Die β-Zerfallsenergie der Technetiumisotope Tc103, Tc104 und Tc105

Molybdenum fission products from Uranium were rapidly separated using a sublimation technique. Their Technetium daughters could be separated from the Molybdenum sample by a second sublimation. The decay of Tc¹⁰³, Tc¹⁰⁴ and Tc¹⁰⁵ was investigated using scintillation counters and coincidence methods. Tc¹⁰³ decays by the emission of twoβ-groups at energies of 2·0 Mev and 2·2 Mev followed byγ-lines of 135 kev, 215 kev and 350 kev. According to a proposed decay-scheme Tc¹⁰³ decays with aQ-value of 2·35±0·10 Mev into Ru¹⁰³. Tc¹⁰⁵ emits aβ-group of about 3·4 Mev maximum energy followed by a 110 kevγ-transition. TheQ-value of the Tc¹⁰⁵ decay was estimated to be 3·4±0·2 Mev. Fromβ?γ- andγ?γ-coincidence spectra of Tc¹⁰⁴ fourβ?γ-γ-cascades could be identified, which populate excited states of 0·36 Mev, 0·89 Mev, 2·5 Mev, 3·5 Mev and 4·05 Mev in Ru¹⁰⁴. TheQ-value of the Tc¹⁰⁴ decay was found to be 5·85±0·10 Mev. TheQ-values and spin assignements of the groundstates of Tc¹⁰³ and Tc¹⁰⁵ are discussed in a more detailedβ-decay systematic.     

Spins und γ-Multipolordnungen beim Zerfall Fe59→Co59

In the decay of Fe⁵⁹ the following quantities have been measured:γ-ray intensities, conversion coefficients andβ-(circularly polarizedγ) correlations. The conversion coefficients were found to be: for the 1.10 MeVγ-transition, α_tot.=(1.36±0.10)·10^?4 and for the 1.29 MeVγ-transition, α_tot.=(1.07±0.08)·10^?4. The asymmetry parameterA of the correlationβ(0.27 MeV)?γ(1.29 MeV) were measured to beA= ?0.17±0.10, and forβ(0.46 MeV)?γ(1.10 MeV),A=?0.13±0.04. From these data and publishedγ?γ angular correlation measurements the following spins of Co⁵⁹ levels could be deduced: 1.10 MeV,I=5/2^?; 1.29 MeV,I=5/2^?; and 1.43 MeV,I=3/2^?. The two strongβ-ray groups are pure Gamow-Teller transitions (ΔI=1). The multipolarities of all fiveγ-rays are given.     

Die Bestimmung des Kern-Quadrupolmomentes des 247 keV-Niveaus des Cadmium-111 durch Messung der zirkularen Polarisation der γ-Strahlung

The interaction of the nuclear electric quadrupolemoment with an electric field gradient at the position of the nucleus changes the angular correlation of two successiveγ-rays and should also produce a circular polarization of theγ-rays. By measuring this polarization it should be possible to distinguish between electric and magnetic attenuation of theγ-cascade. In the electric case this measurement leads to determine not only the absolute value of the interaction product\(Q \cdot \frac{{\partial E}}{{\partial z}}\) but also the sign of it and therefore the sign of the nuclear quadrupolemoment. In the following paper the measurement of the circular polarization of the 247 kevγ-ray of Cadmium-111 is described. A polarization ofP=(0.8±0.2)% leads to the determination of the quadrupolemoment of the first excited state toQ=+0·9·10^?24cm².     

Derg R -Faktor des 2+-Rotationsniveaus von Er168

The rotation of the angular correlation between theγ-group at about 820 keV and the 80 keV radiation in the decay of Tm¹⁶⁸ has been observed in an external magnetic field of 20300 gauss. The result:ω _R·τ=0,485±0,051 yields for theg _R -factor of the 80 keV state of Er¹⁶⁸:g _R =+0,25±0,03. The evaluation includes a paramagnetic correction factor of:β=7,26, (B _eff=β·B _ext). The angular correlation is slightly attenuated by internal fields. For a liquid source of Tm (NO₃)₃ solved in 3 n HNO₃, a measurement of the differential angular correlation as a function of the delay time gave:λ ₂=(5,8±2,9)·10⁷sec^?1, assumingA ₂(t)=A ₂(0)·e ^?λ ₂·t. The half life of the 80 keV state was found to be:T _1/2=(1,92±0,04)·10^?9sec in agreement with earlier measurements.     

