In April 1944, Emilio Segrè received the first sample of reactor-bred plutonium from the X-10 reactor and discovered that reactor-grade plutonium was not as pure as cyclotron-produced plutonium by a significant degree.

In April, 1944 tests on the first plutonium-239 produced with neutrons in a nuclear reactor rather than a cyclotron, revealed an unexpected problem: the reactor-bred plutonium contained five times more plutonium-240 ( a result of reactor neutron bombardment ), an unwanted isotope that spontaneously decayed and produced neutrons that promised to cause a pre-detonation, without sufficiently quick critical mass assembly.

* April 5: At Los Alamos, Emilio Segrè receives the first sample of reactor-bred plutonium from Oak Ridge, and within ten days discovers that the spontaneous fission rate is too high for use in a gun-type fission weapon.

Also, gallium metal easily alloys with many metals, and was used in small quantities as a plutonium-gallium alloy in the plutonium cores of the first and third nuclear bombs, to help stabilize the plutonium crystal structure.

They had been unable to find detailed maps of the area, which contained the Soviets ' first military plutonium production facility at Mayak, making knowledge of the area vital in the event of war with the Soviet Union.

Some former Soviet scientists said they were actually hampered by Fuchs's data, because Beria insisted that their first bomb (" Joe 1 ") should resemble the American plutonium bomb (" Fat Man ") as much as possible, even though the scientists had discovered a number of improvements and different designs for a more efficient weapon.

All of the elements with higher atomic numbers, however, have been first discovered in the laboratory, with neptunium, plutonium, americium, curium, berkelium and californium later also discovered in nature.

The first nuclear bomb used in war, Little Boy, relied on uranium fission, while the very first nuclear explosive ( The gadget ) and the bomb that destroyed Nagasaki ( Fat Man ) were plutonium bombs.

* July 16 – The Trinity Test, the first of an atomic bomb, using about six kilograms of plutonium, succeeds in unleashing an explosion equivalent to that of 19 kilotons of TNT.

The first Soviet bomb was more or less a deliberate copy of the Fat Man plutonium device.

Working under assumed names, in 1943 Enrico Fermi and his colleagues developed the X-10 Graphite Reactor, the world's first production nuclear reactor, to demonstrate the production of plutonium.

The historic B Reactor, the world's first plutonium production reactor, is visible in the distance.

Established in 1943 as part of the Manhattan Project in the town of Hanford in south-central Washington, the site was home to the B Reactor, the first full-scale plutonium production reactor in the world.

The B Reactor ( 105-B ) at Hanford was the first large-scale plutonium production reactor in the world.

The reactor went critical in late September and, after overcoming nuclear poisoning, produced its first plutonium on November 6, 1944.

This first batch of plutonium was refined in the 221-T plant from December 26, 1944, to February 2, 1945, and delivered to the Los Alamos laboratory in New Mexico on February 5, 1945.

The first large batch of plutonium was refined at Hanford in the " 221-T plant ", using the bismuth phosphate process, from December 26, 1944, to February 2, 1945.

Uranium irradiated in this reactor was used in North Korea's first plutonium separation experiments in 1975.

The young Colonel Matthias was so proud of his work the he accompanied the first plutonium produced at Hanford to Los Alamos.

It was only after the first Gulf War that the full extent of Iraq's nuclear programs, which had switched from a plutonium based weapon design to a highly enriched uranium design after the destruction of Osiraq, became known.

Theodore Alvin Hall ( October 20, 1925 – November 1, 1999 ) was an American physicist and an atomic spy for the Soviet Union, who, during his work on US efforts to develop the first and second atomic bombs during World War II ( the Manhattan Project ), gave a detailed description of the " Fat Man " plutonium bomb, and of several processes for purifying plutonium, to Soviet intelligence.

But her prettiness was what he had noticed first, and all the other things had come afterward: cruelty, meanness, self-will.

There was an artificial lake just out of sight in the first stand of trees, fed by a half dozen springs that popped out of the ground above the hillside orchard.

The first part of the road was steep, but it leveled off after the second bend and curled gradually into the valley.

No one was behind it, but in the rear wall of the office I noticed, for the first time, a door which had been left partially open.

The herd was watered and then thrown onto a broad grass flat which was to be the first night's bedground.

Once again, Tom Horn was the first and most likely suspect, and he was brought in for questioning immediately.

For Matilda, it was the first she had known in many a night.

Even the knowledge that she was losing another boy, as a mother always does when a marriage is made, did not prevent her from having the first carefree, dreamless sleep that she had known since they dropped down the canyon and into Bear Valley, way, way back there when they were crossing those other mountains.

Stevens was grunting over the last empty pocket when Russ abruptly rose and lunged toward Carmer's hat, which had tumbled half-a-dozen feet away when he first fell.

The Indian's arm whipped sidewise -- there was a flash of amber and froth, the crash of the bottle shattering against the side of the first car.

It was her first smile.

At first, I thought he was out of his head, talking wildly like this.

Hell, I gave him the first decent job he ever had, six, seven -- how many years ago was it, Rob ''??

Miss Langford ( her first name was Evelyn ) was an attractive girl.

School began in August, the hottest part of the year, and for the first few days Miss Langford was very lenient with the children, letting them play a lot and the new ones sort of get acquainted with one another.

It was just as well that the ignorant Dandy enjoyed himself to the hilt that first evening, for the room was to become his prison cell.

`` Bastards '', he would say, `` all I did was put a beat to that Vivaldi stuff, and the first chair clobbered me ''!!

In 1961 the first important legislative victory of the Kennedy Administration came when the principle of national responsibility for local economic distress won out over a `` state's-responsibility '' proposal -- provision was made for payment for unemployment relief by nation-wide taxation rather than by a levy only on those states afflicted with manpower surplus.

The first systematic thinking about this Pandora's box within Pandora's boxes was done four years ago by Fred Ikle, a frail, meek-mannered Swiss-born sociologist.

The smell at first was more surprising than unpleasant.

His collaboration with Washington, begun when he was the general's aide during the Revolution, was resumed when he entered the first Cabinet as Secretary of the Treasury.