Messungen derK-Konversionskoeffizienten und der Aktivierungsquerschnitte der isomeren Atomkerne Se77m,Se79m,Ge75m und Ge77m

TheK-conversion coefficients α _K of the nuclear isomers Se^77m , Se^79m , Ge^75m and Ge^77m have been measured by detecting theK-röntgen- andγ-radiation from neutron-irradiated Se- and GeO₂-samples with the aid of scintillation counters to be α _K =0.79±0.06, 7.4±0.6, 1.44±0.13, and 1.2±0.6, respectively. In all cases, the values obtained, are in agreement with those taken from the tables ofRose under the assumption of anE3-transition, thus confirming this assignment which was proposed earlier by other authors. In addition, the cross sectionsσ for inducing the activities by slowed down neutrons have been measured to beσ=22±2, 0.40±0.04, 0.20±0.02, and 0.12±0.03 barns, respectively, and are compared with earlier data of several authors.     

Der Zerfall des Lu176m

The decay of Lu^176m has been investigated. TheK-conversion coefficient α _K of the 88,3 keV niveau of Hf¹⁷⁶ has been determined to α _K =1,35±0,07. Theβ-branching ratio to the 0+ and 2+ niveau of Hf¹⁷⁶ has been measured by means of aβ-γ-coincidental technique. (60,4±6,1)% of Lu^176m decay into the 2+ niveau and (39,6±6,1)% into the 0+ niveau of Hf¹⁷⁶.K-capture of Lu^176m to Yb¹⁷⁶ was not found. If there is any, it is less than 0,1% of all decays.     

Die Konversion des Hg199m

Hg^199m was produced from natural HgO by fastn irradiation. The cascade decay was investigated with scintillation spectrometers by application of the summing technique. The following results were obtained: half-lifeT _1/2=(43±0,5) min; energy of the isomeric transitionE _γ1=(375±3)keV; conversion coefficients α _K375=3,05±0,25; α_total=5,45±0,25; yielding the multipole order of the isomeric transition to beM4+(25±15)%E5; energy of the second transitionE _γ2=(159±2)keV; conversion coefficients α _K159=0,30±0,03; α_total=0,9±0,1, confirming the multipolarityE2 of this transition.     

Die Konversion des79m Br

⁷⁹ mBr was produced by irradiation of natural Br with fast neutrons. The half-lifeT _1/2=(4.87±0.15) sec and the energyE _γ=(208±1) keV were remeasured. For the first time the conversion coefficients were determined to beα _K=0.25±0.02 and α_total=0.28±0.05, yielding the multipolarityE3 for the isomeric transition.     

Der Zerfall des Tb158m

Tb^158m was produced from Tb¹⁵⁹ by (n, 2n) reaction and investigated using scintillation spectrometers. The following results were obtained: half-life\(T_{\tfrac{1}{2}} = (10.5 \pm 0.2)\) sec; energy of the isomeric transitionE _γ =(109.9±1.4) keV; conversion coefficients α _K =56±3; α _L +α _M +?=50±8; α_total=106±10;K/L-ratioK/L=1.3±0.3, yielding the multipole order of the isomeric transition to beM3. Upper limits for the direct beta transitions from the isomeric state to the ground states of the neighbouring even-even nuclei Gd¹⁵⁸ and Dy¹⁵⁸ are 10^?4 and 6·10^?3, respectively.     

Der Zerfall Co58m →Co58g

Co^58m , Co^58g and Co⁵⁵ were obtained by radiating nickel-foiles with deuterons of energies 11,5 MeV and 2,07 MeV. The γ-radiation was measured with NaJ scintillation spectrometers. For the isomeric transition of Co^58m was determinedT _1/2=(9.15±0.1)h,T _γ=(25±1)keV,α _K=2200±300 and α_L+M=1100±300. From these values it follows, that the radiation is ofM3-type. Twoγ-energies of 95 keV and 1322 keV were found belonging to Co⁵⁵.     

