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The Lp3/LP4, Lyf/Lpf, Ln2/Lef, Lp2 fg/Lo'f and the Lp 2 f5/Le2 transition probabi]ities have been measured for some 27 elements ranging in atomic number from 57La to 92U. Other L transitions have also been measured for a smaller number of elements in the same range of atomic numbers. This has been accomplished by bombarding these elements with a constant energy electron beam and measuring their x-ray emission spectrum. The measured ratios are compared with the most recent calculation based on a relativistic Hartree-Fock-Slater (RHFS) potential, and screened Coulomb potential. In general, the form of the dependence of these ratios on atomic number predicted by calculations based on a RHFS potential is favored and the agreement between theory and experiment ranges from excellent for the Le2/Lnf ratio to a discrepancy of about 22% in the Lp 2 fs/Lcyf ratio for elements of large atomic number.

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Phys. 43 3067 (1965). The spin-orbit-coupling correction is negligible for 0(P2)-0 ( P(g2).~4The Ly&/Lps, LV3/Lpa, Lq/Lp&, Lp5/Lo&, Lp&/Ln&, and Ll/Lu, radiative-transition probability ratios have been measured for 13 elements ranging in atomic number from 62Sm to 92U. This has been accomplished by bombarding the elements with an electron beam of constant energy and flux, and counting the x-ray photons emitted by a given electronic transition. The corrected measured ratios are compared with the results calculated on the basis of the relativistic-Hartree-Fock-Slater (RHFS) potential and those calculated on the basis of the relativistic-screened-Coulomb QSC) potential. In general, values calculated on the basis of RHFS potential are favored except for the Ll/Le& ratio where the measured values and those obtained from a RSC-potential calculations are in excellent agreement and are as much as 40% lower than the values obtained assuming a HHFS potential, The L, y2/Lp3 and Ly3/Lp3 values obtained with a RSC potential are as much as an order of magnitude greater than experimental values at high Z, and are not included in the graphs. The estimated error of the experimental results is from 10 to 15%. Other experimental values are also included for comparison.

The existence of emission lines at the low-energy sides of the L(3 2t 15 and Lk x x-ray lines in the rare-earth elements has been experimentally detected. Their intensities and positions relative to those of the Lp 2t 15 and Ly x lines have been measured and are presented as functions of the atomic number of these elements.Rare-earth elements in the form of foils 0.13 mm thick and 99.9% pure were placed at the surface of a metallic dish filled with 31 Ga. The water-cooled melt gallium proved to be very satisfactory in keeping the thin foils from evaporating under electron bombardment. The constant-energy electron beam was provided by a 74 W filament fitted in a stainless-steel focusing cup. A power supply connected in series with a voltage-line regulator and a ripple suppressor, and delivering a steady voltage with less than 0.3% ripple at a full load of 120 keV and 30 mA, was used to accelerate the electron beam. The vacuum in the locally designed and built chamber in which the samples were exposed to the electron beam was maintained at about 10" 6 mm of Hg, and the x-ray emission spectra of the elements were analyzed by means of a modified single-crystal high-angle goniometer. The recorded intensities of the LP 2l5 and the accompanying lines of several rareearth elements are shown in Fig. 1. They have been lined up in this fashion for comparison. The points are experimental and were taken by stepping the detector 0.01 deg in the Bragg angle 20. A detailed description of experimental procedure and technique has been presented elsewhere. 1 The emission lines Lfi 2 15 (L s -N 4t 5 ) and Ly x (L 2 -N 4 ) of nine elements ranging in atomic number from 59 Pr to 69 Tm have been studied. The recorded intensities were fed into a computer and the newly observed structures, hereafter referred to as Lp 215x and Ly^, were unfolded. The computer program was based on the fact that the diagrammed emission line is symmetric about its maximum. The position and intensity of the I^is 1 an <* L y\ relative to those of the Lp 2 15 and Ly 19 respectively, were calculated. The results as functions of atomic numbers are shown in Figs. 2 and 3. An error analysis was carried out for these quantities and the results are indicated by error bars.The rare-earth elements have partially filled 4/ shells. This situation is parallel to that for the partially filled 3d shells in elements with atomic numbers 21 < Z < 29, where asymmetry of the Ka x and Ka 2 x-ray lines has been observed 2 and has been interpreted as being the result of the splitting of the 2p electronic levels. 3 The partially filled 4/ levels in the rare-earth elements contain electrons that are divided into two subgroups differing in the direction of their spins. The spin interaction of these two subgroups with the electrons in the 4d 3/2 and 4d 5 / 2 levels contributes to the energy of these levels and causes each of the 4d levels to split into two sublevels. The relative intensity of the radiation emitted as a result of electronic transitions from 69 Tm 66°y 65 Tb 62 Sm 60 Nd