SCIENCE & TECHNOLOGY

Saying goodbye to nuclear bombs
Dr Paul Singh

On September 11, 2007, Russia successfully tested the world’s most powerful “Vacuum Bomb”, which unleashed destructive shockwaves with power equivalent to that of a nuclear blast. The bomb has been dubbed as the “father of all bombs” (FOAB). It weighed 7,100 kilograms and has a destructive radius of 300 metres. According to Alexander Rukshin, Russia’s deputy armed forces and chief of staff, test results of this new weapon have shown that its efficiency and power are at par with a nuclear weapon.

PROF YASH PAL
THIS UNIVERSE

When we talk on telephone the speech travels back and forth almost instantaneously. This is true even when we speak to someone in the US. But sound waves do not seem to travel that fast. Why this difference?

Prof Yash Pal

Prof Yash Pal

 


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Saying goodbye to nuclear bombs
Dr Paul Singh

On September 11, 2007, Russia successfully tested the world’s most powerful “Vacuum Bomb”, which unleashed destructive shockwaves with power equivalent to that of a nuclear blast. The bomb has been dubbed as the “father of all bombs” (FOAB). It weighed 7,100 kilograms and has a destructive radius of 300 metres. According to Alexander Rukshin, Russia’s deputy armed forces and chief of staff, test results of this new weapon have shown that its efficiency and power are at par with a nuclear weapon.

The main destruction in an FOAB is inflicted by the ultrasonic shockwaves emitted and an incredibly high temperature attained during the test. This bomb has an edge over the nuclear and conventional bombs that it does not contaminate the environment as it does not radiate any radioactive material. According to Russians, it is detonated to match the United States’s “Massive Ordnance Air Blast” (MOAB) bomb or the “Mother of All Bombs”, claimed to be the most powerful non-nuclear weapon. The FOAB is four times more powerful than MOAB and it yields the equivalent of 44 tonnes of TNT.

The MOAB is the largest-ever satellite-guided, air-delivered weapon in history. The 21,600-pound MOAB is an improved version of the unguided 15,000-pound BLU-82 Daisy Cutter. It is 30 feet long with a diameter of 40.5 inches.

The warhead is a blast-type and was developed in only nine weeks to be available for the Iraq war, but it was not used in combat. The basic design of MOAB is similar to that of the BLU-82 Daisy Cutter, used in the Vietnam War and in Afghanistan for clearing the rocky areas.

The Vacuum Bombs are also termed as Thermobaric bombs. The term thermobaric is derived from the Greek words for thermo means “heat” and baric means “pressure”. The explosion of such bombs release heat and pressure waves. There are other names given to these bombs such as high-impulse thermobaric weapons (HITs), fuel-air explosives (FAE) or sometimes fuel-air munitions, heat and pressure weapons, or vacuum bombs. For a given size, these produce more explosive energy than conventional explosives, but have the downside of being less predictable in their effect. Thermobaric weapons are different from the conventional explosive weapons in the sense that these use atmospheric oxygen for the burning of fuel, instead of carrying it in an oxidizer.

A thermobaric weapon consists of a container filled with either a volatile liquid or a finely powdered solid, which could be an explosive or metal powder and it has two separate explosive charges. It works in two stages. In the first stage, a cloud of powder or liquid explosive using a small charge is dispersed in the space. In the second stage, the cloud of powder is ignited with a charger. After dropping or firing, the first explosive charge bursts the container at a predetermined height and disperses the fuel all around in the form of a cloud. The cloud gets mixed with atmospheric oxygen. Once the fuel is appropriately mixed with oxygen, the second charge detonates it, thus, propagating an explosion through the cloud. Generally used fuels in explosions are ethylene oxide and propylene oxide and they act like mustards. In case the fuel fails to ignite completely, then, the device can be dangerous as it can lead to the production of the chemical weapon.

The weapon can be detonated either dropping it by an aircraft or firing it from a platform. The recently used FOAB was dropped by a Tupolev Tu-160 strategic bomber over a testing ground. A large explosion followed it. The pictures of the site looked like a flattened multi-storey block of flats surrounded by scorched soil and boulders. The bomb is reported to contain 7.8 tons of thermobaric explosive, although less than that of explosives (8 tons) in the MOAB, but it was said to use more highly efficient explosive. The bomb was reported to have a blast radius of 300 metres, about double that of the MOAB, while the temperature at the epicentre was also reported to be twice as high.

