A low-temperature X-ray camera

The paper contains a description of a low-temperature X-ray camera suitable for the examination of small plates. The specimen under examination is cooled in a stream of air for temperatures in the range between room temperature and -170° C, and by dropping liquid air on it for the lowest temperature reached (-194° C). Temperatures were measured directly with a copper-constantan thermocouple for single specimens or by reference to the lattice parameter of a standard material for double specimens. These temperatures were taken whilst the specimens were being simultaneously rotated and oscillated. The results obtained with silver and iron are quoted. The coefficients in the expansion equation a t = a 0 (1 + α t + β t 2 + γ t 3 ) for these metals were found to be as follows: Silver: α = 18.2606 × 10 -6 , β = 3.9156 × 10 -9 , γ = - 17.2794 × 10 -12 , and a 0 , the lattice parameter at 0° C, is 4.0760 kx ; Iron: α = 11.9784 × 10 -6 , β = 15.8447 × 10 -9 , γ = - 3.2973 × 10 -12 , a 0 = 2.8598 kx .