The Fat Man and the Little Boy

By P. Lal

HE finalised the deal, within five minutes, on the telephone, signed a cheque for $ 5 million by way of an advance payment, and despatched it to Edwin Jones, the President of J.A. Jones Construction Company. The contract finalised was for the erection of a huge power plant which was to supply electricity, equivalent to that required by a large city like Boston, to the gaseous diffusion plant coming up at Oak Ridge, Tennessee, USA, to separate the lighter uranium from its heavier counterpart. This was part of the secret Manhattan Project, set up under a decree signed by President Roosevelt himself, which was to lead to the production of a fission bomb, and which was eventually to cost the Americans more than $ 2 billion.

And the person who had signed the cheque was Brigadier-General Leslie R, Groves, a military engineer, who had taken charge of the most secret military project on September 23, 1942, under a warrant of appointment authorised by the President. Groves was, indeed, signing such cheques for hundreds of millions of dollars nearly every month. Until 1944, however, his own monthly emolument was no more than $ 663.40, which, towards the end of the war, rose to $ 828.67 a month. And yet, there was no allegation ever of kickbacks or commissions or misappropriation, against him or any of his subordinates!

Earlier, the Germans had split the atom, albeit on a laboratory scale. It had been accomplished by Otto Hahn and his colleagues, Liese Meitner and O. R. Frisch, In January, 1939, at Kaiser Wilhelm Institute, Berlin. It was nine months before Hitler’s invasion of Poland. He was now desperate to produce the bomb.

Albert Einstein, impelled by three Hungarian refugee physicists —Leo Szilard, Eugene Wigner and Edward Teller — wrote to Roosevelt to take note of the development, lest the Fuehrer ruled the world. The letter was delivered at the White House on October 11, 1939 by Alexander Sachs, a New York financier, and a friend of, and economic adviser to the President. Sachs also briefed the President who immediately authorised governmental financial assistance for research and development, and also constituted a committee to monitor the progress.

The progress was, however, dishearteningly slow. The problem was how to produce sufficient quantities of lighter uranium (U-235) for making the bomb. Natural uranium contained no more than one part of U-235 in 140 parts. And uranium was one of the rarest metals known. It was named after the planet Uranus, which was once thought to be the outer most planet in the solar system, and uranium was then the last metal in the periodic table, the heaviest one known.

It was extremely difficult to extract and purify uranium from its ore Pitchblende, till then known to be occurring only in Central Europe and the Great Bear Lake region of northern Canada. No wonder, therefore, that before 1940, no more than a few pounds of it alone existed even in the impure state, that is the natural uranium containing its isotopes U-235, U-238 and U-233. And nobody till then knew as to what was the critical mass required of U-235 to make it into a bomb. (It became known only much later towards the end of 1944 that it was close to 2 kg or about 5 pounds). It was, however, estimated that thousands of tonnes of natural uranium were required to separate requisite amounts of U-235. Thousands of tonnes, when the world knew of only a few pounds!

Groves was a military man but he had to deal with scientists Enrico Fermi, Arthur H. Compton, Ernest O. Lawrence, J. Robert Oppenheimer and Harold Urey, all Nobel Laureates, and thousands of others, eminent and knowledgable in their own fields, and above all, deeply patriotic, and dedicated to the project. Groves himself, however, did not know much of science, and while negotiating with the company executives of Eastman Kodak for operating the yet-to-be established electromagnetic plant at Oak Ridge for the separation of uranium isotope U-235, he repeatedly mispronounced "isotope" as "isotrope".

Electromagnetic process was one of the three methods which had been selected by the Manhattan Project for separating the lighter uranium, the others being the gaseous diffusion and the thermal diffusion. And the process required the erection of huge electromagnets, 250 feet long, known as Calutrons. They, in turn, required coils of copper, weighing 6000 tonnes. And it was virtually impossible to get that much copper with the war-time demand and the consequent scarcity of the metal. So, Lieutenant Colonel Nichols, the junior colleague of Groves, walked into the Treasury Department office, and asked its under secretary to sanction a permit for 6000 tonnes of silver, for use in a top secret military project. And the same was sanctioned, for the Treasury had enough silver. Earlier, Ernest O. Lawrence working on the electromagnetic process had informed Nichols that if copper was not available, silver would do as well!

Besides the uranium-separation route, the graphite-pile method for producing plutonium, another fissionable material fit for making into a bomb, was also being tried, inside the Stagg Field rackets court at the University of Chicago, under Enrico Fermi. The risk involved in making the graphite-pile go critical within the university campus was taken deliberately, for the site selected earlier in Argonne National Forest, 20 miles from Chicago, could not be readied in time (by October, 1942), due to labour trouble. Fermi, however, doing last minute calculations on his small slide-rule held in his hands, watched by about 20 people, made the graphite-pile go critical with controlled self-sustaining chain reaction at 3.20 p.m., December 2, 1942 and thus paved the way not only for building nuclear reactors for generating power but also for obtaining plutonium as a by-product of the chain-reaction. The work on the pile had started on November 7, the same year, and it had taken 50 tonnes of uranium and 500 tonnes of graphite-bricks arranged into 51 layers, to make the pile go critical. The task was accomplished within 25 days!

