Isomerenverhältnisse für die Reaktionen107Ag(α,2n)109g,mIn und109Ag(α,2n)111g,mIn

Isomeric cross-section ratios have been measured for the reactions¹⁰⁷Ag(α,2n)^109g,mIn and¹⁰⁹Ag(α, 2n)^111g,mIn for energies of theα-particles between 19 and 40 MeV. The experimental isomeric cross-section ratios are compared with statistical-model calculations. The program ofHafner et al. was extended by including the competition of the (α,n)- and (α, 3n)-reactions and of charged particle emission. Agreement between experiment and theory could be achieved.     

The influence of the chemical environment on the decay constant of90mNb

An influence of the chemical environment on the decay constant λ of the 2.38 keV isomeric transition of^90mNb was investigated. The relative difference of the decay constants for Nb atoms in Zr metal and in a fluorine complex was determined to be ¦λ_complex-λ_Zr¦/λ_zr<1.8·10^?3. This result is discussed in view of other experimental results and on theoretical estimates.     

Nuclear resonance scattering studies on238U using a dense series of γ-ray photons

Using the¹⁸¹Ta(n, γ) and¹⁴¹Pr(n, γ) reactions to provide a dense series of intenseγ-rays, photoexcitation of the²³⁸U nucleus has been studied in the 4–7 MeV range. It is shown that most of the effective cross sections are in line with an average strength function as given by the GDR Lorentzian line superimposed by Porter-Thomas fluctuations. Resonances of nonstatistical strength are found close to 5.2 MeV.     

Delbrück scattering of 2754 keV photons by Nd,Ce, I,Sn, Mo and Zn

The elastic scattering of 2754 keV photons has been investigated for charge numbers Z between 30 and 92. The lowest-order Delbrück theory was found valid for small Z. A Coulomb correction term proportional to (Zα)⁴ fits the experimental data with few exceptions.     

The slowing-down of low-energy recoil atoms in solids and liquids investigated by nuclear resonance fluorescence

Using the nuclear resonance-fluorescence technique, the slowing down mechanisms of recoiling¹⁴⁰Ce nuclei in La, LaMg₃ and La₂O₃, are studied via the Dopler shift of the 1.596 MeV transition, following the decay of¹⁴⁰La. In LaMg₃ the slowing down time shows a pronounced temperature dependence with a sharp drop close to the melting point. In the oxide, as well as in the metal with only a small oxygen content, the slowing down time is considerably smaller than in the pure metal. These results are in support of a model, describing the slowing down process in solids in terms of a damped oscillation, with a time dependence related to the phonon frequency spectrum.Supported by Deutsche Forschungsgemeinschaft through contract Schu 222     

The perturbation of a γγ directional correlation of75As in gaseous H2 75Se sources

Using gaseous H₂ ⁷⁵Se sources the γγ directional correlation of the 121.0–279.5 keV γγ cascade of⁷⁵As was measured as a function of pressure. The attenuation coefficientG ₂ varied between 0.67 and 0.96 for pressures between 0.1 and 200 Torr. Since the perturbation of the directional correlation is caused by hyperfine interaction of the highly charged ion formed after electron capture, the pressure dependence may be understood as being mainly due to changes of the charge states during collisions with neutral molecules. A simple model is proposed yielding a reasonable fit to the experimental data.     

Der Zerfall des In109m (0,21 sec)

In^109m(0,21±0,01 sec) was produced from natural Ag and enriched Ag¹⁰⁷ byα irradiation and investigated using scintillation spectrometers and coincidence techniques. The mass assignment follows from the excitation function for the (α, 2n) reaction on Ag¹⁰⁷. The following results were obtained: energy of the isomeric level (2,11±0,02) MeV, determined directly by summing up the cascade transitions in a well-type scintillator; four gamma transitions with energies (0,680±0,015) MeV, (0,405±0,015) MeV, (1,035±0,030) MeV and (1,435±0,020) MeV, respectively. The proposed decay scheme contains the isomeric level (19/2⁺) at 2,11 MeV and a further level (13/2⁺) at 1,435 MeV which decays either by the 1,435 MeV transition (80±3)% or by a 0,405–1,035 MeV cascade (20±3)% via an (11/2⁺) level at 1,035 MeV to the 9/2⁺-ground state of In¹⁰⁹.     

The slowing down of atoms with kinetic energies ofW≲5 eV in Noble Gases: Evidence for inelastic interactions

Profiles of the 264.6 keVγ-line of⁷⁵As emitted after the electron capture decay of⁷⁵Se have been measured using nuclear resonance fluorescence in combination withγγ-coincidences as a high resolution, variable-energyγ spectrometer. The sources consisted of gaseous⁷⁵SeH₂ with different amounts of Kr or Xe. From the line profiles information has been obtained about the velocity distribution of the radioactive⁷⁵As ions after electron capture decay and about the slowing down of the⁷⁵As ions in the moderator gas. The⁷⁵As ions obtain kinetic energies of up toW～5 eV by neutrino recoil and Coulomb fragmentation of the⁷⁵SeH₂ molecules, corresponding to velocities of the order of 10⁵ cm s^?1. The slowing down of the⁷⁵As ions has been interpreted in terms of the model of colliding elastic spheres, taking into account the thermalization in an exact way. No satisfactory agreement has been obtained between measured and calculated line profiles. This result indicates that inelastic processes are of great importance in the interaction of⁷⁵As ions or atoms with the noble gas moderator atoms.     

Die Polarisation der von den Betastrahlen des P32 erzeugten Čerenkov-Strahlung

The polarization of?erenkov radiation produced in Plexiglas by theβ-rays of P³² has been investigated by counting coincidences between fast electrons having traversed a thin Plexiglas plate and the light quanta emitted at an angle of 45° with respect to the track of the particles. The radiation was analyzed by a polarizing filter and was found to be linearly polarized, the degree of polarization being at least 87%. The remaining 13% of the observed intensity originate at least partly from weak scintillations which are excited by theβ-rays in Plexiglas and the intensity of which could not be measured exactly. With respect to this, the result is in agreement with the virtually complete linear polarization of?erenkov radiation predicted by theory.