H. Niedrig

Electric hyperfine interaction in solid CF4 at the fluorine site

Using the time differential perturbed angular distribution method (TDPAD), the quadrupole coupling constant for CF4 has been measured to be νQ = 59.7(3) MHz. This value is discussed in connection with measurements of the other carbon tetrahalides and can be well understood in the framework of the Townes and Dailey theory.

The influence of the isospin on the coherence widths in the compound nucleus 51V

Abstract The reactions 50 Ti(p, p 0 ) 50 Ti and 50 Ti(p, α 0 ) 47 Sc were investigated with proton energies between 9.5 and 10 MeV. From an autocorrelation analysis the mean coherence widths were determined for the compound nucleus 51 V. In the proton channel and in the α-particle channel different coherence widths were measured: in the proton channel Γ p = 5.3 ± 1.3 keV and in the α-particle channel Γ α = 2.3 ± 0.4 keV. The direct reaction part in the proton decay was more than 93 %. In the measured cross sections non-statistical structures were present.

Temperature dependence of the electric field gradient in CdSe and HfO2

The time differential perturbed angular correlation technique was applied to study the electric field gradient in the semiconductor CdSe and the insulator HfO2 at different temperatures. Whereas the semiconductor CdSe shows an increasing quadrupole coupling constant with increasing temperature, the insulator HfO2 exhibits no temperature dependence of the electric field gradient over the whole temperature range investigated.

Charge carrier governed temperature dependence of the electric field gradient for111Cd in tellurium

Using the TDPAC-method with the proble nucleus111Cd the electric quadrupole interaction (QI) in the trigonal semiconductor Te has been investigated in the temperature range 77 K≦T≦655 K. In contrast to most metals the quadrupole frequencyvQ increases with increasing temperature. This is a consequence of the fact that in metals the charge carrier density is temperature independent, whereas in semiconductors it strongly increases with temperature. A comparison between the temperature variation of the quadrupole coupling constantvQ and that of the charge carrier density leads to the conclusion that the QI in Te is governed by changes in the free electron density.

The electric hyperfine interaction in solid fluorine

Abstract The quadrupole coupling constant of F 2 in the solid phase has been investigated at a temperature of 17.5 K by means of the time differential perturbed angular distribution technique. For the coupling constant a value of ν Q = 127.2(1.0) MHz results. The data are discussed in comparison with NQR-studies in the molecules I 2 , Br 2 and Cl 2 , and in terms of the Townes and Dailey theory. A small fraction of the 19 F nuclei was exposed to an electric field gradient of 85(5) MHz. Possible explanations are proposed.

Temperature dependence of the electric field gradient for111Cd in antimony

For the temperature dependence of the electric field gradient of111Cd in the semimetal antimony the well knownT3/2 relationship is valid over a wide temperature range. The slope parameterB differs from that for121, 123Sb in antimony by a factor of about 2.3.

THE ELECTRIC QUADRUPOLE INTERACTION IN THE DI- AND TRIFLUORIDES OF THE TRANSITION METALS AND IN THE TRIFLUORIDES OF THE RARE EARTH ELEMENTS

Using the time differential perturbed angular distribution (TDPAD) the electric quadrupole interaction at the 19F site for the di- and trifluorides of the transition metals and the trifluorides of the rare earths was investigated. The measurements show a dependence of ~Q on the 3d-electrons in the first mentioned targets, whereas there is no dependence of ~Q on the 4f-electrons in the rare earth trifluerides.

The temperature dependence of quadrupole interactions at cadmium impurities in Arsenic metal

We have performed time differential perturbed angular correlation measurements over a temperature range from 77 K to 763 K to investigate the static electric quadrupole interaction of111Cd in rhombohedral Arsenic metal. The observed quadrupole interaction frequency decreases with increasing temperature and is consistent with the well knownT3/2 relation, valid for metals.

Lattice defects in CaF2 and SrF2 after proton irradiation

The time differential perturbed angular distribution method (TDPAD) has been applied to investigate the electric field gradient produced by radiation induced defects in the cubic lattices of CaF2 and SrF2. In mixed crystals of the alkaline-earth difluorides CaF2 or SrF2 and the rare earth trifluorides PrF3, NdF3 or SmF3 the amplitudesA22exp in the TDPAD spectra strongly depend on the rare earth trifluoride concentration. From the fact that the observed amplitudes are well described by a simple statistical model the conclusion can be drawn that the defects produced in CaF2 and SrF2 after proton irradiation are F− interstitials.

Experimental proof of radiation induced F- interstitials in CaF2

Abstract The electric field gradient of radiation induced defects in CaF2 has been investigated by observation of the time differential perturbed angular distribution. Using CaF2/PrF3, CaF2/NdF3 and CaF2/SmF3 mixed crystals of the interstitial type it could be shown that the amplitudes Aexp22 in the TDPAD spectra depend on the rare earth trifluoride concentration. The experimental values are well described by a sample statistical model. The nature of the defect in CaF2 is established to be an F- interstitial.