Der Zerfall des Co60m und Zr90m

Co^60m was produced by the reaction Co⁵⁹ (n,γ) Co^60m ; its decay has been investigated by scintillation spectrometers. The half-period has been remeasured yielding a value ofT _1/2=(10·35 ±0·20) min. The isomeric decay mainly leads to the Co⁶⁰ ground state by a (58·6±0·6) keV transition. TheK-conversion coefficientα _K= 41±3 and the total conversion coefficientα=47±3 indicate the transition to beM3 and the spin of Co^60m to be 2⁺. Further Co^60m decays by beta transitions to Ni⁶⁰. The beta component (8·6±1·2)·10^?3%, log ft=7·32 leading to a (2·16±0·02) MeV level has been measured for the first time. A second component (0·24±0·03)%, log ft=7·23 leads to the 1·33 MeV level. The 2·16 MeV level decays to the Ni⁶⁰ ground state mainly by a 0·83–1·33 MeV cascade, in a few cases by a direct transition. The spin of the 2·16 MeV level is 2⁺. Zr^90m was produced by the reaction Zr⁹⁰ (n,n′) Zr^90m . The half-period was measured yielding a value ofT _1/2=(0·83±0·03) sec. Zr^90m decays in the following way: (77±5) % by a direct (2·31±0·02) MeV —E 5 transition to the Zr ground state and (23±5)% by a (132·5±1·5) keV-(2·18±0·03) MeV cascade detected for the first time in the isomeric decay. TheK-conversion coefficient of the 132·5 keV transition isα _k=(2·2±0·3) indicating this transition to beE3 and the spin of the 2·18 MeV level to be 2⁺. The Zr^90m -decay sheme is in accordance with the level sequence of Zr⁹⁰ as measured in the Nb⁹⁰ decay.     

Die isomeren Atomkerne: Yb169m,Yb175m,Yb177m

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 ofT _1/2=(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 Lu¹⁶⁹. Yb^175m [T _1/2=(0,072±0,005) sec] emitsγ-rays of (495±15) keV. The measured K-conversion coefficientα _{K 495}=0,24±0,04 and the total conversion coefficientα _{4 5}=0,6±0,3 indicate the transition to be M3. Yb^177m [T _1/2=(6,4±0,1) sec] decays by a cascade of twoγ-rays. The isomeric (228±3) keV-transition is followed by a (104±1,5) keV-radiation. The measured conversion coefficients areα _{K 228}=4,1±0,4 andα _{K 228}=6,5±0,5 for the first transition andα _{K 104}=0,39±0,05 andα ₁₀₄=0,51±0,05 for the second, indicating a M3-E1-cascade. For the M 3-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 E1-transition.     

Untersuchung des Iridium-191m-Zerfalls

Theγ-radiation of the nuclear isomer Ir^191m (T _1/2=4.5 sec) has been investigated with the aid of a scintillation fast-slow coincidence-spectrometer. Theγ-rays of the 42 keV-transition have been measured for the first time. The conversion coefficient α of this transition was found to be α = 13500 ₊₂₁₁₀₀ ^?5200 in acceptable agreement with the value taken from the tables ofRose under the assumption of anE3-transition. Thus this assignment proposed earlier by other authors has been confirmed. TheK-conversion coefficient of the 129 keV-transition has been remeasured yielding α _K =2.32±0.06.     

Suche nach Zweiquantenprozessen beim Zerfall von Xe131m

The decay of Xe^131m was investigated in order to detect nuclear double decay processes, in which the transition energy is distributed either between twoγ-quanta or between oneγ-quantum and oneK-conversion electron or between twoK-conversion electrons. By analyzing the emittedγ-radiation in a two-dimensional way an upper limit of 2.2 · 10^?5 was derived for the ratio of theγγ- toγ-transition probability. An investigation of theγ-spectrum in coincidence withK-quanta yielded an upper limit of 3 · 10^?2 for the rate ofe _Kγ-transitions relative toγ-transitions. The simultaneous emission of twoK-quanta was actually observed. These doubleK-quanta result either from the doubleK-conversion that was sought or from the internal conversion of the internal Compton-effect. For the doubleK-electron emission toγ-emission probability a value of (3.6±0.7) · 10^?3 was obtained. TheK-conversion coefficient and the half-life of Xe^131m were measured to be 32.1±0.4 and 11.94±0.04 d, respectively.     

