It is the title of an article by Petko Nikolov Triste Sissa 1981. I cannot access this pdf yet I remember that it was once avaliable on libgen and now I cannot find it. Please help.
1 Answer
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Simply trying Google Scholar leads to these two places: https://inis.iaea.org/search/search.aspx?orig_q=RN:14747322 and http://streaming.ictp.it/preprints/P/81/196.pdf.