Testing approaches to fusion

Last month, at the Princeton Plasma Physics Laboratory, physicists and engineers built tracks inside one of its fusion reactors and ran a toy train on them for three days. It was not an exercise in silliness, but in calibration.

The modified model of a diesel train engine was carrying a small chunk of californium-252, a radioactive element that spews neutrons as it falls apart.

“We needed to refine the calibration technique to make sure we are measuring our neutrons as accurately as possible,” said Masa Ono, the project head of the National Spherical Torus Experiment.

The experiment is a small reactor designed to test new approaches to fusion, in which hydrogen atoms are fused together at ultrahigh temperatures to produce energy, as the Sun does. Fusion generates copious numbers of neutrons, which tell how well the reaction is proceeding.

The reactor has been shut down for improvements, and the downtime provided an opportunity for re-calibrating the neutron sensors.

A stationary neutron source was previously used for the calibration, but that did not fully capture how the neutrons bounced around. Putting the californium on the moving train improved the accuracy by about a factor of 10, Ono said. (The same technique had been used two decades earlier at one of Princeton laboratory’s older reactors.) Experiments at the reactor are set to restart in March.

Kenneth Chang
NYT News Service

What does the litmus paper tell?

Litmus paper is used to tell whether a solution is acidic or basic. The paper is dipped in the solution and a colour change either to blue or to red does the trick. Similar, easy-to-use paper strips have been developed for checking the presence of pesticides in food and water.

Tests for detecting pesticides are expensive, time consuming and require complex equipment. The paper strip can produce the same result within five minutes. Researchers from the department of chemistry and chemical biology, McMaster University in Canada described the working of these dips in an issue of Analytical Chemistry. The test strip is one cm wide and 10 cm long. Acetyl-cholinesterase and a colour producing chemical indophenyl acetate (IPA) are deposited on the paper in two different zones: sensing and substrate. Acetyl-cholinesterase is an enzyme responsible for proper nerve impulse transmission. The organophosphate pesticides work by inhibiting the enzyme. The colour of the substrate (IPA) is yellow and  in presence of pesticides, it changes to bluish-purple. To perform the test, the researchers dipped the strip in the substance which could have the pesticide so that it reached the sensing zone.

Then the strip was removed and the opposite end, containing the susbtrate zone, was dipped in purified water. This caused the IPA to dissolve in the water and move towards the sensing zone. The change of the substrate’s colour to bluish-purple was easily visible. The strip can be used by the food industry and in under-developed regions where performing the conventional tests would be difficult in the absence of electricity.

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