Implosion technique

The gun-type method is essentially obsolete and implosion technique is much more suitable in order to reduce weight of the weapon and consequently, increase weight of the fissionable material. Further, gun-type weapons also have some safety related problems. 

In the gun-type bomb,one piece of uranium-235 of subcritical mass is hurled into another piece by a chemical explosive.The two pieces together give a supercritical mass,and a nuclear explosion results. Bombs using plutonium-239 require an implosion technique,in which wedges of plutonium arranged on a spherical surface are pushed into the center of the sphere by a chemical explosive, where a supercritical mass of plutonium results in a nuclear explosion. 

In a nuclear weapon, the fissile material is initially subcritical. The challenge is to produce a supercritical mass so rapidly that the chain reaction takes place uniformly throughout the metal. Supercriticality can be achieved by shooting two subcritical blocks toward each other (as was done in the bomb that fell on Hiroshima) or by implosion of a single subcritical mass (the technique used in the bomb that destroyed Nagasaki). A strong neutron emitter, typically polonium, helps to initiate the chain reaction. 

CA 65, 18416(1966) (Generation of cylin-crically symmetric implosions by mousetrap action "An explosive configuration was developed for going from a single initiation point to a cylindrically symmetric, converging detonation front. This technique... 

Tullis (Ref 26) investigated both of these approaches to a single event FAE and proposed a concept best described as a one-step automatic two-event FAE. Here the second-event explosive is replaced by a very highly hypergolic oxidizer under the implosive dispersal mode. The technique is a one-step process since only one explosive charge need be detonated. The mechanism, however, proceeds via two events as the explosive charge causes a dual dispersal ... 

Using a cunning technique called implosion, in which conventional chemical explosives are used to produce a shock wave which uniformly compresses the plutonium sphere, the volume of the plutonium sphere can be slightly reduced and its density increased. If the original mass of the plutonium is just less than critical it will, after compression, become super-critical and a nuclear explosion will take place. 

Ultrasound extraction (sonication) is based on the conversion of AC current at 50/60 Hz into electrical energy at 20 kHz and its transformation in mechanical vibrations. Due to the cavity, microscopical vapor bubbles are formed and, after implosion, they produce strong shockwaves into the sample. For isolating the (semi)volatile organic compounds, the liquid-liquid ultrasound technique is applied to samples such as soils, sediments, coal, etc. The process is also useful for the biological materials destruction (Loconto, 2001). Sonication extraction is faster than Soxhlet extraction (30-60 min per sample) and allows extraction of a large amount of sample with a relatively low cost, but it still uses about as much solvent as Soxhlet extraction, is labor intensive, and filtration is required after extraction. 

QCM technique can supply in-situ kinetics of the reaction inside the cell. Solubilization of Cu(acac)2 L/SC CO2 was diffusion-controlled. Difftisivities of Cu(acac)2 in L/SC CO2 were also obtained. Ultrasonic waves enhance dissolution of Cu(acac)2 in CO2 mainly due to acoustic streaming. Cavitation/implosion in L/SC CO2 does not occur as often as in water. 

Manothermosonication (MTS), a combined treatment of heat and nltrasonnd nnder moderate pressure, is another alternative to conventional heat treatment in order to inactivate enzymes and microorganisms [120-122], The ultrasound generates the cavitation or bnbble implosion in the media. This implosion can cause inactivation of the enzyme and destrnction of microorganisms. The simultaneons pressnre treatment maximizes the intensity of the explosion, which increases the level of inactivation. The MTS technique avoids the adverse effects of elevated temperatures on quality and also resnlts in reduced energy requirements and therefore rednced costs. 

Action changed Oppenheimer s mood. The Laboratory had at this time strong reserves of techniques, of trained manpower, and of morale, says the technical history. It was decided to attack the problems of the implosion with every means available, to throw the book at it Going over the prospects with Bacher and Kistiakowsky, Oppenheimer decided to carve two new divisions out of Parsons Ordnance Division G (for Gadget) under Bacher to master the physics of implosion and X (for explosives) under Kistiakowsky to perfect explosive lenses. The Navy captain howled, Kistiakowsky remembers ... 

Carefully spaced prearranged wires contacted by the metal sphere as it imploded supplied information not only about the timing of the implosion but also about material velocities at various depths within the core. That provided direct, quantitative data which the Theoretical Division could use to check how well its hydrodynamic theory fit the facts. The Electric Method group began by measuring the high-explosive acceleration of flat metal plates. Early in 1945 it adapted its techniques to partial spheres and eventually to spheres surrounded by HE lens systems with only one lens removed to access the necessary wires. 

A common use of vacuums involves their utility for removing volatiles from reactions or filtering materials. It is common to use house vacuum systems, water aspirators, or vacuum pumps for these purposes. Besides the risks of implosions, there can be potential hazards from exposures to toxic products released from the vacuum exhaust. Maintenance workers have been exposed to toxic chemicals that were allowed to enter into a house vacuum system. Others have been exposed to toxic products from unventilated vacuum pumps used to evaporate volatile organics. It is important to use techniques to set up traps to prevent these kinds of releases of hazardous materials. 

When bubbles reach the resonance size range, they grow to a maximum size within one acoustic cycle and implode. Bubble implosion/collapse is a near adiabatic process. In simple thermodynamic terms, the volume of the bubble decreases instantaneously resulting in the generation of extreme heat within the bubble. Theoretical estimates predict greater than 15,000 K [44, 45]. However, experimental methods estimate about 1000-5000 K [46-50]. A number of techniques have been used to calculate the bubble temperatures. First, the bubble temperature could be theoretically calculated using Eq. (1.4). 

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