When the Cold War abruptly ended in 1991, Vyacheslav Danilenko was a Soviet weapons scientist in need of a new line of work. At 57, he had three decades of experience inside a top-secret nuclear facility and one marketable skill: the ability to make objects blow up with nanosecond precision.

Danilenko struggled to become a businessman, traveling through Europe and even to the United States to promote an idea for using explosives to create synthetic diamonds. Finally, he turned to Iran, a country that could fully appreciate the bombmaker’s special mix of experience and talents.

Fifteen years later, the Russian scientist has emerged as a central character in the still-unfolding mystery that is Iran’s nuclear program. A report last week by the International Atomic Energy Agency highlighted the role of a “foreign expert” — identified by Western diplomats close to the U.N. nuclear agency as Danilenko — in Iran’s efforts to gain expertise in disciplines essential to building a nuclear warhead.

No bomb was built, the diplomats say. But help from foreign scientists such as Danilenko enabled Iran to leapfrog over technical hurdles that otherwise could have taken years to overcome, according to former and current U.N. officials, Western diplomats and weapons experts.

Such assistance also provided a trail of evidence that the IAEA’s investigators were later able to follow. Documents and other records — and, in the case of Danilenko, interviews — would offer a rare glimpse inside a highly secretive program hidden within Iranian universities and civilian institutions, the officials and experts said.

“It’s like being an astronomer studying a black hole: You detect the black hole’s presence by seeing what falls into it,” said Art Keller, a former CIA analyst who specialized in Iran. “With covert programs, you watch for the flow of raw material and outside expertise.”

The process is not infallible. Evidence is often ambiguous, as the same technology can sometimes have peaceful as well as military applications. In the case of Danilenko, the scientist’s synthetic-
diamonds business provided a plausible explanation for his extensive contacts with senior Iranian scientists over half a decade. Danilenko has consistently denied that he ever knowingly aided Iran’s nuclear program.

“I am not a father of Iran’s nuclear program,” he told a Russian journalist last week. E-mails sent to Danilenko seeking comment were not answered.

For U.N. investigators, however, the Russian’s influence was visible in the design and testing of an unusual, half-sphere-shaped detonator the Iranians perfected eight years ago, shortly after Danilenko left Iran for good.

Weapons experts say detonators of the type made by Iran have one known purpose: squeezing a lump of highly enriched uranium to trigger a nuclear chain reaction.

“It remains for Danilenko to explain his assistance to Iran,” said David Albright, a former U.N. inspector who has tracked the investigation of the Russian scientist over several years. “At the very least, Danilenko should have known exactly why the Iranians were interested in his research and expertise. The IAEA information suggests he has provided more than he has admitted.”

Special skills

Danilenko developed his rare expertise at an institution at the foot of the Ural Mountains in a place so secret that it was omitted from the Soviet Union’s official maps. Chelyabinsk-70 was one of the Soviet Union’s “closed cities,” and it was home to one of the country’s most sensitive nuclear installations, NII-1011, now known as the All-Russian Scientific Research Institute of Technical Physics.

The institute’s main mission was designing the Soviet Union’s nuclear weapons. In the 1950s and early 1960s, when Danilenko began work there, its scientists were preoccupied with miniaturizing nuclear weapons so they could readily fit inside missiles, conventional bombs and even artillery shells. In doing so, they faced a significant technical challenge: creating a small but highly precise detonator of conventional explosives that could send a powerful shock wave through a core of plutonium or enriched uranium at the center of the device.

This is where Danilenko’s special skills came in handy, said Albright, who co-wrote a report on Danilenko with his colleagues from the Institute for Science and International Security, a Washington-based nonprofit group specializing in the study of nuclear weapons programs.

Danilenko’s expertise in explosives and gas dynamics contributed to the design and testing of small, high-precision detonators that could produce a perfectly symmetrical shock wave needed to ensure a sustained nuclear chain reaction, the ISIS report said. A tiny lapse in timing would cause the fissile core to blow apart too soon.