Der Zerfall des 1,5 min-Isomers Co54m

Co^54m (T _1/2=1.43 min) was produced in iron-foils by irradiation with_dE=19 MeV deuterons. The gamma ray spectrum was investigated using a NaJ(Tl) scintillation spectrometer, a coincidence circuit and a Ge(Li)-counter. There were observed three gamma rays having the following energies and intensities per Co_54m decay: 411 keV (0.97±0.07), 1130keV (0.98±0.05), 1407 keV (1.00±0.05). The directional correlation between the pairs of gamma rays were determined. These results correspond to spin and parityJ _π=2⁺ for the 1407 keV,J _π=4⁺ for the 2537 keV, andJ _π=6⁺ for the 2948 keV energy level of Fe⁵⁴. The last-mentioned level was not excited in previous scattering experiments. Our results are compatible withE=210keV andJ _π=6⁺ or 7⁺ of the isomeric state of Co^54m .     

Der Zerfall des Au195m,des Hg195m und des Hg195

Theγ-radiation of Au^195m , Hg^195m and Hg¹⁹⁵ was measured with a Ge(Li)-semiconductor detector. Conversion coefficients of most transitions could be determined from the measuredγ-intensities and from already known electron intensities. Spin and parity of the corresponding niveaus and logft-values for the decay of Hg¹⁹⁵ and Hg^195m were determined. Newγ-energies (698 keV, 754 keV, 852 keV) were found in the decay of Hg^195m . With a coincidence method a value of α_tot=13±3 for the 61,5 keV-radiation of Au^195m was measured.     

Study of penetration effects in the <Emphasis Type="Italic">E</Emphasis>1 and <Emphasis Type="Italic">M</Emphasis>1 transitions in <Superscript>44</Superscript>Sc

Conversion coefficients for the E1 and M1 transitions in the ⁴⁴Ti decay have been measured with high accuracy using the sum peak and multidimensional coincidence methods. The following values have been obtained: α_K(E1) = 0.077 ± 0.003 and α_K(M1) = 0.014 ± 0.001. A significant contribution of the penetration effects for the M1 transition has been shown. The penetration parameter λ is determined to be ?260 ± 30 has been determined.     

K-Einfang der Silberisotope Ag110 und Ag108

K-electron capture of Ag¹¹⁰ has been observed for the first time using scintillation spectrometers in anticoincidence technique. The ratio of electron capture toβ ^?-decay was determined to (0.3±0.06)%.K-electron capture of Ag¹⁰⁸ has been remeasured with better accuracy, yielding a relative frequency of (1.73±0.12)% for the capture transition to the ground state of Pd¹⁰⁸.     

Messung der Kernradiusdifferenzen von46Ti,48Ti und50Ti durch elastische Elektronenstreuung

Ratios of differential cross sections for elastic electron scattering from⁴⁶Ti,⁴⁸Ti and⁵⁰Ti have been measured at 29 MeV and 58 MeV. A partial wave analysis, carried out for static Fermi-type nuclear charge distributions, yields differences of the r.m.s. radiiR _m ofR _m ⁴⁸ ?R _m ⁴⁶ =(?0,00₅±0,02₇) fm andR _m ⁵⁰ ?R _m ⁴⁶ =(0,00₃±0,02₁) fm, if the skin thickness parameterz of the charge density is assumed to be constant. If allowance is made for a change inz ofΔz/z=±5% and ±10%, then the errors increase by ±0,01₃ fm and ±0,02₈ fm, respectively. This indicates a relatively small change in nuclear r.m.s. radii below the magic neutron number N=28.     

