Explosive Disintegration Research Articles

Kerogen—Mineral bonding and beneficiation studies with a carbonate oil shale, using carbonic acid attack and a novel explosive disintegration technique

CO 2 and water under pressures up to 5.2 MPa and temperatures up to 200°C have been used to attack the mineral matrix of a carbonate oil shale from Julia Creek, Australia. In most experiments the chemical attack was coupled with an explosive depressurisation process (Siropulper) which produced considerable comminution of the shale. Changes in kerogen—mineral bonding and potential for beneficiation were assessed by float—sink separations. No kerogen was liberated, and only small amounts of kerogen-enriched material were freed by these treatments, even where all the carbonate minerals had been dissolved. Carbonate minerals do not appear to play any special role in bonding kerogen in this shale, and these disintegration techniques show no promise for gravity beneficiation processes with it.

Theoretical studies of shock-initiated detonations

The dynamics of shock propagation have been studied theoretically for a variety of two-dimensional lattices. The approach used is based on molecular dynamics and hinges on the exact numerical solution by computer of the equations of motion for the individual atoms or molecules in each lattice. Shocks have been launched into the lattices under study by methods designed to simulate flyer-plate impact. Two different interatomic potentials have been used, one endothermic and one net-exothermic. For both types of potential, a shock launched at one side of the lattice will spall a group of atoms off the other side. However, the subsequent behavior of the two types of lattice is very different. For endothermic potentials, after the initial atomic spall, the residual lattice is quiescent with little further activity. For net-exothermic potentials, the initial atomic spall injects additional energy into the system in such a manner that subsequently further spall occurs at both sides. Once this new spall is initiated, it leads rapidly to further bond breaking and explosive disintegration of the system.

Explosive deformation and destruction of tubes

1. The energy approach to the problem of disintegration can be used to describe the set of experiments on the dynamic plasticity of tubes made from soft steel. The diameters of the tubes varied by a factor of 7 and the velocities with which the walls of the tubes flew apart by a factor of 13. Accordingly, the effectiveness of the energy approach is not limited to the case of brittle disintegration. It can also be used to describe disintegration in the region of large plastic deformations. 2. The magnitude of the specific work of disintegration of soft steel estimated in the region of large plastic deformations accords with the magnitude of this quantity found from experiments on brittle disintegration (cleavage, brittle disintegration of closed vessels, experiments on the determination of impact viscosity under conditions of brittle disintegration). The estimated value of the viscosity of soft steel agrees with results obtained in other ways. 3. The existence of a maximum in the dependence e(ė) at ė∼μ−1 in the experiments on the explosive disintegration of tubes suggests that this effect may be of a more general nature and may also show up in the disintegration of other simple nontubular constructions made from viscoplastic materials.

Growth of the spark current at the breakdown of short vacuum gaps at steady voltage

The growth time of the spark current at the time of breakdown in vacuum at the constant voltage and pressure existing during this period was investigated with high time resolution. It was shown that, as in the case of a pulsed breakdown: 1) the growth time tc of the current increases in proportion to the length d of the gap and the ratio d/tc is ∼2.5·106 cm/sec; 2) the transition to a rapid rate of current growth (di/dt > 108 A/sec) takes place in 1–3 nsec; 3) during the period of current growth, x-ray radiation appears and a transfer of anode material to the cathode is observed. These results serve as evidence that the origin of current growth is connected with the appearance of efficient electron sources on the cathode. These, as in the case of pulsed breakdowns, are evidently cathode flares, the formation of which has an explosive character and can be identified with the act of breakdown initiation. In essence this event does not change with the rate at which voltage is supplied across the gap and consists of the explosive disintegration of emitting microspikes on the cathode. The appearance of cathode flares indicates the start of an irreversible breakdown of vacuum insulation. The emergence of a burst of x-rays and the erosion of the anode are explained by the action on the anode of a powerful stream of electrons that are emitted from the cathode flares, providing the spark current.

In vitro studies of skin after irradiation by a ruby laser

Summary Changes in the metabolic activity and histology of albino guinea-pig skin slices after exposure to light from a ruby laser were investigated in tissue culture. A graded response to laser radiation was demonstrated by measurement of respiration and uptake of radioactive sulphate into skin mucopolysaccharide. The ED 50 of both dose-response curves was about 2 joules per square millimetre. Histological studies suggested that the laser did not selectively destroy any particular zone of the skin. High energy densities were necessary to produce an immediate effect; these doses resulted in an explosive disintegration of the tissue. Laser energy levels causing damage to skin slices in vitro were comparable with those reported by other workers. It was thought that damage to skin by laser radiation was due to heat.

CVIII. The determination of the mass of energetic helium isotopes emitted in nuclear explosions

Summaey The mass spectrum of energetic helium isotopes, ejected during the explosive disintegration of nuclei, is determined, and the 3He/4He-ratio is found to be less than 0·05. The frequency of emission of energetic 6He-nuclei is probably negligible. Measurements are carried out on the ratio of single protons to deuterons at an altitude of 3500 m, and the result is found to be in accordance with previous estimates. The identification of the particles depends on a particular scattering method which is described.

LXXXVIII. The determination of the charge of heavy particles emitted during the explosive disintegration of nuclei

Summary The charge of heavy nuclear fragments, ejected during the explosive disintegration of nuclei, can be precisely determined if the length of the track in a photographic emulsion is of the order of 1500µ or greater. The method is based on the determination of the number of δ-rays per unit length which contain more than a certain number of grains. The maximum observed energies of ejection of light nuclei, lithium, beryllium and boron are of the order of 500 MeV. The nuclear processes which lead to the emission of heavy fragments with such great energy remain to be explained.

Observations on the Production of Mesons by Cosmic Radiation

IN examining photographic plates ‘exposed' to cosmic radiation at a height of about 10,000 ft. on the Jungfraujoch and the Pic du Midi, and at about 18,000 ft. on Kilimanjaro and Chacaltaya, we have now observed twenty nuclear ‘explosions' which are accompanied by the emission of slow mesons. In this communication we give a number of photomicrographs of the tracks of these ‘ejected' mesons. An analysis of the observed secondary effects which they produce enables us to show that at least the majority of them interact with nuclei and are therefore negatively charged ; and that on the average they produce more vigorous nuclear disintegrations than most of the negative mesons which stop in the emulsions after being generated outside it. The main features of our present knowledge of charged mesons, with masses in the interval from 100 me to 400 me, can be accounted for in terms of two types of particles of different mass1'2, which can be either positively or negatively charged, the heavier being generated in processes associated with the explosive disintegration of nuclei, and decaying spontaneously to produce the lighter ones. The possibility is not excluded, however, that the phenomena are more complicated than has been visualized hitherto.

Emission of Li8 in the Explosive Disintegration of Nuclei

IN a recent communication from this Laboratory1, it was shown that unstable heavy nuclei are sometimes emitted during the explosive disintegrations produced in photographic plates by the passage of cosmic radiation. In some cases., these unstable particles, after being brought to rest in the emulsion, give rise to two particles of equal range, emitted in opposite directions. The characteristic tracks thus produced were referred to as ‘hammer tracks'; and it was suggested that they are due to the emission of a nucleus of Li8 during the disintegration, for this nucleus is known to suffer β-decay with a period of 0·88 sec.2, and simultaneously to decompose into two α-particles. Twenty-eight examples of this process have now been observed in this Laboratory, and it has been possible to establish the correctness of the original interpretation of the phenomenon.