Magnetisches Moment und Quadrupolmoment des 8,42 keV-Zustandes von Tm169 aus der Hyperfeinstrukturaufspaltung in Tm-Metall

The hyperfine transition from the 8·42 kev level to the groundstate of Tm¹⁶⁹ was investigated using the Mössbauer-Effect in Tm-metal in the temperature range between 5° K and 60° K. Well resolved hyperfine spectra were found between 5° K and 25° K indicating an internal magnetic field of about 7×10⁶ Oe and a large electric fieldgradient. The ratio of the magnetic moments of the 8·42 keV rotational state to the groundstateμ _a /μ _g =?2·33±0·04 was deduced from these measurements. The magnetic moment of the groundstate and the quadrupole moment of the 8·42 kev level were deduced from calculated internal fields. These data were analyzed in terms of the “Unified Nuclear Model” and the results compared with other known magnetic moments andM-1-transition probabilities in theK=1/2 rotational band of Tm¹⁶⁹. The complicated hyperfine spectra obtained above 25° K reveal the influence of complex magnetic ordering on the internal fields in Tm-metal.     

Hyperfine-structure measurements on Dy161 and Dy163

In an atomic beam magnetic resonance experiment the hyperfine interaction constantsA andB of the⁵ I ₈ groundstate of Dy¹⁶¹ and Dy¹⁶³ were found to be Dy¹⁶¹:A=?(115.8±1)MHz, Dy¹⁶³:A=(162.9±0.6)MHz,B=(1102±15)MHz,B=(1150±20)MHz. Using an effective value for 〈r^?3〉, the magnetic moments and electric quadrupole moments of the Dy¹⁶¹ and Dy¹⁶³ nuclei were calculated to be Dy¹⁶¹:μ _I=?(0.47±0.09) n.m., Dy¹⁶³:μ _I=(0.66±0.13)n.m.,Q=(2.36±0.4)barns,Q=(2.46±0.4)barns.     

Das magnetische Moment des 2,083 MeV-Zwei-Protonen-Niveaus des gerade-gerade-Kerns Ce140

The nuclearg-factor of the 2·083 MeV-state of Ce¹⁴⁰ has been determined as:g=1·11±0·04 This value suggests the interpretation of the level as the (g7/2,d5/2)₄ two proton shell model configuration. The investigation implies an integral measurement as well as a time dependent differential measurement (spin rotation method) of the rotation of the 329 keV-487 keVγγ-angular correlation in strong external magnetic fields. Liquid sources of lanthanum nitrate solved in 3n HNO₃ were used in these experiments. Some cerium (IV)nitrate was added to make sure that the 4f;-electronic shell remained empty after theβ ^?-decay. This prevented paramagnetic effects. Additional runs were performed without adding cerium (IV)nitrate and finally by using liquid sources of lanthanum chloride solved in 2n HCl with some iron (II)-chloride added. It was expected that the Fe⁺⁺ ions would reduce the primarily formed Ce⁺⁺⁺⁺ ions into the Ce⁺⁺⁺ state. The Ce⁺⁺⁺ shell is paramagnetic and enlarges the effective magnetic field at the position of the nucleus by about 36%. As no definitely faster rotation could be observed, one has to conclude that the ion reaction Ce⁺⁺⁺⁺+Fe⁺⁺?Ce⁺⁺⁺+Fe⁺⁺⁺ takes more than about 10^?8s. The half life of the 2·083 MeV state has been redeterminded asT _1/2=(3·41±0·04)·10^?9s. Differential measurements of the angular correlation of the 329 keV-487 keV cascade as a function of the time delay showed that perturbations by internal fields were very small. The coefficientsA ₂ andA ₄ of the angular correlation and the attenuation parameterλ ₂ were determined from measurements with sources of the first type as:A ₂=?0·105±0·003A ₄=?0·001±0·002 andλ ₂=(0·0065±0·0040)·10⁹S^?1=(0·032±0·020)·λ A comparison with the theoretical coefficients of a (3-4-2)-cascade shows that the multipolarity of the 329 keV radiation is a mixture of 99·83%M1 and (0·17±0·03) %E2.     

