<p>Today, 68 years ago, the atomic bomb was dropped on the Japanese city of Hiroshima (the name means ‘broad island’) lying on the southern coast of Honshu, Japan’s largest island. This was the first time a nuclear bomb was used in a war to decimate a thriving popular city. Three days later, another atomic bomb was dropped in Nagasaki city, leading to Japan’s unconditional surrender, ending the Second World War. The hands on the dial of the half-melted remains of a lady’s wrist-watch (now an exhibit in a small museum) point to 8.16 am, the exact time when the bomb exploded at about 600 metres above ground level — for the maximum destruction effect.<br /><br /></p>.<p>It was a typical morning in Hiroshima, a fine day, when the streets were crowded with people on their way to work, shops and banks just opening and queues near department stores. High up in the sky was the B-29 bomber, the Enola Gay, the plane named after the maiden name of the pilot’s mother. Colonel Paul Tibbets was the chosen commander of the plane destined to drop the atomic bomb named “Little Boy”. At 8.16 am, nearly five tonnes of weight was released and the plane rose suddenly. Tibbets put the Enola Gay into a steep dive banking the heavy plane seawards. At this point, the unearthly howl of the diving bomber could be clearly heard on the ground. A parachute opened and a tiny dot floated slowing down the city centre. Suddenly, there was a gigantic blinding flash, a thundering noise and in one instant more than 10 square kilometres of the city was just flatted. One lakh people died and most people near ground zero were vapourised. Inside the Enola Gay, crew members wearing dark polarised goggles shielded their eyes as the bomb’s detonation released an intense glare of energy many times brighter than the sun.<br /><br /> Heat inside the fireball was calculated to have reached 3 lakh degrees, while at “ground zero”, the centre of the explosion reached 7,000 degrees, hotter than the solar surface. Roof tiles melted, granite building slabs became bubbles and people were vapourised! <br />All wooden buildings within several kilometres were reduced to ashes. The air pressure reached several tonnes per square metre. One minute after the bomb exploded, a fiery mushroom cloud reached a height of eight kilometres and was rising fast. A bustling city of three lakh people was a smoking ruin with half the population decimated. In the aftermath of the explosion, the high radioactivity from the debris killed another lakh within five years. Radiation damage continued to cause painful ailments and death to later generations decades later. Here is a brief history of the nuclear destructive power that destroyed Hiroshima.<br /><br />Just three weeks before Hiroshima, a ‘test’ bomb was exploded at Alamogordo in New Mexico. Again, a blinding flash and an explosion (brighter than a thousand suns, as physicist Robert Oppenheimer put it) which fused the desert sand to glass for a radius of one kilometre heralded the rash uncorking — as another physicist George Gamow put it — of the atomic genie from its hiding place in the nuclear bottle. Once unleashed, nuclear weapons continued to proliferate (more than 2,000 nuclear weapons were tested in the next 50 years, including a 60 megaton hydrogen bomb 5,000 times more powerful than the Hiroshima bomb!)<br /><br />The story starts in 1939 when German Scientists Otto Hahn and Strassman discovered that unlike other elements, when uranium nuclei captured neutrons, they split (or fissioned) into lighter nuclei (like barium), releasing lot of nuclear energy along with more neutrons which could fission other nuclei, initiating a chain reaction. Just then the World War II had started with a large exodus of Jewish scientists fleeing Europe including Einstein, Fermi, Bohr, etc. The potential of a chain reaction leading to a nuclear detonation was clearly realised and the lighter isotope of uranium (U-235) was identified as the fissionable one. These refugee physicists, now in the US, were worried that the fascist Nazi dictatorship could build the nuclear fission bomb, especially as they had closed all the uranium mines. They, especially Leo Szilard, prevailed upon Einstein to write a letter to US President Roosevelt underlying the great danger and urging the US to hurry up with the first nuclear device, before Germany did. The Japanese attack on Pearl Harbour which resulted in the US formally entering the Second World War as an ally of Britton gave