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.Tennessee.-iv- UCRL-16414 AbstractThe ~-ray spectrum of 241 Am from 80 to 850 keV was studied with a high resolution semiconductor ~-ray spectrometer; a-~-and a-electron-coincidence spectra were studied with semiconductor and scintillator detectors. From these ' data and previous results) a decay scheme is constructed. Theoretical a-intensity calculations aided in establishing the decay _scheme. A brief study of 243 Am decay reveals. a similar structure for 23 9Np... Although the energy levels of 2 3 7 Np have received much attention, they continue to be a fruitful medium for testing theories of nuclear structure and the interrelated theories of nuclear decay processes. The present paper reopens this subject in consequence of two major advances in technique. One of these is the use of the germanium ~-ray spectrometer which has given better definition of' known transitions and shown up a large number of transitions not previously observed. For the first time we can be reasonably sure that the details of the 237 Np level spectrum up to an excitation energy of' about 0.4 MeV are characterized. The second major development is an advance in a-decay theory calculation of which permits/ theoretical intensities of a-groups from Nilsson wave functions of the constituent nucleons. One can now, with some confidence, use a-intensity theory as a real aid in making state assignments. The pertinence of microscopic .a,rate on the a-spectrum of theory to the present· case is that detailed information 241Am is available.The levels of 2 3 7 Np have been identified mainly from the 13--decay of 237 241 27-7 U and from the a-decay of Am. A J U decay scheme proposed by Rasmussen, l . 2 Canavan and Hollander ) has recently-been refined by Yamazaki and Hollander ).Some information from the 13--decay process has also come from a study of 2 3 7 Pu electron-capture decay by Hoffman and Dropesk;?). Several groups have measured the a-spectrum of 241 Am: Asaro and co-workers 4 ' 5 ' 6 ), Gol'din and . 8 .co,..workers \ Rosenblum and co-workers ) , Chin-Fan Leang 9 ), and Baranov and co-workers 10 ' 11 ). The last reference (BKS) reports more than 20 levels in 27-7 . 241 J Np discernable through detectlon of 241The many a-groups of Am bespeak a complicated level structure and complicated ~-ray de-excitation processes) but the low intensities of most of the transitions made it impossible to obtain high resolution ~-transition information. Some of the stronger transitions could be observed through their conversion electrons) but for the weaker onesJ only rough measurements using Nai crystals could be made. In the present study more than thirty new ~-ray· transitions have been observed. The elucidation of the level scheme was also helped by some new a-~-and a-e:-coincidence measurements. In the present study) coincidence measurements also were made on 243 Am which decays to 2 39Np.Before presenting the experiments and their results, we give a brief description of a microscopic theory of a-decay based upon Nilsson wave functions (sect. 2). Th...