Design and Construction of Pneumatic Transfer System Controller Unit for Ghana MNSR

Pneumatic Transfer System (PTS) is an auxiliary system of Ghana Research Reactor-1 (GHARR-1) used to transfer sample capsule in and out of the reactor irradiation sites. The PTS’ controller unit design and construction were carried out because the original transfer system was not designed to operate in cyclic NAA. To address these situations, a Programmable Logic Controller (PLC) has been used to design and construct a control unit to facilitate a cyclic neutron activation analysis (CNAA) application for GHARR-1. The design has been simulated successfully using a LOGO Soft Comfort software, version 8. The constructed control unit has been tested experimentally using 220 AC volts electric bulbs to represent solenoid valves. The results show that the sample-IN and sample-OUT bulbs come ON and go OFF to represent the solenoid valves opening and closing for sample transfer. The study has shown that the computer based PLC controller unit for PTS is capable of facilitating both cyclic and conventional NAA application for the GHARR-1.

Nonstoichiometry effects on microstructure in amorphous CdGeAs2

The mechanism of nucleation and growth in amorphous semiconducting CdGeAs2 has been demonstrated with the aid of thermal analysis, TEM, and XRD to be: 1) germanium precursor formation, 2) nonstoichiometric chalcopyrite structure crystal growth from the germanium precursor, and 3) solid state transformation of the precursor to the chalcopyrite structure. This crystallization sequence does not follow the pseudo-binary phase diagram which indicates that only in the case of germanium content in excess of stoichiometric CdGeAs2 should α solid solution form in equilibrium with chalcopyrite structured CdGeAs2 (see Fig. 1). To establish the extent of the germanium precursor nucleation mechanism, samples of deficient (CdGe0.8As2), stoichiometric, and excess (CdGe1.2As2) germanium content were prepared in the bulk amorphous form.Samples were fabricated by water-quenching the molten compound, vacuum sealed in carbon coated (by pyrolysis) fused silica tubes. The amorphous ampoules were broken out of the tubes, sliced to fit the hermetically sealing sample capsule for the differential scanning calorimeter (DSC) and heat treated at 0.5°C/min to various points along the exotherms. The partially devitrified samples were mechanically thinned and ion-milled using a liquid nitrogen cold stage, for examination in the TEM.