further impetus to the work. The fissionable isotope, which was present in a quantity of less than a per cent in natural uranium, had to be isolated. This was done by converting Uranium into a gas, Uranium hexafluoride, which would make the lighter isotope compound to diffuse faster and after several such stages, its concentration would be enriched. Again, it was calculated that several kilograms of the uranium isotope was required for the chain reaction to be sustained, the so called critical mass leading to the explosion. In the “Little Boy” design, for example, the smaller piece was fired into a larger chunk of uranium so that the combined mass exceeded the critical mass and exploded at the planned height above ground. The Nagasaki bomb used plutonium (an unstable element formed when the uranium heavier isotope is bombarded with neutrons) which is also a fissionable element. The plutonium bomb is more compact, weighing less.<br /><br />By 1943, General Grooves as new in-charge of the “Manhattan Project” brought together all scientists in one place and helped to organise all the different departments involved; physics, chemistry, metallurgy, engineers, experimenters, weapon experts etc. <br /><br />Oppenheimer was put in charge. Within two-and-a-half years, they delivered the nuclear weapons. General Grooves also oversaw the vast engineering project to build plants for refining uranium and its derivative plutonium.<br /><br />Two of these plants at Oak Ridge employed 13,000 people. The Calutron, to separate U-235, had a huge electromagnet which needed more copper than was available in the US and the Treasury lent 6,000 tonnes of silver bullion. Simultaneous with the development of the atomic bomb was the development of the B-29 bomber, a parallel technical achievement. It was so complex that many aircraft companies and other industries were needed to manufacture it. It called for industrial cooperation on unprecedented scales. <br /><br />The first B-29 was flown in September 1942 and in about two years, several hundreds were produced. Today, the nuclear powers have 10,000 warheads, ICBMs and ABMs etc. and 40 minutes is all it takes to make the flight to any part of the world -- great potential for an Armageddon.</p>
<p>Today, 68 years ago, the atomic bomb was dropped on the Japanese city of Hiroshima (the name means ‘broad island’) lying on the southern coast of Honshu, Japan’s largest island. This was the first time a nuclear bomb was used in a war to decimate a thriving popular city. Three days later, another atomic bomb was dropped in Nagasaki city, leading to Japan’s unconditional surrender, ending the Second World War. The hands on the dial of the half-melted remains of a lady’s wrist-watch (now an exhibit in a small museum) point to 8.16 am, the exact time when the bomb exploded at about 600 metres above ground level — for the maximum destruction effect.<br /><br /></p>.<p>It was a typical morning in Hiroshima, a fine day, when the streets were crowded with people on their way to work, shops and banks just opening and queues near department stores. High up in the sky was the B-29 bomber, the Enola Gay, the plane named after the maiden name of the pilot’s mother. Colonel Paul Tibbets was the chosen commander of the plane destined to drop the atomic bomb named “Little Boy”. At 8.16 am, nearly five tonnes of weight was released and the plane rose suddenly. Tibbets put the Enola Gay into a steep dive banking the heavy plane seawards. At this point, the unearthly howl of the diving bomber could be clearly heard on the ground. A parachute opened and a tiny dot floated slowing down the city centre. Suddenly, there was a gigantic blinding flash, a thundering noise and in one instant more than 10 square kilometres of the city was just flatted. One lakh people died and most people near ground zero were vapourised. Inside the Enola Gay, crew members wearing dark polarised goggles shielded their eyes as the bomb’s detonation released an intense glare of energy many times brighter than the sun.