For the efficient detonation, the cloud needs a minimum ratio of fuel vapour to air amount, below which, ignition will not occur. Alternately, there is also a maximum ratio of fuel vapour to air, above which no ignition takes place. These limits are termed the lower and upper explosive limits. For gasoline vapour, this limit ranges from 1.3 to 6.0 per cent vapour to air, and for methane this range is 5 to 15 per cent.

The potential damage from a vapour cloud explosion is found to depend upon many parameters such as the mass and type of material released, the strength of ignition source, the nature of the turbulent jet release, and turbulence induced in the cloud. Within the detonation, the pressure can reach up to 3 million Pascal (MPa) and the temperature is raised between 2500 and 3000°C. After the initial blast, the pressure drops below atmospheric pressure creating airflow back to the centre of the explosion (called epicentre) strong enough to suck the humans.

It draws in the unexploded burning fuel to create almost complete penetration of all non-airtight objects within the blast radius, which are then incinerated. Newer types of thermobaric weapons which are on anvil do not disperse the fuel before igniting it, but are single-stage bombs having one explosive charge that both ignites and disperses the fuel.

These bombs disperse an aerosol cloud of fuel in space, which is ignited by an embedded detonator to produce an explosion. The ultrasonic waves, due to overpressure, flatten all objects within the close proximity of the epicentre of the aerosol fuel cloud.

More importantly, the duration of the overpressure gives it an edge over conventional explosives and makes fuel-air explosives useful against soft targets such as minefields, armoured vehicles, aircraft parked in the open, and bunkers. Asphyxiation and internal damage is caused to the persons outside the highest blast effect zone like in deeper tunnels because of the blast wave, the heat, or the following air draw. The effects produced by the long-duration high pressure and heat impulse of FAE are often better than that produced by low-yield nuclear weapons, but without the problems of radiation.

When compared with nuclear bombs it amounts to only 0.3 per cent of the power released by atom bomb dropped on Hiroshima. The Hiroshima explosion was equivalent to 13,000 tonnes of TNT. The most powerful explosive ever deployed i.e.Tsar Bomba was equivalent to 50,000 tonnes of TNT. The explosives used in the thermobaric bombs are oxygen deficient and they suck oxygen from air for complete combustion of the dispersed parts of the bomb. Due to this, they generate more energy than the conventional bombs, but are hard to control.

The pieces originating from the explosion of a conventional bomb can be stopped by walls and generally are unable to pass through the tunnels, bridges, bunkers etc. But in case of vacuum bombs, the blast waves can travel and bend around the corners of any structure, therefore, can penetrate deep in the areas which are otherwise inaccessible to the pieces of bombs. Hence, these new bombs can be used effectively against the enemy hiding in bunkers, caves etc.

The conventional counter measures like sandbags and personal armour are not effective against the vacuum bombs. The blast injuries in such bombs include internal injuries, which would be difficult to diagnose and treat. As these do not radiate any radioactive material and do not contaminate the environment, therefore, have an edge over the nuclear and conventional bombs. In near future, the vacuum bombs will be used in place of nuclear bombs.

The writer is Assoc. Professor (Physics), College of Basic Sci. & Humanities, CCSHAU, Hisar


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PROF YASH PAL
THIS UNIVERSE 

When we talk on telephone the speech travels back and forth almost instantaneously. This is true even when we speak to someone in the US. But sound waves do not seem to travel that fast. Why this difference?

When we use the telephone, we produce sound that travels to the nearby mouthpiece. The microphone converts the sound vibrations into electrical variations. What goes over the wire is the electrical signal. The instrument of the receiver converts the electrical signal into sound.

The electrical signal travels almost with the velocity of light, which is 300,000 kilometres per second. To travel to America and back would take about 1/8 of a second. That is almost instantaneous as far as human perception is concerned.

Sound waves move through compression and decompression of the material medium in which they travel.

Sound is a mechanical wave that is necessarily much slower than an electromagnetic wave, which does not require a medium to travel.

The electrical signal in wires also moves extremely fast because electrons being conveyers of this signal also travel very fast.

In microwave transmission lines electromagnetic waves travel as if they are going through a pipe.

The household TV cable is an example of that. Such cables crisscross large distances on land and under the oceans. These days one also uses optical fiber cables and satellites to convey signals over long distances.

For optical communication the signal is converted to digitally modulated light beam that travels at the speed of light through thin fibers of glass.

When we take the satellite route we have to go up to the satellite 36,000 km above the earth and the same distance back down to a ground station from where the normal telephone network takes over.

Because of this reason it is often found that when we happen to get a satellite channel there is a delay of about a quarter second each way and about half a second between your asking a question off a friend in America and hearing his reply. After a while people learn to live with this inconvenience.
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