Lee, Paul Choon Keat

Studies indicate primary school students' interest and attitudes towards science decline as they progress into the secondary years. Experience shows that Singapore students are no exception. Knowing these students’ perceptions of science and understanding of science concepts should help in developing pedagogical approaches and lesson packages that will address the decline. Therefore, in our on-going study data are collected from students of six secondary one classes in a school in Singapore to learn of their views of science, reasons for liking or disliking science and their understanding of the topics in the science curriculum before and after instruction. This is done for a range of physics topics in their science syllabus. In this paper, we report the preliminary findings on the topic “Forces at Work” consisting of two sub-topics, ‘Moment of Force’ and ‘Work Done’. We group our findings into three main categories, ‘Students’ Perceptions’, ‘Students’ Preconceptions’ and ‘Students’ understanding of concepts’. Among the early findings are 1) students are confused between the two concepts of ‘Moment of Force’ and ‘Work Done’ 2) students are concerned about having to memorize a lot of information and solve many quantitative problems 3) students prefer to be given opportunities to carry out experiments as a means of verifying physics concepts to theory lessons where information is passed on to them verbally, and 4) students are good at using keywords as reasoning without actually understanding what they mean. This study surfaces key issues in understanding these young students’ learning journeys in the world of science. As such, the results from this research can guide curriculum development. We will be developing a curriculum that take into account these research results and the constraints of the school.

A phenomenographic study of Singapore students' understanding of physics was undertaken to compare results to a previous study by Australian researchers. The focus was on simple mechanics concepts related to displacement, velocity and frames of reference study. The research found many similarities but some differences between the two groups of students. There are several implications for successful physics learning and teaching in Singapore.

A 3 kJ plasma focus was operated with a 3He-D2 gas mixture, with partial pressures in the ratio of 2:1, corresponding to an atomic number ratio of 1:1 for 3He and D atoms. The fusion reactions D(3He,p)4He and D(d,p)3H were measured simultaneously using CR-39 polymer nuclear track detectors placed inside a pinhole camera positioned on the forward plasma focus axis. A sandwich arrangement of two 1000 μm thick CR-39 detectors enabled the simultaneous registration of two groups of protons with approximate energies of 16 MeV and 3 MeV arising from the D(3He,p)4He and D(d,p)3H reactions, respectively. Radial track density distributions were obtained from each CR-39 detector and per-shot average distributions were calculated for the two groups of protons. It is found that the D(3He,p)4He and D(d,p)3H proton yields are of similar magnitude. Comparing the experimental distributions with results from a Monte Carlo simulation, it was deduced that the D(3He,p)4He fusion is concentrated close to the plasma focus pinch column, while the D(d,p)3H fusion occurs relatively far from the pinch. The relative absence of D(d,p)3H fusion in the pinch is one significant reason for concluding that the D(3He,p)4He fusion occurring in the plasma focus pinch is not thermonuclear in origin. It is argued that the bulk of the D(3He,p)4He fusion is due to energetic 3He2+ ions incident on a deuterium target. Possible explanations for differing spatial distributions of D(3He,p)4He and D(d,p)3H fusion in the plasma focus are discussed.

The dense plasma focus (DPF) device is a coaxial plasma gun that uses a large electric current to heat and compress a gas to high temperatures (1-2 keV), densities (1025-26 m-3) and pressures (thousands of atmospheres). Under such extreme conditions, the gas radiates copious ultraviolet, X-rays and particle beams such as relativistic electrons and ion beams. At Plasma Radiation Sources Laboratory (PRSL), NIE, Singapore, our group has six plasma focus devices and our research efforts encompass a very wide range of topics covering various fundamental aspects of plasmas to the application of this device to lithography, soft and hard x-ray imaging, material modification and thin film deposition. This review paper reports the use of single shot and “repetitive” PF device for processing and deposition of thin films using plasma focus devices. To synthesize the magnetic thin films, the conventional hollow copper anode was substituted with an anode fitted with suitable material tip (FeCo or CoPt). Si wafer and copper mesh were placed axial down the anode axis at a suitable distance of about 25 cm above the anode top to improve the uniformity of deposited samples over bigger substrate size. The plasma focus device is operated at 1 Hz repetition rate at various combinations of charging voltage and filling pressure of hydrogen gas for different number of focus deposition shots. For the processing of thin films, the magnetic thin films of FePt were initially deposited using pulsed laser deposition and later exposed to energetic ions from hydrogen operated plasma focus device. The morphology, structure and magnetic properties of the synthesized and processed thin films are investigated using TEM, SEM, XRD and VSM, respectively. The paper will also discuss the fundamental of thin film deposition and irradiation mechanisms in plasma focus devices.

