When y-rays or x-rays fall on matter they give rise to ß-rays.
The mechanism involved is not known but it is possibly a result
of the resonance of the atom, or of parts of it, to the short
light waves. And it is remarkable that the y-rays which, as we
have seen, are shorter and more penetrating waves than the
x-rays, give rise to ß-rays possessed of greater velocity and
penetration than ß-rays excited by the x-rays. Indeed the ß-rays
originated by y-rays may attain a velocity nearly approaching
that of light and as great as that of any ß-rays emitted by
transmuting atoms. Again there is demonstrable evidence that
ß-rays impinging on matter may give rise to y-rays. The most
remarkable demonstration of this is seen in the x-ray tube. Here
the x-rays originate where the stream of ß- or cathode-rays
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are arrested on the anode. But the first relation is at present
of most importance to us—_i.e._ that the y-or x-rays give rise to
ß-rays.
This relation gives us additional evidence of the identity of the
physical effects of y-, x-, and light-rays —using the term light
rays in the usual sense of spectral rays. For it has long been
known that light waves liberate electrons from atoms. It has been
found that these electrons possess a certain initial velocity
which is the greater the shorter the wave length of the light
concerned in their liberation. The whole science of
"photo-electricity" centres round this phenomenon. The action of
light on the photographic plate, as well as many other physical
and chemical phenomena, find an explanation in this liberation of
the electron by the light wave.
Here, then, we have spectral light waves liberating
electrons—_i.e._ very minute negatively-charged particles, and we
find that, as we use shorter light waves, the initial velocity of
these particles increases. Again, we have x-rays which are far
smaller in wave length than spectral light, liberating much
faster negatively electrified particles. Finally, we have
y-rays—the shortest nether waves of all-liberating negative
particles of the highest velocity known. Plainly the whole series
of phenomena is continuous.
We can now look closer at the actions involved in the therapeutic
influence of the several rays and in
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this way, also, see further the correlation between what may be
called photo-therapeutics and radioactive therapeutics.
The ß-ray, whether we obtain it directly from the transforming
radioactive atom or whether we obtain it as a result of the
effects of the y- or x-rays upon the atom, is an ionising agent
of wonderful power. What is meant by this? In its physical aspect
this means that the atoms through which it passes acquire free
electric charges; some becoming positive, some negative. This can
only be due to the loss of an electron by the affected atom. The
loss of the small negative charge carried in the electron leaves
the atom positively electrified or creates a positive ion. The
fixing of the wandering electron to a neutral atom creates a
negative ion. Before further consideration of the importance of
the phenomenon of ionisation we must fix in our minds that the
agent, which brings this about, is the ß-ray. There is little
evidence that the y-ray can directly create ions to any large
extent. But the action of liberating high-speed ß-rays results in
the creation of many thousands of ions by each ß-ray liberated.
As an agent in the hands of the medical man we must regard the
y-ray as a light wave of extremely penetrating character, which
creates high-speed ß-rays in the tissues which it penetrates,
these ß-rays being most potent ionising agents. The ß-rays
directly obtained from radioactive atoms assist in the work of
ionisation. ß-rays do not
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