The method of production of mercury-198 is particularly interesting,
pure gold being irradiated with neutrons in an atomic pile to trans
mute it into mercury. This is nothing less than alchemy in reverse!
The krypton isotope lamp and its associated cryostat for liquid
air is depicted in figure 2. The lamp is to the right of the picture,
fastened to the underside of the lid of the cryostat. When the
cryostat is filled with liquid air the lid is placed in position (the
lamp then being inserted into the liquid) and the space above the
liquid surface is evacuated with a fast pump. The liquid air then
cools by evaporation to about 63° K, approximately the triple-
point of liquid nitrogen. The lamp has a thermionic cathode and is
operated by direct current. Krypton isotope is prepared by thermal
diffusion from the natural gas.
Principles of Interferometry
Interference takes place between two (or may be more) mono
chromatic beams of light which are said to be coherent, or in other
words, the light constituting each beam has derived from the same
excited atoms in the source. Such beam division is generally
achieved by using a partially reflecting optical flat, the beam of
light transmitted by it being coherent with the light reflected.
When coherent beams of monochromatic light are recombined
their waves "interfere" to produce darkness at points of opposite
phase and brightness at points of equal phase. These bands of
light or dark are called "fringes" and figure 3 shows two types of
100
Interference of light.
PARALLEL MIRRORS,CONVERGENT BEAM.
INCLINED MIRRORS PARALLEL BEAM.
Fig- 3-
