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.     

Spurenanalyse von Cu in ZnS-Phosphoren mittels Neutronenaktivierung

The half life of the 206 kev state of Re¹⁸⁷ was determined with delayed coincidence technic to be:T _1/2=(5·70±0·05)·10^?7 s. The rotation of the spin of the 206 kev state in a magnetic field has been observed in a differential angular correlation measurement with the 480 kev?72 kevγ?γ cascade. From the observed Larmor frequency a magnetic moment ofμ=(5·02±0·06)μ _K for the 206 kev level has been derived. The 480 kev?72 kevγ?γ angular correlation was found to be undisturbed in an aqueous solution of ammoniumtungstate.     

Possible violation of the δS=δQ selection rule in leptonic decays of σ+-hyperons

We have found a possible example of the rare decayσ ⁺ →nΜ ⁺ Ν, which violatesδS=δQ. The positive decay track of theσ ⁺ comes to rest in the hydrogen bubble chamber and decays into ane ⁺. This track has all the characteristics of a stoppingΜ ⁺. The decay neutron fortuitously scatters twice, producing two recoil protons. The only other possible interpretation of the event isσ ⁺→nγ(π ⁺ →Μ ⁺ Ν), where theπ ⁺ →Μ ⁺ Ν decay produces no deflection (θ<0.1 rad) and no significant change in curvature. Using thep-wave radiative decay predictions ofBarshay et al. we calculate that the integrated branching ratio for such “accidental” events isγ(σ ⁺ →nγ(π ⁺ →Μ _stop ⁺ Ν))/γ(σ ⁺ →nπ ⁺)=1.6×10^?6. Most of the contribution to this “accidental” branching ratio comes from radiative decays where theπ ⁺ mesons have ranges less than 1 mm (p _π<20 MeV/c). If one excludes thoseΜ's with ranges less than 1.2 cm the above “accidental” branching ratio becomes 5.5×10^?7. With this figure we estimate that we should have seen 6.5×10^?2 events of this type thusfar in our experiment. The neutron momentum does not help in deciding between the two hypotheses. We therefore assign a confidence level of 7% for the radiative hypothesis. For the leptonic hypothesis we obtain an estimate of the branching ratio,γ(σ ⁺ →nΜ ⁺ Ν)/γ(σ ⁺ →nπ ⁺)=5×10^?5. If one further accepts theσ ⁺ →nπ ⁺ Ν event reported byBarbaro-Galtieri et al. and theσ ⁺ →ne ⁺ Ν event reported byNauenberg et al., one obtains theδS=?δQ leptonic branching ratio [γ(σ ⁺ →nΜ ⁺ Ν)+γ(σ ⁺ →ne ⁺ Ν)]/γ(σ ⁺ →nπ ⁺)=(4±3)×10^?5.     

Ausbeuteverhältnisse einiger durch Kernphotoreaktionen in Cer und Silber erzeugter Aktivitäten

Samples of metallic silver and cerium-oxide have been irradiated with 31 MeV and 34 MeV bremsstrahlung. Relative yields of the induced activities have been obtained by counting the emitted gamma-quanta or byβ-counting. The yield ratio Y [Ag¹⁰⁷ (γ, n) Ag^106m ]/Y [Ag¹⁰⁷ (γ, n) Ag^106g ] for 34 MeV bremsstrahlung was found to be (0.08±0.02). The corresponding ratio Y [Ce¹⁴⁰ (γ, n) Ce^139m ]/Y [Ce¹⁴⁰ (γ, n) Ce^139g ] at 31 MeV was (0.19±0.01).     

Kern-Isomerie bei77Ir192 und77Ir194

Theβ- andγ-radiation of Ir¹⁹² and Ir¹⁹⁴, produced by slow neutron irradiation, has been studied with scintillation spectrometers. A new isomeric activity with a (47±2) second-half life is found to be Ir^194m , decaying by a 130 kev-transition to Ir¹⁹⁴ and byβ-emission to excited states of Pt¹⁹⁴. Gamma rays of energy (130±4), (323±7) and (625±20) kev were found. An upper limit for the conversion coefficient of the isomeric transition is given, which shows in connection with energy-half life-relations, that the 130 kev gamma ray is anE 3 transition.     

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.     

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.     

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.     

Die Messung der β-γ-Winkelkorrelation bei Au198

The energy dependence of theβ ?γ asymmetry coefficient has been measured. No anomaly at lowβ energies as reported by other authors was found. Theξ-approximation holds andε W/p ² Ν ₁₂=0.027±0.007 was obtained. The matrix elements of theβ transition are discussed.     

Mössbauereffektmessungen am 79,5 keV-Niveau von Gd158

Mössbauer effect measurements with the 79,5 keVγ-transition in Gd¹⁵⁸, populated by thermal neutron capture in Gd¹⁵⁷ are reported. In Gd metal, GdF₃ and GdCl₃, the values obtained for the electric field gradient are (?0.7±0.4), (11.9±5.0) and (?7.5±0.5) · 10¹⁷ V/cm² respectively. The internal magnetic field in Gd metal was measured to beH _int=312±23 kG and we derived for theg factor of the 2 + level the valueg _R=0.385±0.022. The change of the mean square nuclear radius between the ground state and the first excited stateΔ 〈r²〉=+(0.4±0.3) · 10^?3 fm², as extracted from the measurements, will be compared with model calculations of nuclear rotation.     

