|
|
|
New Strategy - Wargames at Discount Prices
100+ Computer and Board games all with free shipping.
|
|
|
| |
|
|
| |
| |
|
|
|
|
|
|
Subject:
So Iran just pursues peaceful nuclear energy?
Hamilcar
11/5/2009 10:18:42 PM
|
link
Quote:
Iran tested advanced nuclear warhead design ? secret report
Exclusive: Watchdog fears Tehran has key component to put bombs in missiles.
The UN's nuclear watchdog has asked Iran to explain evidence suggesting that Iranian scientists have experimented with an advanced nuclear warhead design, the Guardian has learned.
The very existence of the technology, known as a "two-point implosion" device, is officially secret in both the US and Britain, but according to previously unpublished documentation in a dossier compiled by the International Atomic Energy Agency (IAEA), Iranian scientists may have tested high-explosive components of the design. The development was today described by nuclear experts as "breathtaking" and has added urgency to the effort to find a diplomatic solution to the Iranian nuclear crisis.
The sophisticated technology, once mastered, allows for the production of smaller and simpler warheads than older models. It reduces the diameter of a warhead and makes it easier to put a nuclear warhead on a missile.
Documentation referring to experiments testing a two-point detonation design are part of the evidence of nuclear weaponisation gathered by the IAEA and presented to Iran for its response.
The dossier, titled "Possible Military Dimensions of Iran's Nuclear Program", is drawn in part from reports submitted to it by western intelligence agencies.
The agency has in the past treated such reports with scepticism, particularly after the Iraq war. But its director general, Mohamed ElBaradei, has said the evidence of Iranian weaponisation "appears to have been derived from multiple sources over different periods of time, appears to be generally consistent, and is sufficiently comprehensive and detailed that it needs to be addressed by Iran".
Extracts from the dossier have been published previously, but it was not previously known that it included documentation on such an advanced warhead. "It is breathtaking that Iran could be working on this sort of material," said a European government adviser on nuclear issues.
James Acton, a British nuclear weapons expert at the Carnegie Endowment for International Peace, said: "It's remarkable that, before perfecting step one, they are going straight to step four or five ... To start with more sophisticated designs speaks of level of technical ambition that is surprising."
Another western specialist with extensive knowledge of the Iranian programme said: "It raises the question of who supplied this to them. Did AQ Khan [a Pakistani scientist who confessed in 2004 to running a nuclear smuggling ring] have access to this, or is it another player?"
The revelation of the documents comes at a time of growing tension. Tehran has so far rejected a deal that would remove most of its enriched uranium stockpile for a year and replace it with nuclear fuel rods which would be much harder to turn into weapons. The Iranian government has also balked at negotiations, which were due to begin last week, over its continued enrichment of uranium, in defiance of UN security council resolutions.
There are fears in Washington and London that if no deal is reached to at least temporarily defuse tensions by the end of December, Israel could set in motion plans to take military action aimed at setting back the Iranian programme by force, with incalculable consequences for the Middle East.
Iran has rejected most of the IAEA material on weaponisation as forgeries, but has admitted carrying out tests on multiple high-explosive detonations synchronised to within a microsecond. Tehran has told the agency that there is a civilian application for such tests, but has so far not provided any evidence for them.
Western weapons experts say there are no such civilian applications, but the use of co-ordinated detonations in nuclear warheads is well known. They compress the fissile core, or pit, of the warhead until it reaches critical mass.
A US national intelligence estimate two years ago said that Iran had explored nuclear warhead design for several years but had probably stopped in 2003. British, French and German officials have said they believe weaponisation continued after that date and may still be continuing.
In September, a German court found a German-Iranian businessman, Mohsen Vanaki, guilty of brokering the sale of dual-use equipment with possible applications in developing nuclear weapons. The equipment included specialised high-speed cameras, of the sort used to develop implosion devices, as well as radiation detectors. According to a report by the Institute for Science and International Security, the German foreign intelligence service, the Bundesnachrichtendienst, testified at the trial that there was evidence that Iran's weapons development was continuing.
