Техническое чтение для энергетиков. Бухарова Г.П. - 7 стр.

UptoLike

ВУЗ: 

УлГТУ | Ульяновск

Составители: 

Рубрика: 

9
is, like many other heavy-element isotopes, 'unstable'.
What does this mean? Nothing else but the phenomenon which the Curies
discovered in radium. An unstable nucleus is one that is likely to break up into the
nucleus of another element. Professor Otto Hahn found in Berlin in 1938 that when
uranium atoms are bombarded with neutrons they split up in a process which he
called 'fission' (a term used in biology for the way in which some cells divide to form
new ones). The 92 protons of the uranium nucleus split up into barium, which has 56,
and krypton, a gas with 26 protons. Frederic Joliot-Curie, the son-in-law of Marie
Curie, proved some months later that in this fission process some neutrons from the
uranium nucleus were liberated; they flew off, and some struck other nuclei, which in
turn broke up, liberating still more neutrons. Enrico Fermi, an Italian who had gone to
America to escape life under fascism, developed the theory of what would happen if a
sufficiently large piece of unstable uranium broke up in this way – there would be a
'chain reaction': the free neutrons would be bombarding the nuclei with such intensity
that in no time at all the whole lump of uranium would disintegrate.
But it would nut just turn quietly into barium and krypton as in Berlin
laboratory experiment. There were now two smaller nuclei, no longer held together as
before but pushed apart by electric repulsion, and flying off at great speed, with
neutrons shooting about in all directions. And such sudden display of energy–for
movement is energy – would, according to Einstein's famous Mass-Energy equation,
correspond to some loss of mass. If the two parts of a nucleus which has undergone
fission could be put together again, their combined mass would be smaller than that
of the original nucleus. What has become of the missing bits? They have turned into
pure energy – into movement, into heat.
This was the theory that led, within the short space of four years, to the first
atom bombs. On Monday, 6 August 1945, while cheerful crowds in England enjoyed
their first holiday after the end of the war in Europe, one such bomb was dropped on
the town of Hiroshima in Japan. It killed or injured nearly 200,000 people. Three
days later another bomb was dropped on Nagasaki, with 65,000 victims. The centres
of both cities were completely destroyed.
PEACEFUL ATOM
When the world had recovered from the shock of this unimaginable horror,
people everywhere asked the scientists how soon they could apply the immense
power of the fissioned nucleus to peaceful purposes. But this took much longer. It
was considerably easier to use the nuclear chain reaction for distruction than for the
production of usable energy for homes and factories–to control it and release it in
small doses. Many problems had to be solved; the main one was that of 'braking' the
released neutrons efficiently so that the chain reaction would not get out of hand.
The first atomic 'pile' or 'reactor', as the apparatus for the utilization of atomic
energy is now called, had been Set up by Enrico Fermi on the football ground of the
University of Chicago in 1942. It was a somewhat crude assembly, whose main
purpose was to get experimental proof for the theory of chain reaction. Fermi

Страницы