An inquiry has exonerated nuclear engineer Rusi Taleyarkhan of misconduct with respect to allegations made internally at Purdue University in West Lafayette, Indiana, officials announced last week. But the announcement may raise more questions than it answers: researchers in the field have criticized the university for failing to say whether the inquiry considered their concerns that the work may be fraudulent.

Rusi Taleyarkhan's controversial bubble-fusion findings have been upheld by his university. Credit: L. FREENY/US DEPT ENERGY

Taleyarkhan claims to be able to produce fusion by collapsing bubbles in deuterated liquids. His work promised to improve prospects for developing a clean source of energy, but independent scientists have not been able to replicate the result. The work had been subject to several internal allegations of misconduct, including the fact that Taleyarkhan cited a paper by his student and postdoc as “independent” confirmation of his findings1,2.

Purdue announced on 7 February that “the committee determined that the evidence does not support the allegations of research misconduct and that no further investigation of the allegations is warranted”. It has refused to specify the content of the allegations that it considered, except to say that they were “internal”.

Institutional proceedings involving Taleyarkhan began in March 2006, after concerns about his work were reported by Nature3. Purdue's provost, Sally Mason, responded by saying that the university would undertake an objective review. In June 2006, the university said that the review was complete, but declined to make its findings public. Last week's announcement referred to the findings of a second internal inquiry subsequently appointed by Purdue's dean of engineering, Leah Jamieson.

Taleyarkhan has told several news outlets that he feels “vindicated”. But critics have questioned the validity of Purdue's proceedings, and in particular, the apparent decision to limit its inquiry to internal allegations, yet possibly ignoring the concerns, including fraud, communicated by external researchers in the field.

“They apparently narrowly focused the charge and avoided the question of whether the research was doctored,” says Ken Suslick, a chemist at the University of Illinois at Urbana-Champaign who has been attempting to replicate Taleyarkhan's claims. Suslick is one of several researchers worried that Taleyarkhan's work may be fraudulent, and he wrote to Purdue about his concerns in June 2006. These include the apparent duplication of data between reports of supposedly independent experiments4 (first raised by Nature), and a report5 that the spectrum of neutrons that Taleyarkhan claims to have detected from bubble fusion exactly matches that of a standard radioactive source called californium. Taleyarkhan has since replied that when he measures neutrons emitted by californium in his lab, he finds something quite unlike what he sees from his fusion experiments6. But a recent preprint points out that Taleyarkhan omitted some of the original spectral data in his reply, and that the full data set still looks like californium7.

The university never responded to Suslick's concerns. Peter Dunn, Purdue's associate vice-president for research, told Nature that he believes the university followed its procedures. He declined to comment on why he never replied to Suslick, or on whether evidence related to Suslick's concerns was forwarded to either inquiry. Purdue hasn't revealed the identities of the members of the second inquiry panel, but Dale Compton, a professor of industrial engineering at Purdue and a member of the first panel, says he has no recollection of being asked to consider the questions about Taleyarkhan's data.

Purdue's finding is as mysterious as bubble fusion itself.

Lefteri Tsoukalas, who asked Purdue to investigate Taleyarkhan in February 2006, has called the announcement “an outrage”. Tsoukalas was head of Purdue's nuclear-engineering school until he resigned in October 2006 in protest at the way the university was handling the concerns. He notes that the usual procedure for handling allegations of scientific misconduct is to hold a preliminary inquiry, then either proceed with an investigation or close the matter. That did not happen in this case; instead, the university ran a second preliminary inquiry. Apart from Tsoukalas, calls by Nature have failed to locate anyone who raised concerns about Taleyarkhan's work who was interviewed during either inquiry. “Purdue's finding is as mysterious as bubble fusion itself,” says Tsoukalas.

Taleyarkhan, however, strongly defends the university's process. “Purdue University in my opinion and experience has conducted an extremely thorough review and with my full cooperation,” he told Nature. “Allegations made in the press have been known to Purdue, and the administration's thoughtful conclusions have been well-articulated in their statements.”

Beyond the issue of misconduct, Purdue also makes clear that it endorses the scientific value of Taleyarkhan's work. In last week's press release, vice-president for university relations Joe Bennett stated: “Professor Taleyarkhan is engaged in very promising, significant research, and we hope he will now be able to give his full attention to this important work.”

Seth Putterman of the University of California, Los Angeles, who has also been trying to replicate bubble fusion, thinks that Taleyarkhan's work is invalid. “Purdue's defence of Taleyarkhan's approach to scientific research taints their reputation,” he says. “If Purdue were interested in maintaining their credibility they should have appointed external members to their panel.” Mason, who is ultimately responsible for academic affairs at Purdue, did not respond to Nature's requests for comment.

Purdue's announcement appeared on the same day as Suslick, Putterman and others reported their attempt to replicate Taleyarkhan's claims in an experiment built to his specifications8. They did not find any evidence that fusion was occurring.

Suslick, Putterman and Taleyarkhan had received funding from the US Department of Defense's Advanced Research Projects Agency (DARPA) for a project to test Taleyarkhan's original claims. Taleyarkhan has spent around US$200,000 of this money on his bubble-fusion experiments. A spokeswoman for DARPA, Jan Walker, told Nature that although Purdue has not formally notified the agency of the inquiry or its results: “We are aware that an inquiry has taken place and are currently reviewing what, if any, action is required on our part.”