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.     

Der radioaktive Zerfall des Fe61

Fe⁶¹(T _1/2=5.95 min) was produced irradiating Ni⁶⁴ and natural nickelfoils with fast neutrons in the reaction Ni⁶⁴(n, α)Fe⁶¹; Fe was chemical seperated. The gamma and beta spectrum were investigated with Ge(Li)-counters, NaJ(Tl) and plastic scintillation spectrometers. Fe⁶¹ emits five gamma rays having the energies and intensities per Fe⁶¹ decay: 121 keV (0.064), 177 keV (0.027), 298 keV (0.293), 1025 keV (0.461), 1202 keV (0.539). Threeγγ-cascades could be identified: 121–177 keV, 121–1202 keV, 298–1025 keV. Inγ β-coincidence measurements the maximal beta energy was determined:E _βmax=2.86 MeV. A decay sceme Fe⁶¹-Co⁶¹ was constructed: Fe⁶¹, spin and parityJ ^π=3/2^?, decays by means of allowed beta decay to three excited states of Co⁶¹: 1323 keV (1/2^?), 1202 keV (3/2^?), 1025 keV (5/2^?). The energies and intensities per Fe⁶¹ decay of the three beta decay modes are: 2.56 MeV (0.367), 2.68 MeV (0.495), 2.86 MeV (0.138). — A 88 keV gamma ray (T_1/2=33 sec) was observed coming from the Co⁶³ decay.     

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.     

Untersuchung des Magnesium-27-Zerfalls

Theγ-rays of the decay of Mg²⁷ were investigated with NaJ-crystals, andγ-γ-cascades had been sought for by a fast-slow-coincidence circuit. A method for an exact measuring of the random-coincidence spectrum and a stabilisation method of the multiplier gain is described. The twoγ-lines of 808 keV and 988 keV in coincidence with the 842 keVγ-line and the 817 keVγ-line in coincidence with the 1013 keVγ-line, reported by other authors, could not be observed. If these transitions exist, their intensity would be less than 10^?3 per decay.     

Der Zerfall von Er171 und Er165

Theγ-spectrum of a neutronactivated probe of natural Er₂O₃ revealed an additional peak at 55 keV, which was attributed to the characteristicK-Röntgenstrahlung from the decay of Er¹⁶⁵ by measurement of its half-life in a NaJ-wellcrystal. The activation cross section for thermal reactor neutrons for Er¹⁶⁴ (n, γ) Er¹⁶⁵ has been determined to σ _A =20±7 barn. The averaged conversion coefficient of the 111, 116 and 124 keV γ-rays from Er¹⁷¹→Tm¹⁷¹ have been remeasured with scintillation counter equipment.     

Verzweigungsverhältnisse undβ +-Maximalenergie beim Zerfall von Ag108

The branching ratios of Ag¹⁰⁸ have been remeasured with scintillation spectrometers. There is evidence for a weak 177 keV-β ^?-branch going to the 1473 keV level of Cd¹⁰⁸, followed by aγ-γ-cascade of (841+632)keV. Spin and parity 2+ of this level are supported by logft=4.7 of theβ ^?-branch. Theβ ⁺-spectrum has been measured for the first time yielding an end point energy of (880±25)keV, in agreement with the value derived from theK/β ⁺ratio.     

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.     

Messung von fünf β-γ-Zirkularpolarisationskorrelationen beim Zerfall Eu152→Gd152

In the decay Eu¹⁵²→Gd¹⁵² fiveβ(circularly polarizedγ) correlations have been measured (Table). The Fermi matrix element of the 3^?–3^? β transition is small or vanishing. The levels of 344 and 755 keV (I=2⁺ and 4⁺, respectively) seem to be collective states.     

Zerfallsschemata, β-Matrixelemente und γ-Multipolordnungen für die Übergänge Co56→Fe56 und J131→Xe131

In the decay of Co⁵⁶ the following quantities have been measured:γ-ray intensities,β-γ directional correlation, andβ-(circularly polarizedγ) correlation. The directional correlation anisotropy was found to be, forβ energies above 300 keV,A ₂=0.5±0.4 per cent, corresponding to small or vanishing twice forbidden contributions to the allowed decay. The asymmetry parameterA of theβ-(circularly polarizedγ) correlation was measured to beA=?0.01±0.05 which implies a ratiox between Fermi and Gamow-Teller contributions to the decay ofx=?0.10±0.07, in agreement with the isospin selection rule. In the decay of J¹³¹ the following quantities have been measured: shape of the 606 keVβ-ray group,γ-ray intensities, conversion coefficients, andβ-(circularly polarizedγ) correlations. The measuredK/L ratio of the 364 keVγ-transition,K/L=6.0±0.2, is compatible with the conversion tables of Sliv and Band only. The multipolarities of theγ rays of 364, 637, and 723 keV were deduced. The 606 keVβ-364 keVγ cascade was used as a new calibration standard for analysers of circularly polarizedγ-rays.     

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.     

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.     

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.     

Local structure of Tm<Superscript>2+</Superscript> and Yb<Superscript>3+</Superscript> impurity centers in <Emphasis Type="Italic">Me</Emphasis>F<Subscript>2</Subscript> (<Emphasis Type="Italic">Me</Emphasis> = Ca,Sr, Ba) fluoride crystals

The local structure of Tm²⁺ and Yb³⁺ cubic impurity centers in MeF₂: Tm²⁺ and MeF₂: Yb³⁺ (Me = Ca, Sr, Ba) fluoride crystals, as well as Yb³⁺ trigonal and tetragonal impurity centers in MeF₂: Yb ³⁺ crystals, is calculated within the shell model in the pair potential approximation.     

