ARMED SERVICES PATENT ADVISORY BOARD "ASPAB" PATENT SECURITY CATEGORY REVIEW LIST 
JANUARY 1971ARMED SERVICES PATENT ADVISORY BOARD "ASPAB" PATENT SECURITY CATEGORY REVIEW LIST
[Originally classified Confidential - Now Unclassified]
Chapter: GROUP XI - Power Supply
Item 4. Thermionic convertor: a device which will convert heat energy directly (statically) to electric energy by means of emission of electrons from a hot cathode and coUection of these electrons on a cold anode within a vacuum or gas-filled tube. (AP) (NAvy) (NASA)(AMC) S17S (ABC - only if Radioactive Material is used)
How a Thermionic Converter Works - Model Demonstration
Direct production of electric power from heat - C. Guy Suits of the GE Research Lab shows us how a Thermionic generator works. A simple model to show the average person the basics they need to know. caesium vapor between the electrodes determines surface and plasmas properties. we use caesium because it is most easily ionized. Video by the Edison Tech Center in Schenectady, New YorkEdisonTechCenter
> How a Thermionic Converter Works - Model Demonstration
Invention Secrecy Still Going Strong - Secrecy News
There were 5,135 inventions that were under secrecy orders at the end of Fiscal Year 2010, the U.S. Patent and Trademark Office told Secrecy News last week. It’s a 1% rise over the year before, and the highest total in more than a decade.
Under the Invention Secrecy Act of 1951, patent applications on new inventions can be subject to secrecy orders restricting their publication if government agencies believe that disclosure would be “detrimental to the national security.”
The current list of technology areas that is used to screen patent applications for possible restriction under the Invention Secrecy Act is not publicly available and has been denied under the Freedom of Information Act. (An appeal is pending.) But a previous list dated 1971 and obtained by researcher Michael Ravnitzky is available here (pdf).
Most of the listed technology areas are closely related to military applications. But some of them range more widely.
Thus, the 1971 list indicates that patents for solar photovoltaic generators were subject to review and possible restriction if the photovoltaics were more than 20% efficient. Energy conversion systems were likewise subject to review and possible restriction if they offered conversion efficiencies “in excess of 70-80%.”
One may fairly ask if disclosure of such technologies could really have been “detrimental to the national security,” or whether the opposite would be closer to the truth. One may further ask what comparable advances in technology may be subject to restriction and non-disclosure today. But no answers are forthcoming, and the invention secrecy system persists with no discernible external review.Invention Secrecy Still Going Strong | Secrecy News