G. N. Rao

High resolution TDPAC work using CsF and BaF2 fast detectors

Abstract Barium fluoride and cesium fluoride inorganic scintillators offer excellent timing, reasonable energy resolution and good gamma ray detection efficiencies. These characteristics are very desirable for accurate time differential perturbed angular correlation/distribution (TDPAC/D) experiments and enables one to extend the TDPAC/D techniques for the study of many interesting solid state aspects such as near neighbour interactions, conduction electron polarization, short and long range ordering etc. The performance of these detectors is compared with the commonly used ones and their potential for new solid state applications is demonstrated by means of some illustrative examples.

Electric field gradients at probe nuclei in Ti and Re hosts: Comparison with the predictions of the conduction electron charge shift model

The electric field gradients (EFGs) at different probe nuclei in Ti and Re hosts are compared with the predictions of the conduction electron charge shift model. It is found that this model is successful in predicting the sign and, to a zero-order approximation, the magnitude of the EFG when the localized d-contributions are small and the universal correlation is obeyed.

Electric quadrupole interaction and its temperature variation at100Rh in Be metal

The nuclear quadrupole interaction at the100Rh probe nucleus in a Be host is measured from 4.2–968 K using time-differential perturbed γ-γ angular correlations of the 84–75 keV cascade in the de-excitation of100Rh. The sources were prepared by recoilimplanting the parent100Pd activity produced in a heavy-ion reaction. The temperature variation of the electric field gradient can nicely be fitted by aT3/2 law.We discuss the electric field gradient and its temperature dependence in the light of various systematics. The data are also compared with the predictions of the conduction electron charge shift model suggested by Bodenstedt and Perscheid.

Internal field distribution around spin-glas freezing temperature in AuFe-alloys

We demonstrate an application of PAC to the study of magnetic ordering in random alloys. Using111Cd as a probe the spin-glass freezing inAuFe-alloys of different concentrations could be observed. In the Au82Fe18 alloy no indication of ferromagnetism above the freezing temperature was found, due to the fact that the111In probe nuclei are located in a Au rich environment.

Near-neighbour interactions in iron based alloys

Time differential perturbed angular correlation experiments were carried out using111Cd probe nuclei to measure the change in conduction electron polarization at different lattice sites due to scattering around an impurity atom.

Impact of baf2 detectors on nuclear solid-state investigations

High resolution time differential angular correlation, now achievable at low cost by the fast and efficient BaF2 detectors, will be introduced from some examples recently worked out. The results obtained manifest a new impetus for this technique in its extended application to particular problems in nuclear solid state research.

Hyperfine-field measurements inCr Rh andCr Re alloys using perturbed angular correlation technique

The hyperfine fields on111Cd probe nuclei in Cr (1 at% Rh), Cr (0.3 at% Rh) and Cr (0.5 at% Re) matrices are measured using time-differential perturbed (γ−γ) angular correlation of 173–247 keV cascade in the decay of111In to the levels in111Cd. The sources prepared by ion implantation of111In (2.81 d) activity followed by appropriate annealing procedure were found to be of good quality. The addition of impurities, located to the right of chromium in the periodic table such as Rh and Re, to the chromium matrix increases the electron to atom ratio, resulting in an increase in the magnetic moment compared to pure chromium. This in turn is expected to result in an increase in the hyperfine fields at probe nuclei in these alloys. The measured hyperfine fields are in qualitative agreement with the expected changes in these alloys.

Recoil implantation of100Pd(3.6 d) activity in different host matrices following heavy ion reactions

The large recoil energies offered by the heavy ion nuclear reactions were used to implant the100Pd(3.6 d) activity into different host matrices. The sources thus prepared were found to have good strengths and small background activities. The yields were quite high ∼3μCi/1μAh beam current of12C4+ and the efficiencies of implantation were in the range 60–70%. The difference in the recoil energies of the target and the catcher may be used to reduce activities due to unwanted nuclear reactions in the catcher foil. Using this method, we were able to prepare excellent sources of100Pd in Be, Mg, Ti, Zr and Re hosts. The quality of these sources is comparable to that of the100PdBe ion implanted sources for which data are available in the literature.