Long Time,Large Scale Limit of the Wigner Transform for a System of Linear Oscillators in One Dimension

We consider the long time, large scale behavior of the Wigner transform W _? (t,x,k) of the wave function corresponding to a discrete wave equation on a 1-d integer lattice, with a weak multiplicative noise. This model has been introduced in Basile et al. in Phys. Rev. Lett. 96 (2006) to describe a system of interacting linear oscillators with a weak noise that conserves locally the kinetic energy and the momentum. The kinetic limit for the Wigner transform has been shown in Basile et al. in Arch. Rat. Mech. 195(1):171–203 (2009). In the present paper we prove that in the unpinned case there exists γ ₀>0 such that for any γ∈(0,γ ₀] the weak limit of W _? (t/? ^3/2γ ,x/? ^γ ,k), as ??1, satisfies a one dimensional fractional heat equation \(\partial_{t} W(t,x)=-\hat{c}(-\partial_{x}^{2})^{3/4}W(t,x)\) with \(\hat{c}>0\). In the pinned case an analogous result can be claimed for W _? (t/? ^2γ ,x/? ^γ ,k) but the limit satisfies then the usual heat equation.     

Bestimmung des (631)K=1/2, I=1/2-Zustandes im U 239

Theγ-ray spectrometer at the DR 3-reactor at Risø was used to investigate the low energyγ-lines of U 239 which are emitted during neutron-capture in U 238. Very closely lying lines have been found between 500 and 650 keV. The big intensity of the 133 keV line and the lack of other transitions of appropriate energy and intensity point out that this line corresponds to the hinderedE 2-transition from the (631)I=1/2⁺ level to the (622)I=5/2⁺ groundstate. A suggestion was made for the decay possibility of the octupole states at 700 keV found by N.Fiebiger.     

Study of Er171 decay by means of an electron-gamma coincidence technique

The decay scheme of Er¹⁷¹ (7.8 h) has been reinvestigated by means of an electron-gamma coincidence spectrometer and a scintillation spectrometer with a transistorized RIDL-400 channel analyser. A careful unfolding of the high energy region of the gamma-ray spectrum revealed the presence of photopeaks at energies of approximately 371, 404, 543, 572, 618, 675, 738, 796, 869, 910 and 962 keV. The existence of 32 transitions in Tm¹⁷¹ was confirmed. Also, it is proved that the 277, 362 keV transitions are in coincidence with the 210 keV and that the 175 keV transition is in coincidence with the 86 keV transition. We revealed the doubt for the existence of the 166, 210, 236, 277 and 419 keV transitions. From coincidence and single counting rates the followingK-conversion coefficients of the 111, 116, 124, 296 and 308 keV transitions were determined to be: α _K (111)=1.561±0.062, α _K (116)=0.699±0.035, α _K (124)=0.608±0.024, α _K (296)=0.0197±0.0010, α _K (308)=0.0183±0.0009, which give the 116, 124 keV transitions an electric quadrupole character; the 111 keV transition a magnetic dipole character withE2/M1 equal 0.4528; and the 296, 308 keV transitions an electric dipole character withM2/E1 equal 0.0058 and 0.0071 respectively.     

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.     

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.     

Der Zerfall des Mn52m

Mn^52m(T _1/2=21 m) was produced by irradiating iron-foiles with deuterons ofE _d =9 MeV. Coincidences ofγ-rays with the main 1434 keV-transition had been sought for with the aid of a scintillation fast-slow-coincidence circuit. There was no evidence ofγ-lines which had been found earlier byKatoh et al. atγ-energies 700, 940, 1020, 1150, 1370, 1520 keV. If these transitions exist, their relative intensities are less than 0.7% (700 keV) and 0.3% (all others) per decay of Mn^52m.     

Die Lebensdauer des 23/2-Dreiteilchenniveaus des Hafnium 177 und sein Zerfall durchK-verbotene Gamma-Übergänge

An isomeric state of Hf¹⁷⁷ withT _1/2=(1,12±0,10)s was found by a fast chemical separation of the hafnium daughter from the 155d Lu^177m activity. We measured the same half-life by observing the delayedβ-γ-coincidences. A systematic investigation of the whole region 5s≧T _1/2≧10^?7s by the technique of delayed coincidences gave no further isomerism. We assign the observed half-life to the 23/2 three particle state of Hf¹⁷⁷ at 1315 keV and assume that the second hypothetical three particle state at 1337 keV does not exist. The 21/2 rotational state of theK=9/2 band is populated by a strongly converted 14,16 keVγ-transition from the isomeric state at 1315 keV. The 14,16 keVM _I andN _I conversion lines were observed by use of a double focusing magneticβ-spectrometer. The isomerism is caused by theK-selection rule. The retardation of the following threeγ-transitions by different degrees ofK-forbiddeness is discussed. The pulse height spectrum, measured by means of a Li-drifted Ge-detector, does not show the 36,52 keV-γ-transition which was previously assumed to populate the 1301keV-state. In addition to the knownγ-transitions we found a 40,9 keV-line. This is probably the transition between the 1301,1 keV and the 1260,3 keV-states.