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69
The first of the man-made additions were from the machines for the
production of X-rays. They were closely followed by the extraction of
naturally active nuclides, radium and thorium from uranium ores (these
provide mainly gamma rays). There has been the fall-out from detonated
bombs (which have added less than 1% to the inescapable dose). With
the construction of the reactors came not only the isotopes (over 1,000
of them), but also organic compounds tagged with radio-active elements.
Incidental to the production of nuclear fuel came an accumulation of
mixed fission products, and with them the problem of disposal of waste.
Of the hazards, that of greatest potential is from the reactors.
In 1956 the Medical Research Council issued a report on the Hazards
to Man of Nuclear and Allied Radiations. About the dangers of the
different sources of radiation this said : "If the dose of radiation from
natural sources to the gonads of the general population is expressed as
100, then the following percentage figures show the additional estimated
doses that may be expected from artificial sources: diagnostic radiology,
at least 22; radiotherapy, unkown; shoe-fitting, 0.1; luminous watches
and clocks, 10; television sets, much less than 1.0; high-altitude
flying, insignificant; occupational exposure to radiology, at least 1.6;
Atomic Energy Authority, 0.1; fall-out from test explosions, less than
X-Rays. This is considered to be the greatest contribution to
radiation hazard at present. In regard to the risks from X-rays, the report
said—"We consider that the time has come for a review of present
practice in diagnostic radiology, and of certain uses of radiation in the
treatment of non-malignant conditions, particularly in children. Among
the less important sources of radiation, we hope that the use of x-rays in
shoe-fitting will be abandoned except when prescribed for orthopaedic
reasons ; that watches and clocks with radioactively luminous dials will
be confined to necessary uses ; and that the x-ray hazard from television
tubes, at present negligible, will be borne in mind if special types of
high-voltage equipment come to be widely used."
Particularly because of the risk to children whose mothers have been
exposed to x-rays, especially of the pelvic organs during pregnancy,
X-ray exposures are being more carefully controlled, and greater precautions
are being taken to ensure that x-ray apparatus is properly
shielded. Legislation has recently been introduced for the control of
pedoscopes.
Isotopes. Up to ten years ago, the main source of radiation was
argely confined to hospitals, physics departments of universities and some
heavy industry establishments. Today, the situation is very different,
There is widespread employment not only of closed sources but of nuclides
(naturally and artificially produced elements for distributive employment
in solution). Nuclear reactors are the main sources of deliberately
Produced radio-isotopes whether they are the result of nuclei fission or
nuclear bombardment whereby the nuclei of very heavy elements such as
uranium, plutonium or thorium are struck by neutrons and are disrupted,
Isotopes are generally used only in minute amounts. Some are used in
ustry (cobalt, caesium, iridium, tantalium 182, thulium, strontium 90).