Das gyromagnetische Verhältnis des 137 keV Rotationsniveaus von Os185

The rotation of the angular correlation of the 631 keV-137keVγ-γ-cascade in the decay of Re¹⁸⁶ in an external magnetic field of 53 500 gauß was determined to:ωτ=0·098 ± 0·008. The half life of the 137 keV level was measured as: T_1/2=(0·84 ± 0·03) · 10^?9 sec. The coincidences between the 137 keVγ-radiation and theβ-group of 927 keV maximum energy were used in connexion with a time to pulse height converter circuit. The coefficients of the angular correlation of the 631 keV-137 keV γ-γ-cascade were found as: A₂=? 0·073 ± 0·010; A₄=+ 0·310 ± 0·014. These values imply corrections for 3·9% admixture of internal bremsstrahlung and a 1 % contribution by K-X-radiation. The solid angle-corrections were done according to the formula given by E.Rose. The comparison with the theoretical coefficients for a (2⁺ 2⁺ 0⁺)-cascade shows that the multipolarity of the 631 keV radiation is pure E₂, the M₁ admixture being less than 0· 1%. This result is in agreement with the K-selection rule. There is no appreciable attenuation by internal fields. The comparison with the theoretical angular correlation gives for the integral attenuation factor: G₄=0·95±0·04; Assuming only attenuation by electric quadrupole interaction one gets for: G₂=0·92±0·07; The nuclear g-factor of the 137 keV rotational state was derived from these results without any further correction as: g_R= + 0·316±0·028.     

Messung der Lebensdauer angeregter Kernniveaus von Al28, Cs133, Pr141, W182 und Pt195

The halflife of excited states in some nuclei has been measured by the method of delayed coincidences. Two different experimental arrangements have been used: a conventional scintillation counter equipment and a fast gasfilled parallelplate avalanche-counter. The results of these measurements are: 31 keV-level in Al²⁸:T _1/2=(1.91±0.08) · 10^?9 sec, 81 keV-level in Cs¹³³:T _1/2=(6.25±0.05) · 10^?9 sec, 145 keV-level in Pr¹⁴¹:T _1/2=(1.85±0.03) · 10^?9 sec, 100keV-level in W¹⁸²:T _1/2=(1.45±0.04) · 10^?9 sec, 1290 keV-level in W¹⁸² T _1/2=(1.05±0.03) · 10^?9 sec, 99 keV-level in Pt¹⁹⁵:T _1/2≦1.6 · 10^?10 sec, 129 keV-level in Pt¹⁹⁵:T _1/2=(6.2±0.7) · 10^?10 sec. These experimental values are discussed and compared with theoretical model predictions.     

Winkelkorrelationsmessungen an >30y Holmium 166 und Bestimmung desg R -Faktors des 4+-Rotationsniveaus von Erbium 166

The spins of several excited states of Er¹⁶⁶ have been investigated byγγ-angular correlation measurements. The spin sequence 0+, 2+, 4+, 6+ for the ground state rotational band was presumed to be correct. Unique assignments were derived for the states of 1076 keV, 1377 keV and 1785 keV asI=5, 7 and 6 respectively. These results are in agreement with the spins proposed byGallagher jr. andSoloviev. The multipolarities of theγ-transitions of 408 keV, 709 keV, 811 keV and 831 keV were derived as 95%E1+(5±1)%M2, 99·6%E1+(0·4±0·5)%M2, 99·1%E2+(0·9±0·3)%M1, and 96·1%E2+(3·9±1)%M1 respectively. The unusual mixing ratios of the transitions of 811 keV and 831 keV can be understood as a consequence of theK-selection rule. Eachγ-transition from the 1785 keV state should be stronglyK-forbidden and one expects a half-life ofT _1/2≈3·10^?9s. A measurement of the time spectrum of the coincidences between theβ-radiation and the high energyγ-lines gave however:T _1/2(1785 keV state)≦3·10^?10s. The rotation of the angular correlation between the 184 keV line and theγ-group at 820 keV has been measured in an external magnetic field of 53000 gauss as:ω·τ(4+)=0·083±0·006. This value contains small corrections for an additional rotation of the angular correlation of the 831 keV–184 keV triple cascade in the 6+state and for a small attenuation by internal fields. WithT _1/2(4+state)=1·23·10^?10s, andβ=7·08 one gets for theg-factorg _R=+0·266±0·024 in good agreement with recent results for the 2+ state.     

