Health > Protective measures against dangers resulting from the use of radium, roentgen and ultra-violet rays

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Since the intensity of the radiation diminishes proportionately to the square of the
distance, increasing the distance is a very effective means of protection from radiation.
From the equation given above (a = 316 . v/D0. e-^d] we obtain the ratio of two
ranges namely, a/a' = ^/Do/D',,. If, for instance, the range of the injurious radiation
with a tube voltage of 180 kv and a current of 5 ma is to be determined for a protective
wall of 2 mm. lead equivalent, Graph III will show the range to be 5 m. with 180 kv
and 10 ma. For half that intensity (5 ma), the range thus equals 5^/2 = 3.5 m.
Again, it is easy to ascertain what reinforcement of the lead protection is necessary
if the dose output is raised. The above formula yields :
d — d' = . log (ala')
^ TT ' log (D«/D'<>)
r-
If, for instance, the voltage being 180 kv, the current is increased from 5 ma to 20 ma,
then, in order that the protection from radiation may be the same — i.e., in order that
the injurious radiation may have the same range — the thickness of the wall must be
increased by (2.3x20) . log 4 = 0.07 cm. =0.7 mm. lead equivalent. If this rein¬
forcement is not effected, the range increases from 3.5 m. to 3.5 m. 7 m.
In the manner indicated, the requisite protection can be determined for all the
various conditions of operation that may occur.
I he data given are also sufficient for extreme cases. Herrmann and Jaeger \ for
instance, have taken direct measurements with a view to ascertaining what thicknesses
of lead are necessary, given X-rays generated with 400 kv, to secure the same protection
as is afforded, with 200 kv by 4 mm. of lead. No attention appears to have been paid
in either case to the current in the tube ; the measurements indicated, however, the
need for 14.5 mm. of lead with 400 kv and 0.5 ma. Graph II, on the other hand, gives,
for 400 kv, 1 ma and 50 cm. focal distance, a lead thickness of 19.5 mm.; converting
this into terms of 0.5 ma, we get 17.7 mm. Ph. and, reckoning 1 m. focal distance, we
obtain the value of 14.1 mm. Pb. This satisfactory concordance with the value ascer¬
tained by direct measurement can be taken as confirmation of the fact that the data
on which the curves have been constructed are adequate for practical purposes.
7. Protective Measures from the Gamma Rays of Radio-active Substances.
We must now enquire whether and, if so, how far, the curves given can he used
for the gamma radiation of radio-active substances.
In order to establish a connection between gamma radiation and the radiation of
an X-ray tube, we must return to the question of energy and determine the voltage and
current at which a Roentgen tube would have to be operated in order to emit the same
radiant energy as, say, 1 gramme of radium.
Consideration of the gamma rays will he based upon the most commonly used
substance, RaC. This consists of several homogeneous groups of various wave lengths,
of which the 0.02 A. U. wave length is the most intense. Gamma radiation is thus also
not homogeneous, hut it is much more so than Roentgen radiation, even if the latter is
very heavily filtered. Ry way of absorption measurements, we obtain an average wave
1 Fortschritte Rontgenstr., 41, 426, 1930, and 42, 115, 1930.