34 research outputs found
Related Data for: Plasma focus neutron energy and anisotropy measurements using zirconium-beryllium pair activation detectors
No full textZirconium and beryllium fast-neutron activation detectors are used to investigate the fusion neutron emission from the NX3 Plasma Focus (PF) device operated in deuterium gas, with 7.2 kJ bank energy. Both Zr and Be activation cross-sections increase with energy, but with different trends, enabling an effective neutron
energy eff n to be inferred from the Zr/Be count ratio. The relationship between eff
n and Zr/Be count ratio is established by MCNP5 simulation. Compact Zr/Be detector pairs were positioned at 0◦ and 90◦ to the PF axis, permitting measurements of neutron yield, energy- and fluence-anisotropy to be made for each shot. Series of NX3 shots were performed for D2 gas pressures ranging from 1.5 to 10 mbar. Typical effective neutron energies eff n for the 0◦ and 90◦ directions are found to be ∼2.8 MeV and ∼2.5 MeV, respectively. The highest neutron yields of ∼109 neutron/shot were observed for 5 mbar D2 gas pressure. Neutron fluence-anisotropy nBe for individual shots ranged from ∼2.5 to ∼4.5. The mean value ⟨nBe⟩ exhibits a steady decline with increasing D2 gas pressure. By contrast, neutron energy-anisotropy n remains almost constant as the D2 gas pressure is varied. The effect of blocking the forward D+ ion beam with an obstacle plate positioned 6 cm in front of the anode tip is also studied. Marked reductions in both neutron yield and fluence-anisotropy are observed, whilst the effective neutron energy eff n increases slightly at both 0◦ and 90◦ directions. Fusion contributions from thermonuclear or gyrating-particle processes are found to be negligible. All results are completely consistent with a straightforward beam–target model of PF fusion
Meeting the challenge of problem based learning in physics
No full textA modified Problem Based Learning (PBL) approach has been implemented and evaluated for the laboratory sessions of the Thermal Physics first year undergraduate module in academic year 99/00. The principal objective of this PBL approach is to get away from the 'cookbook' approach to teaching laboratories, and instead transform them into micro-research projects which demand higher order cognitive involvement of the students. This modified PBL approach involved conducting two hour laboratory sessions for each experiment: one hour from each of two consecutive weekly classes. The first week's session was rounded off with a question and answer session aimed at promoting higher order cognitive involvement by the students in the experimental work. The students conducted and discussed the experiments in groups of 3 to 4, while I acted as facilitator. One observation is that the weaker students in the class are uncomfortable with the lack of a detailed experimental demonstration. Comparing the student reports for academic year 99/00 (PBL approach) with those from 97/98 (conventional approach), indicates that student's have higher cognitive understanding of the experiments enabling them to answer questions more competently, and their integration and retention of knowledge is enhanced. Moreover the students were more involved and devoted more energy and enthusiasm to the experimental work when the modified PBL approach was employed in comparison to the more conventional approach to laboratory work
First experimental results using singer product apertures
No full textWe present the first experimental results obtained using Singer product apertures. We image X-rays scattered from spherical aluminium targets, using a Crypix detector. Despite the relatively low resolution of the apertures, 13 × 13 and 21 × 21 pixels drilled into a tungsten sheet, much higher resolutions are achieved in practice using Fenimore and Cannon’s fine sampling and delta decoding techniques
Plasma focus neutron anisotropy measurements and influence of a deuteron beam obstacle
No full textThe deuterium-deuterium (DD) fusion neutron yield and anisotropy were measured on a shot-to-shot basis for the NX2 plasma focus (PF) device using two beryllium fast-neutron activation detectors at 0° and 90° to the PF axis. Measurements were performed for deuterium gas pressures in the range 6–16 mbar, and positive correlations between neutron yield and anisotropy were observed at all pressures. Subsequently, at one deuterium gas pressure (13 mbar), the contribution to the fusion yield produced by the forwardly-directed D+ ion beam, emitted from the plasma pinch, was investigated by using a circular Pyrex plate to obstruct the beam and suppress its fusion contribution. Neutron measurements were performed with the obstacle positioned at two distances from the anode tip, and also without the obstacle. It was found that ~ 80% of the neutron yield originates in the plasma pinch column and just above that. In addition, proton pinhole imaging was performed from the 0° and 90° directions to the pinch. The obtained proton images are consistent with the conclusion that DD fusion is concentrated (~ 80%) in the pinch column region.Accepted versio
Correlation Analysis of Intense and High-Energy Deuteron Beam, Pinch Images, and Neutron Yield
No full textPulsed fast neutron yield measurements based on 79BR activation in LaBr3(CE)
No full textThis work aims to test the concept of an activation detector for pulsed DD fusion neutron sources, based on the production of metastable 79m within a LaBr3(Ce) scintillator crystal via (n, n') inelastic scattering. The pulsed neutron source employed is the NX3 Plasma Focus (PF) device operated in deuterium gas, which yields about 109 neutrons per shot. A range of D2 gas pressures, from 1 to 13 mbar are used to vary the test conditions. For the sake of comparison, a beryllium fast-neutron activation detector is used simultaneously with the LaBr3(Ce), and for each NX3 PF shot we derive neutron yield values from both Be and LaBr3(Ce) detectors, denoted YnBe and YnLaBr. The two detectors are positioned in the equatorial plane (θ=90˚) of the NX3 to expose them to bursts of neutrons with energies close to 2.5 MeV, to simulate a thermonuclear DD fusion source. Overall, the shot-to-shot values of YnBe and YnLaBr obtained compare reasonably well. At each D2 gas pressures the 10-shot averaged values〈YnBe〉 and 〈YnLaBr〉are mostly within 10% of one another; for the worst case (10 mbar)〈YnLaBr〉is 25% higher than〈YnBe〉. Overall, it is concluded that LaBr3(Ce) scintillation detectors can function as a capable and readily obtainable fast-neutron activation detector for measuring neutron yields from pulsed DD fusion sources.Accepted versio
Geometrical characterization techniques for microlens made by thermal reflow of photoresist cylinder
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