The product can be used as a neutron initiator: the component of a nuclear bomb that triggers an explosion.
The memo apparently details how some work on the trigger should be outsourced to universities, but other work is too secret and must be carried out by "trustworthy personnel" within the organisation allegedly carrying out Iran's secret nuclear weapons research.
Another document seen by the Times is said to be a memo from Mohsen Fakhrizadeh, naming him as the chairman of the Field for the Expansion of Deployment of Advance Technology (Fedat) - which the newspaper says is a cover for a secret nuclear weapons programme.
In his first public response to the report, Mr Ahmadinejad said the accusations were "fundamentally not true".
In an interview filmed on Friday with ABC News, but broadcast on Monday, he dismissed the documents, saying: "They are all a fabricated bunch of papers continuously being forged and disseminated by the American government."
When asked if there would "be no nuclear weapon in Iran, ever", Mr Ahmadinejad said his view was already known.
"You should say something only once. We have said once that we don't want a nuclear bomb. We don't accept it."
A senior adviser to US President Barack Obama, David Axelrod, said it was "nonsense" that the US had fabricated the documents.
"Nobody has any illusions about what the intent of the Iranian government is," he told ABC.
Iran is already subject to three sets of UN sanctions for its refusal to suspend its uranium enrichment programme.
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