード)核分裂過程のモデルを簡単に紹介し,続いて核分裂過程における多くの物理量を同時計測する実験的研究について,主として筆者らの方法と結果およびBrosaらのモデルによる計算との比較を示す。

A lead slowing-down spectrometer coupled to a 46 MeV electron linear accelerator (linac) was installed at Research Reactor Institute, Kyoto University (KURRI). The size of this Kyoto University Lead Slowing-down Spectrometer (KULS) is 1.5 × 1.5 × 1.5 m3, and it is covered with Cd sheets 0.5 mm thick. One of the eleven experimental holes in the KULS is covered with 10 to 15 cm thick bismuth layers to suppress high energy capture gamma-rays from lead. The characteristics of this KULS have been experimentally obtained and the results are compared with the predicted values by Monte Carlo calculations using the MCNP code. 1) The slowing-down constant K in the relation E = Kt2 between the neutron slowing-down time t and energy E is 190±2 (keV μs2) for the bismuth hole and 156±2 (keV μs2) for an ordinary lead hole, respectively. The K values agree with the calculated ones. 2) The measured energy resolution ΔEE at full-width-at-half-maximum (FWHM) was about 40% for both holes, while the calculated values were lower by about 10% than the measured ones in the relevant energy region. 3) The neutron energy spectrum from 0.01 eV to 20 MeV and the spatial distribution of neutrons in the KULS were measured by the foil activation method. The angular neutron spectrum perpendicular to the linac electron beam was also obtained experimentally in the energy range from a few eV to about 10 MeV by the neutron time-of-flight (TOF) method. The measured results are compared with the calculated ones in which we have used the three evaluated nuclear data JENDL-3, ENDL-85 and ENDF/B-IV for lead. Through the comparison a check on the nuclear data has been performed.

Level density parameters of fission fragments following the thermal neutron induced fission of 235U were determined as a function of the fragment mass by measuring the energy and multiplicity of prompt neutrons from a specified mass. This measurement gave the absolute values of the parameters for the neutron-rich nuclei covering the mass range from 80 to 155u except the region from 115 to 125u. The obtained parameters showed a saw-tooth trend against the mass with the minimum value around the double magic number, 132u, and this trend was close to that for 252Cf(s.f) by Budtz-Jorgensen et al. The analysis by a phenomenological description of the level density parameters including the shell and collective effects suggested the existence of a collective motion of the fission fragment at the moment of prompt neutron emission.

For the purpose of the correlation measurement of fission fragments and prompt neutrons for thermal neutron induced fission, a system consisting of two fragment detectors and a neutron detector was developed. In this system, one fission fragment was detected with a silicon surface barrier detector (SSBD) and the other with a specially designed parallel plate avalanche counter (PPAC). The PPAC had double structures, one for fast timing and the other for position detection. A prompt neutron emitted from a fragment with a specified mass was detected with an organic liquid scintillator (NE213) in this system. The SSBD supplied not only the energy signal of one fragment but also the start timing signal to the time-of-flight (TOF) measurements of the other fragment and the prompt neutron. We tried to carry out the fragment-neutron correlation measurement for 235U(nth, f) with this system, and succeeded in obtaining the neutron energy spectrum in the center-of-mass system and the neutron multiplicity depending on the fragment mass.

The mechanisms of flame stabilization and combustion promotion by plasma jets, observed in scramjet bombustor experiments with transverse fuel injection, were investigated numerically, based on time-dependent, two-dimensional complete Navier-Stokes equations, with a six-species, eight-step reaction model combined with el'dovich chain reactions. Although most designs for scramjet combustors rely on the combination of a rearward-facing step and a plasma torch, the present study is conducted on a simple configuration without the step to make clearer the fundamental aspect of the mechanisms. The following results were obtained: o 1. A plasma jet with adequate input power and feedstock flow rate establishes a high-temperature recirculation zone with an adequate scale, which works for flame stabilization as that produced by the step. The plasma jet is also useful for the combustion promotion of the fuel jet, through the intensification of eddy diffusivity at its injection point and at the following downstream region. 2. The effectiveness of plasma jets in flame stabilization and combustion promotion increases with input electric power and feedstock flow rate, and the plasma jets with oxygen feedstock are more effective than those with air or hydrogen feedstock, as observed generally in scramjet combustor experiments. 3. A decrease of the plasma jet injection slit width, for a fixed input power and a fixed mass flow rate of feedstock, increases the effectiveness of plasma jets in some cases. 4. When the plasma jet injection slit is located downstream of the fuel injection slit, the required input power and feedstock flow rate for a desirable combustion progress are usually smaller than those when it is located upstream, in accordance with a previous supersonic-combustion experiment conducted without the step.

Kinetic energy and neutron multiplicity as a function of fragment mass were measured for the thermal neutron induced fission of 239Pu. By measuring the velocities and energies of two fission fragments simultaneously, both of the pre-neutron emission fragment mass m* and the post-neutron mass m were obtained. The fragment mass dependent neutron multiplicity ν(m*) was deduced by subtracting m from m*. The fragment mass dependent total kinetic energy TKE(m*) was also obtained from this data. The fragment velocity was measured by time-of-flight (TOF) method, for which the start signal was triggered by a very thin plastic scintillation film detector (TFD) and the stop signal was obtained by a silicon surface barrier detector (SSBD) which was also used for the measurement of [he fragment kinetic energy. The present result of ν(m*) is in good agreement with that of Apalin et al. and that in the light fragment region of Fraser et al. The obtained TKE(m*) agrees well with the data of Wagemans et al. A calculation ...