Cross sections of the reactions16O(γ,x)13 N and16O (γ,x)11 C,and Yield of12C (γ, t) up to 55 MeV

Yield curves of the reactions¹⁶O (γ, x)¹¹C,¹⁶O (γ, x)¹³N and¹²C(γ, t) have been measured relative to¹²C(γ, n)¹¹C with bremsstrahlung. The cross section σ[¹⁶O(γ, x)¹¹C] has a shape similar to σ[¹⁶O(γ, t)] and shows a broad maximum near 38 MeV. Differences between σ[¹⁶O(γ, x)¹³ N] and σ[¹⁶O(γ, t)] point to a reaction mechanism via quadrupole absorption in¹⁶O. The yield of¹²C(γ, t) exceeds the¹⁶O(γ,t) yield by a factor of two.     

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.     

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.     

Isomerieverschiebung im Eu151

The isomer shift of the 21.7 keVγ transition in Eu¹⁵¹ has been studied for various divalent and trivalent europium compounds using the Mössbauer technique. Theγ energy is lower by up to 1.1·10^?6 eV in divalent compounds than in trivalent compounds. Using data from atomic spectroscopy it is estimated that the electron density at the nucleus is larger by about 1.9·10²⁶cm^?3 for the configuration 4f ⁶ than for 4f ⁷ due to different shielding of thes ² shells. The difference of the mean square radii of the 21.7 keV state and the ground state is thenδ〈r²〉=+0.03 fm². The measured isomer shift between trivalent and metallic europium and the relatives-electron densities in the rare earth metals measured by the positron annihilation rates are used to establish a calibration scheme for isomer shifts in rare earth metals. This calibration scheme is used to deduce a changeδ〈r ²〉=+0.005₅ fm² between the 26 keV state and the ground state of Dy¹⁶¹.     

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.     

Photoproduction ofN = (1236) by polarized γ-Quanta

The one-pion-exchange model with gauge invariant extension is used to calculate cross sections and decay distributions for the reactionγp→N⁼⁺⁺ π ^? where theγ-quanta are linearly polarized. We show that measurements with polarizedγ-quanta would provide a sensitive check of the model. In particular, the relevance of the terms added to the one-pion-exchange part to guarantee gauge invariance could be tested.     

Messung der Zirkularpolarisation der 478 keV-Gammaquanten aus der Reaktion Li6(d,p)Li7 mit 2 MeV-Deuteronen

The circular polarizationP _γ of 478 keVγ quanta from the reaction Li⁶(d, pγ) Li⁷ with 2 MeV deuterons was measured by forward Compton scattering from magnetized iron. The protons were observed at 25° lab angle. The fast neutron background in theγ detector was suppressed by pulse shape discrimination. The resultP _γ=+ 0.022 ± 0.17 with the Basel sign convention confines the ratio of the reduced widthsΘ _± for the capture of the neutron withj=1±1/2 to the regions ?2.36≦Θ ₊/Θ _?≦?0.74 or ?0.06≦Θ ₊/Θ _?≦+0.61.     

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.     

Cross sections of the photoneutron reaction for <Superscript>141</Superscript>Pr and <Superscript>186</Superscript>W nuclei,estimated from physical criteria of data reliability

Using objective physical criteria for data reliability, cross sections of partial photoneutron reactions (γ, 1n), (γ, 2n) and (γ, 3n) that are free of the shortcomings of neutron multiplicity sorting methods used on beams of quasimonoenergetic annihilation photons are obtained for ¹⁴¹Pr and ¹⁸⁶W nuclei. Evaluation is performed using the experimental–theoretical method (ETM), based on the experimental cross section of neutron yield reaction σ^exp(γ, xn) = σ^exp(γ, 1n) + 2 σ^exp(γ, 2ⁿ) + 3 σexp(γ, 3n) + … and ratios F _i ^theor= σ^theor(γ, in)/σ^theor(γ, xn) calculated within the combined model (CM) of photonuclear reactions, which stipulates that σ^eval(γ, in) = F _i ^theor σ^exp(γ, xn). It is found that for ¹⁴¹Pr and ¹⁸⁶W, ratios F ^exp _i do not contradict the data reliability criteria only at energies up to ~21 and ~22 MeV, respectively. At the same time, there are notable discrepancies between F _i ^theor and F ^exp _i, and thus between the evaluated and experimental cross sections of reactions. It is shown that the discrepancies between the evaluated and experimental cross sections are due to the assumed unreliable experimental distribution of neutrons in the channels with multiplicities 1, 2, and 3.     

Untersuchung ferromagnetischen Materials mit polarisierter γ-Strahlung

Circularly polarized Co⁶⁰ γ-ray quanta have been used to measure the polarization-dependent part of the Compton effect on an iron-cobalt alloy. The asymmetryδ=(N ₊?N _?)/(N ₊+N _?) observed by inversion of the magnetic field direction was investigated as a function of the mean induction¯B between 1 and 23kI ^?. The experimental values of δ do not nearly drop as fast as¯B when going down from saturation to zero.