NEUTRON DIFFUSION MEASUREMENTS IN WATER FROM 18 DEGREES C TO 280 DEGREES C

The pulsed-neutron method has been used to measure the temperature dependence of both the diffusion constant and the extrapolated end point in water. The measured temperature dependence of the diffusion constant was found to be in good agreement with the theoretical values predicted by the Nelkin kernel. Measurements of the extrapolated end point in a cylinder of diameter 7 in. and height 7 in. gave a value of 0·323 ± 0·013 cm, with a similar result for a 7 in. cubical system. For an 8 in. diameter cylinder 4 in. high, however, the value was 0·465 ± 0·039 cm, a change which would not be expected theoretically. The extrapolated end point was also measured at temperatures up to 250°C. For a 4 in. high cylinder no definite temperature dependence was observed, but in a 16 in. high cylinder there was an increase with temperature from 0·340 ± 0·030 cm at 18°C to 0·469 ± 0·021 cm at 250°C.