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High-resolution Ge(Li) and Si(Li) x-ray spectrometers and a wall-less anticoincidence multiwire proportional counter were used for coincidence measurements between various K and L x rays and M x rays of Np (Z = 93) and Cm (Z = 96) following 0' decay of Am 4 and Cf 4, respectively. The effect of multiple vacancies in the M shell was taken into account in the determination of the following mean M-subshell fluorescence yields: v~= 0.The close agreement of the various mean M-subshell fluorescence yields with that of the M4 5 subshells for each element indicates that Coster-Kronig transitions are very strong in the M shell. Including earlier measurements of mean M-shell fluorescence yields at lower Z, corrected for multiple vacancies, and accepting Bhalla's theoretical calculations of radiative M4 5-subshell widths, one concludes that the nonradiative widths of the M4 5 subshells are essentially constant from Z =76 to 96. Comparison of fluorescence yields of the K shell and the L3 and M4 5 subshells at the same energy of the principal radiative transition (i. e. , at different values of & indicates that the ratio of radiative to Auger widths decreases from the 1sf/2 to 2p3/2 state, but remains constant from 2p3/2 to 3d5/2. The resolution of the Si(Li) detector was sufficient to separate the radiative transitions from fillings of the Ml 2and M3 4 5 subshell groups, so that from K and L xray coincidences with the M~2 group of x rays, it was possible to determine the following quantities:~~+f fg el)2 --(2. 0'2'0) x 10 and (7. 5'7 5) &10 at Z=93 and 96, respectively, and u2 =(4. 6 4 6)~1 0 at Z=96. Thus, about 94% of M2subshell vacancies undergo Coster-Kronig shifts to higher subshells before filling from. N and higher major shells occurs. Observation of the radiative Ll-L3 transition was made for the first time in the high-Z region, and its intensity is in reasonable agreement with extrapolated theoretical predictions (6 -7% of x rays filling Ll-subshell vacancies). The radiative fraction~l 3 in the Coster-Kronig yield f~3 is found to be about 2% in the region of Z=93 -96, and~~3 --0.011+0.005 and 0. 009+0. 005 at Z =93 and 96, respectively. The absolute emission rate of M x rays from Am24 was measured with multiwire and single-wire proportional counters, and values are found of (6.35+0.60) &10 M x rays per & decay and 0.470+ 0.045 Mx rays per L~x ray. These intensities were used in determinations of efficiency at 3. 25 keV of the semiconductor x-ray detectors.

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