Technical Report No. 42 May 1, 1950 : The Theory of Nuclear Reactions [ cover title ]
Cambridge, Massachusetts: Laboratory for Nuclear Science and Engineering, Massachusetts Institute of Technology 1950. First Edition. , 185,  pages. 8 1/2 x 11 inches. Printed light grey wrappers, stapled. Tape residue and a few edge tears to the covers. Includes 6 pages of errata in the pagination, plus a distribution list in the back for 120+ copies being sent to scientists and institutions. Very Good. Wraps. 
"This report contains a preliminary draft of two chapters on nuclear reactions of a book on Theoretical Nuclear Physics by [the authors] which will appear in 1951." (first page) The book was actually issued in 1952. "After World War II, Weisskopf joined the physics faculty at MIT, ultimately becoming head of the department. At MIT, he encouraged students to ask questions, and, even in undergraduate physics courses, taught his students to think like physicists, not just to learn physics. He was a memorable teacher. Weisskopf was a co-founder and board member of the Union of Concerned Scientists. He served as director-general of CERN from 1961 to 1966. Weisskopf was awarded the Max Planck Medal in 1956 and the Prix mondial Cino Del Duca in 1972, the National Medal of Science (1980), the Wolf Prize (1981) and the Public Welfare Medal from the National Academy of Sciences (1991). Weisskopf was a member of the National Academy of Sciences. He was president of the American Physical Society (1960–61) and the American Academy of Arts and Sciences (1976–1979)." (wiki)
The survival rate for this draft is fairly small - only 4 copies in OCLC. Perhaps the most interesting portion of this book is the distribution list - who would have been interested in or worth requesting information from in nuclear reactions in 1950.