The main aim of this 3-year project was to develop, implement and evaluate a guided-inquiry curriculum in a local secondary school using the Physics by Inquiry (PbI) “research–development–instruction” iterative approach. Our study showed that students' interest in Science is a key predictor of future aspiration to learn the subject and reinforces the need to shape positive attitudes towards Science, especially at the lower secondary level. Overall, students and teachers held favourable perceptions regarding the inquiry-based curricula and instruction, citing hands-on activities, self-directed learning, learning from peers, and opportunity for consolidation as important features in engaging them in learning. Students' conceptual understanding and reasoning abilities were also enhanced after the intervention. These findings suggest that the curriculum materials have been effective in providing structured guidance to students to promote their learning of Science through evidence-based reasoning, problem solving and argumentation.

The NX2 device, a low energy plasma focus, at the Nanyang Technological University in Singapore, was used as a soft X-ray (SXR) source for micromachining. The gas used was neon which produced SXRs in a narrow spectral range of 0.9 - 1.6 keV. The SXR yield from repetitive operation of the NX2 device was monitored and measured using a cost effective multi-channel SXR spectrometric system. The system consists of filtered BPX65 PIN diodes, with the associated electronics --- an integrator, sample and peak holder, analogue switch, an A/D converter and a microcontroller. The system enables easy shot-to-shot statistical analysis under repetitive operation at adjustable preset trigger frequencies. A total of 4000 shots were fired at 0.5 Hz, using the same gas filling. The SXR production was at an average yield of 60 J/shot and a maximum single-shot yield of more than 100 J. The SXRs emitted by the NX2 device was used for contact micromachining, producing structures with an excellent aspect ratio of up to 20:1 on 25 μm SU-8 resist.

Tungsten (W) is considered as one of the promising candidates for plasma facing components in fusion reactors since it has high threshold energy, high melting point, low threshold shock resistance, and resistance against formation of co-deposits with tritium. Despite these commendable features, helium ions produced during fusion reaction are known to alter the microstructure of tungsten. In this work, dense plasma focus (DPF) device is used to study the effect of helium ion flux on double forged tungsten samples delivering a heat load of 6.27×104J/m2 per shot. The irradiation of virgin W samples is carried out at 5, 10, and 15 DPF helium shots. High heat loads resulted in blisters and micro-cracks on the sample surface. With an increase in the number of shots, the density of the blisters increased and craters on the W surface burst followed by re-solidification of the melted and sputtered surface. Surface nano-structurization, with nanoparticle formation, of W samples (nano-W) is realized by high-energy argon ion exposure of virgin samples in an argon filled DPF device. The average size of nanoparticles is found to increase with the number of shots and also leads to particle agglomeration. At 10 shots, uniformly distributed highly dense nanoparticles of 20–50 nm size have been synthesized. The nano-W samples are then irradiated by instability-accelerated high-energy helium ions in helium filled DPF device for 5, 10, and 15 shots to simulate fusion relevant conditions. The presence of the trapped helium bubbles in virgin-W and nano-W are examined by BSE imaging and XRD, respectively. The nanostructured tungsten shows improved structure and surface properties against Helium ion irradiation.

"The main purpose of this project is to develop, implement and evaluate a guided-inquiry curriculum using the Physics by Inquiry (PbI) instructional approach. We wanted to investigate the effect of the inquiry-based curriculum and instruction on students' conceptual development and attitude towards the learning of Science. The research questions guiding the project were: 1) What are the favourable modifications in adapting the PbI instructional approach for improving the learning of lower secondary Science in Singapore? 2) What are the differences in the learning outcomes when students learn Physics through the inquiry approach as compared to the standard classroom practices? 3) What are the perceptions of teachers and students on teaching and learning Physics by inquiry in the classroom?" -- p. 2.