Schw/~chungskurven der in Aluminiura und Blei durch Co6~ erzeugten Sekund/irstrahlung wurden gemessen und mit der Theorie verglichen. Versuchs~nordnung (Fig. I).
The intensities of the 37keV-and 49keV-y-rays of ]3r 8~ have been measured with the aid of NaJ-scintillation spectrometers and compared with the intensity of the conversion electrons registered by an anthracene split crystal spectrometer. It was possible to separate the 49 keV-y-radiation from the intense 37 keV-line by selctive absorption with balanced Sin-and Gd-filters. The internal conversion coefficients (49 keV) = 298-b 30 and g (37 keV) = 1,59 :k 0, t0 are in good agreement with the calculated values for M3-and El-transitions. The half life was measured yielding a value of ~ = (4,40 :k 0,05) h.
Tb lsSm was produced from Tb ls9 by (n, 2n) reaction and investigated using scintillation spectrometers. The following results were obtained: half-life T~=(10.5_+0.2) sec; energy of the isomeric transition E~=(109.9_+l.5)keV; conversion coefficients CTK=56__3; CtL+CtM-t-.... 50-t-8; Cttotal= 106-+ 10; K/L-ratio K/L= 1.3• yielding the multipole order of the isomeric transition to be M3. Upper limits for the direct beta transitions from the isomeric state to the ground states of the neighbouring even-even nuclei Gd 158 and Dy a58 are 10 -4 and 6" 10 -a, respectively.
Short lived isomers of Yb were produced by neutron irradiation of enriched isotopes and have been investigated with the aid of scintillation spectrometers. Yb 169m decays with a half-life of T,~ = (46 :~ 2) sec emitting only L-radiation. This decay is assumed to be the same as the E 3-transition of 24 keV following the electron capture of Lu 169. Yb 175m [T~ = (0,072 :I= 0,005) sec] emits y-rays of (495 4-15) keV. The measured K-conversion coefficient ~K495 = 0,24 2~ 0,04 and the total conversion coefficient ~4 5 =0,6• indicate the transition to be M3. Yb x77m [T~= (6,4+0,1)sec] decays by a cascade of two y-rays. The isomeric (228 4-3) keV-transition is followed by a (104 4-t,5) keV-radiation. The measured conversion coefficients are ct K 22s = 4,t 4-0,4 and c~22 s = 6,5 4-0,5 for the first transition and CtKlO~ = 0,39 4-0,05 and c~10~=0,51• for the second, indicating a M3-El-cascade.For the M3-transition the measured coefficients agree well with those calculated for a nucleus of finite size, but they differ by a factor of 1,5 for the El-transition.
Die IntensitgLt der 40 keV-y-Strahlung, bezogen auf die Zahl der c~-Teilchen beim ThC-Zerfall, wurde mit einem Szintillationsspektrometer gemessen. Zur Verminderung des stSrenden y-Uniergrunds wurde ein diinner NaJ-Kristall zum Nachweis der Onanten verwendet. Mit 35,r177 ftir das Verzweigungsverhgltnis und 7 t, 5 • t, 5 % Anregung des Niveaus ergibt sich fiir den Faktor der inneren Umwandlung c~ = 22,8 4-1,0. Ans dem Verh~ltnis ~L/e = 0,80 4-0,02 erhiilt man c~ L = 18,24-t,0. Dieser Wert ist niedriger als der ftir einen Ml-l~bergang und punktf6rmigen Kern berechnete. Die {)bereinstimmung zwischen den ftir einen I(ern vom Radius R= 1,2-10 la. A.~cm berechneten ~;erten und dem Experiment ist gut.
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