The IAEA is seeking to find out what the scientists and the institutions involved in the experiments are doing now, but has so far not been given a response. The agency's repeated requests to interview Mohsen Fakhrizadeh, whose name features heavily in the IAEA's documentation and who is widely seen as the father of the Iranian nuclear programme, have been turned down.
The agency has also asked Iran to explain evidence that a Russian weapons expert helped Iranian technicians to master synchronised high-explosive detonations.
The first implosion devices, like the "Fat Man" bomb dropped on Nagasaki on 9 August 1945, used 32 high-explosive hexagons and pentagons arrayed around a plutonium core like the panels of a football. The IAEA has a five-page document describing experimentation on such a hemispherical array of explosives.
According to a diplomat familiar with the IAEA documentation, the evidence also points to experiments with a two-point detonation system that represents "a more elegant solution" to the challenges of making a nuclear warhead, but it is much harder to achieve. It is used in conjunction with a non-spherical pit, in the shape of a rugby ball, or explosives in that shape wrapped around a spherical pit, and it works by compressing the pit from both ends.The IAEA has expressed "serious concern" about Iran's failure to give an account of the research its scientists have carried out.
Descriptions of "two-point implosion" warheads designs have occasionally appeared in the public domain (there are extensive descriptions on Wikipedia) and they were first developed by US scientists in the 1950s, but it remains an offence for American officials or even non-governmental nuclear experts with security clearance to discuss them.
Unquote.
link
Quote:
Implosion-Device
Because of the short time interval between spontaneous neutron emissions (and, therefore, the large number of background neutrons) found in plutonium because of the decay by spontaneous fission of the isotope Pu-240, Manhattan Project scientists devised the implosion method of assembly in which high explosives are arranged to form an imploding shock wave which compresses the fissile material to supercriticality.
The core of fissile material that is formed into a super-critical mass by chemical high explosives (HE) or propellants. When the high explosive is detonated, an inwardly directed implosion wave is produced. This wave compresses the sphere of fissionable material. The decrease in surface to volume ratio of this compressed mass plus its increased density is then such as to make the mass supercritical. The HE is exploded by detonators timed electronically by a fuzing system, which may use altitude sensors or other means of control.
The nuclear chain-reaction is normally started by an initiator that injects a burst of neutrons into the fissile core at an appropriate moment. The timing of the initiation of the chain reaction is important and must be carefully designed for the weapon to have a predictable yield. A neutron generator emits a burst of neutrons to initiate the chain reaction at the proper moment ?- near the point of maximum compression in an implosion design or of full assembly in the gun-barrel design.
A surrounding tamper may help keep the nuclear material assembled for a longer time before it blows itself apart, thus increasing the yield. The tamper often doubles as a neutron reflector.
A thin beryllium reflector (thickness no more than the core radius) can reduce the total mass of the system, although it increases its overall diameter. For beryllium thicknesses of a few centimeters, the radius of a plutonium core is reduced by 40-60% of the reflector thickness. The critical mass for alpha-phase plutonium is 10.5 kg, and an additional 20-30% of mass is needed to make a significant explosion. A thin beryllium reflector can reduce this by a couple of kilograms.
Implosion systems can be built using either Pu-239 or U-235 but the gun assembly only works for uranium. Implosion weapons are more difficult to build than gun weapons, but they are also more efficient, requiring less SNM and producing larger yields. Iraq attempted to build an implosion bomb using U-235. In contrast, North Korea chose to use 239 Pu produced in a nuclear reactor.
Two-Point Detonation Linear Implosion
The two ends of a cylinder, or an ovoid, could be driven toward each other to create a high-density sphere. This two-point detonation greatly reduced the diameter and the weight of the primary.
A linear implosion allows for a low density, elongated non-spherical (football shaped) mass to be compressed into a supercritical configuration without using symmetric implosion designs. This assembly is accomplished by embedding an elliptical shaped mass in a cylinder of explosive. The explosive is detonated on both ends, and an inert wave shaping device is required in front of the detonation points. Extensive experimentation was needed to create a workable form, but this design enables the use of Plutonium as well as Uranium.