Energy spectra of 235 U(n, f) fission fragments were measured with a silicon surface barrier detector (SSBD) being irradiated by neutrons up to a fluence of 2 × 10 12 n/cm 2 . Pulse height decreases of light and heavy fragment peaks were obtained; however, no significant change of peak width was observed. The authors tried to explain this pulse height decrease by an increased recombination effect due to the enhanced resistivity of silicon. The resistivity was reflected in the recombination effect through the charge collection time. For the resistivity estimation, a method of calculating the recombination effect was proposed. This method predicted the pulse height of α particles fairly well. The estimated resistivity showed excellent agreement with the one calculated using the donor concentration of silicon. Applying this method, the increases of the recombination effect were calculated for fission fragments. The calculated increases of recombination were much smaller than the experimentally obtained ones. A possible increase of recombination center concentration during the irradiation was suggested.

For promotion of nuclear science and engineering research, examinations were made on the possibilities and necessary measures to extend joint research at international level. The present article is a summary of the reports of investigations performed during FY 1986 through 1991 by the Special Committee of the AESJ for Feasibility Study on International Cooperation for Promotion of Nuclear Science and Engineering Research, under contract with Science and Technology Agency of Japan. Background information was collected on the present status of scientific research facilities in US, European and Asian countries on one hand, and on the expectations and prospects of Japanese scientists on the other hand. Based on the analysis of these data, some measures necessary to expand the international cooperation were proposed. It was emphasized that international joint research on a reciprocal basis would be effective in order to strengthen the technological basis of peaceful uses of nuclear energy. Problems to be solved for the new development were also discussed.

The cross section of the 232Th(n,2n)231Th reaction for the D-T neutrons was measured using a neutron generator at the Kyoto University Critical Assemblies (KUCA). The neutron energy was determined by the ZrNb ratio method. Irradiated thorium nitrate samples were chemically purified, and their γ-rays were measured with a high-purity germanium detector. The cross section was normalized to the 27Al(n,α)24Na reaction cross section of 119.36 mb, which is the evaluated value in ENDF/B-VI at 14.5 MeV. The result was (1198 ± 65) mb for (14.5 ± 0.2) MeV neutrons, and this agrees with the evaluated values in ENDF/B-VI and ENDL-86 within an experimental uncertainty, but is more than 20% larger than the newly evaluated value in JENDL-3.

Studies on the mechanism of ignition and flame-holding by upstream-injection plasma jets were conducted for H2 diffusion flames in high speed air streams. The plasma jets were operated with Ar gas involving active species such as O2, N2 and H2, in the range of relatively low power. It was observed that for ignition and flameholding, the concentration of active species in feedstock is more important than plasma jet power. This fact suggests the effectiveness of active species produced by plasma jets, rather than that of plasma-jet thermal energy, and also the importance of radical concentration supplied to the ignition-point of a fuel jet, compared to the total quantity of radicals produced. It was also found that the effectiveness of additives is in the order, O2≥N2>H2, and the results of numerical simulation on combustion-reaction promotion by the radicals added agreed qualitatively with the experimental ones.

Making use of a standard neutron spectrum field with a pure Maxwellian distribution, the thermal neutron cross section for the 237Np(n, γ)238Np reaction was measured at a neutron energy of 0.0253 eV by the activation method. The result is 158±3 b, which is obtained relative to the reference value of 98.65±0.09 b for the 197Au(n, γ)198Au reaction. Although the data in JENDL-3 is larger by about 15% than the present value, the recently revised data in JENDL-3.2 is close to the present. The ENDF/B-V, ENDF/B-VI, JEF-2 and Mughabghab's data are also larger by 7–15%. Old measurements are larger by 7–18% than the present data. The resonance integral for the 237Np(n, γ)238Np reaction was also measured relative to the reference value of 1,550±28 b for the 197Au(n, γ)198Au reaction with a 1/E standard neutron spectrum field. By defining the Cd cut-off energy as 0.5 eV for the 237Np(n, γ)238Np reaction, the present resonance integral is 652 ± 24 b, which is in good agreement with the JENDL-3, -3.2, ENDF/B-V, -VI, JE...

The nature and mechanisms of explosions caused by the contact of hypergolic liquid propellants were investigated in detail for several combinations of fuels and oxidizers. It is shown that the explosion phenomena observed can be classified into three categories. 1) In the case of N2H4/NTO, sudden gasification of a superheated liquid layer formed at the boundary of two liquids occurs spontaneously and a detonation-like reaction proceeds in the reactive mixture produced. 2) In the cases of MMH/NTO and UDMH/NTO, the sudden gasification is caused by the shock of a local ignition, and a turbulent-combustion reaction proceeds in the reactive mixture produced. 3) In the cases of hydrazine type fuels/FNA, the sudden gasification occurs spontaneously as in the case of N2H4/NTO, but it is not augmented by chemical reaction, and in these cases the observed explosion is weak. Information on the vapor layer, which is formed between reactive fuel droplet and pool liquid plays an important role for the occurrence of explosion, is also given, that is based on the high-speed motion picture records.