Energy levels of 237Np (I). The alpha decay of 241Am

Abstract

The γ-ray spectrum of 241Am from 80 to 850 keV was studied with a high resolution semiconductor γ-ray spectrometer; α-γ- and α-electron-coincidence spectra were studied with semiconductor and scintillation detectors. From these data and previous results, a decay scheme is constructed. Theoretical α-intensity calculations aided in establishing the decay scheme. Nilsson assignments 5 + 2 [642], 5 − 2 [523] and 1 + 2 [400] for rotational bands based on levels at 0, 59.54 and 332.36 keV are confirmed. A new 1 − 2 [530] band, whose lowest member is the well-known 267.54 keV 3 − 2 level, is positively identified, and a K = 5 − 2 beta-vibrational band established. The latter band decays primarily by M1 transitions, in violation of the vibrational selection rule. A new level at 770 keV with a probable I π = 7 + 2 assignments is also of probable vibrational character. A brief study of 243Am decay reveals a similar structure for 239 Np.