42 USC 1881 - Award of National Medal of Science

(a) Recommendations 
The President shall from time to time award the medal, on the basis of recommendations received from the National Academy of Sciences or on the basis of such other information and evidence as he deems appropriate, to individuals who in his judgment are deserving of special recognition by reason of their outstanding contributions to knowledge in the physical, biological, mathematical, engineering, behavioral or social sciences.
(b) Number 
Not more than twenty individuals may be awarded the medal in any one calendar year.
(c) Citizenship 
An individual may not be awarded the medal unless at the time such award is made he
(1) is a citizen or other national of the United States; or

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(2) is an alien lawfully admitted to the United States for permanent residence who
(A)  has filed an application for petition for naturalization in the manner prescribed by section 1445 (b) of title 8 and
(B)  is not permanently ineligible to become a citizen of the United States.
(d) Ceremonies 
The presentation of the award shall be made by the President with such ceremonies as he may deem proper, including attendance by appropriate Members of Congress.