VIENNA — Iranian scientists have run computer simulations for a nuclear weapon that would produce more than triple the explosive force of the World War II bomb that destroyed Hiroshima, according to a diagram obtained by the Associated Press.
The diagram was leaked by officials from a country critical of Iran’s atomic program to bolster their arguments that Iran’s nuclear program must be halted before it produces a weapon. The officials provided the diagram only on condition that they and their country not be named.
The International Atomic Energy Agency — the Vienna-based UN nuclear watchdog — reported last year that it had obtained diagrams indicating that Iran was calculating the ‘‘nuclear explosive yield’’ of potential weapons. A senior diplomat who is considered neutral on the issue confirmed that the graph obtained by the AP was indeed one of those cited by the IAEA in that report. He spoke only on condition of anonymity because he was not authorized to discuss the issue.
The IAEA report mentioning the diagrams last year did not give details of what they showed. But the diagram seen by the AP shows a bell curve — with variables of time in microseconds, and power and energy both in kilotons — the traditional measurement of the energy output, and hence the destructive power of nuclear weapons. The curve peaks at just above 50 kilotons at around 2 microseconds, reflecting the full force of the weapon being modeled.
The bomb the United States dropped on Hiroshima, Japan, during World War II, in comparison, had a force of about 15 kilotons. Modern nuclear weapons have yields hundreds of times higher than that.
The diagram has a caption in Farsi: ‘‘Changes in output and in energy released as a function of time through power pulse.’’ The number ‘‘5’’ is part of the title, suggesting it is part of a series.
David Albright, whose Institute for Science and International Security is used by the US government as a go-to source on Iran’s nuclear program, said the diagram looks genuine but seems to be designed more ‘‘to understand the process’’ than as part of a blueprint for an actual weapon in the making.
‘‘The yield is too big,’’ Albright said, noting that North Korea’s first tests of a nuclear weapon were a few kilotons. Because the graph appears to be only one in a series, others might show lower yields, closer to what a test explosion might produce, he said.
The senior diplomat said the diagram was part of a series of Iranian computer-generated models provided to the IAEA by the intelligences services of member nations for use in its investigations of suspicions that Iran is trying to produce a nuclear weapon.
Iran denies any interest in such a weapon and has accused the United States and Israel of fabricating evidence that suggests it is trying to build a bomb.
Asked about the project, Iran’s chief IAEA delegate, Ali Asghar Soltanieh, said he had not heard of it. IAEA spokeswoman Gill Tudor said the agency had no comment.
Iran has refused to halt uranium enrichment, despite offers of reactor fuel from abroad, saying it is producing nuclear fuel for civilian uses. It has refused for years to cooperate with the UN nuclear agency’s efforts to investigate its program.
Iran’s critics fear it could use the enriched uranium for military purposes. Such concerns grew this month when the IAEA said Iran is poised to double its output of more highly enriched uranium at its fortified underground facility, a development that could put Tehran within months of being able to make the core of a nuclear warhead.
In reporting on the existence of the diagrams last year, the IAEA said it had obtained them from two member nations that it did not identify. Other diplomats have said that Israel and the United States, the countries most concerned about Iran’s nuclear program, have supplied the bulk of intelligence being used by the IAEA in its investigation.
‘‘The application of such studies to anything other than a nuclear explosive is unclear to the agency,’’ the IAEA said at the time.