A. Flammersfeld

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 yieldsT1/2=(2.17α0.07) sec andEγ=(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

15:003496Data on the energy distribution of the fragments of triple U/sup 235/ fission are presented. It is shown that the ratio of the triple to double fission probability does not depend on the ratio of the masses. Arguments are given that substantiate the relation E/sub d/ = E/sub tr/+ E/sub alpha /, where E/sub d/ and /sub tr/ are the total energies of the double and triple fission fragments and E/sub alpha / is the energy of the long range a particle. The mechanism of triple fission is discussed. (auth)Short lived isomers of Yb were produced by neutron irradiation of enriched isotopes and have been investigated with the aid of scintillation spectrometers.Yb169m decays with a half-life ofT1/2=(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.Yb175m [T1/2=(0,072±0,005) sec] emitsγ-rays of (495±15) keV. The measured K-conversion coefficientαK 495=0,24±0,04 and the total conversion coefficientα4 5=0,6±0,3 indicate the transition to be M3.Yb177m [T1/2=(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 areαK 228=4,1±0,4 andαK 228=6,5±0,5 for the first transition andαK 104=0,39±0,05 andα104=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.

Zur Isomerie des72Hf179

ZusammenfassungDasγ- und das Konversionselektronenspektrum des 19 sec-Hf-Isomers wurden mit Szintillationsspektrometern in 47π-Geometrie gemessen. Dabei wurde die Halbwertszeit neu bestimmt zuT1/2= (18,6+-0,2) sec. Aus den gemessenen Spektren konnten neben den Energien die Konversionskoeffizienten für beide Übergänge ermittelt werden. Für den ersten 161 keV-Übergang wurden ein Gesamtkonversionskoeffizientα161= 35+-2 und ein K-Konversionskoeffizient αK,161=19,4+-1,2 gefunden, die gut mit den für einenM3-Übergang berechneten Faktoren übereinstimmen. Die Messungen ergaben für die Energie des zweiten Übergangs E2= (217±2) keV und für den Gesamtkonversionskoeffizienten α217=0,055+-0,010. Im Gegensatz zur bisherigen Vermutung folgt daraus eindeutig, daß es sich bei diesem Übergang um E1-Strahlung handelt. Spin und Parität des Grundzustands und der angeregten Zustände des Hf179 sind damit im Einklang mit der vonNilsson angegebenen Niveaufolge für deformierte Kerne.BS>The gamma and conversion electron spectra of the 19-sec Hf isomer were measured with scintillation spectrometers in a 4 The effects of geometry. The half life was measured as T/sub 1/2 = 18.6 sintering time 0.2 sec. From the spectra, the conversion coefficients for both transitions could be determined. For the 161-kev transition a total conversion coefficient alpha /sub ,161/ = 35 sintering time 2 and a K conversion coefficient alpha /sub K,161/ = 19.4 sintering time 1.2 were found, which agree well with the factors calculated for an M3 transition. The measurements gave E/sub 2/ = 217 sintering time 2 kev for the energy of the second transition and alpha /sub 217/ = 0.055 sintering time 0.010 for the total conversion coefficient. In contrast to earlier hypothesis, it is clear that it is a matter of E1 radiation in this transition. Spin and parity of the ground state and the excited states of Hf/sup 179/ are in agreement with the level sequence given by Nilsson for deformed nuclei. (tr- auth)

Der Zerfall des Pt195m und des Au195

The decays of Pt195m(4.1 d) and Au195 (192 d) have been investigated with a Ge(Li)-counter and a Ge(Li)-NaJ coincidence circuit. Theγ-spectrum of Pt195m showed new lines with energies 239.5, 140.7 and 211.1 keV found earlier only in coulomb excitation experiments. Theγ-spectrum of Au195 established a new level of Pt195 at 199.8 keV with single particle character. These results led to a modified level scheme and modified reduced transition probabilities for the levels of Pt195. By comparison of theγ-spectrum of Pt195m and Au195 the ratios of electron capture branches of Au195→Pt195 decay have been determined.