Danilenko has publicly acknowledged the sensitive nature of his work at Chelyabinsk-70. In a book chapter cited by ISIS, he says that experiments he conducted were “highly classified; for security reasons, the results were initially contained only in secret reports.”

The research also led to a fortuitous discovery that would affect the course of Danilenko’s post-Soviet career. Russian scientists discovered that they could create synthetic diamonds by bombarding ordinary graphite with the same kinds of precision shock waves. The diamonds produced were tiny and irregular but perfect for industrial applications such as grinding and polishing.

When the Cold War ended, thousands of weapons scientists suddenly confronted a harsh choice: remain at the weapons institutes at drastically reduced wages or reinvent themselves for the post-Soviet, capitalist economy. For Danilenko, the choice was clear: His knowledge of explosively produced diamonds, called “ultra-dispersed diamonds” or “nanodiamonds,” was his ticket out of Chelyabinsk-70.

Danilenko moved to Ukraine, created a company, and searched for investors and partners throughout the West, including the United States. But he struggled as a businessman, and soon his European ventures were short of cash and at risk of collapsing.

In 1995, he decided to do what numerous other Russian weapons scientists before him had done: He contacted the Iranian Embassy to inquire about possible joint ventures, according to the ISIS report, which drew from IAEA documents and interviews.

When a reply came weeks later, it was from an Iranian scientist who was well positioned to understand Danilenko’s background and what he could provide. Seyed Abbas Shahmoradi was the head of Iran’s Physics Research Center, the institution that IAEA officials say was the command center for Iran’s clandestine nuclear research.

“As head of Iran’s secret nuclear sector involved in the development of nuclear weapons,” the ISIS report said, “Shahmoradi would have undoubtedly recognized Danilenko’s value.”

Secret work

Danilenko’s work in Iran initially centered on his diamond-making scheme. But over the course of a six-year relationship, U.N. investigators later concluded, he provided expertise that would help Iran achieve something of far greater value.

The IAEA’s report cites “strong indications” that the unnamed “foreign expert” assisted Iran in developing a high-precision detonator as well as a sophisticated instrument for analyzing the shape of the explosive pulse.

The IAEA verified “through three separate routes, including the expert himself,” the extensive cooperation with Iranian scientists from 1996 to 2002, the report states. While in the country ostensibly to share his techniques for nanodiamonds, the expert “also lectured on explosion physics and its applications,” the IAEA report said.

U.N. investigators would eventually match Danilenko’s published research on detonators with designs produced by Iranian scientists working for the Physics Research Center. In one striking example, a 1992 paper co-authored by Danilenko describes a fiber-optic instrument that measures precisely when a shock wave arrives along thousands of different points along the surface of a sphere. Iran conducted at least one major test of such an instrument in 2003, the year after Danilenko stopped his visits to Iran.

Such instruments have few, if any, applications outside nuclear warhead design, weapons experts say. Indeed, when confronted by the IAEA, Iranian nuclear officials were unable to produce an explanation for why such tests were needed. Iran has consistently denied having ambitions to build nuclear weapons.

“This type of system appears suitable for testing a sphere of conventional explosives designed to compress the fissile core of a nuclear warhead,” said Josh Pollack, a government consultant and contributor to the nonproliferation blog Arms Control Wonk.

IAEA officials eventually interviewed Danilenko after his return to Russia and sought his help in clarifying what the Iranians were seeking to do with the technology. His response then was similar to his explanation last week to a Russian journalist: His work was restricted to nanodiamonds, and he had no knowledge of Iran’s weapons ambitions. “I am not a nuclear physicist,” he told the Russian newspaper Kommersant.

In private conversations, however, the scientist allowed that he “could not exclude that his information was used for other purposes,” the ISIS report said. In that sense, the institute said, Danilenko’s experience is similar to that of numerous other former weapons scientists who ended up traveling abroad to work in a country with nuclear aspirations. Of the dozens of similar cases studied by the institute, each began with an offer of “more benign assistance that provided a plausible cover for their secret assistance.”

“Synthetic diamond production is unlikely to have been a priority” for Iran, ISIS said. “Although it has obvious value as a cover story.”