Initial Developments
In the first months of operations at Los Alamos in the spring of 1943, Oppenheimer and others believed that the first atomic bomb would be a gun that would shoot one piece of uranium or plutonium at a second piece of identical material. When the two pieces came together, a nuclear explosion would take place. From April 1943 until mid-summer 1944, almost all work at Los Alamos centered on designing and building such a gun. Experiments directed by future Nobel Prize winner Emilio Segre, however, demonstrated that plutonium could not be used in a gun. Impurities in the metal, which could not be removed, would cause a fizzle. It seemed, for a short time, that plutonium could not be used to make an atomic bomb. Because of serious problems in producing uranium, the plutonium problem put the entire atomic bomb program at risk.
The technical solution to this problem lay in the use of high explosives. Seth Neddermeyer proposed using the supersonic shock waves produced by high explosives to crush, or implode, a ball of plutonium to a supercritical state. If a ball of plutonium could be imploded symmetrically to a supercritical state, a nuclear explosion would follow. Seeing the technical merit of this approach, Oppenheimer reorganized the Los Alamos Laboratory in the summer of 1944 to concentrate work in this area. However, since this possible solution was new and untried, a test of such a gadget would be necessary.
In the late summer of 1943, experimental work at Los Alamos was focused on the designs for two gun-type atomic weapons. One would fire a uranium "bullet" into a uranium "target," while the other would use plutonium bullets and targets and, to overcome problems that might be caused by impurities in plutonium, would fire the bullet at a higher velocity.
The use of a gun to assemble nuclear explosives had been proposed as early as June 1942, and although it required considerable study of the nuclear properties of uranium-235 and plutonium in the shapes they would be cast in for use as bullets and targets, it seemed the most straightforward way to proceed.
It had also occurred to Richard Tolman, a professor of physics at the California Institute of Technology and vice-chairman of the National Defense Research Committee, that fissionable material might be assembled by detonating a high explosive around a hollow sphere and crushing it into a critical mass. Because of the difficulty of implementing this idea, however, few paid much attention to it. Robert Serber, a University of California physics professor, mentioned it in his indoctrination lectures at Los Alamos in April 1943 as one of "various other shooting arrangements" that had been suggested "but as yet not carefully analyzed."
Upon hearing Serber's lectures, Seth Neddermeyer, another professor of physics from Cal Tech, seized upon the idea enthusiastically. He recognized that blowing a sphere of uranium-235 or plutonium together in this matter would assemble these materials more rapidly than a gun could and proposed that it be explored. Oppenheimer agreed to a small program, which was set up on South Mesa.
The Ordnance Engineering Group (E-5) under Neddermeyer's direction, pursued experiments there and in Pennsylvania, at the Bruceton Explosives Research Laboratory of the NDRC. At Bruceton, "implosion charges" were fabricated for them by George Kistiakowsky of Harvard University, who was head of the project. Neddermeyer and Edwin M. McMillan, a University of California physicist who traveled there with him, were impressed that when a shell of explosives surrounding an iron pipe was set off, it closed the pipe. They returned to Los Alamos to repeat the experiment, varying the explosives, the pipe size and the arrangements, and studying the remains. A small plant was built at Anchor Ranch to cast the high explosives used in these experiments.
In September 1943, Oppenheimer asked John von Neumann, a Princeton mathematician who had been working on shaped charges, fluid dynamics and the computation of ballistic trajectories as a consultant to the Army's Aberdeen Proving Ground in Maryland, to look into the theoretical problems faced at Los Alamos.
Von Neumann agreed to spend some time as a consultant, working primarily in his office at the National Academy of Sciences in Washington, D.C., but with an occasional visit to Los Alamos. His first, in September, acquainted him with the implosion program. He suggested that shaped charges would produce an appropriate spherical detonation wave and pointed out that the method was not only likely to be faster than the gun, but that it would produce higher pressures and reduce the amount of active material required, making the bomb more efficient.
