The beta-spectrum of ${\mathrm{Pu}}^{241}$ measured in a double lens spectrometer on samples containing ${\mathrm{Pu}}^{239}$, ${\mathrm{Pu}}^{240}$, and ${\mathrm{Pu}}^{241}$, exhibits an allowed shape from $E_0=20.5\mathrm{}$ kev to 14 kev, where instrumental effects distort it. Conversion lines found beyond the end point combined with gamma-scintillation counter measurements lead to the assignment of gammas of 39, 53, 100, 124, and 384 kev associated with the alpha-decay of ${\mathrm{Pu}}^{239}$, and a gamma of 49.6 kev accompanying the alpha-decay of ${\mathrm{Pu}}^{240}$; and the existence of 26.4- and 59-kev gammas in ${\mathrm{Am}}^{241}$ alpha-decay is confirmed. A conversion line corresponding to a highly converted 41-kev gamma in ${\mathrm{Am}}^{241}$ was found. Gammas of 100 and 145 kev probably associated with the alpha-branch in ${\mathrm{Pu}}^{241}$ were also found.

The influence of the orbital electronic rearrangement energy on the beta-decay is discussed.

• Received 24 April 1952

DOI:https://doi.org/10.1103/PhysRev.88.1155