Bulletin Summer 1975

Helium Liquefaction Plant has mostly died down, and it becomes possible to study many interesting properties of solids without interference from the thermal effects. It is for the study of these properties that liquid helium is so much in demand for use as a coolant in laboratories all over the world. The liquefaction of helium is a rather complicated process: the helium gas must first be cooled by liquid nitrogen (produced by a separate machine) to about -200°C, then further cooled by expansion under negative pressure to about —240°C befor e it is allowed to undergo a throttling process which reduces the temperature of part of the gas yet further for liquefaction to take place. The machine can produce about 3 litres of liquid helium per hour in this manner. Since helium is a rather expensive commodity, the plant also provides a gas ba g and a large compressor, which allow the recovery of the vaporized gas from the experimental stations where liquid helium is used. A Ge(Li) Gamma-ray Spectrometer System for the Neutron Generator Laboratory The International Atomic Energy Agency, which provided the University with a 14-MeV neutron generator under its Regular Programme of Technical Assistance 1972, has agreed to render technical assistance under its 1975 Programme, which includes the provision of an expert for a period of six months and a complete set of high-resolution Ge(Li ) (Lithium- drifted Germanium detector) gamma-ra y spectrometer system costing US $25,000. Owing to substantial improvement in resolution , compared with other gamma-ray detectors, the Ge(Li) detector is becoming a very important and widely applicable research tool. Many nuclear energy levels which cannot even be seen with other detectors, are identified easily with Ge(Li) detectors. With the installation of the high-resolution Ge(Li) gamma-ray spectrometer, work with the 14-MeV neutron generator can be extended to such projects as: 1. Activation analysis of ecological samples for pollution control, 2. Activation analysis o f archaeological samples found in Hong Kong, 3. Activation analysis of biological and medical samples, and 4. Nuclear decay scheme study by means of beta-gamma coincidence measurements. Revised Academic Programme To make the science curricula more flexible to meet the different needs of the students, two patterns of combination o f degree examination papers will be introduced for Science students in 1975: (a) strong major pattern—with six papers in the major subject and two papers in the minor subject, and (b) major and double-minor pattern 一 with four papers in the major subject and normally two papers each in two minor subjects. Each department will draw up the possible combinations of major and double-minor subjects for its major students, but the minor subjects are not confined to the Science Faculty. 4