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.     

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.     

Elastische und unelastische Streuung von Elektronen an Gasen

The theoretical differential cross section for the elastic scattering and for the excitation of optical transitions in helium by electron impact has been refined in Born approximation by use of the two parameter Eckart eigenfunction for the ground state and for the excited states. The angular distributions of 25 kev electrons scattered elastically and inelastically by helium were measured in the angular range 2·3·10^?4≦?≦4·10^?2. The intensity distribution of the elastically scattered electrons is in accordance with the theoretical curve for?>7·10^?3 and is disturbed at smaller angles by the primary beam. Normalization of the experimental values to the theoretical elastic differential cross section leads to agreement between the experimental differential cross section for the excitation of the 2¹ P and 3¹ P state and the scattering formulae given in this paper. There are small systematic deviations (<20%) for the 2¹ P differential cross section in the angular range 3·10^?3<?<1·10^?2 only. The oscillator strength of these two transitions has been determined from the scattering measurements:f ₂₁=0·312±0·04 andf ₃₁=0·0898±0·006.     

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.     

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.     

Die Hyperfeinstruktur des 32P3/2-Zustands von Natrium im starken Magnetfeld

The hyperfine structure of the 3²P_3/2 State of Na²³has been measured by the optical double resonance technique in a magnetic field of 3.1 kG sufficiently strong to decouple completelyI andJ. In the case of π or (σ⁺+σ^?) excitation the double resonance signal represents the superposition curve of eight unresolved radio-frequency transitions. The dependence of the signal on the pressure of sodium vapour and the radio-frequency field strength has been studied. The analysis of the experimental curves yields for the hyperfine coupling constants the valuesa=(18.7±0.4) Mc/s andb=(3.4±0.4) Mc/s. The nuclear electric quadrupole moment derived from the ratio ofb/a isQ=(0.146±0.02) · 10^?24cm². The Lande factor and the lifetime for the 3²P_3/2state are g_J=1.3344±0.0004 and τ=(1.61±0.07) · 10^?8 sec.     

Der Zerfall des Gd151

The electron-capture decay of Gd¹⁵¹ was investigated by means ofγ- andγ-γ-coincidence spectrometry, using scintillation counters. Besides the knownγ-rays of 22 kev, 154 kev, 175 kev, 244 kev and 308 kev additionalγ-transitions with energies of 107 kev and 350 kev could be assigned to the decay of Gd¹⁵¹.γ-γ-coincidence measurements showed the following cascade transitions: (107 kev–244 kev), (154 kev–175 kev–22 kev) and (308 kev–22 kev). TheK-conversion-coefficients of several transitions were determined by comparing theγ-intensities and the previously known conversion electron-intensities, using a direct measurement of theK-conversion-coefficient of the 175 kev-transition by a delayed coincidence-experiment as a normalization of the relative intensities. With the available information a level-scheme for Eu¹⁵¹ is proposed.     

Kern-Isomerie bei In116

The short lived indium isomer produced by thermal neutron capture is confirmed to be In¹¹⁶. A new determination of half-live andγ energy yieldsT _1/2=(2.17α0.07) sec andE _γ=(164±1) keV. From measurement of theK shell conversion coefficient follows that the multipolarity of the transition isE 3, leading to a spin and parity assignment of 8^? for the isomeric level.     

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.     

Über die mathematische Struktur und eine Klasse strenger Lösungen der Jordanschen erweiterten Gravitationstheorie

Theβ-α. angular correlationW(Θ)=1+a cosΘ+cos² Θ of the decay of Li⁸ was measured for average electron energies ofE _β ≈5 MeV, 11 MeV and 12 MeV. The experiment yields an anisotropyA=(0·0036±0·0011)·E _β (MeV)^?1. This result is in good agreement with the results of the other groups. The measurements were performed in a counting chamber separated from the activation room simultaneously for two sealer positionsΘ=90° and 180°. The result is discussed in terms of the CVC-theory, taking into account the second forbidden Fermi-matrixelements (‖M1‖) and (‖E2‖).