Niederenergetische Gammalinien vom Neutroneneinfang in Lu 175 und Lu 176

The low energy gamma-rays from neutron-capture in Lu 175 and Lu 176 have been investigated by means of the bent crystal-spectrometer at the DR-3-reactor at Risø. From the transitions in Lu 177 3 rotational bands have been determined. The levels of the (404)K=7/2⁺ groundstate rotational band are: 121,62 keV (I=9/2), 268,79keV (I=11/2), 440,66 keV (I=13/2), 636,22 keV (I=15/2), 854,34 keV (I=17/2). The level-sequence of the (514)K=9/2^?-band is: 150,39 keV (I=9/2), 288,99 keV (I=11/2), 451,49 keV (I=13/2), 637,05 keV (I=15/2) and 844,88 keV (I=17/2). At 457,92 keV is the basis for the (402)K=5/2⁺-band the higher levels of which are 552,05 keV (I=7/2), 671,89 keV (I=9/2), 816,63 keV (I=11/2), 985,23 keV (I=13/2), 1176,73keV (I=15/2) and probably 1389,5 keV (I=17/2). The energies of the levels apart from the 1389 keV-level have an accuracy of 7×10^?5. The energy differences between the 3 bands agree very well with the values expected from the Bohr-Mottelson-formulaE=A·I(I+1)+B·I ²(I+1)². The calculated branching-ratios within the 3 bands are in fairly good agreement with the experimental values. Theg _K -factors have been determined for 2 bands: It was found that for the (514)-bandg _K =1,16±0,04 and for the (402)-bandg _K =1,33±0,07.     

Die Faktoren der inneren Umwandlung beim35Br80m (4,4 Std)

The intensities of the 37keV- and 49keV-γ-rays of Br^80m have been measured with the aid of Na J-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-γ-radiation from the intense 37 keV-line by selctive absorption with balanced Sm- and Gd-filters. The internal conversion coefficientsα(49 keV)=298±30 andα (37 keV)=1,59±0,10 are in good agreement with the calculated values for M₃- and E₁-transitions. The half life was measured yielding a value ofT _1/2=(4,40±0,05) h.     

TheK-conversion coefficient of the 321 keVE1 transition in Hf177

TheK-conversion coefficient of the 321 keVE1 transition in Hf¹⁷⁷ has been measured by means of an iron free double focusing beta-ray spectrometer, using the internalexternal conversion method. The result obtained for α _K (321)=0.162±0.016 is in disagreement with the theoretical values for pureE1 transition (α _K =0.0154) calculated bySliv andBand. The large anomaly observed in theK-conversion process of the inhibitedE1 transition is compatible with a largeM2 admixture or, more probable with the presence of penetration matrix elements.     

Radioactive decay of Os191 and Os191m

Beta and gamma spectra of Os¹⁹¹ were studied using a magnetic double-focusing beta-spectrometer and a scintillation spectrometer. The isomeric state Os^191m decays through the 74·4 ± 0·1 keV (E3/M4=50) transition with a half-lifeT _1/2=13·0 ± 0·5 hours. A continuous beta spectrum withE _max=147 ± 3 keV and the gamma transitions 41·83 ± 0·05 keV (E3), 82·5 ± 0·3 keV and 129·4 ± 0·1 keV (70%M1 + 30%E2) were observed in the decay of the ground state of Os¹⁹¹. The conversion coefficient of the last transition was determined as 1·94 ±± — 0·10. Gamma transitions with energies of 47 keV and 185·8 keV were not observed.     

Verzweigungsverhältnisse und Konversionskoeffizienten von angeregten Zuständen des208Tl

The branching ratios of theγ rays of the second and fourth excited states of²⁰⁸Tl have been investigated by coincidence measurements between the α rays of²¹²Bi and subsequent 40keVγ ray. The detectors employed were a silicon surface barrier counter for α particles, and a 1.5 in ×2 mm NaJ (Tl) crystal forγ rays. It has been found that (75.6±3.7)% of all transitions of the 328 keV state and (94±7)% of all transitions of the (492 keV+473 keV) states populate the first excited state of²⁰⁸Tl. The 40 keV state is excited to (3.4±0.3)% by transitions of higher excited states relative to the direct excitation by α particles. The number of α particles with energyE _α = 6.047 MeV and the number of subsequent 40keVγ rays resulted in a conversion coefficient α(40keV)=22.55± 0.46. Similarly coincidence measurements between Tl-x rays and α particles have been used to determine theK- conversion coefficients α_K(328 keV)=0.31±0.03 and α_K(492 keV+ 473keV)=0.100±0.015. The experimental results are in good agreement with the theoretical values ofSliv.