The November 1, 1952 thermonuclear explosion ("Mike") produced all of the uranium isotopes U 239 , U 240 , • • • U 255 through multiple neutron capture by U 238 . The long-lived products of successive 0~ decays from these isotopes were measured mass spectrometrically and radiometrically. The logarithms of the abundances decline smoothly with increasing mass number; the even-mass abundances slightly exceed the geometric mean of adjacent odd-mass abundances. Some nuclear properties of neutron-rich heavy nuclides, not subject to ordinary investigation are inferred.

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takes into consideration the energy dependent effect of the detection efficiency and the effect of the constant "window width" of the scintillation spectrometer, the present data indicates that the 138-kev 7 ray is considerably stronger, and the 77-kev x-ray much weaker than measured by Jensen et al 7 This is consistent with the recent work by Schardt et al*The dotted curve in fig. 3 represents the summing spectrum obtained with the sample in the phosphor. The As K x-rays arising from K capture were cut off by the use of a thin Al absorber. Peaks are noticed at 405, 281, 138, and 98 kev. This infers the following:(1) The highest excited energy level involved is at 405 kev since no sum peak appears above this energy. (It is assumed here that no meta-stable states are present. DeBenedetti and McGowan 9 found no delayed coincidences in the 10~~6-to 10~3-sec range.) Thus, any two 7 rays whose energies add up to more than 405 kev cannot be in cascade.(2) The strong sum peak at 405 kev shows that the 138-and the 269-kev transitions are in cascade.(3) Since no indication of summing is noticed at 346 kev, the 77-kev 7 ray appears not to be in cascade with the 269-kev 7 ray as suggested by Jensen et al., 7 whereas on the basis of the present investigation, there 8 A. W. Schardt and J. P. Welker, Phys. Rev. 93, 916 (1954).The decay scheme of Am 241 is discussed in terms of new information on the conversion electrons, gamma rays, and L series x-rays accompanying its alpha decay. The photons were measured with a scintillation spectrometer and a bent crystal spectrometer and the conversion electron spectrum was determined with a double focusing beta-ray spectrometer.