Der Zerfall des Rh106g

The gamma rays associated with the decay of Rh106g have been investigated using several sizes of Ge(Li)-counters and a Ge(Li)-NaJ(Tl)-coincidence circuit. Energies and relative gamma intensities of 107 transitions have been determined. All except 5 transitions are placed in a level scheme of Pd106 having states at 0, 0+; 511, 8, 2+; 1,128.0, 2+; 1,133.6, 0+; 1,228.9, 4+; 1,557.6, 3+; 1,561.9, 2+; 1,706.1, 0+; 2,001.0, 0+; 2,242.4, 1, 2±; 2,278.0, 0+; 2,308.6, 1, 2+; 2,350.8, 4+; 2,438.6, 1, 2+; 2,500.4, 0+; 2,525.3, 1, 2±; 2,624.4, 0+; 2,706.6, 1, 2+; 2,741.0, 1, 2±; 2,783.5, (2)±; 2,821.2, 2+; 2,829.8, 0+; 2,878.3, 0+; 2,902.7, 2+; 2,917.8, 2+; 3,027.1, 1,2±; 3,037.2, 1,2+; 3,055.2,1, 2+; 3,083.2, 2+; 3,163.4, 1,2+; 3,167.5, 1,2+; 3,221.2, 0+; 3,295.6, 0+; 3,321.3 keV, 0+.

Kernresonanzfluoreszenz in Mo94, Mo95 und Mo96

Coulomb fragmentation of Tc2O7 molecules initiated by the electron capture in Tc94, Tc95 and Tc96 provided a means to broaden theγ emission lines of the Tc isotopes sufficiently that nuclear resonance scattering from Mo94, Mo95, and Mo96 became observable. The mean lifetime of the 766 keV level in Mo95 was determined to beτ=(2.9±1.01.6 psec. The angular distribution of the resonantly scattered radiation is only compatible with spin 7/2 for the 766 keV level and yields an amplitude ratioδ for the mixedM1 —E2 transition of −0.35

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.

Die Richtungsabhängigkeit der Szintillations-Lichtausbeute von dünnen Anthrazen- und Stilben-Kristallen beim Beschuß mit α-Strahlen

The scintillation light yield of thin anthracene and stilbene crystals bombarded with α particles of ThB is investigated. A strong dependence of the light yield on the direction of incidence with respect to the crystal axes is found, confirming the results of previous measurements with thick anthracene crystals. For anthracene, maximum light yield occurs for α particles incident approximately parallel to thec′ axis. With stilbene crystals a minimum of the light output is found in thec′ direction. Furthermore, for thin anthracene crystals the direction of maximum light output depends slightly on the crystal thickness.

Die Anisotropie der Szintillationslichtausbeute organischer Moleküleinkristalle für α-Strahlen

Single crystals of anthracene and trans-stilbene when irradiated by α-particles show a strong dependence of their scintillation light yield on the impact direction of the α-particles with respect to the crystal orientation. This having been established in earlier papers, further investigations of 11 other compounds confirm this effect which now seems to be a common feature of monocrystalline organic scintillators. For explanation a possible relation between the anisotropy of the scintillation light yield and that of the electronic conductivity is proposed.

The excited levels of 79Br

Abstract The resonance fluorescence technique has been applied to study the excited levels of 79Br. Using gaseous sources of 79Kr four well-known levels at 834 keV, 606 keV, 398 keV and 307 keV have been excited. A fifth level excited at 526 keV was newly established. The cross sections for resonance scattering yield the following mean lifetimes: 834 keV level τ = (0.17±0.05) psec, 606 keV level τ = 3.7±0.4 psec, 526 keV level τ = 3.5±1.0 psec, 398 kev level τ = 45±15 psec, and 307 keV level τ = 18±10 psec. The results have been confirmed by a self-absorption experiment. The angular distribution of the resonantly scattered radiation gives further information about the spins of the excited levels. The decay scheme of 79Kr was investigated using a Li-drifted germanium counter and a two-dimensional coincidence spectrometer. In addition to the results of former decay scheme studies γ-transitions of 526 keV, 617 keV, 811 keV, 858 kev and very likely 1165 keV have been identified. Coincidence experiments revealed that 79Kr decays by emission of positons to the ground state (7.6%), to the 261 keV level (0.13%), and to the 398 keV level (0.015%).