[en] Current knowledge of the Solar System, with a particular emphasis on the systems of interplanetary objects, is reviewed, and the theory of meteors and the reflection of radio waves from meteoric ionization is then discussed. A description of the meteor radar is given and a method of calibrating the antenna beam is developed. The main project comprises two parts: A general survey of the radar echo-rate for 20 major and minor meteor streams and the sporadic meteor background, conducted from Grahamstown over the period 1986 April to 1988 January, is described. Definite shower activity was observed for all of the major and some of the minor showers. A method of recovering meteor radiant distributions from the distribution of echo direction was developed. A technique of compensating for possible distortions of the resulting radiant maps, which may arise due to the anisotropic antenna beam was devised. This involved a system of echo-weighting. Radiant maps which showed considerably less distortion were obtained without the weighting procedure. It is concluded that, although the method in its present form introduces spurious features into the maps, the principle is sound and should eventually be refined to produce the desired compensation. 71 refs., 165 figs., 2 tabs

[en] Mean-field theories predict the emergence of strong shell gaps for particle numbers 32 and 40 when the nucleus adopts a non-axial octupole (tetrahedral) shape. There is therefore good reason to expect "7"2Ge, with Z = 32 and N = 40, to be a strong candidate to exhibit such shapes, and this nucleus was therefore studied via the "7"0Zn(α,2n)"7"2Ge reaction at a beam energy of 30 MeV. Coincident γ-rays were measured with the AFRODITE spectrometer comprising nine Clover detectors. We found no evidence for tetrahedral states in our data. However, our extension of the previously existing level scheme included a new, negative-parity, even-spin band. This band is likely the unfavored signature partner of the band built on the previously-known I"π = 3"− state at 2515 keV. The two negative-parity bands are interpreted as involving an aligned octupole vibration which evolves to a four-quasiparticle structure at higher spins. This talk presents spectroscopic evidence for the new band, summarizes the spin-parity assignments, and discusses the proposed configuration. (author)

[en] High-spin states in the nucleus ⁷²Ge were investigated via the ⁷⁰Zn(α, 2n)⁷²Ge reaction at a beam energy of 30MeV, using the AFRODITE spectrometer. One aim of the study was to search for tetrahedral states. There was no evidence for such states in our coincidence data. The existing decay scheme was substantially revised and extended. Several γ -ray placements and level spin-parities were changed, and some 30 new transitions were added to the level scheme. One new negative-parity rotational band was identified. The new band is likely the unfavoured signature partner of the band built on the previously known I^π=3^- state at 2515keV. The two negative-parity bands are interpreted as involving an aligned octupole vibration which evolves to a four-quasiparticle structure at higher spins. The upbend in the yrast band is interpreted as the AB neutron alignment. The band structures are discussed with reference to Cranked Shell Model calculations, the aligned angular momenta, experimental routhians, and moments of inertia. (orig.)

[en] High-spin states in ¹⁹⁷Bi were studied with the AFRODITE γ-ray array at iThemba LABS using the ¹⁸¹Ta(²²Ne, 6n) reaction at a beam energy of 125 MeV. A new shears band was found and linked to the low-lying states in ¹⁹⁷Bi. Its dynamic moment of inertia, I⁽²⁾, is considerably larger than the I⁽²⁾ of the shears bands in the neighbouring Pb isotopes. This is probably a result of the involvement of an additional high-K h_9/2 proton orbital. (orig.)

[en] Excited states in ¹⁶⁴Ta were populated in the ¹⁴²Nd(²⁷Al,5n)¹⁶⁴Ta reaction and investigated using the AFRODITE spectrometer array. The yrast rotational decay sequence up to spin 21^- is identified for the first time and assigned to the π[514]9/2^-(multiply-in-circle sign)ν[660]1/2⁺ configuration. A less intense, excited band is also identified. Low-spin signature inversion is observed in the yrast band, and is compared with the extended total Routhian surface calculations. It is likely that quadrupole pairing plays a role in generating the anomalous signature splitting, but an additional mechanism apart from the assumed mean field and quadrupole pairing interaction may be required to account for the experimental data

[en] The Recoil Shadow Anisotropy Method for measuring nanosecond lifetimes is being implemented on the AFRODITE array and four new isomers were found in ^198,200Bi, ¹⁶⁴Ta and ¹⁶²Lu. (orig.)

[en] Low-spin positive-parity yrare states of ₆₆¹⁵⁴Dy₈₈ were established using the ¹⁵⁵Gd(³He,4n) reaction at a beam energy of E_lab = 37.5 MeV. The AFRODITE spectrometer array at iThemba LABS was used to record γγ coincidences and measure DCO ratios and polarisation asymmetries. The K^π = 2⁺ γ band has been observed up to spin 13⁺ in the odd spins and to 12⁺ in the even spins. The staggering parameter S(I) of the γ band is compared to that found in other N = 88 isotones. Different behaviour of S(I) with increasing spin is observed for each of the isotones. We conjecture that the variation in S(I) is mainly due to mixing of the even-spin states with the same spin and parity states in neighbouring rotational bands. A second K^π = 2⁺ band has been established up to a spin of 12⁺ in the even spins. We suggest that this is a γ band based on the J^π = 0⁺ state at E_x = 660.6 keV. (orig.)

[en] The concept that the first excited 0⁺ states in N=90 nuclei are not a β -vibration but a second vacuum formed by the combination of the quadrupole pairing force and the low density of oblate orbitals near the Fermi surface is supported by the blocking of this collective mode in ¹⁵⁴Gd from coupling to the [505]11/2^- single-particle quasi-neutron orbital in ¹⁵⁵Gd. The coupling of this orbital to the 2⁺ γ -vibration in ¹⁵⁴Gd is observed since this coupling is not Pauli-blocked. (orig.)

[en] We have used the AFRODITE γ-ray spectrometer to measure yrare structures in ^152,154,155Gd using (α,xn) reactions. The measurements on ^152,154Gd have shown that there is no convincing evidence that the lowest excited 0₂⁺ states are β-vibrations based on the 0₁⁺ ground state. Rather these levels may be regarded as a 'second vacuum' each with its own γ and octupole vibrations. This is confirmed by the blocking of the coupling of this core 0₂⁺ state in ¹⁵⁴Gd to the [505]11/2^- single-particle quasi-neutron orbital in ¹⁵⁵Gd. The coupling of this orbital to the 2⁺γ-vibration is observed since this coupling is not Pauli-blocked.

[en] The full-spectrum analysis (FSA) method was used to determine primordial activity concentrations (ACs) in soil, sand and ore samples, in conjunction with a HPGe detector. FSA involves the least-squares fitting of sample spectra by linear combinations of ²³⁸U, ²³²Th and ⁴⁰K standard spectra. The differences between the FSA results and those from traditional windows analyses (using regions-of-interest around selected photopeaks) are less than 10% for all samples except zircon ore, where FSA yielded an unphysical ⁴⁰K AC