9—5.
PROTECTION FROM X—RAYS
199
'electroscopeand is a measure of the intensity of the X_-ray beam.
In a particular instrument, 25 roentgens are required to com—
pletely discharge the collector. An accuracy of one or two per
»
cent may be expected.
.
_
9—5.
Protection from X-rays.——As specied by the Third In-‘
ternational Congress on X-ray and Radium Protection in 1931,
the following thickness of lead should always exist between the
source and the observer.
Thus, for a gas—lled tube operated by
Peak kilovolts across
Minimum thickness of
'
the tube
lead in mm.
75
1.0
_
.
100
1.5
'
125
'
2.0
150
2,5
_
.
,
175
’
'
’3.0
_
‘
200
‘
4.0
_‘
.
250
6.0
_
; .
'
.
“350
‘
12.0
'
,
400 —
15.0
-
‘
500
,
22.0
_
600
,
-
'
34.0
.
a Small induction coil, 1
of lead
ample. With the
-
ratus of gure
continued,“ direct
of
minutes is
…
The student should use a __uoroscopë
‘
‘
tilted at an“ang1e“
the
diréèt rays
'
"
and shouldnot_exposehis handfor more than“15 seconds at a”
time…noroftener than
Ï The danger may be
the
addi—
.
-
fion d‘fahalfmllhmeterofalummumoverthehole;_ 9f.àuoresœnt
monasheetofleadglass<%mchthmk)betweenthe '?9‘1ËCÇ “and
'
9—6AbsorpüonCoements—Themtensmyftheraysemlt