THE SHADE OF J. BALLANTINE HANNAY 235
the
reason for these reactions as far as has been figured out. The atoms of
any crystal are arranged in a fixed pattern that repeats over and over
one unit structure. This structure, or repetition, of units, is called
the "lattice," and in some crystalline substances it is a complicated
arrangement but in the diamond it is quite simple. Each atom consists
of a nucleus and its surrounding electrons, which ceaselessly move in
fixed orbits around the nucleus like planets around a sun. Every
nucleus is made up of protons and neutrons: a proton carries one unit
of positive charge; an electron one of negative charge; a neutron
canies neither, which is why it's called a neutron. The number of
protons in the nucleus is matched by the number of electrons revolving
about it.
When
a diamond is irradiated, it is bombarded by more neutrons, which come
along at such speed and force that they knock some of the diamond atoms
out of position. This starts up a lot of excitement within the crystal.
The knocked-out atoms push other atoms out of place, which in their
turn crowd out yet more, until the entire lattice becomes disarranged,
with atoms hanging halfway between the original positions. Thus the
crystal is to some extent transformed, and some of its qualities are
changed—those qualities which depend on its original atom structure,
chiefly light absorption or, as we see it, color. Changes may also take
place in thermal conductivity, thermal expansion, and electrical
conductivity, but we don't observe these, though Dr. Custers can with
his machines. The general change, or "radiation damage," appears to be
permanent, and it is at ordinary temperature; it is "stable." But it's
not stable when the diamond is subjected to higher temperature. Then
the displaced atoms get stirred up and develop enough energy to go