<br /><br /> Heat inside the fireball was calculated to have reached 3 lakh degrees, while at “ground zero”, the centre of the explosion reached 7,000 degrees, hotter than the solar surface. Roof tiles melted, granite building slabs became bubbles and people were vapourised! <br />All wooden buildings within several kilometres were reduced to ashes. The air pressure reached several tonnes per square metre. One minute after the bomb exploded, a fiery mushroom cloud reached a height of eight kilometres and was rising fast. A bustling city of three lakh people was a smoking ruin with half the population decimated. In the aftermath of the explosion, the high radioactivity from the debris killed another lakh within five years. Radiation damage continued to cause painful ailments and death to later generations decades later. Here is a brief history of the nuclear destructive power that destroyed Hiroshima.<br /><br />Just three weeks before Hiroshima, a ‘test’ bomb was exploded at Alamogordo in New Mexico. Again, a blinding flash and an explosion (brighter than a thousand suns, as physicist Robert Oppenheimer put it) which fused the desert sand to glass for a radius of one kilometre heralded the rash uncorking — as another physicist George Gamow put it — of the atomic genie from its hiding place in the nuclear bottle. Once unleashed, nuclear weapons continued to proliferate (more than 2,000 nuclear weapons were tested in the next 50 years, including a 60 megaton hydrogen bomb 5,000 times more powerful than the Hiroshima bomb!)<br /><br />The story starts in 1939 when German Scientists Otto Hahn and Strassman discovered that unlike other elements, when uranium nuclei captured neutrons, they split (or fissioned) into lighter nuclei (like barium), releasing lot of nuclear energy along with more neutrons which could fission other nuclei, initiating a chain reaction. Just then the World War II had started with a large exodus of Jewish scientists fleeing Europe including Einstein, Fermi, Bohr, etc. The potential of a chain reaction leading to a nuclear detonation was clearly realised and the lighter isotope of uranium (U-235) was identified as the fissionable one. These refugee physicists, now in the US, were worried that the fascist Nazi dictatorship could build the nuclear fission bomb, especially as they had closed all the uranium mines. They, especially Leo Szilard, prevailed upon Einstein to write a letter to US President Roosevelt underlying the great danger and urging the US to hurry up with the first nuclear device, before Germany did. The Japanese attack on Pearl Harbour which resulted in the US formally entering the Second World War as an ally of Britton gave further impetus to the work. The fissionable isotope, which was present in a quantity of less than a per cent in natural uranium, had to be isolated. This was done by converting Uranium into a gas, Uranium hexafluoride, which would make the lighter isotope compound to diffuse faster and after several such stages, its concentration would be enriched. Again, it was calculated that several kilograms of the uranium isotope was required for the chain reaction to be sustained, the so called critical mass leading to the explosion. In the “Little Boy” design, for example, the smaller piece was fired into a larger chunk of uranium so that the combined mass exceeded the critical mass and exploded at the planned height above ground. The Nagasaki bomb used plutonium (an unstable element formed when the uranium heavier isotope is bombarded with neutrons) which is also a fissionable element. The plutonium bomb is more compact, weighing less.<br /><br />By 1943, General Grooves as new in-charge of the “Manhattan Project” brought together all scientists in one place and helped to organise all the different departments involved; physics, chemistry, metallurgy, engineers, experimenters, weapon experts etc. <br /><br />Oppenheimer was put in charge. Within two-and-a-half years, they delivered the nuclear weapons. General Grooves also oversaw the vast engineering project to build plants for refining uranium and its derivative plutonium.<br /><br />Two of these plants at Oak Ridge employed 13,000 people. The Calutron, to separate U-235, had a huge electromagnet which needed more copper than was available in the US and the Treasury lent 6,000 tonnes of silver bullion. Simultaneous with the development of the atomic bomb was the development of the B-29 bomber, a parallel technical achievement. It was so complex that many aircraft companies and other industries were needed to manufacture it. It called for industrial cooperation on unprecedented scales. <br /><br />The first B-29 was flown in September 1942 and in about two years, several hundreds were produced. Today, the nuclear powers have 10,000 warheads, ICBMs and ABMs etc. and 40 minutes is all it takes to make the flight to any part of the world -- great potential for an Armageddon.</p>