The works were spread over several places. At Oak Ridge, the gaseous diffusion plant, the thermal diffusion plant, the graphite-pile and the electromagnetic separation; at Hanford near the town of Richland, Washington, the production of plutonium; and at Los Alamos, the design and assembly of the bomb under J. Robert Oppenheimer. The selection of the latter, however, had been a difficult decision for General Groves.

The FBI files showed that Oppenheimer had had Leftist leanings in the past. During the advanced stage of the production of the bomb, Oppenheimer came again under suspicion, as he had initially refused to divulge the name of an academic figure who had been used as an intermediary by Soviet agents to ferret out information on the bomb project. He was, however, retained at the bomb-lab., after Groves had been satisfied that he himself would not pose a security risk.

The processes had to start from a scratch and almost from a blank. Staggering engineering problems loomed large, including the shielding of men from dangerous radiation who worked in such plants. There was no time for setting up pilot-plants" theoretical predictions and results in laboratories had to be transformed to large-scale productions almost at a single stride.

Thus, the power plant of Oak Ridge was commissioned within a record time of nine months, beating the deadline of March 17, 1944, set by Groves, by 17 days. A labour force of 5600 had worked, day and night, to accomplish the task. The gas diffusion plant employed a work force of 20,000 men. The cleanliness standards for the coming up plant were extremely rigorous. A thumb-print in the whole plant, a U-shaped four-storey building covering 44 cares of ground with each side of the gigantic U, half a mile long, would represent intolerable contamination. At the Nash building, where the barrier for the gas-diffusion was being developed, the women employees engaged in the processing, were refrained from working during their menstrual cycle, as it was believed that during the "periods", their hands perspired more, which would lead to organic contamination of the barriers.

At Hanford near Richland, 600 square miles of land area had to be acquired for Du Pont for setting up the plutonium plant, where 45,000 construction workers worked at the site at a time. Groves also issued instruction to ensure the health of the salmon in the nearly Columbia river, for the water of the river used in the plutonium plant would have been contaminated by radiation. As a child, he had learnt that salmon, a migratory fish born in fresh water, spends two to four years in the ocean before returning to the place of its birth to spawn and die.

Security-measures were extremely tight at the plants and work places. Important scientists had assumed names. Thus, at Los Alamos, J. Robert Oppenheimer was known as "Mr Bradley" Arther H. Compton was "Mr Holly" at Oak Ridge and "Mr Comas" at Hanford. Enrico Fermi was "Dr Farmer", and Eugene Wigner was "Dr Wagner" at Hanford. All mention of the quantity of all types of supplies was forbidden, including the amount of ice-cream or beer consumed! The mail was censored and had to be addressed to the numbered post box. Houses of top men and scientists were guarded by the military police continuously. Their wives and children had to show "passes" before being allowed to re-enter their homes.

Finally, the plutonium weapon, nicknamed the "Fat Man" was ready. The technique adopted to bring the hollow sphere of plutonium into critical contact was ingenious, and was described as "implosion", the opposite of explosion. The explosives strapped around the sub-critical plutonium sphere, when detonated by a charge, would push the plutonium inward, and would make it achieve criticality within a millionth of a second.

The "Fat Man" was taken to Alamogordo, 210 miles south of Los Alamos, on July 12, 1945, for being tested in the desert area called Jornada del Muerto (Journey of Death) at Trinity in southern New Mexico. It was mounted on a specially constructed steel tower, 100 feet tall.

Three observation dugouts were set up in the north, west and south, each over five miles away from the tower. Base camp, at 10 miles, had Oppenheimer, Fermi, Groves and others, lying face down on the ground with their feet towards the tower, as the zero hour, 5.30 a.m., July 16,1945, approached. And then, as the last command was given, through radio, from the Dugout-S, "the fierce light that followed almost blinding , in spite of the closed eyes of the camp observers, was impossible to describe. In a brief moment, the light within 20 miles was equal to several suns at mid-day". It was seen in places as far away as 180 miles.

"It was unprecedented, magnificent, beautiful, stupendous and terrifying. No man-made phenomenon of such tremendous power had ever occurred before.... It (the light) was golden, purple, violet, grey and blue. It lighted every peak and ridge of the nearby mountain range with a clarity and beauty that cannot be described but must be seen to be imagined. It was that beauty that great poets dream about but describe most poorly and inadequately. Thirty seconds after the explosion, came, first the air blast pressing hard against people and things, to be followed almost immediately by the strong, sustained, awesome roar which warned of dooms day.... ", said a military report to the Secretary of War.

Most of the steel tower got vaporised almost instantaneously. The yield of the bomb was equivalent to 10,000 tonnes of TNT.

Meanwhile, enough uranium-235 had also been produced and shipped to Los Alamos, but enough only to make one bomb. There was, therefore, no test explosion conducted. It was nick-named "Little Boy". It had to achieve critically by the "gun-method" and not by implosion. The barrel of a gun had to fire a uranium projectile into a target mass of the metal, and both, when merged, would become critical to cause the fission.

They did not lose a single day since then. Enola Gay, the B-29 bomber, with the "Little-Boy" tucked inside, took off from Tinian island in the Pacific on August 6, 1945 at 0245 hours. Captain Parsons, the weaponeer in the Bomber, dropped the "Little Boy" over Hiroshima, Japan, at 0915 hours (Tinian time) from a height of 32, 700 feet.

Three days later, on August 9, another Bomber dropped a plutonium bomb on the city of Nagasaki. The World War II had come to an end.