The Laboratory was galvanized by von Neumann's insight. Theorist Edward Teller scolded Charles Critchfield, who had been working on the project, for overlooking the greater efficiency to be expected from implosion, and Manhattan Engineer District Commander Leslie Groves chided Navy Capt. William Parsons for focusing on the "safer" gun method.
Teller advocated that the Laboratory should devote major effort to its development. In 1944 he was given the responsibility for all theoretical work on this problem. Teller made two important contributions. He was the first to suggest that the implosion would compress the fissile material to higher than normal density inside the bomb. Furthermore he calculated, with others, the equation of state of highly compressed materials, which might be expected to result from a successful implosion. However, he declined to take charge of the group which would perform the detailed calculations of the implosion.
Kistiakowsky was persuaded to come to Los Alamos to head a new program to develop the high explosives. A diagnostic program, involving X-ray and photographic techniques as well as the "terminal observations" Neddermeyer had employed, was begun.
New ideas for diagnosing an imploding system, including the use of a betatron electron accelerator, magnetic fields, electric pins and natural sources of radioactivity to produce signals that would indicate the rate of collapse inside the sphere, were subsequently introduced.
Calculations showed that an inward-moving spherical shock wave would be disrupted by the interference of detonation waves from the high-explosive segments and by instabilities arising as the tamper material was pushed into the heavier nuclear core by the implosion. This led to a fuller understanding of the behavior of a symmetric implosion and greater doubt that it could be achieved. What was needed was an explosive lens to convert the detonation wave to a spherically convergent form.
Under Kistiakowsky's direction, a new site, Sawmill, off S-Site, was constructed between December 1943 and May 1944. James Tuck, a member of the British Mission at Los Alamos, had worked in England on the use of combinations of different explosives to "focus" detonation waves and headed a group to develop an explosive lens for the implosion gadget. After von Neumann suggested a workable design for the lens, Lt. Cmdr. Norris Bradbury, a Stanford physics professor assigned to the Dahlgren Proving Ground of the U.S. Navy Ordnance Bureau, was recruited in June 1944 to solve the problem of casting the high explosives for the design.
Even if the appropriate explosive lenses could be produced, they would have to be set off simultaneously to create a symmetrical implosion. After experiments with a variety of Primacord and electric detonators, Luis Alvarez, a University of California Radiation Laboratory physicist who had come to the Laboratory from radar work at the Massachusetts Institute of Technology, and his student, Lawrence Johnson, devised such a system in May 1944.
Although progress had been made, Kistiakowsky was skeptical about the success of the program in the spring of 1944. He predicted that by October they might be able to "recommend a design of the gadget that will have a finite chance of properly functioning," but added that in "November or December the test of the gadget failed. Project staff resumes frantic work, Kistiakowsky goes nuts and is locked up." The consequences of such a failure, however, would be devastating to the program.
In the summer of 1944, Emilio Segre's group at Pajarito Site found that plutonium from nuclear reactors had an isotopic impurity, plutonium-240, that prohibited its use in a gun-type assembly. Since all of the plutonium that would be used in the atomic bomb would be produced in reactors, this meant that the vast investment in the Hanford production reactors built by DuPont would go down the drain unless implosion could be perfected.
The Laboratory was reorganized to accomplish this. New division, G for gadget and X for explosives, were set up to develop the nuclear and high-explosive components of the implosion device. The Laboratory's Governing Board was divided into administrative and technical boards to manage the growing effort. Even then, the Technical Board's tasks were increasingly assumed by lower-level interdivisional committees and conferences that coordinated the effort required.
The reorganization of the Laboratory was accompanied by a vast expansion in personnel, as no stone was left unturned in the search for a suitable design and the development of suitable components for the gadget. From roughly 1,100 personnel, Laboratory employment grew within a year to more than 2,500. Implosion meant an explosion of the Laboratory population.
It was not clear, however, that the much more complicated implosion device would work. Before it could be used in combat, a test would be required.
Unquote:
Hello? |
| |
|
|
|
|
|
